Historical Studies in the Physical Sciences, Volume 6 9781400886395

Table of contents :
Contents
Editor’s Foreword
The Emergence of Japan’s First Physicists: 1868–1900
The Reception of the Wave Theory of Light in Britain: A Case Study Illustrating the Role of Methodology in Scientific Debate
Origins and Consolidation of Field Theory in Nineteenth-Century Britain: From the Mechanical to the Electromagnetic View of Nature
Hertz’s Researches on Electromagnetic Waves
God and Nature: Priestley’s Way of Rational Dissent
Laurent, Gerhardt, and the Philosophy of Chemistry
The Lewis-Langmuir Theory of Valence and the Chemical Community, 1920–1928
G. Ν. Lewis on Detailed Balancing, the Symmetry of Time, and the Nature of Light
Rutherford and Recoil Atoms: The Metamorphosis and Success of a Once Stillborn Theory
Notes on Contributors

Citation preview

Historical Studies in the Physical Sciences 6

Notice to Contributors Historical S tudies in the Physical S ciences, an annual publication issued by Prince­ ton University Press, devoted to articles on the history of the physical sciences from the eighteenth century to the present. The modern period has been selected since it holds especially challenging and timely problems, problems that so far have been little explored. An effort is made to bring together articles that expose new di­ rections and methods of research in the history of the modern physical sciences. Consideration is given to the professional communities of physical scientists, to the internal developments and interrelationships of the physical sciences, to the relations of the physical to the biological and social sciences, and to the institutional settings and the cultural and social contexts of the physical sciences. Historiographic articles, essay reviews, and survey articles on the current state of scholarship are welcome in addition to the more customary types of articles. All manuscripts should be accompanied by an additional carbon- or photocopy. Manuscripts should be typewritten and double-spaced on 8½" X 11" bond paper; wide margins should be allowed. No limit has been set on the length of manuscripts. Articles may include illustrations; these may be either glossy prints or directly repro­ ducible line drawings. Articles may be submitted in foreign languages; if accepted, they will be published in English translation. Footnotes are to be double-spaced, numbered sequentially, and collected at the end of the manuscript. Contributors are referred to the MLA Style Sheet for detailed instructions on documentation and other stylistic matters. (Historical Studies departs from the MLA rules in setting book and journal volume numbers in italicized Arabic rather than Roman numerals.) All correspondence concerning editorial matters should be addressed to Russell McCormmach, Department of History of Science, Johns Hopkins University, Balti­ more, Md. 21218. Fifty free reprints accompany each article. Historical Studies in the Physical Sciences incorporates Chymia, the history of chemistry annual.

An illustration from Kanagaki Robun's Seiyo dochu hizakurige (Through the West by Shanks' Mare), published in the early 1870's. Shown right to left: the "uncivilized man" in kimono with traditional hairdo and swords; the "half-civilized man" in kimono, but with Western cap, umbrella, and pocket watch; and the "civilized man" in frock coat, trousers, and top hat, and with beard and cane.

Historical Studies in the Physical Sciences RUSSELL McCORMMACH, Editor Sixth Annual Volume PRINCETON UNIVERSITY PRESS PRINCETON, NEW JERSEY

Copyright © 1975 by Princeton University Press Published by Princeton University Press, Princeton and London All Rights Reserved LCC: 77-75220 ISBN 0-691-08166-2

This book has been composed in IBM Selectric Aldine Roman Printed in the United States of America by Princeton University Press, Princeton, NewJersey

Princeton Legacy Library edition 2017 Paperback ISBN: 978-0-691-61751-0 Hardcover ISBN: 978-0-691-65432-4

Editor RUSSELL McCORMMACH, Johns Hopkins University

Editorial Board JOAN BROMBERG, Simmons College CLAUDE K. DEISCHER, University of Pennsylvania STANLEY GOLDBERG, Hampshire College OWEN HANNAWAY, Johns Hopkins University JOHN L. HEILBRON, University of California, Berkeley ARMIN HERMANN, University of Stuttgart TETU HIROSIGE.t Nihon University, Tokyo GERALD HOLTON, Harvard University ROBERT H. KARGON, Johns Hopkins University MARTIN J. KLEIN, Yale University HERBERT S. KLICKSTEIN, Albert Einstein Medical Center, Philadelphia THOMAS S. KUHN, Princeton University BORIS KUZNETSOV, Institute for the History of Science, Moscow HENRY M. LEICESTER, University of the Pacific JEROME R. RAVETZ, University of Leeds NATHAN REINGOLD, Smithsonian Institution LEON ROSENFELD,t Nordic Institute for Theoretical Atomic Physics, Copenhagen ROBERT E. SCHOFIELD, Case Western Reserve University ROBERT SIEGFRIED, University of Wisconsin ARNOLD THACKRAY, University of Pennsylvania HARRY WOOLF, Johns Hopkins University

Contents Editor's Foreword

xi

KENKICHIRO KOIZUMI The Emergence of Japan's First Physicists: 1868-1900

3

GEOFFREY CANTOR The Reception of the Wave Theory of Light in Britain: A Case Study Illustrating the Role of Methodology in Scientific Debate

109

BARBARA GIUSTI DORAN Origins and Consolidation of Field Theory in Nineteenth Century Britain: From the Mechanical to the Electromagnetic View of Nature

133

SALVO D'AGOSTINO Hertz's Researches on Electromagnetic Waves

261

J. G. McEVOY and J. E. McGUIRE God and Nature: Priestley's Way of Rational Dissent

325

JOHN HEDLEY BROOKE Laurent, Gerhardt, and the Philosophy of Chemistry

405

ROBERT E. KOHLER, JR. The Lewis-Langmuir Theory of Valence and the Chemical Community, 1920-1928

431

ROGER H. STUEWER G. N. Lewis on Detailed Balancing, the Symmetry of Time, and the Nature of Light

469

THADDEUS J. TRENN Rutherford and Recoil Atoms: The Metamorphosis and Success of a Once Stillborn Theory

513

Notes on Contributors

549

Editor's Foreword In the lead article in this sixth volume of Historical Studies in the Physical Sciences, Kenkichiro Koizumi analyzes the introduction of Western physics into Japan after the Meiji Restoration. He shows how the physics discipline was institutionalized in Japan's new universities at the turn of the century, and how popularizers and teachers outside the universities associated physics with Japan's modernization and invested its dissemina­ tion with a sense of national urgency. His article suggests the need for studying the cultural and political preconditions for the emergence of the physics discipline in other countries. It suggests, too, the need for studying comparatively the parallels and especially the contrasts between the development of a professionalized physics community and its supportive teaching and technical activities in different countries. Studies of both kinds illuminate the dual national and international character of the physics community. At the same time Koizumi's article is a contribution to the more general historical problem of identifying and analyzing the role of values in the work of physical scientists. Koizumi shows that despite their markedly different personalities, abilities, and interests, Japan's early physicists held certain values in common, and that these values underlay their joint commitment to building and naturalizing a physics discipline in Japan. He shows that they were motivated in their original decisions to study physics by the values of a combined Samurai-Confucian worldview that their education had instilled in them, especially those stressing moral selfdiscipline and service to the state. He shows further that these same values shaped their attitudes toward physics and helped make possible the im­ plantation of a physics discipline in an alien culture; the emphasis of Japanese physicists on the utility of physics and deemphasis of its philosophy are cases in point. We need historical concepts for analyzing the possible relations between the physicists' pictures of the physical world whose workings they are committed to understand and their cultural world of values. The distinct but related concepts of worldview and the world picture of physics may be useful in this regard. The term "worldview" (Weltanschauung) was and to some extent still is current in academic circles; often ill-defined and loosely used, it stands roughly for the totality of views of an individual on

xii

EDITOR'S FOREWORD

the meaning of the world. It may connote something more as well, a unified, actively developing synthesis of value-enduing views on the world and man's place in it together with a picture of the natural world. 1 The term "world picture" (Weltbild) was and is occasionally used inter­ changeably with "worldview," but to natural scientists it usually means something more precise: 2 an ideal, synthetic construct of concepts and theorems that ultimately encompasses all physical phenomena. Although the concepts of worldview and world picture are particularly appropriate to the German cultural sphere, they may be extended usefully beyond it. The German theoretical physicist Woldemar Voigt likened the world pictures of scientists to the worldviews of philosophers and theologians; world pictures are working hypotheses that render the world comprehen­ sible and make fruitful work possible. 3 In the same vein the German theoretical physicist Max Planck contended that although world pictures cannot be proved scientifically, scientists are deprived of a major source of scientific creativity if they are not committed to one. 4 If, as Planck 1 The theoretical physicist Max Planck argued that just as a viable worldview cannot be based wholly on science, neither can it stand apart from science ("Ansprache," Sitzungsberichte, Akademie der Wissenschaften, Berlin [1913], part 1, pp. 73-76, especially p. 75). For an influential discussion of "worldviews," see Dilthey's Philosophy of Exis­ tence: Introduction to Weltanschauungslehre, trans. W. Kluback and M. Weinbaum (New York, 1957); see in particular Dilthey's discussion of the relation of worldviews to values and willed actions on pp. 25-27. 2 The theoretical physicist Paul Volkmann, who believed that the proper ground for the cooperation of science and philosophy was not worldviews but methodology and epistemology (Die materialistische Epoche des neunzehnten Jahrhunderts und die phdnomenologisch-monistische Bewegung der Gegenwart [Leipzig, 1909], p. 23), commended the zoologist Ernst Haeckel's recent use of the "happier expression Weltbild instead of Weltanschauung" in connection with Darwin and Lamarck (Erkenntnistheoretische Grundzuge der Naturwissenschaften und ihre Beziehungen zum Geistesleben der Gegenwart, 2nd ed. [Leipzig, 1910], p. 236). When physicists spoke of "world picture" (Weltbild) they usually were not making a statement about the "true world" or "physical reality," but about a "picture" or "sign" of that world. "Worldview" (Weltanschauung) signified more than this in going beyond what the natural sciences could say about the world. For the distinction between Weltbild and Weltanschauung see, e.g., Rudolf Eisler, ed., Worterbuch der philosophischen Begriffe, 4th rev. ed., 3 (Berlin, 1930), 506-508; Heinrich Schmidt, ed., Philosophisches Worterbuch, new ed. (New York, 1945), pp. 456-457; Walter Brugger, ed., Philosophisches Worterbuch, 5th ed. (Freiburg, 1953), pp. 370-371. 3 Woldemar Voigt, "Ueber Arbeitshypothesen," Nachrichten von der konigl. Gesellschaft der Wissenschaften zu Gottingen, Math.-physik. Klasse (1905), pp. 114115. 4 Max Planck, "New Paths of Physical Knowledge" (1913), in Planck, A Survey of Physical Theory, trans. R. Jones and D. H. Williams (New York, 1960), pp. 45-55, especially p. 54.

EDITOR'S FOREWORD

xiii

suggested, the physicists' faith in their world pictures is not compelled by scientific facts alone, the origins of world pictures may lie partly in other facets of worldviews. By studying the possible relations between physicists' pictures of the physical world and their more comprehensive worldviews, it would appear that we can deepen our historical understanding of the development of conceptions-of physical reality. On the one hand we may learn in what respects and to what degree we can regard the physicists' world pictures as conditioning and conditioned by their worldviews. On the other hand we may learn if and in what ways the physicists' world pictures condition their perception of the problems of their specialties and with it their technical contributions. Among concepts other than worldview and world picture that have proven useful in analyzing scientists' values, ideology is one of the most important. Values may be gauged from how scientists act in light of the available choices; they may also be gauged from statements by scientists about their actions, and may be referred to their worldviews and analyzed for ideological content. Ideology lends itself to a more or less critical approach to scientists, directing our attention to social forces, group interests, and ego defences. By contrast worldview lends itself to a more or less empathetic approach, directing our attention to scientists' search for meaning, insight, and self-realization. The historical interpretations we construct with the aid of worldview and ideology are in a sense comple­ mentary. Both interpretations are needed. Potentially significant historical problems may be posed by analyzing within concrete historical situations the relations between worldviews, world pictures, values, and perceptions of scientific careers and scientific problems. Other potentially significant historical problems may be posed by interpreting worldviews as ideological expressions of groups of scientists with societal connections. On this interpretation we would seek to relate the more or less static taxonomy of concepts—worldviews, world pictures, and values—to dynamic societal processes; we would seek reasons why the concepts apply at certain times and places. Historical information on professed and implicit values held by physicists is often inaccessible or nonexistent. But as Koizumi and others have shown, the situation is not hopeless when we are dealing with well-known physicists, or even when we are dealing with a national body of physicists. One natural starting point for a study of values is national educational systems and the worldviews and ideologies they may help to transmit to intending physicists. Another is general writings on science, religion,

xiv

EDITOR'S FOREWORD

ethics, and politics by physicists. Yet another is unpublished material by and about physicists now being collected in the Archive for History of Quantum Physics and at the Center for History of Physics at the American Institute of Physics. The motivating values of physical scientists are a well-recognized subject of historical study. It is clear that an understanding of physicists' values bears on such basic historical problems as physicists' career decisions and their perceptions of the nature and needs of their specialties. Ultimately we may hope to have a better understanding of what it means for an in­ dividual to become a physicist and to practice physics at a given time and place. Today there is considerable interest among historians in the role of values, world pictures, and ideologies in late nineteenth and early twentieth century physical research, especially in that done by German-speaking theoretical physicists; for this reason I have written an editor's foreword on the subject.

Historical Studies in the Physical Sciences

6

The Emergence of Japan's First Physicists: 1868-1900' BY KENKICHIRO KOIZUMI* 1. Introduction

4

2. Japan's First Encounter with Western Science

7

The Beginnings of Rangaku (Dutch Learning)

7

The Impact of Rangaku

9

Two Institutional Manifestations of Rangaku

14

Rangaku and Meiji Science: Rupture and Continuity

17

Westernization as Progress: The Bootstrap Psychology

19

The Selling of Western Science

23

3. The Institutionalization of Physics and the Physical Science Disciplines Japan's First University The Problem of Instructional Language

29 29 31

*Chief Science Editor, TBS-Britannica, Eiwa Building, 1-9-18 Nishishinjuku, Shinjuku-ku, Tokyo 160, Japan. 1 This paper was prepared while the author was lecturer at the University of Pennsylvania. It is drawn from a parent study, The Development of Physics in Meiji Japan: 1868-1912 (Ph.D. diss., University of Pennsylvania, 1973), to which the reader is directed for more detailed data and additional bibliographic references. I am indebted to Russell McCormmach for invaluable criticisms and stimulating comments and to the National Science Foundation for support of my research in Japan. I want to make some remarks here on Japanese names. The normal order is family name first, then given name: ARAI Hakuseki. Reference to a person by a single name rather than by his full name, however, follows two rules: in pre-modern times, that is, pre-1868, persons are referred to by their given or chosen names, which often served as their pen names (ARAI Hakuseki would be referred to as Hakuseki); in modern times, that is, post-1868, a person is known by his family name (YUKAWA Hideki would be referred to as Yukawa). In accordance with Western scholarly convention, I have retained these practices. However, in order to avoid confusion in the notes where both Japanese andWestern authors are listed, I have adopted a uniform convention: initial of the given name followed by the family name (H. Yukawa, D. Price). Also in accordance with Western scholarly usage I have employed the Hepburn system for the Romanization of all Japanese names and words. Not all Japanese use this system: Hiroshige Tetsu, for ex­ ample, prefers Hirosige Tetu for his own name and may be found under that Romanization in some publications elsewhere.

4

JAPAN'S FIRST PHYSICISTS

Foreign Teachers

33

Mendenhall and Ewing

35

The Faculty of Science and the Development of Physics

37

The Tokyo School of Physics

39

The Tokyo Mathematico-Physical Society

44

4. The First Generation of Japanese Physicists: The 18 70's

48

Japan's First Physicists

48

The Education of a Samurai

50

Foreign and Domestic Training

53

The English-Language Physicists

54

The German-Language Physicists

55

The French-Language Physicists

57

5. ThreeMajorFiguresinEarlyjapanesePhysics

59

Yamagawa Kenjiro

59

Tanakadate Aikitsu

72

Nagaoka Hantaro

82

6. In Conclusion

95

Appendix

101

Table A. Fief and State Schools and the Evolution of the University of Tokyo

101

Table B. Faculty of Science, University of Tokyo, 1877

103

Table C. Academic Societies and Journals in Japan

104

Table D. The Principal Members of the First Generation of Japanese Physicists Table E. Training of the First Generation of Japanese Physicists

105 106

Table F. Principal Graduates of the French Language Physics Department

107

1. INTRODUCTION In 1868 Japan made one of the greatest decisions in its history. In the face of domestic crisis and international tension Japan decided to transform itself into a great power under the slogan Fukoku kyohei, or "wealth and military strength for Japan." Internal factors that brought about the de­ cision were the feudal government's failure to resolve the problem of agrarian uprisings and a general deterioration in government control over domestic affairs. The external factor was pressure from the West for open

KENKICHIRO KOIZUMI

5

trade. Japan had been closed under a rigidly enforced isolation policy for­ bidding contact with the outside world for more than two hundred years; in the face of new and increasing Western threats, the government's waver­ ing attitude underlined its weakness. Although the pressure exerted by the West on Japan was considerably less than that directed toward China, Japan reacted intensely to it. 2 When China, a country long the object of Japan's admiration, was defeated by powerful British forces in the Opium War of 1840, Japan sensed that it, too, might at any moment suffer de­ feat. 3 The psychological factor of fear inspired by the Opium War oper­ ated alongside a cultural factor in determining the nature of Japan's re­ sponse to external pressure. Under the feudal system in Japan relations between people were understood only as vertical; that is, as relations be­ tween superiors and inferiors or between governors and the governed. Thus, the feudal rulers were not able to conceive of any relationship with Western nations other than one in which Japan would be either dominant or dominated. 4 Feudal Japanese society of the 1850's consisted of about 265 han or fiefs. Each fief was controlled by a daimyo or feudal lord, who in turn owed allegiance to the shogunate or military government headed by the Tokugawa family, members of which had successively controlled the country since 1600. Above this structure was the Emperor, who had no political power, but whose prestige as a symbol of Japan and of its history had to be recognized even by the Tokugawa shogunate. Although the con­ stituents of this complex polity differed in their reactions to the threat from the West, their initial response to the first Western overture was one of almost total unanimity against opening the country and establishing trade. In 1853 Commodore Matthew Perry came to Japan from the United States with modern firearms and steam-powered warships, symbols of the powerful West, demanding that Japan open ports for American whaling ships and set up machinery for trade; in the years that followed, Japanese reactions changed quickly as direct contacts with the West increased. De2 The difference between the external pressure on Japan and that on other Asian countries was directly related to Japan's position as the last Asian country to be ap­ proached by Western powers. Having experienced considerable troubles in dealing with Oriental countries (in China, with the Opium War in 1840 and the Taiping Rebellion in the 1850's; in India, with the Sepoy Rebellion in 1857), the Western na­ tions assumed threatening postures but wished to avoid open military conflict with Japan. See S. Nohara, "Kyokuto ο meguru kokusai kankei," inNihon rekisht—Kindai (Tokyo, 1962), 1, 59-96. 3 C. Blacker, The Japanese Enlightenment (Cambridge, 1964), p. 16. 4 S. Toyama, Aieyi ishin (Tokyo, 1951), pp. 73-74.

6

JAPAN'S FIRST PHYSICISTS

clining opposition to opening Japan to the West was particularly con­ spicuous among the feudal lords and their followers. It was found even among those who had previously been the strongest advocates of isolation­ ism, as in such places as the Satsuma and Choshu fiefs. Satsuma had been bombarded by the British fleet in 1863 in retaliation for so-called "terror­ ism" (the Richardson killing), and a year later Choshu had been fired upon by an allied fleet of British, American, Dutch, and French ships in retalia­ tion for having fired at their ships. Such incidents convinced the Japanese, including the most stubbornly anti-Western, of the technological superior­ ity of "Western civilization" and of the need to open the country and ob­ tain the fruits of this civilization to survive. 5 The changes initiated during the early stages of contact with the West led to the abolition of the closed-country policy, the overthrow of the Tokugawa shogunate, and the establishment of a strong, new, centralized government headed by Emperor Meiji, to whom ultimate power and authority was restored in 1868. The new government abolished the feudal domains and the vertical class system of samurai, peasant, artisan, and merchant. It established a new taxation system and imposed other farreaching reforms. The path Japan took in achieving the Meiji Restoration is very complex and cannot be considered in the present study. It is im­ portant to note, however, that although Japan was awakened by the West and its revolutionary reforms were to a large extent based upon Western ideas, it did not seek to become a Western nation. Rather, Japan sought to become a nation capable of coping with external encroachments and of competing with the West, a nation of people who could be proud of them­ selves before Western people. Their nationalistic attitude was not explicit, however, but latent in the early years of the Meiji period, when they tended to disparage themselves before Westerners and to absorb everything Western. The word "nationalistic" is somewhat inappropriate at this stage, for the attitudes formed under the feudal system and during Japan's long period of isolation hardly resembled modern nationalism. Geographically isolated from the rest of Asia, Japan had evolved its own unique forms of government, language, religion, and culture. It was aware of its own in­ dividuality, but, as one Japanese intellectual wrote in 1875, it was not yet a nation. 6 By the time of the Russo-Japanese war of 1904-1905, however, Japan had risen from feudal obscurity to one of the five most powerful nations in the world and had acquired modern nationalistic attitudes. The history of science, particularly of the physical scientific disciplines, Slbid., pp. 82-87 and pp. 125-127. 6 Ibid.,

pp. 73-74.

KENKICHIRO KOIZUMI

7

in Japan is inextricably linked to these historical events. At times the de­ velopment of science meant to the Japanese the development, even the survival, of the nation; at times words such as "physics" meant "science" and "science" meant "civilization." In the present study I will explore the complex phenomenon of the introduction of Western science into Japan through an examination of the history of Japanese physics. I do so not be­ cause I believe that the process observable in Japan will provide a model of success for other non-Western nations, but, on the contrary, to show among other things that it cannot be duplicated. 2. JAPAN'S FIRST ENCOUNTER WITH WESTERN SCIENCE The Beginnings of Rangaku (Dutch Learning) In 1543 a Portuguese ship ran aground at Tanegashima, bringing the Japanese into direct contact with Europeans for the first time. From that introduction until the 1630's Western knowledge, limited primarily to astronomy (Ptolemaic theory), medicine, and navigation, entered Japan under Christian influence, mainly through the Jesuits. Western knowledge during this period was known as Nambangaku or "southern barbarian studies," a term appropriated from the Chinese, who used it to refer to the learning of the West borne to the East by the "uncivilized" Europeans on ships from the south. The Japanese showed considerable interest in the teachings of the Christian priests on the earth's configuration, falling stars, and other astronomical subjects and inquired about other natural phe­ nomena such as lightning, rain, and snow. 7 By 1639, however, the Japanese government, suspicious of the political implications of aggressive Christian proselytizing, adopted its national iso­ lation policy. The only Europeans permitted to remain and to continue trade were the Dutch, and even they were restricted to a small island near Nagasaki called Dejima. 8 During this sakoku, or closed-country, period from 1639 to 1853 the Dutch became Japan's main source of European knowledge. Rangaku, or Dutch learning, became the new term for Western knowledge; it consisted of the study of Western natural science—mostly medicine, astronomy, and botany—through the Dutch language. It is im­ portant to note that, aside from language study, Rangaku did not include the humanities. 7 A.

Ebizawa,NambangakutO no kenkyu (Tokyo, 1959), pp. 41-42. is the date when Japan's isolation was more or less completed. The first iso­ lation order was issued in 1633 and was reissued every year until 1639. For a discus­ sion of the isolation policy in Japan, see E. Reischauer and J. Fairbank, East Asia: The Great Tradition (Boston, 1960), pp. 595-601. 8 1639

8

JAPAN'S FIRST PHYSICISTS

Western knowledge in Japan—Nambangaku and Rangaku—was not ex­ tensive; Western and Japanese cultures were too different and met on too limited a basis for fundamental changes or profound mutual influence to occur during the early stages of contact. The Japanese were most attracted to the practical sciences—astronomy, medicine, and navigation—with which they could immediately improve their lives. Until the end of the seventeenth century Rangaku developed very slowly due to several factors. The confinement of the Dutch on Dejima severely limited their contact with the Japanese; Japanese interpreters lacked a sound knowledge of the Dutch language; 9 and Japanese authorities pro­ hibited the importation of all Western books as well as their Chinese trans­ lations. The purpose of the book ban was to ensure that no works dealing with Christianity entered the country, but of course books on science such as the Chinese translation of Euclid's Elements 10 were equally victims of the sweeping proscription. The rare contacts between the Japanese and the Dutch were provided by official liaison agents, suppliers, and inter­ preters for the Dutch, by Dutch visitors to the shogun in Edo (present-day Tokyo), and by a few Dutch medical and military tutors. A Dutch physi­ cian, Caspar Schambergen, became the unwitting founder of a type of medicine known in Japan as the Caspar School, and a Dutch gunner, Schaedel, taught the use of artillery to Japanese in Edo; 11 in general the knowledge transmitted during this early period was of such a fragmentary nature that an adequate picture of Rangaku cannot be clearly presented. It was not until the late eighteenth century that the Japanese undertook systematic studies of Rangaku. In the early eighteenth century Dutch learning attracted the interest of a number of important Japanese who influenced the direction of its develop­ ment. Arai Hakuseki, a Confucian scholar and counselor to the shogunate from 1709 to 1716, interviewed an Italian Jesuit, G. B. Sidotti, who in 1708 had illegally smuggled himself into Japan to engage in missionary work and was captured and brought to Edo. Following their interview, 9 Portuguese had been more popular than Dutch up to this time as a result of the more than one hundred years of trade between Japan and Portugal. A record written by a Dutch official in 1675 comments on the lack of efficiency in trade because of the poor knowledge of Japanese on the part of Dutch interpreters. See J. Numata, YOgaku denrai no rekishi (Tokyo, 1966), pp. 6-10. 10 T. Itazawa, Nichiran bunka koshdshi no kenkyu {Tokyo, 1959), p. 456. These Western scientific books were prohibited not'because of their subject matter, but be­ cause they had been translated by Christians. 11 J. Numata, Ydgaku denrai no rekishi, pp. 14-16.

KENKICHIRO KOIZUMI

9

Hakuseki wrote two books, Sairan igen (A Selected View of Foreign Statements) in 1708, and Seiyo kibun (Report of the Occident) in 1713, in which he reported that Sidotti displayed an extensive knowledge of astronomy and world geography. "The man was very learned, and ap­ peared to have studied many subjects. I do not think that we can compete with them [Westerners] as far as the fields of astronomy and geography are concerned." 12 He then modified his praise of the West by saying that Western knowledge was very accurate only in the practical sciences. He also criticized the current shogunate view of the dangerous, aggressive character of Christianity. Through his position as counselor to two shoguns, through his recognition of the value of Rangaku and the superiority of Western practical sciences, and through his insistence on the separation of Western science from Christianity, Hakuseki opened the way to the further development of Rangaku within the context of the prohibition of Christianity. 13 The Impact of Rangaku In 1720 the eighth shogun, Tokugawa Yoshimune, decided to ease the ban against the importation of Western books by making them available to certain officially recognized scholars. The decision grew mainly out of Yoshimune's interest in calendar reform, but it was also influenced by his desire to improve domestic commerce through appropriate practical Western techniques and by his fascination with the exotic. 14 Yoshimune agreed with Hakuseki that Rangaku was superior in practical matters, and after the ban was eased, most of the books that were imported dealt with astronomy and calendar making. Other subjects such as the geography of foreign countries, the species of Western animals and plants, and machinery 12 Quoted

in S. Sato, Yogakushi kenkyu josetsu (Tokyo, 1964), pp. 11-12. Sato holds the opposite view on this point. He says that the recognition of the superiority of Western science with respect to application was more or less common among intellectuals (i.e., men such as the Confucian scholar, Kaibara Ekken, and the astronomer, Nishikawa Jyoken); it was not Hakuseki's contribution. He also says that the Western sciences were never considered to be part of Christianity, and that it is therefore meaningless to emphasize Hakuseki's role in separating the two. I wish to emphasize on the contrary that Hakuseki was not just a scholar but a counselor to the shogunate. Even if Sato's claims were true, Hakuseki's restatement and confirmation of the practical nature of Western science and his reassurances about the dangers of Christianity, voiced in the inner circles of the shogunate, are of considerable sig­ nificance. Ibici., pp. 29-41. 14 A. Saito, "Tokugawa Yoshimune to seiyo bunka," Shigaku zasshi, 47 (1936), 1356-1377. 13 S.

10

JAPAN'S FIRST PHYSICISTS

were also encouraged by Yoshimune and were studied under the guidance of the Dutch. 15 In 1740, when scholarly interest in Western learning had grown suffi­ ciently to allow a full-scale development of Rangaku, Yoshimune ordered the two scholars Aoki Konyo and Noro Genjo to study Rangaku. Genjo, with the help of interpreters, studied mainly botanical science and trans­ lated a few Dutch books into Japanese; Konyo wrote several books on the Dutch language. Although the level of their studies was relatively low— Konyo's writings, for instance, reveal a mediocre knowledge of Dutch grammar at best—Konyo and Genjo were the first scholars, as opposed to mere interpreters, to be concerned with Rangaku. Their work may thus be regarded as the start of serious study of Western learning in Japan. 16 By easing the restrictions against books and encouraging the study of Western knowledge, Yoshimune created a favorable atmosphere for the de­ velopment of Rangaku. Sugita Gempaku in 1815 in his book Rangaku kotohajime 17 (The Beginnings of Dutch Learning [in Japan]) wrote: "There was no one well versed in Western things; it is just that somehow or other people no longer seemed indifferent to Western things. Although there was no relaxation of the ban on the ordinary person possessing Dutch books and the like, the temper of the time became such that one frequently encountered people who did possess them." 18 The study of Rangaku gradually and spontaneously increased among the ordinary Japanese. The most important manifestation of their new interest was the private translation of a Dutch book on anatomy 19 by a group of Japanese led by Sugita Gempaku and Maeno Ryotaku. Most members of the group were physicians who, under a variety of circumstances, had become in­ terested in Dutch medicine. In his Rangaku kotohajime, Gempaku de­ scribes how they came to translate the Dutch text. Gempaku, Ryotaku, 15 For detailed information, see for example G. K. Goodman, The Dutch Impact on Japan (1640-1853) (Leiden, 1967), pp. 63 ff. 16 J. Numata, YOgaku denrai no rekishi, pp. 31-46. 17 TVie original title is Ranto kotohajime (The Beginnings of Dutch Learning in Japan), but the work was better known as Rangaku kotohajime. Rants and Rangaku are synonyms. 18 G. Sugita, Ranto kotohajime in Nihon koten bungaku taikei (Tokyo, 1964), 95, 486. 19 This book, called Kaitai shinsho (A New Book of Anatomy) in its Japanese trans­ lation, was a Dutch translation of a German anatomy book by J. A. Kulmus, The Dutch translation from which they were translating was called Ontleedkundige Tafelen, Benevens de daar toe behoorende Afbeeldingen en Aanmerkingen, Waar in het Zaamenstel des Menschelijken Lichaams, en het gebruik van alle deszelfs Deelen afgebeeld engeleerd word (Amsterdam, 1734).

KENKICHIRO KOIZUMI

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and others had been invited to view the dissection of the body of an old woman who had been executed for a crime. At the dissection Ryotaku showed Gempaku a copy of the Dutch book on anatomy which he had ob­ tained in Nagasaki and which he had brought to the dissection for com­ parison. Gempaku, too, had just received a copy of the same book from a Japanese interpreter and had likewise brought it with him in order to com­ pare the illustrations with what he would observe at the dissection. The two physicians found to their mutual astonishment that the anatomical drawings in the Dutch book agreed completely with the corpse's anatomy. On the way home the group of physicians marveled over the accuracy of the Dutch drawings and their superiority over the philosophical explana­ tions of the human body of the Chinese texts on which they had pre­ viously depended. They lamented that they had been practicing medicine for all these years without a knowledge of human anatomy, 20 and al­ though only Ryotaku knew any Dutch and that sketchily they determined to translate the book. To the eighteenth-century Japanese, it was far from obvious that anat­ omy and medicine are closely connected, and that without a knowledge of the former one cannot adequately practice the latter. That Gempaku and his colleagues were able to make this connection was highly significant for Japanese medicine. The assertion of the connection, however, did not lead to fundamental methodological changes in medical studies. Instead of a methodological shift from Chinese theory to Western pragmatism, Japa­ nese medical science after Gempaku merely shifted the source of medical authority from Chinese medical tomes to Dutch ones. In short, Gempaku's association of anatomy with good medical practice did not turn Japanese from a book-oriented knowledge of medicine to an entirely new and ex­ perimental methodology. It is hard to say definitely that Gempaku did not somehow glimpse new possibilities for medicine, even methodologically, but we can definitely say, even if such were the case, that those who followed him did not interpret his Dutch orientation to mean anything more than that Dutch books were better than Chinese ones. Gempaku's contributions to Rangaku drew others, mainly physicians, to him and Ryotaku for the study of Dutch learning. Among them, Otsuki Gentaku was especially important to the further progress of Rangaku. Gentaku came to Edo in 1778 to study Rangaku under Gempaku, com­ pleting his studies in 1785 and becoming physician to the Edo members of the Sendai fief. In the following year, he opened in Edo the largest and 20 G.

Sugita, Ranto kotohajime, pp. 489-492.

12

JAPAN'S FIRST PHYSICISTS

best known private school for Rangaku, the Shirando. He wrote many books, among them Rangaku kaitei (The Ladder of Dutch Learning), an advanced work on the origins of Japanese-Dutch contacts and an analysis of the Dutch language, published in 1788, and Rangaku haikei (Introduc­ tion to the Study of Dutch Words), a beginner's language text, published in 1795. These two works were read from this period on by almost everyone who was interested in Rangaku, 21 Other Japanese "scientific" fields were, of course, influenced by Dutch learning; I have discussed mainly the development of medical science in relation to Dutch learning because it tended to dominate the field. Never­ theless, other subjects such as astronomy, calendar making, and botany also developed under the influence of Dutch learning. Since Rangaku had influenced some traditional Japanese sciences such as medicine, the question arises whether or not it could have furthered the development of other traditional sciences. A related question is whether or not Rangaku itself could have been developed in private research along purely scientific lines simultaneously with its utilitarian development under official support. Here we must keep in mind that when Western science was first introduced through Rangaku, traditional Japanese "sci­ ence" consisted only of medicine, astronomy, botany, and mathematics, and that Western science affected each of these fields differently. Whereas medicine, astronomy, and botany had felt an immediate impact, mathe­ matics was at first very little influenced by Western science, particularly as far as the orthodox Japanese mathematics known as wasan was concerned. The wasan mathematicians claimed that in mathematics Japan was better than the West. 22 They were proud of having developed a mathematics unique to Japan and of having created the only pure, as opposed to ap­ plied, science among the traditional sciences. As a consequence, recog­ nition of the practical value of Western mathematics came from men out­ side the ranks of mathematicians. Despite the aloofness of the wasan mathematicians themselves, however, the debate leading to the adoption of Western mathematics began. In 1857 an elementary book on Western mathematics using only Western notation and computation was published by Yanagawa Shunsan, not a wasan mathematician but a scholar of Dutch. 23 Whereas Japanese mathematics had early departed from its sourceChinese mathematics—and had developed in its own direction, other sci211. Sugimoto et al.,Kagakushi (Tokyo, 1967), pp. 262-263. 22 K. Ogura, Sugakushi kenkyu (Tokyo, 1948), 2, 99-100. «Κ. Ogura, Sugakushi kenkyu (Tokyo, 1935), 1, 318.

KENKICHIRO KOIZUMI

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ences in Japan never achieved independent status. For example, Chinese astronomy dominated until Western astronomy took its place in the 1730's. The Japanese showed little interest in exploring astronomical matters on their own or in experimenting with practical uses of astronomy such as calendar making; they simply adopted the Chinese calendar and did not reform it until 1684. 24 Having developed no astronomy of their own, therefore, they were more disposed to adopt Western astronomy than Western mathematics. In a study of the development of Western physics in modern Japan, we cannot ignore all reference to physics in the pre-modern period. The Japanese, however, had no science resembling physics among their tradi­ tional sciences, and Japanese scholars knew little of Western physics until the nineteenth century, when they first began to give serious attention to Dutch books on "natural philosophy." The most notable study of Western natural philosophy was a work called Rekishd shinsho (New Handbook on Calendrical Phenomena) by Shizuki Tadao, an official interpreter in Nagasaki. The book was excerpts and summaries in Japanese of John Keill's Introductiones ad veram Physicam et veram Astronomiam Quibus aceedunt, Trigonometria, de viribus Centralibus. De legibus Attraetiones (editio novissima, London 1739), which was prepared from Johan Lulofs' Dutch translation Inleidinge tot de waare Natuur- et Starrekunde (Amster­ dam, 1741). After retiring as an interpreter, Shizuki Tadao devoted more than twenty years to the study and translation of this Dutch text and completed it in three manuscript volumes in 1798, 1800, and 1802. The work, which was never published but circulated only in manuscript form, introduced Newtonian natural philosophy into Japan for the first time. 25 Other Japanese scholars also became interested in the study of natural philosophy. Hoashi Banri, a Confucian scholar who had read Shizuki Tadao's translation, was one of the first to write a book on physics. His KyUri tsii (Proficiency in Natural Philosophy) was based on about thirteen Dutch books 26 and comprised eight volumes of manuscript. In 1860 three 24 S. Nakayama, A History of Japanese Astronomy (Cambridge, Mass., 1969), pp. 116 ff. 2 s Ibid., pp. 180-186; Nihon gakushiin, ed., Meiji zen Nihon butsuri kagakushi (Tokyo, 1964), pp. 62-79. 26 Some of the Dutch books are Petrus van Musschenbroek, Beginsels der natuurkunde beschreeven ten dienste der landgenooten; J. J. Lalande, Astronomia of sterrekunde; P. F. Prinsen, Geographische oefeningen of leerboek der aardrijkskunde; S. Ypey, Sijstematisch handboek der scheikunde; C. L. Willdenow, Handleiding tot de kennis der planten; A. Richerand, Natuurkunde van $en mensch; J. de Gelder, Algemeene aardrijksbeschrijving. See Nihongakushiin, ed., op. cit. (note 25), p. 155.

14

JAPAN'S FIRST PHYSICISTS

volumes of the work were published posthumously; the others remained in manuscript. In 1827, Aochi Rinso, a Rangaku scholar and student of Chinese medicine, published the first physics book in Japan. It was en­ titled Kikai kanran, which loosely translated means something like Obser­ vations of the Billowing Waves of Air and Sea, and was most likely based on two Dutch works by Johannes Buys, Natuurkundig Schoolboek and Volks-Natuurkunde, Rins5's small work explained briefly, in one or two pages per subject, such phenomena as rain, snow, light, color, temperature, attraction, and electricity. Despite its brevity, it treated almost all basic concepts then considered part of physics, and it was read widely by scholars. Rinso's son-in-law, Kawamoto Komin, published a sequel for physicians called Kikai kanran kogi (Observations of the Billowing Waves of Air and Sea, Enlarged) in fifteen volumes between 1851 and 1856. 27 In 1856, the physician Hirose Genkyo published a two-volume work called Rigaku teiyo (Summary of Natural Philosophy). It was based on a German work by J. N. Isfording which had been translated into Dutch by Epen and published in 1826 as Natuurkundig handboek voor leerlingen in de heel- en geneeskunde. Genkyo stated in his preface that his translation was in­ tended for physicians, as the original probably was. In the West, he ex­ plained, physicians study natural philosophy first before going on to anatomy and physiology and other biomedical subjects, and its study is therefore basic to medical training. 28 One notices connections with medicine in the careers of several of the early investigators of Dutch natural philosophy; however, primary sources are so scant and modern research so little advanced that we cannot dis­ cover the motivation, aim, or use of these early studies of physics in Japan. All that is clear is that the significance of physics in pre-Meiji Japan was slight. The difference between the natural philosophy of the Rangaku period and the physics of the Meiji period is great. Two Institutional Manifestations of Rangaku After flourishing in a more or less free and private atmosphere, Rangaku changed again into an official arm of the shogunate. The threat of the West had begun to be felt seriously around the time of the Opium War in 18391842, and the uneasiness of the times was reflected in a shift of emphasis in Rangaku. Whereas before students interested primarily in Western medi­ cine or astronomy had dominated Rangaku studies, now those primarily interested in military science predominated. Rangaku as a whole became ^rjIbid., pp. 121-136 arid pp. 163-177. 28 IbiU, pp. 181-189.

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more and more the study of military science, and translations of Dutch books on military science gradually increased. The shogunate began to adopt Western military arts and to manufacture firearms such as guns and cannons. From the 1830's to Perry's arrival in 1853, a power struggle within the shogunate caused the official attitude toward Western military science to vary, but the number of samurai studying Western military science steadily increased. 29 After Perry's arrival, a number of new governmental institutions for the study of military science and Western learning were set up. The increase in shogunal business with foreign countries and pressures from Japanese leaders to create a Western style army for protection compelled the sho­ gunate to establish a better source of information than their small, limited Rangaku Yakukyoku (Translation Bureau for Dutch Texts). The latter had been set up in 1811 mainly to translate Huishoudelijk Woordenboek by Noel Chomel, a work better known as Chomel'sEncyclopedia. 30 In 1855 the shogunate set up the Nagasaki Kaigun Denshusho (Nagasaki Naval Academy), in 1856 the Bansho Shirabesho (Office for the Investigation of Barbarian Books) and the Kobusho (Military Academy), and in 1857 the Gunkan Sorensho (Training Academy for Battleships) and the Nagasaki Igaku Denshusho (Nagasaki Medical School). Of these several institutions, the Office for the Investigation of Barbarian Books was especially significant. It was intended specifically as a means of meeting the shortcomings of the old Translation Bureau for Dutch Texts. In 1855 the Translation Bureau was replaced by a ydgakusho, or a bureau of Western learning, and in 1856 the new bureau was named the Office for the Investigation of Barbarian Books. The new institution was not only made responsible for the translation of sensitive foreign documents and for the teaching of subjects related to military science, but it was also given authority over aspects of Dutch learning unrelated to government business; in short it was both a governmental office and a training academy. At first only the Dutch language was taught, but in 1860 the curriculum was ex­ panded to include English, French, German, Russian, and some chemistry. In 1862 the office changed its name to Yosho Shirabesho, or Office for the Investigation of Western Books. 31 The Nagasaki Naval Academy was significant, too, because it was the 2 ®S.

Sato, Yogakushi kenkyu josetsu (Tokyo, 1964), pp. 138-139. Chomel, Λ lgemeen Huishoudelijk Natuur, Zedekundig en Konst Woordenboek (Leiden, 1778-1786). The original version was in French, compiled by Chomel in 1709. Later J. A. de Chalmot translated it into Dutch with alterations and additions. 31 I. Sugimoto et al., Kagakushi, pp. 331-336. 3 ®N.

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JAPAN'S FIRST PHYSICISTS

first institution in which Western science was taught by Western instructors hired by the Japanese government. At the request of the shogunate, the Dutch sent a steam-powered gunboat and crew to set up a training center at Nagasaki in July 1855. 32 The first training period lasted a year and three months. A second gunboat with crew was sent to Japan in August 1857, and although the training of a second Japanese group was begun, the program was terminated in January 1859 because of domestic turmoil and financial difficulties. The Dutch taught subjects related to navigation, but, according to Com­ mander PelsRijcken, the leader of the first group, they encountered a serious obstacle in the Japanese trainees' lack of knowledge in such funda­ mental subjects as mathematics. After a year of study, however, students who at the start of training had been unable to compute without the help of an abacus could now calculate square and cube roots and even solve some of the most difficult problems in arithmetic. Some went on to study algebra and trigonometry, and a few came to understand the theory and practical use of logarithms. 33 On the second gunboat was a medical officer, Pompe van Meerdervoort, who came to Japan at the request of the shogunate to teach medical sci­ ence. In addition to medicine he taught the Japanese trainees such subjects as physics, chemistry, and physiology, and he, too, recognized that "a serious hindrance to their progress" was "the want of elementary instruc­ tion in arithmetic, algebra, and mathematics." 34 In spite of these diffi­ culties, however, the trainees were anxious to learn, and showed a great interest in the application of physics and chemistry. Meerdervoort wrote: By means of physics and chemistry the people also are anxious to im­ prove their manufactories and institutions of arts; and my pupils so far as they are able, communicate to others what they themselves have ac­ quired. By this method several manufacturers and merchants have al­ ready introduced improvements in their cotton fabrics. These improve­ ments are observable in their application of both chemical ingredients and mechanical forces. The numerous questions which they have daily to propose, in regard to their instruction, give me pleasing evidence of their success, showing that they are not only indefatigable in their study of 32 The

gunboat arrived as a goodwill gift from the King of Holland. Numata,Bakumatsu ySgakushi (Tokyo, 1950), pp. 90-94. 34 P. van Meerdervoort, "On the Study of the Natural Sciences in Japan,"Journal of the Royal Asiatic Society of Great Britain and Ireland, North China Branch, 2 (1859), 214. 33 J.

KENKICHIRO KOIZUMI

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books, but also most untiring in their experiments to work out satis­ factory results. 35 Thus, through the urgent, practical concerns which brought Western military science to Japan, the mathematical and physical sciences were in­ troduced, gained acceptance, and began to reveal their usefulness. Western sciences were beginning to find a home in officially supported institutions, which was one of Rangaku's most important legacies to modern science. Rangaku and Meiji Science: Rupture and Continuity It becomes clear that, apart from the institutional or administrative con­ tributions of Rangaku, neither Rangaku nor the traditional Japanese sci­ ences provided the basis for the great successes of science in the Meiji period. The career of Nagaoka Hantaro, one of Japan's early physicists, is evidence for this view. As a young student in the early Meiji period, Nagaoka gave no thought to the achievements of Rangaku; before deciding on a scientific career, he sought reassurance through Chinese science (rather than through Japanese work with Rangaku or through the tradi­ tional Japanese sciences) that Orientals had a potential for scientific achievement. He was able to ignore Rangaku and early Japanese science precisely because there was so little continuity between the Dutch and Japanese learning and Meiji science. In its attempt to Westernize, Japan dis­ carded many of the inheritances of the pre-Meiji period. The discontin­ uity between Rangaku and Meiji science can be further illustrated by the rapid rise of English, French, and German learning during the Meiji period and a concomitant rapid decline of Dutch learning. The foreign scientists who were invited to teach in Meiji Japan were mostly from America, England, France, and Germany, not from the Netherlands. The Japanese had been shocked to discover that there were actually very few Western­ ers who understood Dutch, and that the various nations of the Western world differed widely in their cultures. The departure of Rangaku is a conspicuous characteristic of Meiji Japan. Nevertheless, a certain continuity between Dutch learning and Meiji sci­ ence can be detected in the ways in which knowledge was acquired from foreign sources. One was the use of foreign instructors. Before the Meiji period, the visit by Philipp von Siebold was perhaps the most important by any Westerner. A German physician employed by the Dutch East India Company, Siebold was sent to Japan to practice medicine among the 35 Ibid.,

p. 215.

18

JAPAN'S FIRST PHYSICISTS

Dutch at Dejima Island. He later received permission from the commis­ sioner of Nagasaki to leave Dejima to teach medicine and other natural sciences to the Japanese outside the foreign settlement; 36 he thus became one of the earliest officially recognized foreign teachers for Japanese students. Important in this connection were foreigners invited from abroad to teach Japanese trainees at the Nagasaki Naval Academy; although the main subject taught there was military science, the systematic instruction by foreign experts resembled that by foreign scientists in the Meiji period. The continuity between Rangaku and Meiji science is also seen in con­ tinued translations of Western books and the dispatch of students to Western countries for advanced studies. 37 Meiji translations of Western books differed from the earlier only in their sources; Dutch books were replaced by English, French, and German ones; the eagerness with which translations of Western books was undertaken continued unabated, and when all restrictions were lifted, the number of translations greatly in­ creased. The dispatch of students to the West was largely a Meiji endeavor, but in 1862, before the Meiji Restoration, the Office for the Investigation of Barbarian Books had already sent students to Holland to study not only the natural sciences but also philosophy and law. 38 Thus, in spite of the fact that Dutch learning ceased to exist and its accomplishments were ignored in the Meiji period, the methods by which the Japanese pursued Western learning and the foundations on which Japanese science was built remained largely the same during the shift from Rangaku to Meiji science. Because it was the one concrete source of continuity between the old and the new age of Japanese science, the establishment of the Office for the Investigation of Barbarian Books can be considered the most important contribution of Rangaku; it was this institution which, combined with others, formed the core of the University of Tokyo, and it was the Uni­ versity of Tokyo that was almost wholely responsible for the introduction and institutionalization of the Western science disciplines in Japan. The bridge between the pre-Meiji and post-Meiji "scientific" institutions in Japan was the samurai, who saw clearly the need for a strong Japanese 36 J.

Numata, Yogaku denrai no rekishi, pp. 137-139. 1862 to 1868 there were five occasions when students were sent abroad by the shogunate to study the natural and social sciences. During this period forty-seven students were sent to France, England, Holland, Russia, and the United States. In ad­ dition to those sent by the government, a number of students were sent abroad by various fiefs. See M. Watanabe, "Japanese Students Abroad and the Acquisition of Scientific and Technical Knowledge," Journal of World History, 9 (1965), 254-293. 38 Ibid., p. 258. 37 From

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military stance in a newly threatening world. Japan's first generation of physicists, indeed almost all of the early Japanese scientists who modeled themselves on the Western scientist, were former samurai. Japan's con­ frontation with the West in the early 1800's resulted in a strong reaction by the samurai rulers to the encroachment of the West and in their quick recognition of the superiority of Western military technology. In this re­ spect Japan presents a startling contrast to China, which failed to respond in any effective way at all. 39 The speed and relative accuracy of Japan's perception of Western military strength were partly owing to its long his­ tory of military rule by feudal warriors, the samurai. Although the samurai were essentially military men, they constituted at the same time Japan's intellectual class. Prior to the seventeenth century the average samurai had been primarily a warrior occupied with the civil wars that had disturbed Japanese society for centuries. However, after Japan's reunification about 1600 had brought a peace that was to last some two hundred and fifty years, the samurai was forced to adopt a role appropriate to a peacetime society. It became the duty of the samurai to pursue both military train­ ing and general learning to make themselves better governors. By the end of the seventeenth century they had become "a reasonably literate and culturally polished class dedicated to the problem of civil administra­ tion." 40 As the intellectuals of the nation, they constituted the main body of Rangaku scholars and, under the threat from the West from around 1830, the body best equipped to study Western military science. The emergence of Western military science as a major subject for study was of great importance to the development of science in Japan for at least two reasons. First, it created a body of men who later went beyond the study of military science per se to the study of the natural sciences. Second, it led to the establishment of the various institutes for military science to which foreign experts were invited and in which Western natural sciences such as mathematics, physics, chemistry, and medicine were taught systematically for the first time in Japan. Westernization as Progress: The Bootstrap Psychology Since there was no common and fully developed understanding of Western science in Japan during the first half of the nineteenth century, it is important to determine the forces that united Japanese attitudes toward - i9 J. F. Fairbank et al., "The Influence of Modern Western Science and Technology onjapanand China," Explorations in Entrepreneurial History, 7 (1955), 196. 4 0 J. W. HalljJapaM; From Prehistory to Modern Times (New York, 1968), p. 196.

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science in the Meiji era. Aside from military need as a conspicuous unifier, the Japanese shared an appreciation of the practical value of Western science generally. An account of the process whereby the Japanese attitude toward Western science changed from a narrow and suspicious stance to one of widespread enthusiasm is crucial to our understanding of the ulti­ mate success of Western science in Japan and of the physics discipline in particular. During the closing days of the Tokugawa period, while Rangaku was still Japan's only source of knowledge about the West, the Japanese looked upon Western scientific techniques as expedients to adopt for self protec­ tion; they ignored the rest of Western civilization, if they did not hold it in contempt. Their attitude was captured in the slogan Toyo dotoku, Seiyo gakugei, or "Eastern ethics, Western techniques," coined by the samuraischolar Sakuma Zozan. Zozan, a Confucian, took up Western gunnery, be­ came interested in chemistry, tried his hand at manufacturing glass and cannons, and in general advocated the adoption of Western military tech­ niques. He favored the opening of Japan to Western knowledge, but only to learn the techniques for defending it from the outside world. As far as the cultural or ethical side of civilization was concerned, he believed with most of his contemporaries that Japan was unquestionably superior. 41 His viewpoint was completely appropriate to a society in which the ruling class sought to reinforce the old feudal order while supplementing it in material ways. With the Meiji Restoration in 1868, however, the distinctions between ethics and techniques were lost sight of in the initial wave of enthusiasm for all things Western. The old dichotomy between Eastern ethics and Western techniques would surface again after the Western enthusiasm had subsided; but for the first decade or so, Western civilization was imported and emulated so extensively that it began to affect all of Japanese life. A new national slogan emerged reflecting the new age of the fully opened door: Bummei kaika, or "Civilization and Enlightenment." Efforts by the Japanese to live up to the slogan resulted in considerable confusion. There were those who, wanting to be "civilized," threw out their traditional clothing and started to wear Western clothes. They also began to eat meat, a food that for economic and, more important, for religious reasons had never been eaten in Japan. Such emulation might seem superficial, even amusing, yet there were sound reasons for the Japanese to adopt some of 41 R. Tsunoda et al., ed., Sources of Japanese Tradition (New York, 1959), pp. 603-616.

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the material aspects of Western civilization: flowing robes, wooden foot­ gear, and traditional hair styles produced indulgent smiles, if not guffaws, in Washington or London. Japan was urgently seeking equal status with the great powers, and it made the sad discovery that Westerners took a Japa­ nese statesman more seriously in a frock coat and with a beard than in a kimono and with a shaved forehead. The change in values that underlay the concerted effort to Westernize everything from architecture to food and clothing in the new Japan is ap­ parent from an illustration in a book published in the early 1870's (see frontispiece). Three Japanese are shown: one wears the traditional kimono and swords, and has his forehead shaved and his remaining hair tied back in the traditional chommage hairdo; the second wears a half-traditional, half-modern (half-Western) costume consisting of the kimono, an umbrella and a pocketwatch instead of a sword, and a Western cap instead of the chommage hairdo; the third wears a modern (Western) frock coat, trousers, and top hat, and carries a cane. The captions identifying the three read "uncivilized," "half-civilized," and "civilized" man. 42 The illustration is neither naive nor trivial; by identifying the civilized or cultured man with the Western costume, the Japanese artist testified to the new sentiment. He expressed another important idea by presenting the three figures in a single picture. If the picture had shown only a man dressed in Western clothing and identified him as "civilized," it would have indicated a par­ ticular understanding of the concept of "civilized" as defined by a foreign model; but since the three figures are juxtaposed, the picture shows that the artist was aware that Japan was undergoing "progress" in the change from the old Japan to the new. Words like "progress" and "civilization" were attractive and inspiring to the Japanese of the latter half of the nineteenth century. They fully be­ lieved that progress, whatever that might be, was possible for Japan. The Japanese attitude toward these words was, of course, a result of the con­ frontation with the West in the 1850's, but there were other factors that contributed to it. In his discussion of the legacy of Tokugawa education, R. P. Dore points to some of them. According to Dore, the level of literacy in Meiji Japan was not low; education was widespread and eagerly sought, and it was not a case of the government's subjecting the people to un­ welcome instruction or "civilization." Dore argues that the "voluntary choice and sacrifice" of the Japanese to educate themselves in new ways 42 a reproduction of this illustration can be found in J. Fairbank, E. Reischauer, and A. Craig, East Asia: The Modern Transformation (Boston, 1965), plate 23.

22

JAPAN'S FIRST PHYSICISTS

and their belief in the possibility of self-improvement are evidence that Japan was a society that had overcome one of the most difficult and most frequently encountered obstacles to modernization: the view that man's fate is unchangeable. In the ideal-typical "traditional society," things are as they are, and the individual does not see himself as offered the choice of doing, or not doing, anything to alter his society or his position in it. Japan was not such a society. By taking thought one could add an inch to one's, or one's children's, stature, perhaps improve their opportunities in a mate­ rial sense, certainly—in a society in which learning was generally valued— enhance their prestige and self-respect. This awareness, and desire for self-improvement, ensured that opportunities created by the technologi­ cal and political changes would be eagerly taken up. A competitive society could be more easily created because a large proportion of the population had been psychologically prepared to offer themselves as competitors. And where the notion of individual self-improvement was widely diffused the notion of national improvement could be more readily understood and accepted. 43 Under these circumstances, therefore, it is not surprising to find that upon their encounter with the West the Japanese saw themselves as already ad­ vancing toward civilization, and they were eager to fully attain it. They expressed their desire for advancement in both domestic and international concerns. The strong conviction that a nation could improve itself appeared quite often in Japanese writings of the period. When the Darwinian theory of evolution and the Spencerian theory of social evolution were introduced into Japan in the late 1870's and early 1880's, they were, therefore, easily accepted, even welcomed. 44 Both of these theories had a great influence 43 R. P. Dore, "The Legacy of Tokugawa Education," in Changing Japanese Atti­ tudes Toward Modernization, Μ. B. Jansen, ed. (Princeton, 1965), pp. 101-102. 44 M. Koizumi, Nihon kagakushi shiko (Tokyo, 1943), pp. 457-458. The ease with which Darwinian theory was introduced into Japan is partially due to the lack of Christian influence at that time; there was even a certain hostility to Christian tenets. R. S. Schwantes has commented that "the missionaries quickly realized that the strongest opponent [to the conversion of the Japanese to Christianity] was not the religions and superstitions of old Japan but the skepticism of modern Europe"; the latter entered Japan with Western learning. See R. S. Schwantes, "Christianity versus Science: A Conflict of Ideas in Modern Japan," Far Eastern Quarterly, 12 (1953), 124.

KENKICHIRO KOIZUMI

23

on Japanese views of society, especially in underscoring their belief in Japan's ability to lift itself out of a feudal middle age and compete on terms of equality with modern Western nations. At the same time the con­ cept of competition as represented by the Darwinian expression "survival of the fittest"—yusho reppai, or "superior wins, inferior loses," as it was translated into Japanese—contributed to a broadening of the competitive spirit in Japan. For more than a thousand years the Japanese had valued an ethic of self-improvement that meant literally that one competes with oneself to improve oneself. Now that Japan was confronted with an ap­ parently superior and powerful West, the ethic no longer referred to indi­ vidual self-improvement, but to a national competition in which the entire nation lifted itself by its own bootstraps so that it could compete with the encroaching Western nations. The Selling of Western Science Apart from the government, which encouraged the adoption of various aspects of Western learning and civilization through its policies and through the founding of institutions, private popularizers played an indispensible part in the creation of Japan's positive attitude toward Western science and modernization. No man outside the government was more influential in this regard than Fukuzawa Yukichi, the most famous propagandist for Western learning and civilization in Meiji Japan. Born to a low-ranking samurai family in 1835, Fukuzawa went to Nagasaki in 1854 to study Dutch and Western gunnery with Rangaku scholars, a move that a number of samurai made in response to Perry's threatening arrival the year before. In 1855 he moved to Osaka to continue his Dutch studies and to learn the rudiments of Western physics, chemistry, and medicine from a well-known physician. In 1858 he was asked by his fief to start a school in Edo-which later became Keio University, one of Japan's first and most famous private universities—to teach Dutch to fief members residing there. On a visit to Yokohama, however, Fukuzawa was stunned to learn that the residents in the small foreign settlement there could not understand a word of Dutch and that his years of study had been in vain. He immediately set about teaching himself English, and in 1860 he signed onto a Japanese ship sailing to San Francisco as personal servant to the captain. Two years later he was sent to Europe as an interpreter for a treaty delegation; an avid ob­ server of Western life, he made prodigious notes on Western institutions and on anything that he felt would not be explained in books. His note­ books provided the basis for a book he wrote in 1866, Seiyo jijo [Con-

24

JAPAN'S FIRST PHYSICISTS

ditions in the West), which became a best seller and established Fukuzawa as one of the country's chief authorities on the West. 45 Fukuzawa felt that at a time when Japan's confrontation with the West was marred by confusion about the West, his primary task must be to offer guidance to the Japanese public by informing them of the true nature of Western civilization and its potential contribution to Japan. Fukuzawa, though an educator and journalist and not a scientist, also played a key role in inculcating in the Japanese public an attitude receptive to Western science. 46 He was fascinated by science, and he believed that as long as the Japanese did not view their natural environment as Westerners did, i.e., in a "scientific way," they would never grasp the spirit of Western civilization nor acquire a "civilizing" level of material and technical affluence. In 1868 he wrote Kummo kyuri zukai (Elementary Natural Philosophy with Illus­ trations), a book that was popular throughout the 1870's. Through it he hoped to instill in the general reader an appreciation of the necessity of examining his natural environment in light of the new Western explana­ tions of natural phenomena. The Japanese had always lived close to nature, but they had had an accepting, not a probing and questioning, relationship with nature. Western science now provided a new way of looking at and explaining the world. The new attitude is illustrated by the rejection of traditional explanations of lightning, one of which was that it was the anger of the lightning god, and the acceptance of the modern explanation of lightning as electricity. Although the view of lightning as electricity and that of lightning as the anger of a god might have been equally satisfying as explanations, the practical implications of the new explanation made it superior to the traditional one. In Japan the Western explanation of lightning was introduced together with a practical electrical device that could save people's lives, the lightning rod, and with vivid accounts of its efficacy in preventing disasters in the West. 47 The traditional Japanese ex­ planation of lightning suggested prayer to the lightning god as the only 45 For full details on Fukuzawa, see Y. Fukuzawa, The Autobiography of Yukichi Fukuzawa, trans. E. Kiyooka (New York, 1966). 46 Fukuzawa's Gakumon no susume (Encouragement of Learning), written between 1872 and 1876, and Bummeiron no gairyaku (Outline of Civilization), written in 1875, were probably the most frequently read books of this period, arousing interest not only in the cities but also in rural areas. To this day it is possible to uncover copies of his works stored away among the treasured belongings of old Japanese farming families in remote areas. See D. Irokawa, Meiji no bunka (Tokyo, 1970), p. 68. 47 A. Obata, Tempenchii (Tokyo, 1868). Part of it is reprinted in Nihon kagaku gijutsushi taikei (hereafter abbreviatedNKGT), 8, 144-145,

KENKICHIRO KOIZUMI

25

protection, and that had not proved thoroughly reliable. The new explana­ tions, allowing for applications, served to break down old superstitions, to reduce fear, and to establish a new relationship between man and his environment. In his Kummd kyuri zukai, Fukuzawa compared the man who lives in the midst of nature and yet is oblivious to its true workings to a horse that eats without knowing what it is eating. His discussion dealt mainly with phenomena of daily life: heat, air, water, weather, universal attraction, the seasons, and eclipses. Since he wrote the book for the general public, he confined himself to illustrating the new explanations of natural phenomena; he did not present natural philosophy or physics as something worth pursuing as a pure science. Fukuzawa urged the reader to reflect upon the various natural phenomena, but he did not provide a methodology or a theoretical basis for explaining all phenomena. He talked about universal gravitation, for instance, but only to explain the relation­ ship between the sun and the earth and to show why objects on earth do not fly away under the influence of centrifugal force. 48 Fukuzawa, in short, gave Western science a popular formulation that allowed his Japa­ nese audience, which up to that time had been either indifferent or mis­ informed, to examine a selection of its contents for themselves. Although he made no pretense of teaching physics per se, he prepared the Japanese mind for the idea that, above all else, the principles of nature should be studied by the new citizen of the new age. In 1882 Fukuzawa published a short article "Butsurigaku no yoyo" ("The Necessity of Physics") which clarified his view of science: 49 Physics is a study based upon the laws of nature which clarifies the properties of things, perceives their functions, and applies these findings in the service of human affairs, and it naturally has some elements which differ from other branches of knowledge. For example, although we now speak of economics and commerce and refer to both as branches of knowledge, under present circumstances things like economics and commerce still do not in the least base themselves upon the laws of nature. The reason I say this is that in economics and commerce there are those who advocate a free economy and those who are protectionists, 48 Y. Fukuzawa,Kummo kyuri zukai (Tokyo, 1868). The third edition (1872) is re­ printed in Fukuzawa Yukichi zenshu (Tokyo, 1960); see pp. 269-272. 49 Y. Fukuzawa, "Butsurigaku no yoyo," Jiji shimpo (22 March 1882), reprinted in Fukuzawa Yukichi zenshu, 8, 49-52.

26

JAPAN'S FIRST PHYSICISTS

and these two do not share the same basis. Scholars in England say that a free economy is reasonable, while scholars in America say that a pro­ tective economy is the proper way, and listening to them, it seems that both make sense. Thus we are compelled to say that the principles of economics and commerce in England and America are of different molds. [However,] the principles of nature are not at all that way. From the beginning of creation up until today the world has remained the same throughout ancient and modern times and has not changed. Water in the prehistoric age boiled when it met with heat at a temperature of 212°F, and water in the [present] Meiji period reacts in the same way. Steam in the West and in the East do not differ in expansive force. If an American dies of taking too much morphine, a Japanese also dies if he takes the same dosage. These we call the principles of nature, and the search for them and the use of them we call physics. There should be nothing which escapes these principles. If there is something which seems not to follow them, one should understand it to be a case where the search for principles has been insufficient. 50 Fukuzawa was by no means the only spokesman for Western science, al­ though he was the most articulate and famous. He was unusual among scholars and popularizers of Western studies in being one of the first and most influential writers to demonstrate a concern for making Western science generally accessible in Japan. Japanese men of science did not devote much of their time to the popu­ larization of Western science. Only a few tried to reach beyond the scholarly community to explain science and its uses to the Japanese public and to affect public opinion. Some advocated science as the source of a new morality. Sugiura Jugo, for instance, who had been educated as a chemist in England from 1876 to 1880 and had returned to become a wellknown educator and nationalist, in 1888 attempted to explain all human affairs by means of the energy conservation law and the wave theory. According to Sugiura, the energy conservation law explains why a person who does good goes to heaven and one who does otherwise goes to hell: to do good is to store up the energy required to enter heaven. 51 His use of the wave theory is as crude as his use of the energy conservation law. He sees all phenomena as possessing a cyclic nature to which the wave theory s o Ibid.,

p. 49. Sugiura, ''Jinji mo mata butsuri no teisoku ο hanarczu," Yomiuri shimbun (22 June 1888), reprinted in Sugiura JtigS sensei zenshu (Tokyo, 1945), 1, 126. 5 1 J.

KENKICHIRO KOIZUMI

27

can be applied; for him the rise and decline of a nation or person point to the application of the wave theory to all affairs in the universe.52 Sugiura's application of the energy conservation law is reminiscent of the philosophy of energy held by the German physical chemist Wilhelm Ostwald. Around 1902 Ostwald tried to explain all phenomena, natural and social, by a single reality, energy. However, Ostwald's objective differed greatly from that of Sugiura, who seems to have had two purposes. One was to establish a moral system based upon science rather than religion. The other was to create a new theory by which all future mun­ dane events would become as predictable as astronomical phenomena, for Sugiura believed predictability to be one of the most important attributes of physics.53 In all of his considerations, however, he was much more con­ cerned with society than with nature, and it was perhaps this concern that led him to give up chemistry and to become an educational administrator and writer after his return from England. It is noteworthy that he in­ terpreted physics not as a weapon against nature, as it was so often in­ terpreted in the West, but as a key to the establishment of a new type of society. In this respect his view of physics resembled Fukuzawa's. One of the most articulate spokesmen for pure science was Kikuchi Dairoku, a graduate in mathematics from Cambridge University in 1877, who returned to Japan to become the first Professor of Mathematics at the University of Tokyo and to later serve as President of the University (1898) and Minister of Education (1901). In 1884 Kikuchi gave a speech about science in which he sought to clear up popular confusion about the difference between pure and applied science. Kikuchi felt no need to ex­ plain applied science, which was understood and which was indeed the main concern of government leaders. Rather he took particular pains to elucidate the importance of pure science. Using the discoveries of elec­ trical engineering as examples, he explained that without the foundation provided by prior basic research on electric current even hundreds of Edisons and Bells could not have developed electric lights or the telephone.54 Kikuchi's defense of pure science shows how highly Japanese society valued practical science at that time. In emphasizing the benefits of pure science, he shows himself, too, a product of his age and he indicates an understanding of his audience. s 2 Ibid.,

pp. 127-128. pp. 129-130. 54 D. Kikuchi, "Rigaku no setsu," in NKGT, 2, 533-534. Originally published in Toyogakugei zasshi, 2 (1884), 75-81. 5 3 Ibid.,

28

JAPAN'S FIRST PHYSICISTS

In the writings of both Kikuchi and Sugiura, pure science is justified solely by its benefits. They differed from their contemporary Sakurai Joji, who had received his education in chemistry at the University of London from 1876 to 1881, during the time that Sugiura was in England, and re­ turned to become Professor of Chemistry at the University of Tokyo and, later, Dean of the College of Science. In 1888, he published a short article, "Rigakusha no kairaku" ("The Pleasure of the Scientist"), 55 in which he viewed science as an autonomous entity and described the scientist as the craftsman of a "castle of knowledge," who, by adding new knowledge to the castle, gains pleasure and honor. Sakurai's nonconformist interpreta­ tion of science and his failure to draw any moralistic conclusion from science point to an attitude close to one that values science for its own sake. That attitude was at best short-lived; science for its own sake does not seem to have had other advocates in Japan until Poincare's writings appeared there in the early decades of the twentieth century. 56 Despite his early view of science, Sakurai gradually came to emphasize the value of science as a source of power for the nation. In 1899, eleven years after publishing his article "The Pleasure of the Scientist," Sakurai expressed this new view in his "Kokka to rigaku" ("The Nation and Science"). 57 At the beginning of the article he reiterated the view he had expressed in his 1888 article, but he used a different image. He said that science is that which advances human knowledge and which investigates the structure and operation of the vast machine called nature. He was evi­ dently the first in Japan to refer to nature as a machine placed at man's disposal. 58 He used an image familiar to the machine age—to the age of steamships and locomotives that Japan had entered—and one more realistic and practical than that of a castle of knowledge. Sakurai's main point was that the nation in which pure science flourishes best acquires the most power. The change in Sakurai's position from insistence on the autonomy of scientific activity to an emphasis on the advantages the nation derives from science reflects the modernization process Japan had been under­ going during those years and the growing national self-confidence that accompanied it. 55 J.

Sakurai, "Rigakusha no kairaku," Tdyo gakugei zasshi, 5 (1888), 437-442. for example, M. Mitsumori, "Tokyo butsuri gakko zasshi dainihyakugo hakkan ni tsuite," Tokyo butsuri gakko zasshi, 17 (1908), 279-280, and A. Kuwaki, "Henri Poincare," Toyo gakugei zasshi, 29 (1912), 457-466. 57 J. Sakurai, "Kokka to rigaku," in NKGT, 2, 504-508. Originally published in Taiyo, 5 (1899), 10-17. 5 i I b i d . , p. 505. 56 See,

29

KENKICHIRO KOIZUMI

Sakurai's "The Nation and Science" was written four years after Japan's victory over China in the Sino-Japanese war of 1894-1895. That war was Japan's first after the outside world had begun to threaten it, and the first foreign war in its history. It was a time of rising self-esteem and national­ ism; after the war the Japanese spoke less of survival and more of pulling abreast with and surpassing the West. The West, which had tended to look indulgently on the "superficiality" of Japan's modernization, was amazed by the "reality" of its victory over China. Europe became extravagantly enthusiastic about Japan: its arts were admired and the kimono became a fad. Edwin Arnold wrote in The Spectator that "in attacking China in Corea, [Japan] is guarding the civilized world."59 The Western reaction further encouraged Japan's drive toward scientific excellence. The Japa­ nese could now believe that through science Japan had already pulled itself up by its bootstraps. It had survived, and now science was to lead it to the heights of civilization.

3.

THE THE

INSTITUTIONALIZATION OF PHYSICS PHYSICAL SCIENCE DISCIPLINES

AND

Japan's First University Throughout Japan's modern history the University of Tokyo has played the major role in the introduction of Western knowledge, especially of Western science. Table A (Appendix) shows in detail the gradual develop­ ment of educational institutions leading up to the founding of the Uni­ versity of Tokyo. In 1870 the Japanese government began to combine several educational institutions into one loosely coordinated "university." Its origins dated from the 1630's when the Hayashi family started what might be called a state university with the backing of the Tokugawa shogunate and offered a curriculum largely devoted to the Chinese classics and Confucian studies. This school was designated the core of the newly expanded institution and was referred to as the Daigaku or Uni­ versity. The descendent of the Office for the Investigation of Barbarian Books, known as the Kaiseijo (Kaiseijo Office), was renamed Daigaku Nanko, or University, Southern Division, in 1870, and was intended to 59 Quoted in D. Keene, "The Sino-Japanese War of 1894-95 and Its Cultural Effects in Japan," in Tradition and Modernization in Japanese Culture, D. Shively, ed. (Princeton, 1971), pp. 173-174. The original can be found vaThe Spectator (1 Sep­ tember 1894), p. 263.

30

JAPAN'S FIRST PHYSICISTS

specialize in Western studies. Another division, Tokyo Igakko, or the Tokyo Medical School, also joined the complex. Ironically, it was the original state university that failed to survive the transition. Debates over the nature of its role in the complex of facilities and the desirability of its concentration on Chinese and Confucian studies divided the faculty and administrators and led to the total collapse of the university. The Daigaku Nanko, or University, Southern Division, however, prospered and became more or less independent, simplifying its name to Nanko or Southern Division in 1871, to Daiichi Daigaku Ku Daiichiban Chugakko (The First Middle School of the First University) in 1872, and to Tokyo Kaisei Gakko (The Tokyo Kaisei School) in 1873; in 1877 it was combined with the Tokyo Medical School to form the University of Tokyo. The Tokyo Kaisei School was the descendent of the Office for the Investigation of Barbarian Books, separated from its ancestor by a period of seventeen years and many name changes. Similarly the Tokyo Medical School had evolved over a period of ten years and under various names from the Edo Shutojo (Edo Vaccination Office). Both original institutions had been established as the result of the impact of the West; their aims be­ came those of the University of Tokyo, which they ultimately formed. In 1886, in the last major change in university education, the Ministry of Education under the Meiji government issued the Imperial University Ordinance, which designated the University of Tokyo as Teikoku Daigaku, or Imperial University. For the first time, the University's role in a new Japan was clearly defined, as is clear from the first article of the Ordi­ nance: "The Imperial University is to take as its aim the teaching of the liberal and vocational arts which respond to the needs of the nation, as well as the pursuit of the deepest principles behind them." 60 The University of Tokyo at its inception in 1877 had four faculties, those of law, medicine, literature, and science. Upon becoming the Im­ perial University in 1886, however, a college of engineering was added by absorbing into the University the Kobu Daigakko, or School of Engineer­ ing, that had been run by the Ministry of Engineering since 1873. The latter, an independent scientific educational institution, had trained more than two hundred engineers for the Ministry by the time it joined the Imperial University. The decision to include the School of Engineering in the University clearly reflected the needs of the time in Japan; from the

60 Quoted

in T. Okubo,Nihon no daigaku (Tokyo, 1943), p. 315.

KENKICHIRO KOIZUMI

31

standpoint of educational policy it was an unusual and farsighted move, recognized as innovative even by foreign observers.61 In 1886 the first graduate school was established, marking the com­ pletion of a modern university in Japan. The Imperial University went through one more name change when, in 1897, another Imperial Univer­ sity was built in Kyoto. The original Imperial University then took the name Tokyo Imperial University, and the new one the name Kyoto Im­ perial University. The Problem of Instructional Language In 1873 the Tokyo Kaisei School, one of the predecessors of the Uni­ versity of Tokyo, made the important decision to adopt English as its major foreign language.62 Since 1868, the students of the institution had been studying their subjects using English, German, and French. The abrupt change to English proved impossible for some students and com­ pelled school officials to find a device that would enable some to complete their studies in French or German. They created two temporary divisions of the Tokyo Kaisei School for this purpose: Shogeigakka and Kozangakka. The former was a Japanese equivalent of an Ecole polytechnique and was intended for students whose only foreign language was French; the latter was a newly formed Department of Mining which received all students who knew only German.63 Thereafter the school officials accepted no new ap­ plications for admission to these departments, for they planned to termi­ nate them as soon as the original students had graduated. The significant point is that educational divisions were made on the basis of the language of instruction, not on the basis of subject matter. However, these divisions proved too great a financial burden on the school, which was reluctant to provide the equipment necessary for the various subjects. The divisions 61 Tanakadate Aikitsu, a physicist, recorded in his diary the following comment that W, K. Rontgen made to him when he visited Rontgen in 1898. Rontgen said, "It was certainly farsighted of your country to class the engineering school on a level with the university. Although we are about to set up that sort of organization [in Ger­ many] , obstinate old men of theology and law object to it as if they understand everything, and so we have been hindered by them." Tanakadate's diary is deposited at the National Science Museum in Tokyo. ^2NeedIess to say there were no textbooks concerning scientific subjects written in the Japanese language. All books selected for classroom use were written in foreign languages. 63 Tofeyo teihohu daigaku gojunenshi (hereafter abbreviated as TTDG) (Tokyo, 1932), 1, 258-259.

32

JAPAN'S FIRST PHYSICISTS

were abolished in 1875, two years after they had been set up, and new divisions were organized for the remaining students. The school established two more limited departments: French Physics for the old Shogeigakka students and German Chemistry for the Kozangakka students.^ Since only ten students applied to the German Chemistry Department as compared to forty-three applicants to the French Physics Department, the school officials decided to cancel the German Chemistry Department. 64 The French Physics Department, called Futsugo Butsurigakka, or Department of French Language Physics, survived until 1880 when the last students graduated from it; in all, it graduated twenty students: five in 1878, seven in 1879, and eight in 1880. 65 By 1880 English was the main foreign language for all students. That year German became the required second foreign language, and French was discontinued as an option for students in the sciences. 66 But from 1877, when the University of Tokyo was established, to 1880, physics had been taught separately in both French and English, The expensive duplica­ tion had the unforeseen advantage of preventing the dominance of any one Western country in the introduction of Western sciences. If in its efforts to modernize, Japan had fallen under the exclusive or predominant influence of a single Western country, it would have lost the freedom to choose whatever it wanted from different countries. In medicine, for instance, Japan adopted the German system and invited medical doctors from Germany to practice, teach, and help set up a national medical system. Or again, the Japanese navy was established according to the British system, the army according to the French system with later German modifications. The great advantage that Japan derived from free access to all of Western civilization was partly offset by the many problems arising from the im­ portation of various institutions from different countries with their differ­ ent cultures. Thus, Japan not only had to make an adjustment between her own traditional culture and Western culture, but also had to make effec­ tive compromises between different Western cultures. For instance, the Japanese army bought weapons from Germany, while the navy bought battleships from England. Since Germany and Britain used different mea­ suring systems, the standardization of imported industrial goods was a difficult problem; neither the army nor the navy was willing to compro6 4 Ibid.,

pp. 301-302. p. 626. 6 6 Ibid., pp. 640-646. 6 5 Ibid.,

KENKICHIRO KOIZUMI

33

mise. 67 In this example the conflict is clear, but subtler cases make it diffi­ cult to determine the overall effect of European cultural heterogeneity on Japan's modernization. The differences in approach to national problems, to education, and to personal relations among Europeans forced the Japa­ nese to conclude that they could successfully carry out the task of mod­ ernization only by a piecemeal introduction of Western civilization, select­ ing what seemed useful from the various countries. Nevertheless, the im­ portation of Western civilization in this way caused the Japanese living in the transitional period to feel a lack of continuity and to sense the lack of something capable of holding together the different cultures. Foreign Teachers Specialists, too, were imported along with Western learning. Between 1872 and 1898, the Japanese government employed more than 6,000 foreigners, mainly English, French, German, and American. If privately employed Westerners are included, there were more than 18,000 foreign specialists in Japan at various times during this period. 68 The specialists were called oyatoi gaikokujin, or "honorable foreign em­ ployees," a term frequently abbreviated to oyatoi, or "honored em­ ployees." Although oyatoi gaikokujin had been brought to Japan prior to the Meiji period, the peak of their importation came in the mid-1870's; there were 524 employed by the government in 1874, and 527 in 1875. Thereafter, the number fell rapidly, decreasing by half in five years; in 1894 fewer than a hundred remained. The number of privately employed foreigners increased steadily, except for a short period of decline around 1886, reaching a maximum of 765 in 1897. 69 The reason for the rapid de­ crease of the number of foreign employees in the government was largely financial. The salaries of the oyatoi gaikokujin employed by the University of Tokyo in 1877 made up as much as one-third of the entire budget of the Ministry of Education, a financial burden that hastened the replace­ ment of the oyatoi gaikokujin by Japanese in government institutions. 70 Of the oyatoi gaikokujin employed by the government in 1880, the engineers and schoolteachers outnumbered all others. Throughout the Meiji period, the teachers of the natural sciences formed the largest class of 67 N.

Umetani,Oyatoi gaikokujin (Tokyo, 1968), 1, 215. pp. 52-53. 6 9 Ibid. 7 0 Ibid., pp. 207-208, and I. Sugimoto et al.,Kagakushi (Tokyo, 1967), p. 377.

6 s Ibid.,

34

JAPAN'S FIRST PHYSICISTS

foreign experts in the government (about forty-six percent). Of these, one half were German, approximately one fifth were British and another fifth American, and the remainder were largely French, with a few teachers from other countries. The engineers, however, were largely from England; the British contingent accounted for almost seventy-eight percent of the total. 71 Generally speaking, therefore, German and British influence was strong in the natural sciences and engineering. With regard to physics I must qualify my conclusion: no German physics specialists were invited to Japan, so that there was no direct German contribution from the oyatoi gaikokujin to Japanese physics. However, from the 1880's on, a consider­ able number of Japanese physicists went to Germany for postgraduate work. 72 The original members of the Faculty of Science, consisting of the five departments of Chemistry, Mathematics-Physics-Astronomy, Biology, En­ gineering, and Geology-Mining, are given in Table B (Appendix). Berson and Mangeot, together with a third professor, Prosper Fouque, who left in 1877 when the University of Tokyo was established, had been members of the French Physics Department. Mangeot left the University in 1879 and Berson in 1880 when the department was terminated. 73 Most of the origi­ nal faculty were oyatoi gaikokujin, which indicates that Japan was still dependent on foreign expertise. Fourteen years later, however, the oyatoi gaikokujin in the College of Science had been completely replaced by Japanese professors. Two processes were at work during this period. First, as their contracts ran out the old oyatoi gaikokujin were replaced by new ones; by 1882 the original oyatoi gaikokujin had all left the University. Second, Japanese began to be promoted to professors. Of the faculty members representing physics or closely related disciplines, R. H. Smith, Professor of Mechanical Engineering, left the department in 1878, and in October of the same year James A. Ewing, a Scot, came as his replace­ ment; P. Veeder, Professor of Physics, also left in 1878, and Thomas C. Mendenhall, an American, was invited to replace him. In 1879 Yamagawa Kenjiro was promoted to Professor of Physics, and Mangeot, Professor of " i l Ibid., p. 54 and pp. 88-89. 72 For fuller discussion, see below, Chapter IV, section on "Foreign and Domestic Training." 73 TTDG, 1, 675-677. Unfortunately the above source does not give foreign names in roman letters but transcribes them all phonetically into the Japanese script, making them hard to identify. E. Ueno's Oyatoi gaikokujin, 3 (Tokyo, 1968) is helpful in identifying some names in their original language. The rest, which are my guesses, are marked with an asterisk. I also used Ueno's work for identifying nationalities.

KENKICHIRO KOIZUMI

35

Mathematics, left. In 1880 Hiraoka Morisaburo 74 was appointed Professor of Physics, and Debsky and Berson left. In 1881 Mendenhall left, as did Ewing in 1883, the year Cargill Knott, an Englishman, was hired. In 1886, when the University of Tokyo became the Imperial University and the Faculty of Science became the College of Science, only two oyatoi gaikokujin, Knott and another Englishman Edward Divers, Pro­ fessor of Chemistry, remained. 75 The Physics Department consisted of two full Professors of Physics, Knott and Yamagawa Kenjiro, one Assistant Professor, Tanakadate Aikitsu, and one Lecturer, Muraoka Han'ichi. In 1888, when Tanakadate left for the University of Glasgow to study elec­ tricity and magnetism under William Thomson, Nagaoka Hantaro, then a graduate student, was invited to take over Tanakadate's duties while he was abroad. In 1890 Nagaoka was promoted to Assistant Professor of Physics, and in 1891 Tanakadate, returning from abroad after three years of study, was promoted to Professor of Physics to replace Knott who left Japan the same year. 76 Knott was one of the last of the oyatoi gaikokujin. Mendenhall and Ewing Of the foreign scientists, Mendenhall and Ewing were especially impor­ tant for Japanese physics. Mendenhall, born in Ohio, had never received a formal higher education. He had studied science on his own and had taught in high schools when, in 1873, he was invited to teach physics and me­ chanics at Ohio Agricultural and Mechanical College (now Ohio State University). He was invited to Japan on the recommendation of E. Morse, one of the oyatoi gaikokujin. Mendenhall taught physics and directed the laboratory work of students majoring in chemistry and physics at the University of Tokyo. In training the physics students, he did not limit the laboratory experiments to mere repetitions of known experiments. To­ gether with his students, he measured the force of gravity in Tokyo, and in 1880 he took his students to the top of Mt. Fuji to determine the density of the earth. A year later, after he had left, his students carried out 74 Hiraoka

MorisaburS was born Ichikawa Morisaburo; he was adopted into the Hiraoka family in 1875. See J. Sugiura, "Ichikawa MorisaburS kun ryakuden," TByo gakugei zasshi, no. 14, pp. 362-363. 75 TTDG, 1, 675-684 and 1360-1362. Besides these scientists at the University of Tokyo, there were a number of oyatoi gaikokujin at the engineering school. When Kobu DaigakkS was erected in 1873, all eleven of the faculty members were oyatoi gaikokujin. After the institution became the College of Engineering at the Imperial University, only three out of twenty-two faculty members were foreigners: two pro­ fessors and one lecturer. See ibid, t, 1264-1266, and ibid., 2, 1316-1317. 1 ^Ibid., 1, 1361-1364.

36

JAPAN'S FIRST PHYSICISTS

the same experiment in Sapporo on the northernmost island of Japan, where they also measured the strength of terrestrial magnetism. In the years that followed, similar experiments were carried out all over Japan and formed an important part of Japanese scientific activity. Although Mendenhall spent less than three years in Japan, his influence on Japanese physicists was great: he was the first professor of physic^ at the University of Tokyo (the earlier physics professors had been in the French Language Physics Department), and he initiated experimental geophysical research that his students, especially Tanakadate Aikitsu, continued. 77 Ewing was born in Dundee, Scotland. He was a graduate of the Uni­ versity of Edinburgh, where he studied engineering under Fleeming Jenkin. Jenkin, who together with William Thomson was in the business of manu­ facturing and installing submarine telegraph cables, recommended Ewing for a position on three cable-laying expeditions in South America. In 1877 Ewing accepted a professorship in mechanical engineering at the University of Tokyo, where he taught such subjects as mechanical engineering and heat engines to engineering students, and mechanics, electricity, and mag­ netism to physics students. However, it was through activities outside teaching, especially through his research in magnetism and seismology, that Ewing exercised most influence on Japanese physicists. The physics stu­ dents working under him, in particular Tanakadate Aikitsu, Fujisawa Rikitaro, Tanaka Shohei, and Sakai Saho, participated in his research on magnetism, conducting graduate experiments that were related to his hysteresis investigations. Although Ewing's contributions to hysteresis were largely rediscoveries of phenomena studied earlier by such physicists as Kohlrausch, Fromme, Cohn, Stoletow, Rowland, and Warburg, 78 he and his students carried out their experiments without knowing the work of their predecessors. By allowing his students to aid him in his experi­ ments, Ewing gave them invaluable experience and training; he also made it possible for them to gain the confidence that the Japanese could make 77 M. Watanabe, "T. C. Mendenhall no sh5gai to katsudo," Kagakushi kenkyu, 79 (1966), 113-114. E. Uchida, "T. C. Mendenhall no Nihon ni okeru kenkyu gyoseki ni tsuite," Kagakushi kenkyu, 83 (1967), 133-136. S. Nakamura, Tanakadate Aikitsu sensei (Tokyo, 1946), pp. 54-66. Mendenhall left $2,500 m his will to the Japanese Imperial Academy for the establishment of a Mendenhall prize for physics. 78 R. T. Glazebrook, "James Alfred Ewing 1855-1935," Obituary Notices of Fel­ lows of the Royal Society, 1 (1932-1935), 475-492. E. Warburg wrote a letter to the Philosophical Magazine complaining that Ewing's work was repetitious in nature, and that in particular his research on magnetic hysteresis had already been carried out by Warburg himself, the result of which had been published in 1880, a year prior to Ewing's publication on the same subject. See Philosophical Magazine, 15 (1883), 246-247.

KENKICHIRO KOIZUMI

37

original contributions to science if they had the proper apparatus. Tanakadate expressed his gratitude to Mendanhall and Ewing for taking the initia­ tive among the oyatoi physics teachers in encouraging students to partici­ pate in their researches and for showing their students that their researches contributed to science in a fundamental way. 79 Like Mendenhall's, Ewing's research on magnetism was continued and developed, though on a small scale and by only one of his students, Tanakadate. In 1888 Nagaoka Hantaro, one of the younger graduate students, also began related research on magnetism under Knott's influence, building on the groundwork Ewing had laid earlier. Nagaoka applied himself vigor­ ously to experiments related to the study of magnetostriction, and as a re­ sult was invited to report on magnetostriction at the First Physics Inter­ national Congress held in Paris in 1900. 80 One of Nagaoka's students, Honda Kotaro, in turn carried on Nagaoka's investigations, moving grad­ ually on to the study of ferromagnetic substances, and playing a crucial role in the development of metallurgy in Japan. Mendenhall and Ewing initiated two different types of physical research that became institutionalized in Japanese physics. The research initiated by Mendenhall, namely, measurements of the force of gravity and terrestial magnetism in various parts of Japan, had local significance. By contrast, Ewing's work had universal significance for the properties of matter. Mendenhall's field activity and Ewing's laboratory activity represented different approaches to the conduct of physics. These two approaches were transmitted by the oyatoi gaikokujin to the Department of Physics and both continued to be developed by their students. The Faculty of Science and the Development of Physics T. Hiroshige has pointed out that the Faculty of Science at its birth in 1877 was oriented toward engineering and the practical. 81 The structure of the Faculty of Science, indeed the orientation of the University itself, tended to favor sciences that were useful in solving practical problems facing the nation. Mathematics, physics, and chemistry were combined to make up one department, whereas engineering and geology-mining consti­ tuted separate departments. The practical orientation is also apparent in some of the arguments that emerged when the University curriculum was "S. Nakamura, Tanakadate Aikitsu sensei, p. 70. 80 H. Nagaoka, "Sur la Magnetostriction," Rapports presente au Congres Interna­ tional de Physique feuni aParis en 1900 (Paris, 1900), 2, 536-556. 81 T. Hiroshige, "Shakai no naka no kagaku (1)," Shizen, 26 (1971), 100-101, and TTDG, 1, 467-472.

38

JAPAN'S FIRST PHYSICISTS

formulated. There were two conflicting opinions. One was that as long as the institution bore the name "University," it ought to base its curriculum on that of Western universities and provide advanced studies to train scholars. The other was that in view of the practical problems Japan faced at the time, the University should establish a curriculum that was simple and useful to the Japanese people. Both opinions had shortcomings, and in the end the school officials decided to combine them in a curriculum that required each department to offer both pure and applied studies. 82 The emphasis on applied subjects, however, does not sufficiently explain the apparent slighting of mathematics, physics, and astronomy in assigning the three subjects to one department. Tanakadate, recalling his days as a student in the department, says that the three subjects had been combined because University officials were concerned about the future careers of students. They worried that a student majoring in only one of the subjects, say physics, might not be able to find a job directly related to it after graduation. 83 At the same time, physics was taught in both the chemistry and the engineering departments to first- and second-year students. The explanation is that the Japanese thought it less significant to pursue the discipline of physics in its own right than to use it as a tool in other disci­ plines. The subsequent development of physics shows how it emerged as an autonomous discipline. In the curriculum of 1877 there was still almost no difference between the programs for students of either mathematics, physics, or astronomy; by 1880 students were required to choose one of the fields as a major in their sophomore year. Physics students were re­ quired to take analytical chemistry but were not required to take pure mathematics or astronomy. A year later, when mathematics, physics, and astronomy were made into independent departments, pure mathematics and astronomy became requirements for physics students. The next great changes took place in 1886: the University of Tokyo be­ came the Imperial University, the Faculty of Science changed its name to the College of Science, and the School of the Ministry of Engineering was absorbed by the Imperial University as the College of Engineering. The engineering departments of the old science faculty were transferred to the College of Engineering, and for the first time the study of science in Japan became independent of the study of engineering. This did not mean, how­ ever, that science was to be studied for its own sake, free from all practical considerations. As indicated in the 1886 Ordinance, the Imperial Uni­ versity was to be useful to the nation; like all other researchers and edu82 IbiU, 83 A.

p. 471. Tanakadate, "Buturigaku Omoide," Nihon butsuri gakkai shi, 5 (1950), 316.

KENKICHIRO KOIZUMI

39

cators in the Imperial University, scientists were bureaucrats who served the state. During the same year, 1886, graduate programs were established in each College, making the Imperial University the first institution in Japan capable of conducting advanced research. The University became the country's main center of academic and research activity in science; it remained so even after the establishment in 1897 of a second Imperial University in Kyoto. Turning to the production of trained physicists, we find that between 1878 and 1880 twenty men graduated from the old French Language Physics Department. The Mathematics-Physics-Astronomy Department of the University of Tokyo produced its first three graduates in physics in 1882, trained by men like Mendenhall, Ewing, and Yamagawa. From 1883 to 1892 there were one to three graduates each year, and from 1893 on there were six to ten each year (except in 1895, when there was only one graduate). 84 Derek Price, in his Little Science, Big Science, gives some statistics about Japanese physicists on the basis of E. Yagi's study. He plots various curves, one giving the change in the number of Western physicists invited to Japan and of Japanese trained in the West; another shows the first generation of physicists trained in Japan, i.e., the students of those in the first curve; and a third gives the figures for second- and third-generation Japanese physi­ cists trained in Japan by Japanese physicists. On the basis of these curves, Price concludes that "there was a lag of nearly 20 years while the second generation [which grew in exponential fashion from 1894 to World War II] prepared. It seems important that the steady state arose only with this crop of entirely home-grown physicists." 85 His study is revealing, but since it is based entirely upon the statistics of University of Tokyo graduates, it shows only part of the total picture. The Tokyo School of Physics Although the Imperial University was the center for physics research and teaching in Japan during the last decades of the nineteenth century, physics was also taught at a private institution, the Tokyo Butsuri Koshusho, or Tokyo Physics Training School, founded in 1881. This insti­ tution, which two years later was renamed Tokyo Butsuri Gakko, or Tokyo School of Physics, represented another side of physics education in Japan. Its contribution has been largely overshadowed by that of the pres-

^Tokyo teitoku daigaku sotsugyosei shimeiroku (Tokyo, 1926), pp. 283-285. 8 5 D. Price, Little Science, Big Science (New York, 1965), p. 100.

40

JAPAN'S FIRST PHYSICISTS

tigious University of Tokyo, and. consequently it has been ignored by some scholars. Until 1907 it was the only private institution in Japan that taught Western science; its primary aim was to train science teachers for Japanese secondary schools. The circumstances that led to the founding of this school deserve close attention. The school came into existence because some of the former students of the French Language Physics Department of the University of Tokyo wanted to expose the Japanese public to the principles of the physical sciences. The Japanese were then very much involved in politics and generally with the future of Japan. Law and political science were the main concern of youth, and consequently educational institutions, both governmental and private, emphasizing such disciplines flourished. In­ spired by such institutional activity and by a concern for Japan's future, a group of young physicists felt compelled to publicize the study of science. At first they planned a public lecture series on science reminiscent of the popular lectures on science given throughout France by former students of the Ecole polytechnique in the 1820's and by the members of Auguste Comte's "Association Polytechnique" of the 1830's and 1840's. 86 At that time, however, there was considerable political turmoil; 87 the Free Rights Movement was at its height and was pressing for the immediate establish­ ment of a Diet or Congress, and laws had been enacted to prevent this movement from getting out of hand. Policemen, teachers, and government officials were forbidden to meet in groups in public. Since most of the French-language physicists had become either teachers or government officials, their request for the lecture series was denied, despite its nonpolitical nature. Frustrated, they decided after long, serious discussions to create a school through which they could educate the public in the physi­ cal sciences and mathematics. Of the twenty-one founders of the Tokyo School of Physics, nineteen were graduates of the French Language Physics Department of the Uni­ versity of Tokyo, and the remaining two had studied there. Since six of the twenty-one founders were not in Tokyo when the school was set up, the actual teaching was carried on by the other fifteen. The faculty members received no compensation for their labors; they worked at their respective professions during the day and taught at the school at night. 88 H. Hoffding, A History of Modem Philosophy (New Y ork, 1955), 2, 326-327. details on the political situation, see J. Fairbank et al.,East Asia: TheModern Transformation (Boston, 1965), pp. 278-287. s s Tokyo butsuri gakko gojunenshi (hereafter abbreviated TBGG) (Tokyo, 1930), pp. 1-3. 87 For

KENKICHIRO KOIZUMI

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Without financial support from governmental or private organizations, they had no school building of their own and no experimental apparatus for teaching physics. They rented a room in a primary school, and they borrowed apparatus from their alma mater, the Faculty of Science at the University of Tokyo. Despite initial small successes that made it possible for them to build a small schoolhouse and to add mathematics and chem­ istry to the original physics program, they eventually faced a serious finan­ cial setback. When the school was inaugurated, there were about twenty students in attendance, but because the teachers were inexperienced and the teaching schedule was poorly managed, the number of students de­ creased until at one point only one student remained. Serious discussions about the future of the school followed, in which some of the teachers proposed that the school be terminated. In 1885 they drew up a formal document outlining the measures they were to take to save the school. Each faculty member was to pledge an immediate donation of money to the school. He was further to agree to teach two nights a week or pay a fine if he failed to appear. Sixteen of the original twenty-one founders signed the pledge; one of the original twenty-one had died, two had earlier left the group, and two declined to sign for financial reasons. As a result of these stringent measures and the continuous efforts of the teachers, the school survived its most difficult years, and by 1887 it was able to balance its budget through the income from tuition. 89 At the end of that year the school graduated its first student from what was then a one-year course. That same year the faculty extended the curriculum to two years, and eight years later, in 1893, they extended it to three years. The number of graduates was very small through 1888, but from 1889 to 1903 it in­ creased to between twenty and thirty a year, with the exception of two smaller classes in 1892 and 1893. 90 During these years, there were two hundred to five hundred students attending the school, most of whom therefore did not complete the course. s9 Ibid., pp. 16-26; and Z. Katano, "Meiji junendai no kagaku kyoiku no ichidammen—Tokyo butsuri gakko no soritsu,"Kagakushi kenkyii, 73 (1965), 35-36. 90 A new program on weights and measures was temporarily added in 1891 at the request of the Ministry of Agriculture and Commerce. Since the opening of Japan, various Western systems of measurement had been brought in and used together with traditional Japanese systems. Government officials and scientists worked to resolve the resulting confusion until weights and measures were standardized by law in 1891. Thus there was an immediate need for people familiar with the new system of weights and measures. For this reason a new program was temporarily created at the Tokyo School of Physics; two years later it was terminated. During the two years sixty-eight persons graduated.

42

JAPAN'S FIRST PHYSICISTS

The school offered three courses of study: a major in mathematics, one in physics and chemistry, and a double major combining the two. Among those who graduated, very few were physics and chemistry majors; most concentrated either on mathematics or selected the curriculum combining mathematics with physics and chemistry. In 1930 statistics were gathered on the postgraduate careers of the students; they revealed that out of 1,878 graduates, 1,056, or more than fifty percent, had become secon­ dary school science teachers. The rest had become businessmen, public officials, or had taken other jobs. 91 Ogura Kinnosuke suggests that the large number of secondary school teachers among the graduates can be explained by the large proportion of the school's teachers who were them­ selves involved in secondary school education as their main occupation. He further points out that although education at the Tokyo School of Physics was not designed specifically to qualify students for the teachers' licensing examinations, students tended to view the school as a means to that end rather than as a place for gaining a profound understanding of science per se.92 The Tokyo School of Physics had similarities with a religious movement. The founders were motivated and behaved as if they were missionaries of science, and despite difficult years they more or less succeeded in their mission. The large numbers of Japanese youths who responded to the founders' efforts are an indication that at that time the Japanese—both the founders of the school and the people in general—willingly answered the demands of a new age. The Meiji Restoration had been carried out 91 A

detailed breakdown of the careers of the graduates shows the following:

Teachers

Public officials Businessmen

Workers in private research institutes Other Unknown Total

Universities and professional schools Junior high schools Other Insurance companies Banks and private companies Independent enterprises

80 1056 23 209 81 83 68 28 9 241 1878

See TBGG, p. 246. 92 K.. Ogura, "Meiji kagakushijo ni okeru Tokyo butsuri gakko no ichi," Tokyo butsuri gakko zasshi, 600 (1941), 310. For information on the number of graduates, see TBGG, pp. 235-242.

KENKICHIRO KOIZUMI

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from "above"; the people had had no part in initiating that momentous change. Similarly the importation of Western civilization, particularly of science and technology, was carried out as part of the policy of the Meiji government. The establishment of a national university was an official act aimed at bringing to the Japanese people a knowledge of various Western techniques and ideas. Foreign experts were brought into the Uni­ versity of Tokyo and into other government institutions at great expense. All of these efforts were initiated not by the people but by the govern­ ment. Nonetheless, people from all levels of society, rather than displaying indifference to a remote government's initiatives, responded in their own way. It was the mission of the University of Tokyo to educate Japanese scien­ tists to a level of competence equivalent to that of their Western counter­ parts, so that they could replace the foreign specialists and continue their work. The mission of the Tokyo School of Physics, however, was quite different. It was in no way motivated by the desire to advance research in physics, but solely by the desire to spread a knowledge of the physical sciences to the population at large as a service to society. The University of Tokyo and the Tokyo School of Physics differed in their positions and in their functions in society. The University of Tokyo had the best of everything; it had the best teachers, students, and equip­ ment in Japan, and, more important, it had the full backing of the govern­ ment. Those who taught there and those who graduated from there were the nation's elite. The Tokyo School of Physics was not comparable in any sense. The teachers were inexperienced, and since they had been among the earliest graduates from the University of Tokyo, they had re­ ceived a kind of transitional or intermediary education consisting of a mixture of astronomy, meteorology, mathematics, and electrical engineer­ ing. Products of the soon defunct French Language Physics Department, they did not succeed in becoming active physicists. The two institutions differed most, however, in the level of student ability. Anyone with a rough understanding of arithmetic and the ability to take lecture notes was admitted to the Tokyo School of Physics. Unlike the University of Tokyo, the school did not require students to pass an entrance examination or to study a foreign language. Needless to say, the facilities and equipment were poor. The success of two such different institutions illustrates the magnitude of change that Japan was undergoing: people of all strata in society were responding to the modernization process initiated by the Meiji government

44

JAPAN'S FIRST PHYSICISTS

by assuming technical or scientific tasks. They not only imported science but domesticated it, making it a vital and natural part of the Japanese social order. The new society developed in such a way that not only the elite who graduated from the University of Tokyo but the common citi­ zens who graduated from the Tokyo School of Physics could also play a useful role. The Tokyo Mathematico-Physical Society The establishment in 1884 of the Tokyo Mathematico-Physical Society (Tokyo Sugaku Butsuri Gakkai), an enlargement of the Tokyo Mathemati­ cal Society (Tokyo Sugaku Kaisha), also contributed to the institutionaliza­ tion of physics in Japan. The Tokyo Mathematical Society had been formed in 1877 by two mathematicians, Kanda Takahira and Yanagi Narayoshi, and had a regular membership of fifty-five. Almost all members were mathematicians; they included specialists in wasan mathematics, in Western mathematics, and in both. A few of the original members such as Muraoka Han'ichi and Terao Hisashi were physicists who had been trained in German or French. 93 The aim of the Tokyo Mathematical Society was to promote mathematics through activities such as the creation of a mathe­ matical archive, the translation of Western mathematical treatises into Japanese, the circulation of mathematical problems for solution, and the publication of a journal. 94 The society was not rigorously structured; its original bylaws contained only six articles regulating membership, fees, and the publication of the journal. 95 In 1880 the society recognized that inadequate bylaws and poor financing had created a situation in which the society was not only failing to develop as expected, but was actually de­ clining. The resulting twenty-six formal regulations that were drawn up to replace the original six added astronomy and surveying as disciplines to be promoted by the society, revised the financing, and placed admissions under a new tight control that required all new members to have the sponsorship of an old one. 96 The new regulations resolved the difficulties and injected new life into the society. The members elected new officers, asked certain members to assume responsibility for specific fields of mathematics so as to answer the questions and problems that were pre93 Tofeyo

sugaku butsuri gakkai kiji (hereafter abbreviated TSBGK), 1 (1885), 3. K. Ogura's Sugakushi kenkyii (Tokyo, 1948), 2, 229, for detailed informa­ tion on the originally stated purpose of the journal. 9 s TSBGK, 1 (1885), 2-3. 9 6 TSBGK, 1, 14-18. 94 See

KENKICHIRO KOIZUMI

45

sented to the society, made rules for the library, and set up a committee for establishing Japanese language equivalents for Western mathematical terms. The monthly meetings and monthly journal continued as before. At the same time, a basic change was taking place in the membership of the society. In its formative years it was comprised of people of varying backgrounds—navy and army officers, government officials, and school teachers—and of mathematicians representing both wasan and Western mathematics. This diversity in the backgrounds and interests of the mem­ bers gradually vanished as the society became dominated by people who were or had been connected with the University of Tokyo. The change was inevitable because the University of Tokyo was almost the only source of recruitment for an academic society, and because the new restrictions re­ quiring sponsored admissions tended to limit new admissions to the stu­ dents or colleagues of old members. In 1884 Kikuchi Dairoku, then the Professor of Mathematics at the Uni­ versity of Tokyo, initiated a proposal to include the promotion of physics among the activities of the society. Kikuchi, an active membef of the society, was one of the twelve officials responsible for academic disciplines and the journal, and was the society's specialist on mechanics and solid analytical geometry. He had been instrumental in ending inefficient figure­ head administration in the society by abolishing the presidency, a move that was interpreted as an effort to purge the society of officers who sup­ ported traditional wasan mathematics. Kikuchi may also have been the member who persuaded the society to move its monthly meetings to the University of Tokyo. In his proposal to include the discipline of physics in the society, Kikuchi emphasized what he considered to be the still inade­ quate quality of the Tokyo Mathematical Society. He argued that to im­ prove the society just as to improve Japanese science it was necessary to expand the sphere of activities in Western science. In forming the Tokyo Mathematical Society mathematicians had acknowledged this need, but they had not yet succeeded in satisfying it. Kikuchi proposed the new Tokyo Mathematico-Physical Society specifically as a means to improve the quality of the Tokyo Mathematical Society, not just to enlarge it. Physics and mathematics, he argued, are closely related; to master physics one must master advanced mathematics, and to master mathematics one must seek to apply it in physics. Because physics and mathematics depend on each other, Western academic societies and journals combine the two disciplines. He concluded that since we already have several physicists in our society, and since the current state of science does not permit a

46

JAPAN'S FIRST PHYSICISTS

society of only one discipline to flourish, it is both natural and necessary for the success of our society to promote the study of both. 97 Kikuchi's proposal was approved unanimously by the members of the society. 98 Whether Kikuchi's motion was political or purely academic, we cannot say; but with hindsight we can see that the move to include physics was indeed necessary for the survival of the society. Both its restricted membership and its dependence on the University of Tokyo as the sole producer of mathematicians had brought the society to an almost zero growth rate. Without the combined forces of both physicists and mathe­ maticians the society probably would have died out. Outside the society, Japanese physicists had come together on at least one project. A committee for the establishment of equivalents in Japanese for Western physical terms had been formed in 1883 under the leadership of Yamagawa Kenjiro, then Professor of Physics at the University of Tokyo. The translation of Western scientific terms was a horrendous task because science had been brought into Japan and studied through several European languages more or less simultaneously. Up to 1878 "physics," an entirely new concept to the Japanese, had appeared in at least five different translations: kakuchigaku, kakubutsugaku, kyUrigaku, rigaku, and butsurigaku. To add to the resulting confusion these expressions were sometimes used interchangeably in the same book, and the Japanese trans­ lator's task was further complicated by the existence of two expressions in English, namely, "physics" and "natural philosophy," for the same field of study. By 1878 all but one of the terms had dropped out of use; butsurigaku, which means the study of the underlying reasons behind, or

principles of, matter or things, became the standard Japanese word for physics. Still, the confusion continued with respect to other terms. In 1880 the mathematician Nakagawa Masayuki came out strongly for unified translations in his field; soon engineers, chemists, and physicists pressed for similar agreement. When setting up his committee on physical terms, Yamagawa drew not only on physicists but on chemists, mathematicians, and engineers as well. 99 Part of the working procedure of the committee, of which little is known, was to select three foreign language specialists in English, German, and French, respectively, and to have them draft equivalents; their recom­ mendations were voted on at the full committee meetings that were held 9rj Ibid.,

pp. 89-90. p. 92. "NKGT, 1, 547. 9 Hbid.,

KENKICHIRO KOIZUMI

47

twice a month. 100 Tanakadate Aikitsu, then Assistant Professor of Physics at the University of Tokyo, recalls the disagreement over the Japanese equivalent of "energy": some committee members argued that since the concept of energy is extremely important in the study of physics it should be translated into Japanese; others argued exactly the opposite; namely, that it is such an important term that it should not be translated, but adopted as is. The committee finally decided to leave it untranslated, transcribing it phonetically into Japanese as enerugi. 101 They completed the first draft of a dictionary, Butsurigakujutsugo waeifutsudoku taiyaku jisho (Japanese Dictionary of Physics Terminology from English, French, and German), in three years and published the work in 1888. The meetings of the committee had great significance for Japanese physicists. There they could discuss the different scientific terminology in different languages, clarify the ambiguities inherent in these terms, and draft a dictionary which would give Japanese scientists a tool to help them think, discuss, and write about physics in Japanese. The work of the com­ mittee also reveals that the physicists had a leader to organize such meet­ ings and that there was cohesiveness among physicists despite the extra­ ordinary differences in their physics education. It appears that the physi­ cists could easily have formed their own academic society; there are no documents to explain why they did not. Physicists responded eagerly to Kikuchi's proposal for broadening the conception of the mathematical society. Three physicists were voted to membership in May 1884, the same month the proposal was approved, seven more in June, four in July, and another five in September. 102 After adopting its new name, the Tokyo Mathematico-Physical Society set out to reshape itself and establish new regulations. Admission requirements were raised further. The society's journal was changed from a monthly publication to one that was to come out "at least three times a year." Aside from making certain members responsible for business matters and editing the journal, the society appointed ten members to report on foreign scientific journals at the monthly meetings, four on English journals, three on French, and three on German. 103 In contrast to the Tokyo Mathematical Society, the new Tokyo Mathematico-Physical Society of 1884 emphasized specialization; it reflected its l o o Ibid.,

p. 548. Tanakadate, "Butsurigaku Oraoide," Nihon Butsurigakkai shi, 3, 321. 1 0 2 TSBGK, I, 92, 128, 135-136, 139. 1 0 3 Ibid., pp. 119-122.

101 A.

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JAPAN'S FIRST PHYSICISTS

specialist orientation in both the new members it admitted and the new journal. The more academic and specialized the new society became, the more it became a closed society that was increasingly dependent on the University of Tokyo. In October 1884, a few months after the founding of the Tokyo Mathematico-Physical Society, thirty of the eighty-two members were connected with the University of Tokyo; of the members who attended the monthly meetings half had University affiliation. By the following year, the percentage of academics had increased so much that the monthy meetings were dominated by members from the University. 104 A second major characteristic of the new society was the extent of its reporting on foreign scientific journals. In short while the society became restricted and closed domestically at the turn of the century, it remained open to the West, eager to absorb whatever was available in print from scientists abroad.

4. THE FIRST GENERATION OF JAPANESE PHYSICISTS: THE 1870's Japan's First Physicists Although physics emerged in Japan less than a hundred years ago, the names of all but the most famous of the first generation of Japanese physicists and all data on them are already hard to discover. One good source of names is the Japanese Dictionary of Physics Terminology from English, French, and German of 1888. The dictionary does not provide the names of all physicists in the 1880's—for example, six graduates of the French Language Physics Department at the University of Tokyo were not included—but it does list the persons who were considered active physicists at that time. In a study of early Japanese physicists, Yagi Eri has attempted to classify some of the physicists listed in the Dictionary by the language through which they learned physics. 105 Yagi's classification, however, has short­ comings that produce peculiar groupings. She has a French-language group all of whom studied in Japan, and a German-language group all of whom studied in Germany; 106 her English group is composed of those who studied in America and those who studied physics in English in Japan. Two l 0 4 Ibtd.,

3, 1-3, 119-138. Yagi 1 "Nihon saisho no butsungakusha tachi," Butsurigakushi kenkyu, 1 (1959), 237-262. 106 This includes Strasbourg, which from 1871 to 1918 belonged to Germany. 1 0 5 E.

KENfcICHIRO KOIZUMI

49

other groups are not language groups at all, nor are they made up of physicists; one is made up of engineers, irrespective of language, the other of yogakusha, of scholars of Western studies in a general sense, all of whom studied in Japan, mainly in English. Even the groups based purely on language present problems because, al­ though most of the dictionary's compilers were physicists, not all were; some of the language groups such as the English group that was trained abroad contain only one physicist, a category that can hardly be called a group. The German group should have been divided into the one man who was trained abroad and the rest who were trained in Japan but later studied in Germany. Perhaps the one interesting phenomenon Yagi observed is that those who had studied physics through English dominated the Physics Department at the Imperial University, but those who had studied physics through Ger­ man became faculty members only in the College of Agriculture or College of Medicine of the University. The reason for this, no doubt, was that English by that time had become the official language of the Physics De­ partment, whereas in the Colleges of Agriculture and Medicine, German was the primary language. Of those who had trained through French in the early French Language Physics Department, most became high school teachers or government employees; one became a member of the Astron­ omy Department at the University of Tokyo; and a very few joined the Physics Department as assistant professors, but were never promoted to professor and ultimately went elsewhere. 107 It is more significant for a history of physics in Japan to define the char­ acteristics common to the first-generation physicists as a group and then to point out the distinctions between them and the physicists who came later than to divide them by language groups. The first generation was composed of some twenty-seven physicists. For some of these we know only their names and nothing at all of their careers. The twenty-one for whom data exist are given in Table D (Appendix). The sudden emergence in the late 1870's and early 1880's of such a sub­ stantial group of physicists is remarkable both in its own right and in its contrast with the situation that existed in the late 1880's. After the initial 107 E. Yagi, op. cit. (note 105), pp. 242, 246, and 252. In the case of chemists in Japan, those who studied chemistry through English or German had almost identical careers to the physicists mentioned above. There were no chemists, however, who had studied through French, although a number had studied through Dutch and were naturally older than those whose language was English or German. See K. Sugawara, "Meiji shoki no kagakusha tachi (1859-1880)," Butsurigakushi kenkyu, 6 (1970), 1-25.

50

JAPAN'S FIRST PHYSICISTS

group, no clearly identifiable groups or blocks of physicists were pro­ duced; rather, the first group was followed by a more or less regular se­ quence of a few physicists a year who had remarkably uniform training and who, with a few exceptions, left no particular mark on the develop­ ment of Japanese physics. From the late 1880's the discipline of physics was established, the curriculum stabilized, and the educational machinery firmly installed and running smoothly. The first generation of Japanese physicists was born in the 1850's, which means that they experienced in their youth one of the periods of most rapid change in Japanese history. Instead of turning their backs on the changing situation, as some Japanese did, they eagerly sought new values. Another common characteristic of the group is that they came from samurai families and thus shared a strong background in Chinese studies. 108 In order to understand the significance of this background, it is necessary to understand the nature of the samurai education these men had received before they studied physics. I will give a brief outline of this large subject. The Education of a Samurai Two aspects of the education of a samurai are relevant here: the curric­ ulum itself, including the teaching methods, and the philosophical con­ cepts upon which the educational process was based. The scientific education of Japan's first physicists was built upon a foundation comprising both these aspects. The two skills considered fundamental to Western ele­ mentary education, writing and arithmetic, were not a part of a formal samurai education; their pursuit was beneath his dignity. Writing in Japa­ nese was thought too easy a task to aid in the development of self-disci­ pline, which was one of the main purposes of Japanese education, and, in any case, the vernacular literature for centuries had been considered a matter for women. Arithmetic calculation for monetary or other material­ istic purposes was a crass occupation suited to merchants rather than the elite. Sometimes schools did not even bother to teach these subjects, so that the samurai often had to acquire writing skills in his native language, i.e., in calligraphy, and arithmetic outside the fief schools, either at home or from a private tutor. 109 108 Probably all were samurai but the official record is unclear in one or two cases. What is known of their education indicates that even if the latter were not officially samurai, they had been educated as such. 109 R. P. Dore, Education in Tokugawa Japan (Berkeley and Los Angeles, 1965),

p. 126.

KENKICHIRO KOIZUMI

51

The traditional curriculum for a samurai of the Tokugawa period con­ sisted primarily in the study of the Chinese Confucian classics, in lessons on how to conduct himself on all occasions according to his station in life, and in the mastery of various military arts such as swordsmanship, riding, archery, and strategy. After entering the fief school at the age of six or seven, a young samurai devoted the next seven years of his educational life almost entirely to rote memorization of Chinese philosophical texts. Mili­ tary training usually did not begin until a samurai was eleven to thirteen years old. The object of reading Chinese philosophy was not to analyze or criticize the text or even—for the first few years—to understand it, but to make it one's own. The educational process was designed to tame childish inclinations to haste and superficiality. Although it was extremely boring and difficult for young samurai, no other training was deemed as effective in producing strict physical and mental self-control or in curbing impetuous curiosity. The Japanese practice of reading Chinese Confucian texts resem­ bles religious methods of achieving discipline. Normally the samurai had to master the "reading" of five major Con­ fucian classics—which he did by the age of thirteen or fourteen—before his teacher discussed their content or meaning. Even then the texts were pre­ sented dogmatically, not debated or interpreted. The student was asked to accept that all necessary explications had already been made by later Chi­ nese philosophers and that only in extraordinary cases had outstanding Japanese scholars written commentaries to Chinese works.110 Another reason for the emphasis on classical Chinese in samurai educa­ tion was that, although the Japanese had a rich and ancient tradition of belle lettres written in Japanese, almost all works on history, medicine,

astronomy, law, and military strategy were in Chinese—the Latin of East Asia. Indeed the first works on Western science reached Japan through Chinese translations or through texts written in Chinese by the Jesuits. When the samurai completed his study of the Confucian classics and pro­ ceeded to higher learning at the age of fourteen or fifteen, he would ac­ quire it through Chinese texts no matter what subject he pursued. The close connection between Japanese higher learning and a foreign language, i.e., Chinese, molded Japanese attitudes toward the process of acquiring knowledge. Since its introduction via Buddhist scriptures in the fifth century, at a time when the Japanese had no written script of their own, Chinese had been the vehicle for transmitting "learning," and it rel l o Ibid.,

p. 133.

52

JAPAN'S FIRST PHYSICISTS

mained so even after the Japanese created a script for their own vernacular and used it in their poetry and creative literature. Chinese writing and even the content of learned works were conspicuously non-Japanese; the Japa­ nese intellectual became used to the idea that the source and the language of learning were foreign. R. P. Dore writes of the "alienness of Chinese studies" and says it "lends force to the argument that the Japanese were more easily able than the Chinese to exchange the Confucian for the West­ ern world-view in that Confucianism was still for them only a 'suit of borbowed clothes'." 111 Although the Confucian worldview was perhaps easier to shed than a natively conceived one, there was another, more positive factor influencing the Japanese attitude toward Western studies. That Confucian studies were foreign meant that for centuries, despite geograph­ ical and political isolation, the Japanese recognized that knowledge prized by the governing class could and did come from beyond her borders. Equally important as the source, content, and vehicle of Chinese studies was their purpose; education had both a moral and a vocational goal. Schools taught the samurai the full extent of his duty to his lord and molded him into a loyal and useful servant and good administrator. In the seventeenth century Kaibara Ekken gave one of the simplest and most intelligible explanations of the Confucian worldview, of man's place in that world, and of the role education played in it. 112 The Confucian world centers on tenchi, which is a physical heaven, an anthropomorphic deity, and a physical and ethical "natural law." Tenchi is the creator of the uni­ verse, and man is the favored progeny because he is endowed with mind, heart, and the five virtues of kindness, justice, wisdom, trustworthiness, and a knowledge of proper social conduct. Out of gratitude from being selected to be born a man rather than any of the other 10,000 life forms, man is under obligation to tenchi to devote his life to cultivating to its highest level of perfection his tenchi-given nature. His five virtues are con­ stantly threatened by natural appetites and materialism. To fight these threats, man models his conduct on that of the ancient Chinese sages who left the classics as a guide to succeeding generations. It is each man's duty to learn the Chinese classics as a precondition for a virtuous life; a success­ ful education is marked not by knowledge, but by virtuous conduct. Other scholars, including the founders of rival schools of Japanese Confucian thought, defined the Confucian worldview in different terms, but their ll^Ibid.,

p. 137, note 1. Kaibara, Y a m a t o z o k u k u n (1708). See T. Tsukamoto, ed., E k k e n j u k k u n in Yuhodo bunko (Tokyo, 1913-1928), 1, 67 ff. 112 E.

KENKICHIRO KOIZUMI

53

intent was the same. The samurai's duty was not only to the powers of the universe that created him, but to the state as well. To be a samurai was to be a member of the governing elite; good government depended upon the proper moral training of those who were to govern; moral training, there­ fore, was occupational training. Whether moral or practical values were emphasized, both elementary and advanced study always implied training in self-discipline to achieve a higher moral nature rather than the acquisi­ tion of pure knowledge; samurai education was oriented toward an end that would serve the state. Education in the Tokugawa period was not conducive to innovation; rather it consisted in the passive absorption and transmission of tradition. To open new fields of knowledge was not part of scholarly activity; even to pronounce new interpretations of the Chinese classics was heresy and was severely criticized and even prohibited. Needless to say, a learning activity that consisted of man's search to satisfy his curiosity about his environment was not worthy of pursuit. Like all samurai, Japan's first physicists had received Confucian educa­ tions: they had been trained in the Chinese classics until they were about fifteen. Then they were chosen to pursue Western studies in Japan or abroad, rather than following the usual course of higher learning in Chi­ nese. Foreign and Domestic Training The institution that is of greatest importance to the history of early physics in Japan is the Southern Division, in existence from 1870 until the merger in 1877 that produced the University of Tokyo. The Southern Division was the first school under the Meiji government that was given the responsibility of educating large numbers of students in Western stud­ ies. The original plan called for a thousand students to enter in 1870, the first year, at least half of whom were to come from the fiefs in numbers proportional to their sizes. The fiefs sent about three hundred students the first year. The course of study was to extend over five years; applicants had to be between sixteen and twenty. 113 The latter requirement is impor­ tant to note, since it means that most matriculating students were born in the 1850's and were of the same generation as the first physicists. It also means they had already completed their elementary Confucian training. The problems involved in inviting students from the fiefs were so great that the system collapsed a year after it began. InJuly 1871 the Southern n 3 TTDG,

1, 147-149.

54

JAPAN'S FIRST PHYSICISTS

Division closed temporarily and all students were dismissed. By October 1871 the Southern Division had reopened, readmitting the students who had been doing well when the school closed. 114 Among those readmitted, we find seven 115 of the twenty students who graduated from the French Language Physics Department of the University of Tokyo in 1878-1880. They had survived the University's false starts and transitions during its opening years as it changed from the Southern Division to the Tokyo Kaisei School to the University of Tokyo; they had also survived the 1873 decision to change the instructional language to English. Instead of the originally planned five years of study they had undergone an eight- to tenyear course in a constantly shifting science curriculum. At the same time that the Southern Division was established and students were sought from the fiefs, a policy encouraging study abroad was adopted and was another influence on the careers of some of the first generation of physicists. 116 In 1870 Kitao Jiro (or Diro, as he preferred to spell his name), one of the first students at the Southern Division, was sent from there to Germany, and the next year Yamagawa Kenjirc- was sent to America from his fief in Aizu, the only one of the first-generation physi­ cists to study there. The English-Language Physicists Yamagawa and Tanakadate became the most famous of the first genera­ tion of physicists. That both men studied physics through English and later taught at the Imperial Univeristy points up the importance of first-genera­ tion English-language physicists in Japan. The other two English-language physicists on the first-generation list had little impact on the physics disci­ pline. Ichikawa Morisaburo (who changed his name to Hiraoka) became Professor of Physics at the University of Tokyo in 1880, but he died two years later at the age of thirty at the very beginning of his career. Goto Makita was a somewhat unusual case. He studied at Keio University, a pri­ vate school founded by the social philosopher and scholar of Western studies Fukuzawa Yukichi, who had exerted such influence on the educa­ tional policy of the early Meiji period. Goto, therefore, had been trained in 114 Zfetci.,

p. 151. seven were Kobayashi, K. Nakamura, Sakurai, Samejima, Sembon, and Yatabe. Nothing beyond their names is known about Kobayashi and Samejima. See Tables D, E, and F for the others. 116 T. Okubo, "Bummei kaika," in Nihon rekishi—Kindai (Tokyo, 1962), 2, 264. For more detailed statistical information, see M. Watanabe, op, ctt. (note 37), pp. 285-293. 115 The

KENKICHIRO KOIZUMI

55

an environment in which the general problems of Westernization were perhaps more on his teachers' minds than those of the development of the physics discipline per se. Although he was technically a physicist and even did postgraduate work in physics at the Universities of Glasgow and Man­ chester, Goto was more an educator than a physicist, and like his mentor, Fukuzawa, he became a popularizer of his field, writing many articles for the general public on such topics as the elementary principles of elec­ tricity. 117 The German-Language Physicists Despite the importance of the official use of English to the development of the discipline of physics and the ultimate fame of two out of the four English-language physicists in the first generation of physicists, the Germanlanguage physicists, too, had an impact on the University, if not on the Physics Department directly. As in the English group, there were four physicists in the German group, of whom one had studied abroad and three had started their studies in Japan. Kitao, the first of the students of the Southern Division to be selected in 1870 to go abroad to Germany with government support, stayed fourteen years and married a German. He studied first at the University of Berlin, then at the University of Gottingen where he received a Ph.D. in physics, and finally returned to Berlin to re­ sume his research under Hermann von Helmholtz. His research in Germany probably dealt with hydrodynamics and optics; for he devised an optical instrument called a Leukoskop which was used to test color blindness, and after his return to Japan he wrote a famous series of papers on the dynam­ ics of typhoons. 118 By the time he had returned to Japan, however, the Physics Department at the Imperial University had adopted English as its official language, so that despite his extensive training abroad he was un­ able to obtain a position there. He became instead Professor of Physics in the Agriculture Department, where German was a language of instruction. Of the other three German-language physicists, Muraoka was the most successful. He entered the Southern Division in 1870, the year it was 117 M. Fukushima, "Goto Makita—Meiji kaikaki no rika kyoiku," Butsurigakushi kenkyu, 6 (1970), 1-35. 118 K. Kitao, "Beitrage zur Theorie der Bewegung der Erdatmosphare und der Wirbelstiirme (1)," Journal of the College of Science, Imperial University, Japan, 1 (1887), 113-402. The second and third parts were published in 2 (1889), 329-412, and 7 (1895), 293-402. For a brief biography of Kitao, see 0. Inagaki, "Ko Noka daigaku kyoju sho yoni kun santo rigaku hakushi Kitao Jiro sensei no ryakuden," Kagaku sekai, 1 (1907), 262-264; "Kitao hakushi," Taiyo, 13 (1907), 29-32.

56

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organized, and studied German in preparation for a career in physics. Al­ though he survived the initial readjustments when English became the of­ ficial language in 1873, he was in effect shut out in 1875 when the univer­ sity cancelled the German Chemistry Department, its last concession to its earlier students who had the misfortune to start their careers in German. Finding employment with the Ministry of Education, he continued to study physics on his own and did part-time physics teaching at Joshi Shihan Gakko, the Women's Teachers' College. In 1878 the Ministry of Education sent him to Strasbourg to study educational administration; dur­ ing his four years there he graduated from the Strasbourg Teachers' College and earned a B.S. in physics from the University of Strasbourg. After re­ turning to Japan in 1881 he became a lecturer in physics in the Medical Department, in which German was used, of the University of Tokyo, and in 1883 he was promoted to Professor of Physics in that department. In 1886 when the University of Tokyo became the Imperial University, Muraoka also began to lecture in the Physics Department, the only Germanlanguage physicist of the first generation to do so. Muraoka became well known as an educator; he wrote many articles on physics education in pri­ mary and secondary schools, and in 1896 he became Professor of Physics in the Science-Engineering Department of the newly established Kyoto Imperial University. 119 Shiga Taizan had begun German studies in 1872 when the Southern Division was called The First Middle School of the First University. He apparently failed to survive the language change and dropped out to teach physics at Tokyo Shihan Gakko (Tokyo Teachers' College). In 1884 he taught physics at Diagaku Yobimon (The University Gateway School), a preparatory school for the University of Tokyo. Possibly he also worked for the Ministry of Education and Commerce at that time. He was sent to Germany in 1885 where he concentrated his studies on agriculture and forestry, and upon his return to Japan he worked for the government, be­ coming an official of rank by 1890. In the same year he was also appointed Professor of Agriculture at the College of Agriculture at the Imperial Uni­ versity. Shiga is listed as a physicist because he began as a teacher of phys­ ics and wrote elementary books on physics and science for lower school students; he spent the later part of his career almost completely outside the physics discipline. 120 Iimori Teizo (or Ihmori as he preferred to spell his name), the last of the 119 e . Yagi, op. cit. (note 105), pp. 243-244. 1 2 0 Ibid., pp. 244-245.

KENKlCHIRO KOIZUMI

57

German-language physicists, was not educated at the University of Tokyo but later taught there. He had begun his study of German at a government institution called Tokyo Gaikokugo Gakko (Tokyo Foreign Language School); he seems to have pursued the study of physics on his own by reading in German sources. In 1875 he began to teach at the Tokyo Medi­ cal School, one of the two institutions which joined to form the University of Tokyo in 1877. In 1879 he wrote a popular physics text for medical students which was used by the University of Tokyo Medical Department. At the same time he was employed by the University Gateway School as a physics teacher. Iimori used his own funds to go to Germany in 1884, and two years later he received a doctorate in physics from the University of Freiburg. On his return to Japan he became a teacher of physics at a pres­ tigious Tokyo high school, the Fourth Higher School, and then moved to Tokyo Joshi Koto Shihan Gakko (Tokyo Women's Higher Teachers' Col­ lege, a successor to the Women's Teachers' College). 121 To summarize, two of the four German-language physicists became Pro­ fessors of Physics at the University of Tokyo: Kitao in the Department of Agriculture and Muraoka in the Department of Medicine. Iimori taught in the Department of Medicine but reached professorial rank only at another institution. Shiga left physics to become Professor of Agriculture and thus managed to stay at the University of Tokyo. Despite the language handicap the German-language physicists were important to the teaching of physics in Japan, but they did not equal the English-language physicists Yamagawa and Tanakadate who made contributions of great significance to physics as a scholarly discipline. The French-Language Physicists The number of graduates of the French Language Physics Department and their activities made them into a true group. Table F (Appendix) gives data on the thirteen of the twenty-one graduates of the program for whom career information exists. If one is to judge by the prestige of their positions, the four French-lan­ guage physicists who achieved greatest recognition were Terao Hisashi, Namba Tadashi, Miwa Koichiro, and Nakamura Tokio. The first three be­ came professors at one of the two Imperial Universities and the fourth be­ came Director of the Central Meteorological Observatory in Tokyo. Their contributions, however, were not to physics but to other sciences and were of a practical nature. 1 2 1 Ibid.,

p. 244.

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JAPAN'S FIRST PHYSICISTS

Terao was the outstanding man of the group. One of the first graduates of the French Language Physics Department in 1878, he went to France the next year, studying for four years at the University of Paris under Tisserand and receiving the licencie es science mathematiques. After his re­ turn to Japan he became lecturer in astronomy and mathematics in the Department of Astronomy at the University of Tokyo in 1883 and was promoted to professor the next year. In 1888 he also became the first Director of the Tokyo Astronomical Observatory, a facility of the Imperial University. 122 Terao was a good mathematician but uneasy about the pleasure he derived from "pure" mathematics. In an address to young mathematicians at a meeting of the Tokyo Mathematico-Physical Society in 1889, he asserted that the difference between pure and applied mathematics is that it is only through the latter that one can contribute to society. 123 He felt that it is not good for a person to study mathematics solely because of its inherent interest, and that to have no interest in applied mathematics is to have an asocial attitude. It was consistent with his interest in the practical aspects of science that he was one of the strongest supporters of the Tokyo School of Physics and was indeed its first president. Two other French Language Physics Department graduates, Namba and Miwa, became professors at the Kyoto Imperial University, but neither of them in physics. Namba graduated from the department in 1879 and then worked there briefly as an assistant professor. In 1880 he went to the University of Paris and two years later received a licencie es science phy­ siques. He stayed on in Paris for another two years, then returned to Japan to work first for the Ministry of Education and then to teach at var­ ious higher middle schools. From 1896 to 1898 he studied electrical engi­ neering in France and the United States, and upon his return was appointed Professor of Electrical Engineering at Kyoto Imperial University. In 1919, a year before his death, he became head of the Society for the Study of Electricity. 124 Miwa, who graduated in 1880, never studied abroad. He was employed by the University of Tokyo upon graduation and was promoted to Assis­ tant Professor of Mathematics in 1882. He was still teaching mathematics in the College of Science at that rank in 1886 when the Imperial University 122 TBGG, 123 Part

pp. 113-115. of the speech is quoted in K. Ogura, Sugakushi kenkyu (Tokyo, 1935), 1,

252. 124 TBGG,

pp. 110-112.

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KENKICHIRO KOIZUMI

was established; in the next year he accepted a full professorship at Gakushuin Diagaku (Peers' University) without, however, severing his ties to the Imperial University. Finally, in 1893 he resigned from the Imperial University, and in 1900 he was made Professor of Mathematics in the College of Science and Engineering at Kyoto Imperial University. 125 More than any other, the career of Nakamura was oriented toward the practical. Immediately upon graduation in 1879 Nakamura was employed to do meteorological studies for the Land Survey Division of the Geo­ graphical Department of the Ministry of Internal Affairs. In 1886 he went to Europe at his own expense and spent threfe years there studying meteo­ rology. After his return to Japan he was employed in 1890 as a technician at the Central Meteorological Observatory, and five years later he was made Director of that facility, a position he retained for twenty-eight years.126 The members of the French-language group shared certain characteristics. Although all were trained in physics, none pursued physics as a career. Most were involved in occupations that were of direct, practical benefit to the development of modern Japan. Three of the thirteen for whom we have data attained life positions in government ministries; at least eight more spent part of their careers working for a ministry. Eleven of the thirteen had teaching experience, but only four became university professors, and none of them professors of physics. They taught in secondary schools, teachers' colleges, and military academies. A few of the French language group made significant contributions to the development of physical sci­ ence disciplines other than physics, but in general the men in this group committed themselves not to the advancement of knowledge but to the task of building a new Japan by applying the knowledge they had acquired from the Western sciences. The principal expression of their collective commitment was their establishment of the Tokyo School of Physics.

5. THREE MAJOR FIGURES IN EARLY JAPANESE

PHYSICS

Yamagawa Kenjiro Yamagawa was born on 17 July 1854 in the castle-town of Aizuwakamatsu, about one hundred and thirty miles north of Tokyo (then called Edo). 127 He was the third son of Yamagawa Shigekata and his wife 1 2 5 Ibid., 1 2 7 For

pp. 101-104.

1 2 6 Ibid.,

pp. 153-157.

a study of Yamagawa's life the following primary and secondary sources are available: Ko danshaku Yamagawa sensei kinenkai (comp.), Danshaku Yamagawa

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JAPAN'S FIRST PHYSICISTS

Karaginu. 128 The family's standing was quite high, since Kenjiro's grand­ father Shigefusa was one of the councillors under the head of the Aizu fief. Because of the early death of his father when Kenjiro was six his mother and grandfather came to play an important role during his formative years. In his reminiscences Kenjiro describes his mother as a woman who was neither sophisticated nor progressive in her ideas of education, but who seriously and enthusiastically looked after her children's training and their moral education. His grandfather was progressive in his views; he believed in smallpox vaccination at a time when Chinese medicine was still domi­ nant in Japan, and he tried unsuccessfully to persuade the military offi­ cials of his fief to adopt Western guns, which he favored over match­ locks. 129 Education in the Aizu fief varied even within the samurai class. Since Yamagawa's family status was high, he received the best education the fief could offer. When he was eight, he entered the only school in the Aizu fief, the Nisshinkan, and studied there until he was fourteen. The Nisshinkan consisted of several divisions, providing education to all levels of students; its traditional curriculum was dominated by ancient Confucian texts and the military arts. The only subject resembling Western scientific studies was arithmetic, taught in the form of abacus practice. Yamagawa did not study that subject and did not learn arithmetic until he was fifteen. The purpose of education in the Aizu fief as in all fiefs was to make the samurai ruling class into an effective force for the preservation of feudal society. Without a sense of the moral code of feudal society and the devotion to uphold it even a man who was highly skilled in the various arts and letters would not have been regarded as educated. 130 In 1868, the year that Yamagawa finished his basic education, the Nis­ shinkan was shut down because of the turmoil of the Meiji Restoration. The Aizu fief was loyal to the shogunate and fought against the Imperial army in an effort to prevent the restoration of imperial powers the shogun had usurped. Yamagawa was assigned to a corps of fourteen- to sixteen-

sensei den (Tokyo, 1939); Ko danshaku Yamagawasensei kinenkai (comp.), Danshaku Yamagawa sensei iko (Tokyo, 1937); M. Watanabe, "Shoki Nichibei kagaku koshoshi no ichimen: Yamagawa Kenjiro no bawai," in Bunkashi ni okeru kindai kagaku (Tokyo, 1963). Hereafter the first will be abbreviated as Den; the second, Iko; the third, "Yamagawa." 1 2 s Den, pp. 1 and 7. They had twelve children, but only seven survived. Yamagawa, though born the third son, became the second when his eldest brother died. 1 2 9 Iko, pp. 13 and 8. 1 3 0 Ibid., pp. 89-99 and pp. 50-51.

Figure 1. Yamagawa Kenjiro around 1911 when he was president o f Kyushu Imperial University.

61

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JAPAN'S FIRST PHYSICISTS

year-old youths called the White Tigers, but he was quickly released again when the corps started training in the use of firearms that were too heavy for fourteen-year-olds to handle. 131 The war between the shogunal and the Imperialarmies resulted in the shogunate's defeat. As the ruling class of a defeated enemy of the throne, the Aizu samurai were forbidden to leave their territory, were stripped of the power to conduct normal fief activities, and were condemned to years of uncertainty and waiting. During this time they secretly dispatched an observer to travel around the country, and Yamagawa was assigned to accompany him. For several adventurous months Yamagawa travelled in disguise and under the threat of death if apprehended. During the waiting years he also read many Japanese and Chinese classics and studied a little French. 132 Around 1870 Yamagawa went to Tokyo; his youth and status in the fief suggest that he did not make the decision on his own, but that one of his teachers or one of the officials in the Tokyo office of the Aizu fief rec­ ommended that he go. By 1870 the defeated fief had been given permission to reconstitute itself and had resumed administrative functions. During the postwar period the finances of the fief were in poor condition, leaving Yamagawa without any means of support for his studies and thus exposed to considerable deprivation during his first year in Tokyo. Lack of financial support also prevented him from entering one of the more important educational institutions such as the Southern Division or Keio Gijuku, the private school founded by Fukuzawa Yukichi. Although Yamagawa does not say so in his autobiographical memoir, he seems to have been interested in Western studies from the start. 133 He studied introductory English in a class held at a temple called Tokusuiin for three months and then managed to gain entrance to a private establish­ ment called Numata Juku, where, for the first time, he studied elementary algebra and geometry. 134 After only three or four months of study at the Numata Juku, Yamagawa suddenly received an order from the new Meiji government to go to Russia to study technology. 135 The government had set for itself the task of 131 Yamagawa owed his life to the release of the fourteen-year-olds from the corps. When the shogunate forces were defeated by the Imperial army, the surviving mem­ bers of the White Tigers committed harakiri or ritual suicide at the fall of Aizu castle. Had Yamagawa been one year older and not released from the corps, he would have done the same. 1 3 2 IkD, pp. 192-193. l 3 3 Ibid., pp. 43 and 63. l 3 4 Ibid., pp. 51-52. 135 See Dajokan nisshi of 3 December 1870. Reprinted in Shimbun Shusei Meiji hennenshi (Tokyo, 1935), 1, 351.

KENKICHIRO KOIZUMI

63

developing Hokkaido, the northernmost island of the Japanese archipelago, which in those days was barely inhabited. For that purpose the government established in 1869 an ad hoc division. The division decided to send thir­ teen young students abroad to obtain the knowledge necessary for devel­ oping a northern frontier. The selection of students was largely political; ten of the thirteen were chosen from the two fiefs whose forces had con­ tributed in a major way to the defeat of the shogunate and which were now rewarded with major responsibilities in the new Meiji government. The remaining three students were chosen from three different fiefs with cold climates; they were considered best for developing a cold island like Hokkaido. Aizu was one of the fiefs with a cold climate and for reasons that are not clear the division chose Yamagawa as the student from that fief. 136 The original plan to send the students to Russia was soon dropped 137 because Japanese returning from abroad reported that Russia was too un­ developed to serve as training grounds. 138 Yamagawa and the other stu­ dents now were to go to the United States where study was judged to be more fruitful. The use of such simplistic criteria indicates inadequate plan­ ning. Yamagawa had studied very little English, had almost no background in Western learning, and was certainly ill-prepared for study abroad. Nevertheless, he left for the United States on 1 January 1871; he was seventeen years old. Before his trip to the United States Yamagawa had never dreamed of becoming a physicist. 139 The incident that changed the course of his life took place while he was still in the middle of the Pacific Ocean on his way to America. Yamagawa records it in his recollections: At that time I was still not quite able to throw off that rather oldfashioned anti-foreign attitude and still could not bring myself to feel respect for the likes of foreigners. But right off the thing that surprised me the most and made me feel that I must without fail learn from them was something that happened while I was still in the middle of the Pa­ cific Ocean. "Late tonight or at dawn tomorrow," they said, "we will 136 IfeiJ,

pp. 44-45. in Dajokati nisshi of 3 July 1871. See Shimbun shusei Meiji hennenshi,

137 Printed

1, 382. 138 None of the students liked the idea of going to Russia; when they heard that the division had been advised about the uselessness of training in Russia, they successfully negotiated with the officials for permission to go to the United States instead. See Den, p. 65. 139 Ibid., p. 25.

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meet the shipping company's Pacific Mail Ship. Those who wish to send letters back to Japan, please make correspondence ready." To say that the paths of two ships that had come to the middle of the ocean would precisely meet on such a vast sea was really a little too pretentious a boast, I said to myself dubiously. Nonetheless I wrote a letter. But it was about 3 or 4 in the morning, I think, when I saw at a distance of about 700 feet from us that a ship had come to stop and our ship was sending a boat out to receive letters and to deliver our items to the other ship. When I saw this I was profoundly convinced of how great their learning was, that Japan could be in no way a match for them, and that foreign learning was an unfathomable thing. 140 In telling of his startling experience, Yamagawa did not specifically indi­ cate what he wanted to study, but he showed that he was strongly at­ tracted to scientific matters. The event transformed him from a passive traveler into an active seeker after knowledge, and made him an enthusias­ tic participant in the plans for his study abroad. After arriving in America Yamagawa entered a junior high school in New Brunswick, New Jersey, with the help of a Japanese who was already in the United States. He soon left there, however, and moved to Norwich, Connecticut, because he was anxious to avoid being distracted from his studies by the social activities of the many Japanese then living in the New Brunswick area. At times there were as many as thirty to forty Japanese studying there, and Yamagawa found it difficult to concentrate on his studies in such a lively community. Under the guidance and probably at the suggestion of the principal of his new junior high school in Norwich, Yamagawa prepared for the entrance examinations for the Sheffield Scien­ tific School at Yale University. In May 1872 he was granted admission pro­ vided he would study trigonometry during the summer. 141 The Japanese government was not involved in Yamagawa's plans and movements; it had sent him off to learn, but left it to him to select the institutions and sub­ ject. By this time Yamagawa had formed a definite idea as to what he wanted to do in the future. The process by which he decided on a career and the way in which his decision reflected his earlier training are significant. He tells us in his recollections: 1 had never thought about my future as much as I did in those days. It was just at the time when Herbert Spencer's new philosophical works 140 Jkff,

pp. 48-49.

i ^ l Ibid.,

pp. 52-53, and Den, pp. 68-69.

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65

were being published, and they had a tremendous influence on young people's thinking. A man by the name of Dr. Youmans [Edward Living­ ston Youmans ] in New York started to publish a magazine called The Popular Science Monthly [the first issue appeared in May 1872] which strongly advocated Spencer's principle [in a series of articles by Spencer starting with the first issue]. The more I thought about Youmans' idea, knowing that we must work to perfect Japan, the more I felt that in order to do so we must work to improve our government. But to improve government, one must improve society. To improve society, it is neces­ sary to study sociology. To study sociology it is necessary to learn biology as well as other natural sciences. Believing that above all to en­ rich the nation and strengthen the military one must bring to perfection the sciences of physics and chemistry, I made up my mind to study physics. 142 Youmans' discussions of the applications of scientific methods in the early issues of his journal did not link the efforts of the individual scientist to a national goal. He limited himself to the argument that scientific in­ vestigation can and should be applied to all subjects: 143 "[i] ntellect, feel­ ing, human action, language, education, history, morals, religion, law, commerce, and all social relations and activities." 144 He said nothing spe­ cifically about biology, physics, or chemistry. 145 Spencer, too, had spoken only of the need of scientific methods in sociology. Yamagawa connected Youmans' and Spencer's ideas to Confucian logic and ethics; the argument by which he decided upon a career links the idea of the usefulness of West­ ern science to the main tenets of his early education. One of the first Confucian texts Yamagawa would have learned as a child, The Great Learning, contains a passage that played a key role in Japanese education and was frequently quoted. The passage reads: Things being investigated, knowledge became complete. Their knowledge being complete, their thoughts were sincere. Their thoughts being sin­ cere, their hearts were rectified. Their hearts being rectified, their persons were cultivated. Their persons being cultivated, their families were regu­ lated. Their families being regulated, their states were rightly governed. 142 Jfeo,

p. 53. Popular Science Monthly, 1 (1872),113-115. 1 ^Ibid., p. 113. 145 But in a summary of Spencer's thought in the "Editor's Table" of the December issue, Youmans mentioned biology as indispensable to the study of sociology. See ibid., 2 (1872), 240. 143 SeeThe

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Their states being rightly governed, the whole kingdom was made tran­ quil and happy. 146 The argument of the Confucian text is almost the same as Yamagawa's, although the order in which the argument is carried out is reversed: in The Great Learning it proceeds from the individual to the general; Yamagawa argues from the general to the specific. Through perfecting learning, Yamagawa wanted to perfect society in Japan, bringing his decision to study physics into perfect harmony with Confucian ethics and reasoning. When Yamagawa entered the Sheffield Scientific School in 1872, the school offered chemistry, civil engineering, agriculture, natural history, medicine, and mining and metallurgy as majors, but not physics. Yamagawa chose civil engineering "in the hope that it would provide a foundation for physics." 147 The science course at Sheffield was designed to take three years. During the first year all science majors took introductory courses in mathematics, chemistry, physics, and related subjects; in the second and third years they concentrated on one of the majors. The civil engineering program included courses in differential and integral calculus, mechanics, astronomy, and hydraulics, but it was after all a major for civil engineers and not at all adequate training for a physicist.148 In his Recollections, Yamagawa reports that he audited a graduate course in mathematics and read various physics books on his own; 149 his account does not allow us to to judge the full extent of his study of physics. The only existing descrip­ tion of Yamagawa as a student at Sheffield occurs in a letter of introduc­ tion, dated 4 May 1875, from W. A. Norton, a professor of civil engineering who taught astronomy and applied mechanics at Sheffield, to S. Newcomb, an astronomer at the astronomical observatory in Washington, D.C. Norton explained that Yamagawa was "remarkably earnest and diligent in the prosecution of his studies, and maintained a distinguished rank in scholar­ ship." 150 Despite further financial difficulties after the Japanese govern­ ment ceased to send money for his support, Yamagawa completed all of his courses with financial help from an American and returned to Japan in May 1875. 151 146 Quoted

in Dore'sEducation in Tokugawa Japan, p. 41. pp. 68-69. 14 ^The information about the courses at the Sheffield Scientific School is from Watanabe's "Yamagawa," pp. 114-115. 149 Jfeo, pp. 68-69. 150 Quoted in "Yamagawa," p. 119. 151 Yamagawa's problems were the result of a policy by which in the 1860's and early 1870's various organizations took the initiative to send students abroad without standard examination requirements or procedures. Thus, the first students to be sent 147 Zfeo,

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InJanuary 1876 Yamagawa was appointed Assistant Professor of Physics at the Tokyo Kaisei School, one of the predecessors of the University of Tokyo. He must have been an attractive applicant since scientific training was still a rarity among Japanese at that time. 152 He was required to assist Veeder, Professor of Physics, in instructing students in physics experiments. In 1879 Yamagawa was promoted to Professor of Physics, the first Japa­ nese to reach that rank. When foreign professors such as Mendenhall, Ewing, and Knott were invited to Japan to teach physics at the University of Tokyo, Yamagawa did not become assistant to the Western physicists again but continued in his rank. He was also influential in the Japanese scientific world through his leadership in the scientific dictionary project. After his student Tanakadate began teaching physics at the University of Tokyo in the 1880's, Yamagawa was able to limit his own teaching to such subjects as optics, thermodynamics, and acoustics. In 1888 the University granted its first doctorates and awarded Yamagawa a Doctor of Science degree. 153 He did not retire from his professorship until 1901, the year of his twenty-fifth anniversary of teaching physics at the University of Tokyo; and the same year he became president of that institution. 154 Since Yamagawa was the first Japanese professor of physics, I shall ex­ amine his scientific activities during his years at the University of Tokyo. Yamagawa wrote only two or three papers that might be considered scien­ tific; these dealt with the relation between the occurrence of fires and weather, with capillary action, and with the measurement of the thermal conductivity of marble. 155 His other publications included popular essays

abroad were not all the best. A debate arose in Japan over whether or not such stu­ dents should be called home immediately. Since it was difficult to screen the stu­ dents already abroad, it was decided that all but the truly exceptional students were to be recalled to Japan. Yamagawa, too, received the order to return, but he wanted to complete his studies and decided to stay at his own expense. Yamagawa recalls that the relative of one of his classmates who helped him out of his financial diffi­ culties required him to sign a pledge that after graduating and returning to Japan he would do his best for his country. Seelko, pp. 54-55. 1 5 2 Yamagawa's return was reported in the newspaper Tokyo nichintcht shimbun with the comment that "it is widely held that, without doubt, he is a person who will be of enormous use to Japan." See Shimbun shuset Meiji hennenshi, 2, 338. 1 5 3 In 1888 the Japanese government issued an ordinance stating that the Imperial University was to set up a system whereby doctoral degrees could be granted in rec­ ognition of outstanding work. The university complied by awarding fifteen doctor­ ates, five each in science, medicine, and engineering. 1 5 4 Den, pp. 80-102. 1 5 5 K. Yamagawa, "Fires in Tokio," Memoirs of the Science Department, University of Tokio, 7 (1880), 71-81; "Mokan gensho no josu ο sokuteisuru shimpo," Tokyo sUgaku butsuri gakkai kiji, 3 (1886), 140-145; "Determination of the Thermal Con·

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on magnetism and on the use of the spectroscope, and the Japanese Dic­ tionary of Physics Terminology from the English, French, and German, which he edited. 156 He did not do much research for two reasons: he had never been trained as a physicist, and he preferred administrative work and teaching. That Yamagawa published on science at all is due to the presence of the foreign physics professors such as Ewing, Mendenhall, and Knott in Tokyo in the 1880's, and to the stimulating scientific atmosphere they created through their experimental work. His paper on "Fires in Tokio" was in fact suggested by Mendenhall. Just at that time, too, the first Japa­ nese academic journals began to appear; Memoirs of the Science Depart­ ment was started in 1879 and the Journal of the College of Science in 1887. (See Table C [Appendix].) Yamagawa may have felt obliged to support the journals by publishing in them. 157 Yamagawa's teaching was praised and criticized. Kuwaki Ayao, a physi­ cist who studied under Yamagawa in the 1890's, recalls that Yamagawa's lectures were well prepared and easy to take notes from. On the other hand Takagi Teiji, a mathematician who was studying during the same years, re­ calls that while Yamagawa lectured, he constantly copied his lecture notes onto the blackboard in English and would become so engrossed in copying he even accidentally omitted sections of his notes at times. 158 He was probably not a very stimulating professor. He was important all the same because he was one of the very few Japanese teaching physics at that time and the only full professor among them, and because he recognized the value of both academic and applied physics and passed this understanding on to his students. One crucial aspect of Yamagawa's thinking was that, in contrast to earlier Confucian-trained Japanese scholars, he firmly believed that learning should have a theoretical basis. Engineering, which in his view lacked theory, should be based upon mathematics, physics, and chemistry. His view of learning was supported, he felt, by the achievements of Fresnel

ductivity of Marble," The Journal of the College of Science, Imperial University, Japan, 2 (1889), 263-281. 156 See "Yamagawa," pp. 123-126. is7 When the discovery of X rays reached Japan in early 1897, Yamagawa was one of the earliest to successfully repeat X ray experiments in that country. Although he gave speeches on X rays, he never published accounts of his experiments in academic journals. Neither did he publish accounts of his investigations on ESP and psychophotography (with the exception of one very brief essay). 158 See A. Kuwaki, Kagakushi ko (Tokyo, 1944), p. 507, and T. Takagi, "Meiji no senseigata," inSugaku to jinsei, Y. Yoshida et al., eds. (Tokyo, 1962), p. 210.

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and Leverrier; he claimed that both Leverrier's prediction of Neptune and Fresnel's wave theory and explanation of the phenomena of light were based on mathematical reasoning alone and represented the "victory of learning." 159 That Yamagawa communicated these views to his students at a time when physics or, more generally, Western learning was being estab­ lished is important to the history of physics in Japan. He also defended the importance of pure research in public. In a series of public lectures in 1907 Yamagawa mentioned a newspaper article written by a reporter after visiting the College of Science at Tokyo Imperial University. Upon ob­ serving research on the parasites of earthworms, the reporter wrote that "scholars are those who study such trivial things as this." Yamagawa re­ sponded: In the first place science took as its aim the search for truth about physi­ cal matter. It has nothing to do with the importance or triviality of the subject matter being researched. No one can know whether that which is being studied is ultimately important or trivial, insignificant or weighty, until we have looked at the results after the research has been concluded. If we make clear this truth, it will without fail yield us a useful and bene­ ficial result. About a hundred years ago Galvani discovered that if one inserts a copper wire into a frog's leg, inserts a steel wire into his back, and then touches the steel and copper wire together, the frog's leg will contract, and he investigated this phenomenon. If we had shown this to that newspaper reporter he would certainly have laughed at such non­ sense. How could it have been known then that the lights that illuminate this very room, or the streetcar by which you came here today, or even the wireless telegraph that succeeded so brilliantly in the Russo-Japanese War would all be the result of that research. 160 Yamagawa was most successful as an administrator. He was made dean of the College of Science at the Imperial University in 1893 and president of the University in 1901; in 1904 he became a life member of the House of Peers. He organized and was the first president of the Meiji Semmon Gakko or Meiji Technical School, which opened in 1909. He became president of Kyushu Imperial University 161 when it was founded in 1911, pp. 92-93. 160 Printed

in Gakujutsu tsuzoku k&enshu (Tokyo, 1907), pp. 1-3. Imperial University was the fourth Imperial University. It had two Colleges: Medical and Engineering. Its College of Science was not set up until 1930. A third Imperial University had been established in Tohoku in 1907, its College of Science opening in 1911. 161 Kyushu

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but resigned two years later to resume the presidency of Tokyo Imperial University in 1913, a position he retained until 1920. Concurrently with the latter post, from 1914 to 1915 he held the post of president of Kyoto Imperial University. It is unique in Japanese educational history that one man was not only president of three Imperial Universities, but at one point held two presidencies concurrently. To have been president of Tokyo Im­ perial University twice would in itself have been enough to assure him lasting fame. In 1915 he was granted the title of baron in recognition of his achievements. I want to comment on the Meiji Technical School, which was a private engineering .school founded in 1909 by Yasukawa Keiichiro, a business­ man who had made a fortune during the Russo-Japanese War of 19041905. Yamagawa, having resigned from his first presidency of Tokyo Im­ perial University in 1905, was in semiretirement when Yasukawa approached him with the idea of the school in 1906. Yamagawa accepted the task of setting up the institution because he agreed with Yasukawa that science would make Japan capable of coping with the West and be­ cause he deplored the lack of training programs in scientific engineering in Japan's private universities. Yasukawa gave him complete freedom in the administrative and financial concerns of the school. Yamagawa selected faculty members from graduates of the College of Engineering of Tokyo Imperial University to teach three programs: mining, metallurgy, and machinery. Although in most respects the institution resembled other en­ gineering schools, it also incorporated the routines and disciplines of a military academy; in addition to the academic curriculum the program re­ quired target practice, drilling, field operations, and other forms of mili­ tary training. 162 Yamagawa's educational innovation aimed at producing Meiji Technical School graduates who combined the skills of engineer and soldier and reflected the high value he attributed to loyalty and patrio­ tism. 163 Yamagawa's second term as president of Tokyo Imperial University from 1913 to 1920 belonged to an important period in Japanese science. In the 1910's two major scientific institutions had been established: Rikagaku Kenkyusho, or the Institute of Physical and Chemical Research, in 1917, 162 The

school had a four-year course. Twenty students studied mining, fifteen metallurgy, and twenty machinery. See Den, p. 166. Although the school is reminis­ cent of the Ecole polytechnique in France, that institution was not Yamagawa's model. The school was an embodiment of the educational values he personally prized. 1 63 Den, pp. 161-172.

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and Koku Kenkyusho, or the Aeronautical Research Institute, in 1918. The Institute of Physical and Chemical Research was set up with funds from both government and industrial circles and was modeled after foreign na­ tional research institutes such as the Imperial Physico-Technical Institute (Reichsanstalt) and the Kaiser Wilhelm Institutes in Germany, the National Physical Laboratory in Great Britain, and the National Bureau of Stan­ dards in the United States. Yamagawa did little lobbying for the establish­ ment of the Institute, but he was on its ad hoc planning committee, and he was appointed as its first consultant. 164 He was more actively involved in the establishment of the Aeronautical Research Institute, probably be­ cause of the importance of airplanes to military affairs. At least two years prior to its establishment, he had lobbied the government for such a research center. After the budget of the new Institute was finally ap­ proved by the Diet, he pressed for an affiliation between the Institute and Tokyo Imperial University and devised a system whereby professors appointed to the University could devote themselves to the Institute's re­ search. In 1919, when the Japanese army and navy on the one hand and the Ministry of Education on the other independently announced pre­ liminary plans to establish a national aeronautical institute, Yamagawa firmly opposed these plans and succeeded in expanding the Aeronautical Research Institute instead. 165 Yamagawa studied physics for the sake of Japan, believing that the sci­ ences serve the state; he also praised pure science such as Fresnel's and Leverriers' "victories of learning." Contradictory though these two aspects of his view of physics may be, he did not see them that way; they were reconciled by his primary concern that Japan be a first-rate country. He expressed no view of nature nor of matter, an aspect of Western science that was never his concern. In later life he became increasingly concerned with moral education in addition to scientific education, using the Meiji Technical School to cultivate both. His ideas on moral education were a 164 K. Itakura and E. Yagi, "Rikagaku kenkyusho no setsuritsuki ni okeru kagaku kenkyu taisei (2)," Kagakushi kenkyti, 42 {1957), 24, and Den, p. 283. After the death in 1917 of Kikuchi Dairoku, the first director of the Institute, Yamagawa was asked to take over the directorship; he declined. He was asked again in 1921, when the second director Furuichi Koi resigned for health reasons; again he declined. Although he did not want to become director himself, he apparently influenced the ultimate choice of directors. SeeDen, pp. 283-285. 165 Den, pp. 331-332. When the Aeronautical Research Institute was enlarged in 1919, Yamagawa was asked to become director. He agreed to serve as acting director, but he declined, as he did in the case of the Institute of Physical and Chemical Re­ search, to become its permanent director. See ibid., pp. 320-321.

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hybrid of traditional and Western concepts. The school dormitory bore a patriotic ancient Chinese name taken from an early classic, yet the young students living there were taught to become "'gentlemen," even to the ex­ tent of applying the English term to themselves and learning the proper behavior of a gentleman from anecdotes about Western men. 166 With ref­ erence to General Nogi, one of the last of the great traditional samurai and loyal supporters of the Emperor, Yamagawa was called "General Nogi in a frock coat," 167 an expression that well describes the cultural dualism he represented. To transform Japan into a first-rate country was the goal that determined Yamagawa's whole life; the means toward that end were pa­ triotism, morality, and the pursuit of physics or science in general. He conceived of the Meiji Technical School as the instrument with which to produce men with these three concerns. Yamagawa considered such men indispensable for the survival of Japan. Tanakadate Aikitsu The first son of Tanakadate Inazo and his wife Kisei, Tanakadate Aikitsu was born in 1856 in the Nambu fief (present-day Iwate Prefecture) on the northeast coast of Japan's main island of Honshu. 168 His father was a teacher of the Jitsuyo school of military tactics, a profession the men in his family had already pursued for four generations; his mother came from a family of Shinto priests. As was customary for the first son of a samurai, Tanakadate began his studies at the age of four by learning Japanese writing and the art of callig­ raphy. At eight he began to study swordsmanship under the tutelage of a local samurai while continuing to study calligraphy. In the following year he entered a small private school, the Reisaijo, where he started Chinese studies while continuing his study of swordsmanship. In 1867 at the out­ break of the hostilities that were to lead to the Meiji Restoration, the Reisaijo was closed. Tanakadate briefly studied Chinese with Terii Kosaku, 166 Jfeo,

pp. 324-326 and pp. 285-289. p. 515. Nogi Maresuke became general during the Russo-Japanese War and was particularly famous for winning the battle at Lii-shun. Out of loyalty to the emperor he and his wife committed ritual suicide at the death of Emperor Meiji in 1912. 168 For a study of Tanakadate's life see the reliable biography Tanakadate Aikitsu sensei (Tokyo, 1946) by his former student Nakamura Seiji. This biography, here­ after abbreviated as Tanakadate, was written while Tanakadate was still alive and checked by him for accuracy. Its first part is composed of Tanakadate's reminiscences and hence can be used as a primary source. 167 Den,

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Figure 2. Tanakadate Aikitsu (front, second from right), NagaokaHantaro (front, right), and Honda Kotaro (back, second from right) with their students at the 1903 commencement at Tokyo Imperial University.

a samurai tutor in Morioka, the capital of the Nambu fief, but soon en­ tered the fief school, known as the Shubunsho, where his curriculum in­ cluded not only Chinese studies but the relatively new field of Japanese studies which was devoted to Japanese historical texts. The Meiji Restora­ tion brought the abolition of the fiefs and put the central government in charge of education. The old fief schools experienced major changes in 1871 when it was decided to adopt Western studies as the main curricu­ lum; outraged at the change, the Chinese studies faculty resigned. Tanaka-

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date was unhappy with the decision, too, and withdrew from school, con­ tinuing his Chinese and Japanese studies privately. 169 At this time external circumstances made it advisable for the Taihakadate family to move to Tokyo. With the abolition of the fiefs, everyone throughout Japan began for the first time in Japanese history to look to Tokyo as the center of educational and political opportunity. Before, in­ dividual success had largely depended on a man's role in his fief; now his career depended on powerful persons in Tokyo. The Meiji Restoration had also officially abolished the samurai's role in society. This was difficult for all samurai, but hardest on samurai from fiefs that were suffering financial difficulties. During the fighting preceding the Restoration, the Nambu fief had supported the shogun and had engaged in some fighting with a neigh­ boring fief that supported the Imperial forces. As a consequence Nambu was required to pay reparations to the Meiji government after the Restora­ tion and was financially drained. Tanakadate's father, no longer able to function as a samurai or to teach military tactics in a fief suffering a de­ pression, had to seek a new livelihood and decided to become a merchant. To pursue this new career and to assure the best possible education for his children, he moved his family to Tokyo in 1872. 170 By this time Tanakadate realized that to survive in the new Japan he would have to involve himself in someway with the Western studies he had previously spurned. In September 1872 he entered Keio Gijuku, a private college, and began studying the Western alphabet to learn English. There existed then two accepted methods of learning a foreign language: seisoku, or the exact method, and hensoku, or the altered method. The former re­ quired the student to master all aspects of the language. The latter aimed only at developing reading skills and ignored proper pronunciation. In 1873, Fukuzawa Yukichi, the founder of Keio Gijuku, formulated a major educational idea that was to influence Tanakadate's thinking. He said that the terms seisoku and hensoku should be given a broader meaning; they should no longer refer to language instruction only but to all study. Seisoku was the method whereby learning is pursued according to certain prescribed steps, the student moving from the basics to higher levels. Hensoku was the method whereby the student omits the basics and plunges directly into the study that is relevant to his immediate needs. Both types of education were found in Japan at that time, and Tanakadate was deeply impressed by Fukuzawa's insight into their distinction. Con169 Tanakadate, 170Zbici.,

p. 20.

pp. 2-18.

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vinced that education in any field has proper steps that must be taken in the proper sequence and that in true learning one thing must be built upon another, Tanakadate decided that seisoku 171 would be his educational method. The high costs of living in Tokyo and attending Keio Gijuku, a private institution, forced Tanakadate to find a less expensive school. When he learned from a friend about Kobu Daigakkd, or School of Engineering, a government institution that was considerably cheaper, he prepared for entrance examinations there. For this purpose he studied geometry and algebra on his own and was tutored in English by the wife of Montague Fenton, a teacher of Western music employed by the navy. Tanakadate did not go to the School of Engineering to inquire into the details of admission until some time later that year. His reaction shows us that his views were still determined by his past and early education. I went to the School of Engineering and got a copy of their catalogue. Looking at it I found that there was not a word on how to govern the nation, which was what I had previously been learning through Chinese studies. There was nothing mentioned but such things as how to build a lighthouse or how to construct a bridge, or, say, how to put up electrical wires. "It's meaningless to learn nothing but this sort of thing," I said to myself, and lost all interest in matriculating. After considerable thought my choice shifted to the University, Southern Division. 172 Although Tanakadate refers to the University, Southern Division in this quotation taken from his recollections in 1943, the institution had already changed its name to the Tokyo Kaisei School when he decided to enter it in 1874. He entered the school in 1876 after two years in the English Division of the Gaikokugo Gakko, or School of Foreign Languages, where he had made up a language deficiency that had delayed his admission. The course of studies at the Tokyo Kaisei School extended over six years; it consisted of two years of preliminary general education, followed by four years of specialized study in a major. Tanakadate was critical of the new approach to learning: The curriculum of the first two years was not divided up according to majors, and for that reason the true flavor of our school life was found simply in the pleasure of pure learning itself. However, there were among 17l Ibid., pp. 23-24. See also "Tanakadate hakase ο kakomite Meijishokinowaga kagaku ο shinobu," Kagakushi kenkyu, 6 (1943), 56-57. l7 ^Tanakadate, p. 25.

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us quite a few who were determined to become politicians and govern the country. In fact, I was one of them. People like us felt that physics and astronomy and the like were no more than trivial skills, and the atmosphere there was permeated by the sentiment that in order to govern the country, such skills are of no use whatsoever. 173 Tanakadate's exposure to Western science during his first two years at the Tokyo Kaisei School made him see that learning could also lead to something other than methods of governing men. He was required to take a physics course taught by Yamagawa who, only two years older than Tanakadate, had just returned from the United States. The text Yamagawa used was Balfour Stewart's Physics, which he followed very closely, re­ quiring the students to all but memorize it. 174 At the same time he illustrated the physical principles it contained with examples from ex­ perience. He related that during the military encounters at the Aizu fief before the Meiji Restoration, the warriors ran toward the enemy cannon positions when fired upon to escape the heaviest pieces of shrapnel. Yamagawa explained that a military man learns from experience, but his behavior can also be justified in terms of the principles of physics. Tanaka­ date recalled Yamagawa's accounts of Franklin and Fresnel, and he prob­ ably heard him speak of Fresnel's "victory of learning." Through such interpretations that were not contained in Western scientific texts, Tanakadate began to understand for the first time the Western concept of learning. He understood that "learning" could encompass something be­ sides a person's moral training in preparation for governing the country. 175 Other events influenced the revision of Tanakadate's concept of learning. Most of the oyatoigaikokujin teaching in Japan were practicing Christians, many of whom contended that if Japan were to become an "advanced" nation, it would have to be converted to Christianity. There were skeptics among the foreigners as well, however, particularly those who believed and taught Darwin's theory of evolution. The resulting tensions among the foreign faculty sometimes created open conflict as when Edward Morse's lectures on Darwinism drew theological objections from colleagues. Such conflicts also caused considerable discomfort on the part of the Japanese, most of whom considered Christianity to be the intolerant religion of bar­ barians who had little or no spiritual sensitivity. No doubt in response to 173 Zbid.,

p. 31. Tanakadate, "Buturigaku Omoide," Nihon butsurigakkai shi, 5 (1950), 315. l ^ s Tanakadate, pp. 30-31.

1 7 4 A.

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these tensions, Veeder, the ProfessorofPhysics at the University of Tokyo, took up the question of religion in education in an address at the gradua­ tion ceremonies in 1878. Veeder stated that since the university is the capital of learning and research, religion and politics should be banished from its halls. 176 His view so impressed Tanakadate that he remembered it clearly the rest of his life. The idea that learning could, or even should, be detached from social considerations must have been startling to the young ex-samurai who had been taught that politics was the main concern of education. In the same year, 1878, Tanakadate finished his preliminary two-year course and had to decide upon his specialization for the remaining four years of study. It was a time of indecision and inner conflict for him. He knew that he had to pursue Western studies in order to be effective in Japan, and yet he found it hard to abandon the maxim that "learning is for governing." He had been unable to discover anything conforming to that maxim in his studies at the Tokyo Kaisei School, by now the Uni­ versity of Tokyo. "Man's aim is to train himself and govern the country," the local elders had admonished me, "and so if you are unable to find employment use­ ful to your country you must leave written works for the benefit of later generations. To that end study letters." Up to this point, therefore, I had attempted to study the proper way of governing the nation. But as far as governing a country is concerned, from what I have seen so far, there are no Western books explaining how to train oneself and govern the nation that measure up to the teachings of Confucius and Mencius. On the other hand, in the field of science there are things I would like very much to study. And so I feel that I want to master physics, which is the basis of all science, so as to make up on full measure for our country's deficiencies. 177 The reasons for Tanakadate's choice of a physics career are obscure; but we can see in his decision a merging of several influences. His decision is, first, a compromise between his interest in physics and the old Confucian idea that learning serves the country: he will study physics because he wants to, but he is reassured that his training will contribute to the govern­ ment of the country. Second, his decision to do physics and not to educate himself for direct political action in government reflects Veeder's insisll6Ibid., lll Ibid.,

p. 37. p. 39.

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tence on the "independence of learning." Finally, his words show that Fukuzawa's seisoku—the view that in true learning one thing must be built upon another—still informed his thoughts: "I want to master physics, which is the basis of all science. . . ." 178 Tanakadate's letter in which he informed his father of his choice is lost, but we have his father's reply. The elder Tanakadate told his son that all he wished for him was that by his choice of career he could make some contribution to mankind throughout the world. That reply must have been encouraging, recognizing possibilities for service even beyond the needs of Japan. 179 For the next four years, from 1878 to 1882, Tanakadate studied with Yamagawa, Ewing, and Mendenhall. The two foreigners allowed him to participate in their research during this period: Mendenhall in his work on geophysics, Ewing in his on electricity and magnetism. After he graduated in 1882 from what was by then called the Department of Physics, he was made a lecturer in that department and for the next several years served as Yamagawa's assistant. In 1886, the same year that the University of Tokyo became the Imperial University, he was made assistant professor. When two years later the University sent him abroad to study, he went to the University of Glasgow with an introduction from Ewing to study with William Thomson. To the end of his life he spoke of the deep impression Thomson had made on him. 180 At Glasgow he worked on experiments re­ lated to the work in electricity and magnetism that he had done under Ewing in Japan, and he published papers in English on such problems as the magnetization of soft iron bars and the thermal effects of magnetiza­ tion reversals. 181 After two years at Glasgow, he spent a year in Berlin attending lectures by Helmholtz and I. L. Fuchs and a colloquium given by Planck, Kundt, and others. 182 On his return to Japan in July 1891 he 178 Italics

are mine. ^ 9 Tanahadate, pp. 39-40. 180 Thomson treated him well in his laboratory and sometimes invited him to his house. When Tanakadate left Glasgow for the Continent, Thomson gave him about ten of his personal cards to use freely for introductions, an uncommon kindness in those days according to Tanakadate. See ibid., p. 80. 181 A. Tanakadate, "Mean Intensity of Magnetisation of Soft Iron Bars of Various Lengths in a Uniform Magnetic Field," Philosophical Magazine, 26 (1888), 450-456, and A. Tanakadate, "The Thermal Effect Due to Reversals of Magnetisation in Soft Ixon," Philosophical Magazine, 27 (1889), 207-218. 182 A. Tanakadate, "Tabi no Omoide," p. 3. "Tabi no Omoide" is a fourteen-page typescript written in romanized Japanese which was prepared for publication. I found this document among the Tanakadate papers deposited at the National Science

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was immediately promoted to full professor and in August 1891 received the Doctor of Science degree from the Imperial University. From then until 1916 he remained at the Imperial University as Professor of Physics; when he retired in 1916 at the age of sixty, he was honored with a celebra­ tion of the twenty-fifth anniversary of his promotion to full professor. 183 Tanakadate's scientific activity encompassed three subjects which to a certain extent corresponded to three different periods of his career. Tanakadate was introduced to the first subject, electricity and magnetism, by Ewing; he worked in it from the time he was a student until he returned in 1891 from a trip abroad. He had also early become interested in the second subject, geophysics, when he participated in geomagnetic measure­ ments under Mendenhall. This subject became his major concern after his return from Europe, largely because of the Nobi earthquake of 1891, which caused enormous damage and the loss of more than two thousand lives in the neighborhood of the city of Nagoya. As early as 1887, the year after he had become an assistant professor, he, Knott, and their stu­ dents measured Japan's geomagnetism; Knott was responsible for the northern half of the country and Tanakadate for the southern part in­ cluding the Nagoya area and the Nobi Plains. 184 Tanakadate was, there­ fore, the Japanese scientist who was most experienced in geomagnetism at the time of the earthquake, and the University asked him to investigate its aftermath. His resulting new geomagnetic measurements differed from those he had helped make four years earlier, proving that earthquakes change the geomagnetism of an area. 185 The discovery further increased his interest in the subject, and in 1893 he organized a four-year expedition sponsored by the University to make new geomagnetic measurements throughout Japan. 186 His work in geophysics continued into the first Museum in Tokyo, but could not determine the name of the journal to which the paper was submitted. 183Tanakadate, pp. 87-141. 184 A. Tanakadate and C. Knott, "A Magnetic Survey of Japan, Carried out by Order of the President of the Imperial University," Journal of the College of Science, Imperial University, Japan, 2 (1888), 163 ff. 185 Tanakadate's investigation led to more systematic investigations shortly there­ after, the results of which were published jointly with H. Nagaoka: A. Tanakadate and H. Nagaoka, "The Disturbance of Isomagnetics attending the Μίηδ-Owari Earth­ quake of 1891," Journal of the College of Science, Imperial University, Japan, 5 (1892), 149-192. 186 Under Ewing he had learned that the magnetism of a metal changes under mechanical stress. Since the earth is a magnet, it was thought that the presence of mechanical stress inside it should change the earth's magnetism. By observing varia-

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decade of the twentieth century, when it was supplanted by work in aero­ nautics and the problem of weights and measures, his main concerns through World War II. In 1918, two years after his retirement from the University, he was appointed supervisor of the Aeronautical Research Institute; he also frequently traveled abroad to attend conferences on weights and measures. After World War II, Tanakadate's scientific activity gradually decreased because of his age; he was ninety-four when he died in 1950. Tanakadate's career represents a clear contrast to Yamagawa's despite the similarity of their backgrounds. Unlike Yamagawa, Tanakadate was not an administrator. His greatest influence on his students at the University and in Japan in general was in experimental physics. Like Yamagawa he chose physics to serve his country, but because of his training under Mendenhall and Ewing, which was far better than Yamagawa's, he also came to enjoy doing experimental physics for its own sake. Yamagawa and Tanakadate differed further in their contacts with Western scientists. Whereas Yamagawa never went abroad again after his four years of foreign study as a young man, Tanakadate traveled abroad with exceptional fre­ quency for a Japanese of that period. In addition to his first three-year trip to Glasgow and Berlin when he was in his thirties, Tanakadate went abroad more than twenty times between 1898 and 1935, sometimes sent by Japan and sometimes invited to attend international conferences. 187 Most of his missions were scientific, but he also participated in the Inter­ national Congress of Linguists because he was interested in romanizing the Japanese language, and he was involved with the Committee on Intellectual Cooperation of the League of Nations. Tanakadate enjoyed going abroad; he used English as his main foreign language and broken French or German when necessary. Physics was Tanakadate's passport to the West; his discipline provided him with interests that he could share with foreign colleagues. By contrast, Yamagawa's interests were centered on the administration of Japanese institutions, an activity that did not re­ quire travel abroad and would have given him little to talk about with foreign physicists.

tions in geomagnetism, the Japanese physicists hoped to make it possible to predict earthquakes. is ^Tanakadate, pp. 145-172. Tanakadate first participated in an international conference on geodesy held in Stuttgart in 1898. He was accompanied by Kimura Hisashi, a geophysicist and astronomer who had graduated from the Department of Astronomy at the Imperial University in 1892.

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Tanakadate went further than Yamagawa in seeking to relate the values of Western civilization to Japanese and Confucian values. Although Yamagawa was able to discern the value of physics, he never questioned the Confucian tradition in Japan, and he tried to superpose Western civiliza­ tion on a more or less intact Japanese civilization. To the end of his life he could not conceive of learning or of schools without Confucianism. Tanakadate, on the other hand, questioned the simplistic dichotomy drawn between the East and West. In a 1915 lecture to a committee of the House of Peers on the status of current research on airplanes Tanakadate challenged what he assumed to be the common view of the West: As I proceed to inquire into your opinions on the subject, I find that the question of the harmony of Eastern and Western civilizations seems to present a problem. As I understand you, gentlemen, you feel that West­ ern civilization is a materialistic and mechanistic civilization. In other words, that it is a physical culture lacking in spiritual direction. And you feel that Eastern civilization is a metaphysical culture, and is spiritual; that humanity and a sense of duty are the unique characteristics of the East. It is my understanding that you hope somehow or other to har­ monize these two cultural viewpoints. But I question whether or not it is all right to interpret Eastern and Western civilizations in such an elementary manner. 188 Tanakadate opposed the Japanese view that Western scientists and in­ ventors worked for material goods. He argued that Western civilization cannot be so trivial if Galileo was willing to die for his scientific beliefs. He insisted that Western civilization, which the Japanese condemned as materialistic, had spiritual values. Tanakadate was comfortable in both the Eastern and the Western world, and he functioned in the world of physical research which in principle recognized no national or cultural barriers. Tanakadate has been described as a man who failed to escape from the Confucian context. 189 I agree inso­ far as Tanakadate justified his work in physics by Confucian arguments in the beginning; but he rapidly moved beyond that narrow context. The task of bringing Eastern and Western cultures into harmony ceased to be a real, personal problem for him. He was not a General Nogi in a frock coat, but a Japanese physicist of the new order. l88 Quoted

in Tanakadate, p. 194. Nakayama 1 "Shushin saika jikoku heitenka to kagaku—Tanakadate AiKitsu ο chushin to shite," Butsurigakushi kenkyU, 2 (1963), 155-168. 189 S.

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Nagaoka Hantaro Yamagawa and Tanakadate were representatives of the first generation of Japanese physicists who decided to study physics largely because as physicists they could be of service to Japan. By contrast, Nagaoka Hantaro represented a new phenomenon in the history of Japanese physics: he chose a career in physics from purely personal motivations and partici­ pated fully in the competitive world of theoretical and experimental physics. Nagaoka was born on 18 August 1865, the son of Nagaoka Jisaburo, a samurai of the Omura fief (present-day Nagasaki prefecture) in Kyushu, Japan's southernmost island. 190 During the disturbances prior to the Meiji Restoration, the Omura fief had fought on the side of the Imperial forces. Because of his enthusiastic support of the Emperor during the fighting, Nagaoka's father was invited in 1871 to join the prestigious Iwakura Mis­ sion, a group of more than one hundred Japanese headed by leading states­ men like Iwakura Tomomi, Ito Hirobumi, and Okubo Toshimichi. The purpose of the mission was to initiate talks that might lead to the revision of the unequal treaties then in force between Japan and Western countries and at the same time to study Western institutions in situ. 191 Nagaoka's father was deeply concerned about the education of his children, teaching them calligraphy and Chinese studies himself. While he was in England on the Iwakura Mission he bought used textbooks at Eton and Rugby, including a history of England, for his children. Although there is no record of the titles of the books, they were probably the texts used for the liberal arts and natural science courses then taught at the preparatory schools. The elder Nagaoka was so impressed with Western education that upon his return to Japan in 1873 he apologized to his son for having taught him the wrong subjects, "jl am not worthy to be your father for having misled you," he said to his eight-year-old son. "Western­ ers are studying these books and you too must become a person able to read them. Since I cannot teach you, you must study English." Nagaoka's father even tried to study the books he had brought back himself although he could read no English. 192 190 Just as I completed the present article, the first full-length biography of Nagaoka appeared. I refer the reader to this lengthy and detailed study for further informa­ tion: K. Itakura, T. Kimura, and E. Yagi, NagaokaHantarS den (Tokyo, 1973). 191 H. Nagaoka, "Chichi Hantaro ο kataru," Shizenkagaku to hakubutsukan, 30 (1963), 88. 192lbid., p. 89.

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Ϋ •%$

y

Figure 3. Nagaoka Hantaro around 1934 when he was president of Osaka Imperial University.

The elder Nagaoka's extraordinary enthusiasm and determination to re­ place traditional learning with Western studies cannot be due entirely to his experiences in Europe. Since the Omura fief was close to Nagasaki, the the original center for Dutch studies and Japan's only window to the rest of the world during more than two hundred years of isolation, Nagaoka's father was probably psychologically better prepared for the trip than his countrymen from other parts of Japan and went with less hostility and greater receptiveness toward foreigners than was typical in his day. His attitude must have had a profound effect on his son, making it possible for

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the young Nagaoka to escape any inordinate reverence for Chinese studies which, under other circumstances, he might have retained. 193 Nagaoka entered the Omura fief school, the GokySkan, at the age of six. Two years later, in 1873, the fief schools were abolished. The Nagaokas moved to Tokyo in 1874, where for the next four years Nagaoka tried one Tokyo school after another, apparently seeking better English training. In 1877 he entered the University Gateway School to prepare for entrance to the University of Tokyo, but when his father was transferred to Osaka soon afterwards, Nagaoka was forced to change schools again, studying first at the Osaka English School and then at the Osaka Technical School; after the family's return to Tokyo in 1880 he re-entered the University Gateway School. As early as 1877 the twelve-year-old Nagaoka showed an interest in science books. He wanted to read G. P. Quackenbos' A Natural Philosophy, which proved to be too expensive for him, and he bought instead R. G. Parker's First Lesson in Natural Philosophy. 194 Nagaoka's interest in these books may not have been exclusively scientific. It is known that some schools used such books as texts for studying English, and Nagaoka may have wanted them for the same reason. 195 In 1882, at the age of seventeen, he entered the University of Tokyo. Nagaoka's frankness and self-awareness as well as his indifference to social concerns and his strong personal ambition set him apart from his prede­ cessors: A year after I had entered the University of Tokyo I became more or less acquainted with the things that were being studied in Europe and America, but I did not plan to follow the work of others or to devote my life to importing learning from abroad and to disseminating it among the Japanese. There was no point in my having had the good fortune to be born a man, if I failed to enter the advanced ranks of researchers and to contribute to the development of some field of learning. 196 19 ^Nagaoka Hantaro's son goes so far as to say that his father would not have become famous if he had not been born in Omura and had not had the father that he did. See ibid., p. 90. 194 H. Nagaoka, "Gakusei jidai no Maruzen kaiko," in Butsurigakusha no me, Y. Yoshida et al., eds. (Tokyo, 1961), p. 206. 195 K. Itakura et al., Nagaoka Hantard den, p. 25. 196 H. Nagaoka, "Chugaku sotsugyo go no shishin," NKGT, 8, 199. This is a speech given at a junior high school, Kaisei Chugakko, in 1946. The speech had been un­ known to historians of science until it was recently discovered in the Nagaoka-Col­ lection deposited at the National Science Museum in Tokyo.

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Nagaoka presents us with the picture of a young man as yet undecided about a specific goal, but certain of his desire to make a unique contribu­ tion to scholarship. At some time during his first year at the university Nagaoka was defi­ nitely attracted to science. However, the fear that the Japanese were some­ how, as a race, inferior to Westerners—a fear many Japanese had at that time—caused him temporarily to interrupt his university studies. The su­ periority of Western technology may have been one reason for this fear. Another may have derived from Western attitudes toward the Japanese; foreign visitors were often contemptuous of the Japanese or, worse, pa­ tronizing, treating them as children. 197 Specifically, Nagaoka feared that because of his race he might not be able to become a great scientist. He recalled that none of the lectures he heard during his first year at the University referred to an Oriental contribution to physics. 198 He said that in his second year at the university "I felt it would be a good plan first to clarify whether or not Orientals have a talent for scientific research, and then to take my time in determining my future course . . . and with firm resolve I asked for a year's leave of absence and tried investigating things related to science in China." 199 During his year of research in Chinese science he found that the Chinese had such remarkable accomplishments as the invention of the south-pointing carriage and of gunpowder, the independent discovery of sunspots, and calendar making. He recalled that "in view of the fact that such research had already been achieved, I came to have confidence that Orientals, too, if they devoted themselves to it [science], would, in the end, reach a level not inferior to that of Europe and America." 200 He goes on to say that if he had failed to find evidence 197 An example that illustrates the racism in Japan at that time is the Normanton incident of 1886. A British cargo boat, the Normanton, was shipwrecked off the coast of Wakayama Prefecture. The British captain and the crew of the ship quickly escaped to safety, abandoning the twenty-three Japanese passengers on board, all of whom drowned. The Japanese responded to the incident with great anger and became even more outraged when at the trial of the British personnel the British Consul judged them innocent of any wrong doing. That judgement would have been im­ possible had the passengers been British. Protests by the Japanese government re­ sulted in a second trial at which the captain was finally declared guilty, but sentenced to only three months in jail. The whole episode caused considerable bitterness among the Japanese and aggravated racial antagonisms. See J. Eto, Soseki to sono jidai (Tokyo, 1970), 1, 123-124. 198 H. Nagaoka, "Kenkyfl to dokusho," in his Zuihitsu (Tokyo, 1936), p. 611. The paper was originally published in the Teidai shimbun (Tokyo Imperial University Newspaper) in 1935. 199 NGKT, 8, 199. ™>lbid„ p. 399.

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that Orientals are able to do science, he would have given up his wish to be a scientist and would have become a historian of Asian culture. Both alternatives reflect a basic element in his character: an overwhelming de­ termination to make Westerners aware of the greatness of Oriental man. His recollections further reveal that neither Yamagawa's work nor Tanakadate's was sufficient to convince him that Japanese could become great pioneers in physics. In 1884 Nagaoka started to study physics at the university. In addition to attending lectures he did extensive outside reading in physics texts, studying, for example, Thomson and Tate's Natural Philosophy. He con­ sidered independent study an important part of his training, but he was handicapped by the high cost of Western books in Japanese bookstores. Some he obtained from Knott, who ordered his own books directly from England and included orders for Nagaoka and others. 201 One year before Nagaoka graduated in 1887, the University of Tokyo became the Imperial University and established a graduate school. The change enabled Nagaoka to go on immediately to advanced studies at the graduate level and made him one of the first products of Japan's new, fully-established educational program in physics. In 1888 Nagaoka was asked to take over Tanakadate's experimental physics class when the latter was sent to Glasgow. Nagaoka, who was still a graduate student, was clearly recognized as a promising physicist. For Nagaoka himself, recognition, particularly by Western physicists, was still related to the racial question. His preoccupation with the question is vividly expressed in an English letter he wrote to Tanakadate in Glasgow. Imperial University 7-6-'88

Dear Tanakadate, I have received yours dated 17th April together with experimental notebooks. These notebooks are indeed convenient. . . . You seem now to be hard at work; how do you like the place? I think you'r[e] not yet muchu [totally involved], because you speak so much about the western weaknesses. I find from your letters, that western civilizations were mostly superficial, the works of the tengu's [big-noses] very rough and not at all trustworthy, just [as] you supposed. I think those who praise the height of western civilization, and try to introduce everything done by the whites, considering whatever the whites do are 201 H.

Nagaoka, "Gakusei jidai no Maruzen kaiko," p. 270.

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just, and correct, and trustworthy, and accurate, and . . . , are but cowards, who turn pale at the glittering light of the surface decorations assumed by the white men. I think it is our duty to go ahead of those whites, beat them, and expose their real nature. This indeed as you say depend[s] on mv 2 /2. This of course can be near parallel with the whites; but I think the first difficulty we meet with in this country is this factor v 2 . Everything is rather injun [indecisive], and there is a great amount of lagging or reaction or friction in doing anything, either in personal affairs or official business or in almost every undertakings We must work actively with an open eye, keen sense, and ready under­ standing, indefaticably and not a moment stopping. We must not allow those classes of people within our doors and interrupt our work, who though appearing as if they were intently at work, soon stops working whenever there comes anything that attract[s] the eye, or the mouth, or the purse. There is no reason why the whites shall be so supreme in everything, and as you say, I hope we shall be able to beat those yattya hottya [pompous) people in the course of 10 or 20 years: I think there is no use of observing the victory of our descendants over the whites with the telescope from jigoku [hell]. Another great requisite in beating those whites is how to make our work known. This is a great difficulty. As a first step we can not write in Japanese and make the westerners understand our writings. We must borrow their language and make the whites understand. Indeed, as you admit, the whites can speak upon any­ thing, but in our case, we are sometimes unable to speak even though there is sufficient material for talk. I think this is our great defect, and we must, if possible, learn to write and speak clearly and fluently. I don't think there is any choice of language, be it English, French, or German. Please reflect on this point. Now quitting these dreams, I shall speak of something that is going on here . . . . 202 The letter shows that Nagaoka's motivations and goals with respect to physics contrasted sharply with Yamagawa's and Tanakadate's. Instead of Yamagawa's dedication of his life and work to the creation of a safe and 2021 have added translations for the few Japanese words he inserted and a few words or plurals to clarify the meaning, while the rest stands as written. I found this letter among the Tanakadate papers deposited at the National Science Museum in Tokyo. I also found several other letters addressed to Tanakadate from Nagaoka, all written in Romanized Japanese.

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stable Japan or Tanakadate's confident, internationalist attitude, we see in Nagaoka an aggressive, almost agonizing sense of racial rivalry with the West. Tanakadate, too, was not uncritical of the West and sometimes pointed out the weaknesses of Westerners. But Nagaoka's aim was to prove to the world that Japan could equal, if not exceed, Western achievements. Nagaoka was not a samurai afraid that Japan would be militarily over­ whelmed by Western technology; rather he sought to impress the West with Japanese intellectual capability by proving his worth in physics and through it that of his countrymen. It is hard to call Nagaoka's attitude simply a manifestation of nationalism; his letter suggests that he was driven by personal hatreds and psychological compulsions. He represents a dif­ ferent type of man than we have seen before. Throughout his life, Yamagawa identified his will with Japan's needs; Tanakadate, too, was motivated by devotion to Japan, but stopped short of a complete submis­ sion of his life and work. Nagaoka, however, was guided by his own needs, responsive to but not absorbed by Japan's needs; he believed that the Japanese were the coming race, and that he was in the vanguard. In 1890 Nagaoka became an assistant professor. In 1893 he received the Doctor of Science degree and was sent to Europe by the Imperial Uni­ versity for further study. There he went to the Universities of Berlin, Munich, and Vienna, -listened to the lectures of Helmholtz, Planck, Kundt, Fuchs, Schwarz, Boltzmann, and others, and did experimental research. 203 During his three-year stay he produced at least seven English or German articles on magnetism, especially magnetostriction, that he published in European journals; in addition he produced at least two English papers on Fraunhofer diffraction that he published in Japan. 204 Nagaoka was pro­ moted to Professor of Physics on his return to Japan in 1896 and from that time on taught applied mathematics and theoretical physics at the Imperial University; at the same time he carried on both theoretical and experimental research. 205 203 A. K[uwaki], "Professor Hantaro Nagaoka," Anniversary Volume Dedicated to Professor Hantaro Nagaoka (Tokyo, 1925), p. i. 204 Some of the papers are: "Hysteresis Attending the Change of Length by Mag­ netization in Nickel and Iron," Philosophical Magazine, 37 (1894), 131-143. "Verteilung der Magnetisirung in Nickeldraht bei gleichzeitiger Wirkung von Longitudmalzug und Torsion," Annalen der Physik und Chemie, 53 (1894), 481-486. "Lines of Equal Intensity about the Point of Intersection of Fraunhofer's Diffraction Bands," Journal of the College of Science, Imperial University, Japan, 9 (1895), 9-13. 205 Nagaoka taught only applied mathematics until 1901, when he started to teach theoretical physics as well. See TTDG, 2, 467-468.

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In general his scientific research can be divided into three subjects: magnetostriction, geophysics, and atomic structure and spectroscopy. He became interested in magnetostriction as a graduate student under Knott, who had performed experiments in this subject before his appointment to the University of Tokyo in 1883. 206 Nagaoka continued his work in the subject while abroad and after his return to Japan, bringing it to a close only in 1904. He worked especially on the phenomenon of volume change accompanying magnetization and in general on the magnetization of metals. 207 In recognition of this work he was invited to give a paper at the First International Congress of Physics held in Paris in 1900. 208 He had succeeded in his goal of making the work of Japanese physicists known to their Western colleagues. Nagaoka's research, like Tanakadate's, was influenced by the Nobi earth­ quake of 1891. He was still an assistant professor at the time and had not yet gone abroad. As a member of one of several groups under the general supervision of Tanakadate, he carried out geomagnetic measurements after the quake and then continued to investigate both geomagnetism and the gravitational constant g until the early 1900's. Eventually he gave up field work, moved to laboratory and theoretical work in geophysics, and pub­ lished on seismology, tidal waves, volcanic action, and many other geo­ physical subjects. He retained an active interest in geophysical research throughout his life. 209 Nagaoka first became interested in the third area of his scientific activity, atomic structure and spectroscopy, in 1900 at the First International Congress of Physics, where he saw Marie Curie's demonstration of radium and realized how complicated atoms must be. He was also impressed by Poincare''s remark that the study of atomic structure would be facilitated 206 K.

Itakura et al., NagaokaHantaro den, p. 94. to Nagaoka, Joule observed only a change in length in his experi­ ments on magnetostriction. Nagaoka and Honda also observed a change in volume, which W. Thomson called the "Nagaoka-Honda Effect." See H. Nagaoka, "Kaikodan," Nihon butsurigakkai shi, 5 (1950), 324. 208 H. Nagaoka, "Sur la magnetostriction," Rapports presente au Congres Interna­ tional de Physique reuni a Paris en 1900, 2, 536-556. In addition to Nagaoka, four other Japanese attended the Congress, but they had not been invited. Two were physicists: Yamaguchi Einosuke, who had graduated from the Physics Department three years before Nagaoka and was in Germany in 1900 doing research, and Mizuno Toshinojo, who had graduated three years after Nagaoka. The other two, Odagiri Enju and Ohdachi Gentaro, were connected with the Japanese navy. See Travaux au Congres International de Physique (Paris, 1901),4, 129-169. 209 T. Kimura, "Nagaoka Hantaro no chikyu butsurigaku ni kansuru kenkyti no keiko," Butsurigakushi kenkyu, 3 (1966), 35-40. 207 According

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by proper attention to the spectral properties of an atom. 210 In 1902 William Thomson (then Lord Kelvin) proposed an atomic model 211 to which Nagaoka responded with a model of his own. 212 While attempting to devise a better model than Kelvin's, he recalled Maxwell's paper "On the Stability of the Motion of Saturn's Rings," which he had read in Munich and which now allowed him to visualize his atomic model. In De­ cember 1903, he went before the Tokyo Mathematico-Physical Society and proposed his "saturnian atom," a large, positively charged central particle surrounded by many equidistant electrons revolving with a com­ mon angular velocity. He published a paper in English describing his model in the proceedings of the Tokyo society and again in the Philosophical Magazine the following year. 213 J. J. Thomson also proposed an atomic model at this time. 214 The response to Nagaoka's atomic model in Japan was rather cool at first. He recalled sardonically that the Japanese worshippers of such worldshaking names as Kelvin and J. J. Thomson offered no comment at all; other Japanese physicists felt that the atomic structure he proposed would be unstable under collision in gases. 215 Physicists in Europe were attentive, but skeptical. G. A. Schott criticized the instability of the "Saturnian atom." 216 Poincare' called Nagaoka's model "a very interesting attempt, but not yet wholly satisfactory" and thought that "this attempt should be renewed." 217 Nagaoka's model was received with so little enthusiasm that Rutherford had not read Nagaoka's paper nor heard of his model when he 210 H.

Nagaoka, "Genshikaku tankyu no omoide," Kagaku asahi, 10 (1950), 23. Kelvin, "Aepinus Atomized," Philosophical Magazine, 3 (1902), 257-283. 212 E. Yagi, "On Nagaoka's Saturnian Atomic Model," Japanese Studies in the History of Science, J (1964), 33, and E. Yagi, "Razafodo to Nagaoka Hantaro— Genshi mokei ο chushin ni," Shizen, 26 (1971), 100. 213 H. Nagaoka, "Motion of Particles in an Ideal Atom Illustrating the Line and Band Spectra and the Phenomena of Radioactivity," Proceedings of the Tokyo Mathematico-Physical Society, 2 (1904), 92-104, and "Kinetics of a System of Particles Illustrating the Line and Band Spectrum and the Phenomena of Radio­ activity," Philosophical Magazine, 7 (1904), 445-455. 214 J. J. Thomson, "The Magnetic Properties of Systems of Corpuscles Describing Circular Orbits," Philosophical Magazine, 6 (1903), 673-693, and "On the Structure of the Atom," Philosophical Magazine, 7 (1904), 237-265. 215 H. Nagaoka, "Genshikaku tankyu no omoide," p. 25. 216 G. A. Schott, "A Dynamical System Illustrating the Spectrum Lines and the Phenomena of Radio-activity," Nature, 69 (1904), 437, and "On the Kinetics of a System of Particles Illustrating the Line and Band Spectrum," Philosophical Maga­ zine, 8 (1904), 384-387. 217 H. Poincare, The Value of Science, trans. G. B. Halsted (New York, 1958), p. 109. This book was originally published in 1905. 211 Lord

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proposed the nuclear atom, as we know it today, in 1911. 218 Although Nagaoka's study of atomic structure and his atomic model did not con­ tribute significantly to the subsequent development of atomic physics, his work did influence Japanese science. It contributed to a growing confi­ dence in Japan that Japanese could work in the mainstream of world physics and have their work known internationally; it also resulted in the legend that Nagaoka had been the first to propose an atomic model that pointed in the right direction. Kuwaki Ayao adopted that view of Nagaoka when he wrote in 1921; "As a matter of fact, the atomic models conceived at [the] present time are not the same as those of 1903, but in so far as they resemble the solar system in miniature, his original conception still persists. That Professor Nagaoka was the first to propound the nuclear structure of the atom will ever stand to his credit in the history of sci­ ence." 219 Through his involvement with atomic models, Nagaoka became interested in spectroscopy, but from about 1908 all of his work was ex­ perimental and no longer theoretical. He investigated the spectra of a wide variety of substances, showing a particular interest in the Zeeman effect of mercury. His papers on spectroscopy ultimately constituted at least forty percent of his published work. 220 Unlike Yamagawa, Nagaoka loathed administrative responsibilities and managed for most of his life to avoid them. When a sixth Imperial Uni­ versity was established in Osaka in 1931, Nagaoka for once could not escape administrative duties. In a sharp controversy between the city of Osaka, which had long lobbied for its own Imperial University, and the Ministry of Education over an appropriate person to become the univer­ sity's first president, Nagaoka's name emerged as the only one acceptable to both sides, and he was, for all practical purposes, forced to accept the 218 Rutherford wrote to Nagaoka on 20 March 1911: "You will notice that the structure assumed in my atom is somewhat similar to that suggested by you in a paper some years ago. I have not yet looked up your paper; but I remember that you did write on that subject. I gave a preliminary account of my results to the Manchester Lit. and Phi], Soc. recently, and hope soon to be published in the Philosophical Maga­ zine." Rutherford's letter is printed as Appendix I to E. Yagi, "On Nagaoka's Saturnian Atomic Model," pp. 46-47. The quotation is from page 47. Thus, Ruther­ ford mentioned Nagaoka in his 1911 paper ("The Scattering of a and β Particles by Matter and the Structure of the Atom," Philosophical Magazine, 21 [1911], 669688), but only in a footnote. Rutherford heard of Nagaoka's paper from W. H. Bragg on 11 March 1911, but he had already given his report on his atomic model to the Manchester Library and Philosophical Society four days earlier. See E. Yagi, "Razafodo to Nagaoka Hantaro—Genshi mokei ο chushin ni," p. 102. 219 A. K[uwaki], "Professor Hantaro Nagaoka," p. iii. 220 See the table at the end of T. Kimura, op. cit. (note 209).

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post. But he was furious, and considered the three years during which he held the post to be his years "in prison." 221 The nonteaching positions he held were always closely related to physics; he was, for example, Chairman of the Physics Division of the Institute of Physical and Chemical Research from 1917 to 1922, and he served as Chairman of the Physics Division of the National Research Council of Japan from 1920 to 1943. Nagaoka's work won him recognition both at home and abroad. He was made an honorary member of the Societe' des Physiques et d'Histoires Naturelles in Geneva in 1901. In 1912 he was elected an Honorary Fellow of the Physical Society of London, which at that time had such distin­ guished foreign members as Marie Curie and H. A. Lorentz. Cambridge University awarded him an honorary degree in 1925, a distinction Nagaoka's father had surely never dreamed of when buying used Eton and Rugby texts some thirty years before. Nagaoka was elected to the Japanese House of Peers in 1937, and the same year he and his student Honda Kotaro received Japan's first Imperial Order of Culture, awarded for their work in physics. In 1939 he became president of the Imperial Academy, Japan's highest honorary learned society, of which he had been a member since 1905; he served in that capacity until 1948. Throughout his career Nagaoka was interested in philosophical or theo­ retical questions on the one hand and in the application of physics on the other. He not only read the works of Chinese philosophers for pleasure, but he related philosophy to physics in seeking an answer to the question: What is matter? It was an intellectual question that he could detach from the problems of Japan's technological advancement and from political and moral questions. 222 Nagaoka's interest in atomic models was chiefly moti­ vated by the philosophical or theoretical challenge it presented. His probings into the philosophical question of the nature of matter led him to write articles in Japanese for intellectual and philosophical magazines; the subjects he wrote on can be seen from titles such as "The Development of Ideas on the Structure of Minute Particles of Matter" and "Recent Views on Matter." 223 From 1904 on, Nagaoka advocated at every opportunity the application of physical principles to problems of technology. He denied that physics 221 T. Kimura, "Handai socho to shite no Nagaoka to kare no daigakukan no henrin," Koko bursuri kenkyii, 4 (1970), 4-5. 222 H. Nagaoka, "Chichi Hantaro ο kataru," pp. 90-92. 223 H. Nagaoka, "Busshitsu no biryushi kozo ni kansuru shiso no hattatsu," Toyo gakugei zasshi, 22 (1905), 402-468, and "Saikin busshitsukan," Tetsugaku zasshi, 21 (1907), 637-661, and 22 (1907), 725-745.

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was only a matter for physicists, or that engineering should be left to the engineers. In 1911 in a speech to secondary school physics teachers, he went so far as to say that the main aim of physics is to find ways of apply­ ing the principles of physics to technology. 224 He engaged in a number of strictly utilitarian efforts such as the compilation of a table of elliptic functions and their integrals for the purpose of facilitating calculations of self-inductance and mutual inductance of circular coils. 225 From time to time over a period of ten years he even worked on the problem of trans­ muting mercury to gold. 226 It was consistent with Nagaoka's competitive nature that he also became an aggressive advocate for science in general. Unlike either Yamagawa or Tanakadate, he was constantly urging the advancement of Japanese sci­ ence. "Warning to our Scientific World," was the title of a speech he gave in 1913 in which he attributed the slow development of Japanese science to an insufficient "spirit of scientific research" and to a dearth of people to preach the values of science and to create opportunities for its advance­ ment. 227 Writing on the state of physics research in Japan in a popular Japanese journal, he criticized blind imitation and chided that "when physicists in Europe and America look at the Japanese scientific world it must present as curious a sight as a silk top hat being worn on top of a samurai's top-knot." 228 Although by the time he died in 1950 Nagaoka had published more than three hundred papers, far exceeding Tanakadate, who had published fewer than forty, he had made almost no written contributions to quantum or relativity physics, major areas of twentieth-century physical research. For this reason, even though his scientific activities fall entirely in the twenti­ eth century, we must consider him essentially a ninteenth-century physi­ cist. Ironically, in his recollections he derides the many Japanese scientists 2 2 4 H. Nagaoka, "Butsurigaku ο manabu mono no kokoroe (3)," Rigaku kaishi, 8 (1911), 3. 2 2 5 H. Nagaoka and S. Sakurai, "Tables of Theta-Functions, Elliptic Integrals K and E, and Associated Coefficients in the Numerical Calculation of Elliptic Functions," Scientific Papers of the Institute of Physical and Chemical Research, Tokyo, TableI (1922), pp. 1-67, and "Tables for Facilitating the Calculation of Self-Inductance of Circular Coils and of Mutual Inductance of Coaxial Circular Currents," ibid., Table 2 (1927), pp. 69-180. 226£. Yagi j "Nagaoka no suigin kankin jikken to sono haikei (1924-1930) sono 1," Butsurigakushi kenkyu, 8 (1972), 36-56. For part two, see ibid., 8 (1972), 22-42. 2 2 7 H. Nagaoka, "Waga kagakukai ni keikokusu," Siim Nihon, 3 (1913), 134. 2 2 8 H. Nagaoka, "Nihon ni okeru butsurigaku no kenkyu," Shin koron, 28 (1913), 41.

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who studied under the "great names" of Western science in Europe only to swallow totally the nineteenth-century worldviews of the Western scien­ tists and to return incapable of doing innovative work in the twentiethcentury world. 229 Nagaoka was not unlike those he criticized. He had con­ siderable respect for Helmholtz, and devoted to him at least three of the many short biographies he wrote on major Western scientists. He also seems to have admired Boltzmann. The mechanistic worldview held by these men was shared by Nagaoka. 230 Nagaoka nonetheless conveyed the image of a modern physicist; Yamagawa and Tanakadate had failed him as models, but he became an inspiring model for young Japanese growing up in the twentieth century. Yukawa Hideki 1 Japan's first Nobel Prize winner in physics, wrote in 1967: "Look­ ing back on it, I feel that probably the one decisive factor in causing me as a high school student in the early 1920's to choose unhesitatingly the path of research physics, was the fact that one could find among the Japanese ahead of one [on the path] such a great physicist [as Nagaoka Hantar5] ." 231 Nagaoka's conspicuous activity in both theoretical and ex­ perimental physics, his articulate advocacy of high standards of achieve­ ment for Japanese science, and, behind it all, the legend of his role in the discovery of the atomic model made him perhaps Japan's first true physi­ cist. From his time on, physics was a naturalized discipline in Japan; or perhaps one should say that with him Japanese physicists entered the mainstream of world physics. Japan's first generation of physicists comprised many types of men with differing talents, driven by differing needs and motives. They lived through one of the most turbulent and yet stimulating periods of Japanese history. The groundwork they laid against incredible odds was firm enough to sup­ port the development of physics in Japan to the point where, some sixty years later, Japan had produced a Nobel Prize winner in physics. When Yukawa won his Nobel Prize the old ex-samurai Tanakadate was still 229 H.

Nagaoka, "Kaikodan," p. 325. Helmholtz, Nagaoka wrote "Heruman fuon Herumohoruzu (Hermann von Helmholtz) sensei shoden," Toyo gakugei zasshi, 11 (1894), 575-578. "Herumu­ horuzu (Helmholtz) sensei no jusshuki," Tokyo butsuri gakko zasshi, 14 (1905), 81-88. "Herumuhoruzu sensei shoden (1)," Taiyo, 13 (1907), 161-166; part 2, 13, 171-176; part 3, 14 (1908), 173-176. Nagaoka published a summary of the speech on recent developments in mathematical physics given by Boltzmann in Munich in 1899 in H. Nagaoka, "Suri butsurigaku no susei ni kansuru Boruzuman sensei no iken," Toys gakugei zasshi, 16 (1899), 504-512; part 2, 17 (1900), 15-28. 231 H. Yukawa, "Nagaoka sensei no kyugaku," Bungei Shunju, 45 (1967), 82. 230 On

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alive. 232 Nagaoka, who cared so desperately about proving the Oriental's abilities in science to the West, also lived long enough to see it happen. He did not, as he had feared, have to observe the victory through a telescope from hell.

6. IN CONCLUSION I will conclude my discussion of the first stages of the development of physics in Japan with a look at the state of Japanese physics shortly after the turn of the century. By that time physics in Japan had grown from nothing to a level where it was sufficiently institutionalized to permit Japanese participation in the international physics world. By 1900 Japan had established two universities that were producing physicists, Tokyo Imperial University and Kyoto Imperial University. The former, which was Japan's main center for physics teaching and research, had graduated over one hundred physicists by 1900, and it continued to produce at least four or five physicists a year thereafter. 233 Its physics faculty consisted of three professors, three assistant professors, and two lecturers of physics, all Japanese. In 1901 the Physics Department was divided into a theoretical and an experimental section; by 1903 the newly organized department had graduated four theoretical and four experimental physicists. 234 Kyoto Imperial University was not established until 1897 and hence did not pro­ duce any physics graduates until 1902; but its physics faculty in 1900 in­ cluded at least three professors. 235 In the years around 1900 Japanese physicists drew international atten­ tion of various sorts. Invitations were extended to Tanakadate to attend the 1898 geodesy conference in Stuttgart and to Nagaoka to give a paper at the 1900 Paris Physics Congress. Yamaguchi's paper "Zur Kenntniss des thermomagnetischen Transversaleffect im Wismut" 236 found recognition when Paul Drude cited it in his extremely influential paper "Zur Elek-

232 Yukawa won the Nobel Prize in physics in 1949 for his theoretical prediction of the meson. 233 Tofeyo teikoku daigaku sotsugyosei shimeiroku, pp. 283-285. 234 Ifcid., p. 285, and TTDG, 2, 444-445. 235 JOyofo teikoku daigaku sotsugyosei shimeiroku (Kyoto, 1967), pp. 460 and 465. 236 InylnnaZen der Physik, 4th ser., 1 (1900), 214-224.

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tronentheorie der Metalle." 237 Nagaoka's paper on atomic structure stimu­ lated comment from several Western scientists in 1904 and after. 238 In addition to the establishment of physics as a disqipline in Japanese academic institutions and the international recognition of the work of Japanese physicists, there were other signs that the transplant of Western science had taken root in Japan. By 1901 the Tokyo MathematicoPhysical Society had a membership of 175. 239 Its journal, Tokyo sugaku butsuri gakkai kiji, contained articles written not only in Japanese, but in romanized Japanese and in English, and in 1901 it also began to publish the Proceedings of the Tokyo Mathematico-Physical Society in which most articles were written in English. Tokyo Imperial University's Journal of the College of Science, published since 1887, also contained mostly English articles by Japanese physicists (see Table C). We can conclude that by 1900 the physics discipline in Japan was ca­ pable of autonomous development, even though Japanese physicists still felt the need of further stimulus from Western physics. Postgraduate stu­ dents, especially those who planned to become university teachers, con­ tinued to go to Europe for advanced study. When the establishment of Tohoku Imperial University was approved in 1907, almost all members of the proposed science faculty were sent to Europe for further training be­ fore the College of Science opened in 1911. 240 Men like Tanakadate and Nagaoka visited as many academic and commercial laboratories as possible on their trips to European conferences, and they purchased new scientific instruments abroad to take back with them to Japan. Generally speaking, at this time Japanese physicists tended to work on physics problems that Western physicists worked on, and they continued to do so after 1900. But a new era was beginning. The development of physics after the early 2 3 7 Seeibid.,

3 (1900), p. 400. the earliest indication that Japanese physics was given serious attention can be found in a conversation recorded by Tanakadate. When he met Heinrich Hertz, probably in 1890, Hertz made complimentary remarks about Japanese physicists saying, "It looks as if from now on we are going to have to learn Japanese. 2 3 8 Perhaps

What a problem that is going to be." Possibly Hertz was merely being polite; he was certainly exaggerating. Nevertheless, the remark showed recognition of Japanese achievements. See M. Yoshida, ed., "Tanakadate hakase ο kakonde," in Gendai Nihon kiroku zenshii (Tokyo, 1970), 9, 39. 2 3 9 Tofeyo sugaku butsuri gakkai kiji, 1 (1885), 120. The society doubled its membership every twelve years until World War II. In 1945 when it split into the Physical Society of Japan and the Mathematical Society of Japan, 1,812 of the members were physicists. H. Masuda, "Kaiinsu sonota no hensen," Nihon butsurigakkai shi, 5 (1950), 351. 2 4 0 M. Yuasa, Kagakushi (Tokyo, 1965), p. 239.

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1900's belongs to another period in the history of Japanese physics that lasted until World War IL This period saw the maturation of physics in Japan. Not everyone was happy with the way in which the Japanese were im­ porting Western science, however. Some foreign science educators in Japan remained skeptical that their efforts had been successful. Erwin von Baelz, a German physician invited to Japan in 1876 to teach medicine at the newly founded University of Tokyo, vividly described his initial enthusi­ asm and final disenchantment at a celebration in 1900 marking his twentyfifth year of service in Japan: It seems to me that in Japan erroneous conceptions about the origin and nature of western science are widely prevalent. It is regarded as a ma­ chine which can turn out so much work every year, and therefore, as a machine which can without further ado be transported from the West to any other part of the world there to continue its labours. This is a great mistake. The western scientific world is not a piece of machinery, but an organism, and, like every other organism, if it is to thrive it needs a par­ ticular climate, a particular atmosphere. . . . 241 He went on to say that to achieve the present "mental atmosphere" in the West, great minds labored through the ages to solve the secrets of the uni­ verse, and their "highway of the human spirit" was watered with their sweat and blood and lighted by execution fires. This spirit that will "sus­ tain us Europeans until the end of the world" 242 cannot be learned in the lecture hall. It can be grasped only by working side by side with other re­ searchers. He chided his Japanese audience for having often failed to understand the intent of the Western teachers who came to Japan to teach science. The Western teachers "have been looked upon merely as purveyors of scientific fruit, whereas they really were, or wanted to be, the gardeners of science. Often you have expected them to hand over to you the finished 'product' of contemporary science, whereas their business was to sow the seeds out of which in Japan the tree of science could continue its inde­ pendent growth." 243 Baelz's criticism reveals the feeling of superiority over Orientals often 2 4 1 E. Baelz, Awakening Japan: The Diary oj a German Doctor, ed. T. Baelz and trans. E. and C. Paul (New York, 1932), p. 149. The original German version was published m 1931 under the title Das Leben eines deutschen Arztes im erwachenden Japan. i 4 2 Ibid., p. 150. 243 Ibid.

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found in European teachers; his highest compliment to a Japanese was that "he is just like a German." 244 It also reveals the frustrations of a man who has spent twenty-five years of his life among a foreign race, guided by his own vision of what his mission was and finding that the Japanese saw his mission somewhat differently. Baelz's criticism, based upon long experi­ ence in Japan as a medical teacher, should not be treated lightly. However, in medicine, through its concern with human lives, theory and practice tend to merge more completely than in other sciences. Baelz had little occasion to observe the theoretical work done by Japanese in other sci­ ences like physics; by evaluating science on the basis of medicine, he no doubt obtained a distorted picture of the contemporary Japanese view of science. It is fair to say that Japan's success in producing the fruits of science was accompanied by continuous Western doubts about the quality of both seed and soil, largely because, despite enormous change, both remained somehow non-Western. In such a context even the "tree of science" seemed a priori an impossibility. There was in Baelz's day the insistence that "true" science is an "organism" that will grow only in one kind of climate, the kind that produced science in the West in the first place. Not only did foreigners such as Baelz believe this, but Japanese intellectuals such as Fukuzawa preached it too. Baelz did not want to be a fruit seller to Japanese ex-samurai; he wanted to "garden" in Japan until he had pre­ pared a soil recognizably Western. Only then could he trust the soundness of the fruit. Despite such views, two things are clear: no manner of cultivation could possibly transform Japanese soil into that of Europe; and yet still, Japan did, nevertheless, cultivate institutional "trees" that in turn pro­ duced recognizably Western-style scientists. An important observation by T. Hiroshige suggests reasons why Japan was able to develop these institu­ tions and scientists without having to meet the impossible demands of men like Baelz and Fukuzawa. 245 Although there was a time lapse of two hun­ dred to three hundred years between the scientific revolution in the West and the period when Japan began to import Western science, the time lapse between the institutionalization of science in the West and in Japan was 244 S. Hirakawa, "Changing Japanese Attitude Toward Western Learning, 7: Dr. Erwin Baelz and Mon Ogai," Contemporary Japan, 29 (1968), 140. 245 T. Hiroshige, "Shakai no naka no kagaku (2)," Shizen, 26 (1971), 68-78, and "Shakai no naka no kagaku (3)," ι bid., 26 (1971), 86-95.

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only about fifty years. Hiroshige has also noted that the more systematized Western science became in the nineteenth century, the more it shed its original philosophical and cultural aspects and became more readily ex­ portable. 246 Hiroshige contends that these two factors played a key role in the success of the Japanese transplantation of Western science. 247 The contention is certainly valid, especially with regard to the role of the University of Tokyo in the development of science in Japan. But the analysis also presents problems. First, it does not take into account the characteristics of the country into which Western science was imported. Although science may have become culturally more neutral and therefore more easily exportable in the nineteenth century, the social, political, and intellectual conditions of the importing country are the decisive factor. One may even ask whether or not it is necessary for science to be stripped of its philosophical and cultural aspects before it can be effectively im­ ported into a country where the cultural base is quite different. The ob­ servations of Erwin von Baelz throw some light on the subject. Indeed, if we accept at face value Baelz's criticism of the Japanese attitude toward the study of Western science, we must conclude that it was the Japanese themselves who stripped Western science of its philosophical and cultural aspects when they imported it. It is important, too, to realize that the successful importation of science into Japan between 1868 and the 1920's, cannot be viewed in isolation from the other social and political changes taking place at that time. Japan had transformed itself into a unified political state, and by 1910 it had won two major wars and thus tested its strength as a modern nation. Japan had survived the onslaught of Western pressure, which had been its motiva­ tion for modernization in the first place. The successful institutionalization of science in Japan was not merely due to the shortness of the fifty-year lapse between it and the institutionalization of science in the West, but was part of the larger Japanese success in modernization. Without this broader view many aspects of Japanese physics—the success of the Tokyo School of Physics, for example—cannot be understood properly. Despite their shortcomings, Hiroshige's observations are the most important to have emerged from studies of the development of science in Japan. 2 4 6 Such science, he says, is what Thomas Kuhn calls "normal science." See T. Kuhn, The Structure of Scientific Revolutions (Chicago, 1962), and T. Hiroshige, "Shakai no naka no kagaku (3)," ibid., 26 (1971), 95. 2 4 7 T. Hiroshige, "Shakai no naka no kagaku (2)," ibid., p. 68 and pp. 94-95.

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ACKN OWLEDGMENT I am especially indebted to Professor Russell McCormmach under whose guidance and direction the research for this study was first conceived and carried out. The present paper has greatly benefited from his invaluable editorial recommendations. I was fortunate in receiving helpful comments and criticisms of my original study from Professor Nakayama Shigeru and Professor Arnold Thackray. Professor Hiroshige Tetsu's advice and criti­ cisms have been especially helpful to me at various stages during the prepa­ ration of the earlier and the present manuscripts. OtherJapanese scholars who generously shared their time and ideas include Professors Hashimoto Mampei, Itakura Kiyonobu, Kimura Tosaku. Watanabe Masao, Yagi Eri, and Yoshida Mitsukuni. I am also grateful to Mr. Sakai Yasushi of the National Diet Library in Tokyo for his kind assistance, and to Mr. Aoki Kunio of the National Science Museum in Tokyo who rendered me in­ valuable service and made available to me unpublished manuscripts de­ posited in the Museum's archives. I am grateful to him and to the Museum for permission to quote from Nagaoka's unpublished letter and from Tanakadate's diary. Research in Japan for the parent study was supported by a doctoral grant from the National Science Foundation to which I express my sincere thanks.

APPENDIX

TABLE A. Fief and State Schools and the Evolution of the University of Tokyo 720's 730 1630 1632 1630's 1635 1636 1637 1640's 1670's 1690 1691

1716-1745 1755 1774 1790

1800 1811 1838 1843 1849 1853 1856

1857 1861 1862 1863 1867

Daigaku or university established in the capital (Nara). Hospital established in the capital, School started by Hayashi Razan with the support of the shogunate. Confucian shrine built on the grounds of Hayashi school. Anti-Christian measures intensified. All travel abroad forbidden. Fief school established in Morioka fief; probably the first fief school in Japan. A school in Kyoto established by Matsunaga Sekigo. Final exclusion of all foreigners except Chinese and Dutch. Height of neo-Confucian revival. Hayashi Razan ordered to establish a larger school. Hayashi Hoko named daigaku no kami (rector of the university), thereby becoming hereditary head of the Daigaku or state university. Symbolic break with the medieval identification of Buddhist priests with education when Hayashi obtained permission to let his hair grow. Shogun Tokugawa Yoshimune's reforms; greater interest in Western learning. School started by the Kumamoto fief. Translation of Dutch anatomy book. The shogunate school reorganized along more conservative Confucian lines. New heterodox doctrines banned. Fief schools increasing throughout Japan. Schools in all large fiefs. Dutch translation office established by the shogunate. Mito fief school established; center of nationalism. Teachers of Dutch medicine appointed by the Sakura and ChSshu fief schools. Experiments carried out by Japanese on smallpox vaccination. Arrival of Commodore Perry's gunships. Establishment of schools of Western studies by the shogunate and the Choshu fief. Founding of the Bansho Shirabesho (Office for the In­ vestigation of Barbarian Books). Edo Shutojo (Edo Vaccination Office) established. Edo Shutojo renamed Seiyo Igakujo (Western Medical Center). Bansho Shirabesho renamed Yosho Shirabesho (Office for the Investiga­ tion of Western Books). Yosho Shirabesho renamed Kaiseijo. Seiyo Igakujo renamed Igakujo (Medical Center). Igakujo renamed Tokyo Igakko (Tokyo Medical School).

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JAPAN'S FIRST PHYSICISTS TABLE A (Continued)

1870 1871 1872 1873

1875

1877

1878-1880 1880

1881

1882

1886

1890 1897

Kaiseijo renamed Daigaku Nanko (University, Southern Division). Teaching through English, German, and French. Daigaku Nanko renamed Nanko (Southern Division). Nanko renamed Daiichi Daigaku Ku Daiichiban Chugakko (The First Middle School of the First University). Daiichi Daigaku Ku Daiichiban Chugakko renamed Tokyo Kaisei Gakko (Tokyo Kaisei School). English declared official instructional lan­ guage. Shogeigakka (Ecole polytechnique) and Kozangakka (Depart­ ment of Mining) set up to accommodate remaining French-language and German-language students, respectively. Shogeigakka abolished and Futsugo Butsurigakka (French Language Physics Department) established. Kozangakka abolished. Study of physics through German terminated. University of Tokyo established by combining Tokyo Kaisei Gakko and Tokyo Igakko. Four faculties'. Law, Science, Literature, and Medi­ cine. Five departments in the Faculty of Science: Chemistry, Mathematics-Physics-Astronomy, Biology, Engineering, and GeologyMining. Graduation of twenty men and abolishment of the French Language Physics Department. Through 1880 German or French required as the second foreign lan­ guage; after 1880 German required as the second foreign language. English still required as the first foreign language. Mathematics-Physics-Astronomy Department (University of Tokyo) divided into three independent departments. The Tokyo Butsuri KCshusho (Tokyo Physics Training School), later renamed the Tokyo ButsuriGakko (Tokyo School of Physics), established. First graduates (three) of the Mathematics-Physics-Astronomy Depart­ ment under the English language program. Tokyo Semmon Gakko, a private university, established in Tokyo; later renamed Waseda University. University of Tokyo renamed The Imperial University. The Faculty of Science renamed the College of Science. Engineering Department de­ tached from the College of Science and combined with the Ministry of Engineering's School of Engineering, forming the College of Engi­ neering. Graduate school established. Imperial Rescript on Education promulgated. Second Imperial University established as Kyoto Imperial University. Original Imperial University renamed Tokyo Imperial University.

103

KENKICHIRO KOIZUMI TABLE Β. Faculty of Science, University of Tokyo, 1877 Courses

Staff Professors

Peter V. Veeder, USA

Physics and Laboratory

Robert W. Atkinson, England

Analytic and Applied Chemistry

Robert H. Smith,* England

Mechanical Engineering

William E. Parson,* USA

Mathematics

Edmund Naumann, Germany

Geology

Gustave F. Berson, France

Physics and Mechanics

Frank F. Jewett, USA

Chemistry and Analytic Chemistry

Winfield S. Chaplin, USA

Civil Engineering

Edward S. Morse, USA

Zoology and Physiology Mathematics

Stephane Mangeot, France KIKUCHI Dairoku, Japan

Pure and Applied Mathematics

YATABE RySkichi, Japan

Botany

Curt Netto, Germany

Mining and Metallurgy

IMAI Iwao, Japan

Metallurgy and German

Alexander Debsky,* France

Physics, Mechanics, and Mathematics

Extraordinary Professors

ITO Keisuke, Japan

Botany

Assistant Professors

KOGA GotarS, Japan

Physics and French

YAMAOKA Jiro, Japan

Chemistry

YAMAGAWA KenjirS, Japan

Physics

WADA TsunashirS, Japan

Geology

Lecturer

MATSUMOTO Soshiro, Japan *See note 73 above.

Drafting

104

JAPAN'S FIRST PHYSICISTS TABLE C. Academic Societies and Journals in Japan Names of societies; dates and titles of journals

1873 1877

1878

1879

1880 1881 1882

1884

1885 1886 1887

1888 1891 1893 1902 1904

Meirokusha (The Sixth Year of Meiji Society); 1874,Meiroku zasshi. Tokyo Sugaku Kaisha (Tokyo Mathematical Society); 1878, Tokyo sttgaku kaisha zasshi. Gakugei shirin (published by the University of Tokyo, containing speeches given at the University and translations of articles in Western journals). Tokyo Kagaku Kai (Tokyo Chemical Society); 1880, Nihon kagaku kaishi. Tokyo Seibutsu Gakkai (Tokyo Biological Society). Ko Gakkai (Engineering Society); 1881 ,Kdgaku shoshi. Tokyo Gakushi Kaiin (Tokyo Academy); 1879, Tokyo gakushi kaiin zasshi. Tokyo Chigaku Kyokai (Tokyo Geographical Society); 1879, Tokyo chigaku kydkai hOkoku. Memoirs of the Science Department, University of Tokio, Japan, Nihon Jishin Gakkai (The Seismological Society of Japan). TOyo gakugei zasshi (published by Sugiura Jugo et al.; intellectual journal; articles contributed mostly by University of Tokyo professors). Tokyo Seibutsu Gakkai (1878). Split into: 1) Tokyo Shokubutsu Gakkai (Tokyo Botanical Society); 1887, Shokubutsugaku zasshi; and 2) Tokyo Dobutsu Gakkai (Tokyo Zoological Society); 1887, DObutsugaku zasshi. Tokyo Jinrui Gakkai (Tokyo Anthropological Society); 1886,Jinruigaku zasshi. Tokyo Sugaku Kaisha renamed Tokyo Sugaku Butsuri Gakkai (Tokyo Mathematlco-Physical Society); 1885, Tokyo sugaku butsuri gakkai kiji. Nihon Kiseichu Gakkai (Parasitological Society of Japan). Nihon Kogyo Kai (Mining Society of Japan). Kenchiku Gakkai (Architectural Society). Tokyo Igakkai (Tokyo Medical Society). Journal of the College of Science, Imperial University, Japan. Mitteilungen aus der Medizinischen Fakultat der Kaiserlichen Universitat zu Tokyo. Bulletin of the Imperial College of Agriculture and Dendrology. Denki Gakkai (Electrical Society). Tokyo butsuri gakko zasshi (published by Tokyo School of Physics). Nihon Chishitsu Gakkai (Geological Society of Japan); 1893, Chishitsugaku zasshi. Proceedings of the Tokyo Mathematico-Physical Society. Journal of the College of Engineering, Tokyο Imperial University, Japan.

105

KENKICHIRO KOIZUMI TABLE D. The Principal Members of the First Generation of Japanese Physicists M. Goto M. Hiraoka a T. Ihmori T. Kiriyarna D. Kitao c K. Miwa H. Muraoka K. Nakamura T. Nakamura T. Namba T. Nobutani F. Sakurai Y. Sembon T. Shiga M. Takanose A. Tanakadate H. Terao Y. Wada K. Yamagawa M. Yasuda U. Yatabe

1853-1930 1852-1882 1851-1916 1856-1928 1853-1907 1861-1920 1853-1929 1853-1934 1855-1916 1859-1920 1856-1893 1852-1928 1854-1918 1854-1934 1852-1915 1856-1952 1855-1923 1859-1918 1854-1931 1856-1919 1857-1903

^Born Ichikawa Morisaburo; adopted by the Hiraoka family. Iimori romanized his family name with the unconventional spelling Ihmori. c Kitao Jiro romanized his given name with the unconventional spelling Diro,

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JAPAN'S FIRST PHYSICISTS TABLE E. Training of the First Generation of Japanese Physicists

I. Those who began the study of physics abroad: A. English Language 1) K. Yamagawa

B. German Language 1) D. Kitao

Sent by his fief to the Sheffield Scientific School, Yale University (Bachelor of Philosophy).

1871-1875

Sent from the Southern Division to Berlin and Gottingen (Ph.D.).

1870-1884

II. Those who received their initial physics training in Japan A. English Language 1) M. Goto 2) M. Hiraoka 3) A. Tanakadate B. German Language 1) T. Ihmori 2) H. Muraoka

3) T. Shiga C. French Language 1) T. Kiriyama 2) K. Miwa 3) K. Nakamura 4) T. Nakamura 5) T. Namba

6) 7) 8) 9) 10)

T. Nobutani F. Sakurai Y. Sembon M. Takanose H. Terao

11) Y. Wada 12) M. Yasuda 13) U. Yatabe

Later studied physics at the Uni­ versities of Glasgow and Manchester. Died at age thirty in 1882. Later studied physics at the Uni­ versity of Glasgow. Later studied physics at the Uni­ versity of Freiburg (Ph.D.). Later studied physics at Strasbourg Teachers' College (B.A.) and the University of Strasbourg (Ph.D.). Later studied physics and agriculture in Germany.

1887-1890

1888-1891

1884-1886 1878-1881

1885-1887

Europe. University of Paris. (Bachelor of Science.) France and the USA.

1886-1889 1880-1884 1882 1896-1898

France and England St. Cloud Teachers' College.

1882-1883 1885-1888

University of Paris (Bachelor's degree in mathematics).

1879-1883

Univ. of Paris 1880-1884 (Science degree, 1882); Paris and USA, 18961898 (Elect. Engi­ neering)

T. Nakamura

T. Namba

T. Nobutani

1879

1879

1879

Univ. ofTokyo (Dept. of Science)

TJniv. ofTokyo; Univ. Gateway School; 1st Higher Middle School; 2nd Higher Middle School

Europe, 1886-1889 (Meteorology)

Nagasaki Teachers' College; President, Fukushima Pro­ vincial Teachers' College; Principal, Niigata Middle School

K.. Nakamura

1878

Observatory work

Navy Meteoro­ logical Observa­ tory

Univ. of Paris Director, Tokyo 1879-1883 (Science Imperial Univ. and Mathematics Astronomical degree) Observatory

Univ. of Tokyo (Astronomy Division)

H. Terao

1878

France and England 1882-1883 (Chemistry)

Travel or study abroad

Tokyo Teachers' College

Early teaching experience

F. Sakurai

Name

1878

Grad. yr.

TABLE F.

Asst. Prof., College of Science, Tokyo Imperial Univ.; Director of Student Affairs; Secretary of the Univ. Corporation

Prof, of Astronomy, Tokyo Im­ perial Univ.; Director of its Astro­ nomical Observatory

Teacher and Faculty Supervisor, 5th Higher Middle School

Final employment

Min. of Educ.

Prof, of Math., Army Military Academy

Prof, of Electrical Engineering, Kyoto Imperial Univ.

Min. of Internal Director, Central Meteorological Affairs (Land Observatory Survey Div.)

Min. of Educ.

Employment in ministry office

Principal Graduates of the French Language Physics Department

Name

Y. Sembon

M. Takanose

Y. Wada

U. Yatabe

T. Kiriyama

K. Miwa

M. Yasuda

Grad. yr.

1879

1879

1879

1879

1880

1880

1880

St. Cloud Teachers' College, France, 1885-1888 (Teachers' Educa­ tion)

Univ. Gateway School; 1st Higher Middle School

Univ. of Tokyo (Mathematics); Prof, at Gakushuin (Peers' Univ.)

Univ. of Tokyo (Mathematics)

Central Meteoro­ logical Observatory

Observatory work

TABLE F (Continued) Travel or study abroad

1st Higher Middle Consul in Manila, School; Faculty Super­ 1888-1890 visor, Yamaguchi Higher Middle School

Komaba Agricultural School (Predecessor to College of Agricul­ ture of Univ. of Tokyo)

Army Military Academy

Early teaching experience

Min. of Agr. and Comm.

Prof., Tokyo Teachers' College

Final employment

Min. of Educ.

Teacher, 1st Higher Middle Schoo

Prof., College of Science and En­ gineering, Kyoto Imperial Univ.

Principal, NagasakiMiddle School

Min. of Foreign Teacher, Higher Commercial Col­ Affairs (Trans­ lege; Min. of Agr. and Comm. portation) ; Min. (Patent Div.) of Agr. and Comm. (Patent Div.)

Min. of Internal Min. of Internal Affairs (Meteoro­ Affairs (Meteo­ logical Div.) rological Div.)

Min. of Agr. and Comm.

Min. of Educ.

Employment in ministry office

The Reception of the Wave Theory of Light in Britain: A Case Study Illustrating the Role of Methodology in Scientific Debate BY GEOFFREY CANTOR* Two major legacies that Newton left his eighteenth-century followers were his writings on the nature of light and those on scientific method. Yet little more than a century after Newton's death the generally accepted Newto­ nian position on both these subjects was overthrown. Although in the eighteenth century almost every British natural philosopher accepted with­ out question the corpuscular interpretation of Newton's writings on op­ tics, by the 1830's most British natural philosophers had rejected Newton's corpuscular theory in favor of the wave theory of light. Intimately bound up with this scientific "revolution" in optical theory was a change in scien­ tific methodology: the replacement of the method of induction by the method of hypothesis. This paper sets out to examine the optical debates of the early nineteenth century with particular reference to the role played by methodological arguments.

1. THE TWO SCHOOLS OF METHODOLOGY To many eighteenth-century writers the works of Bacon and Newton offered the key to understanding the true method of scientific discovery. By this method of "induction," the scientist started with the observation of effects and deduced from them the manifest and true causes in nature. Bacon and Newton warned against adopting a false method that super­ ficially appealed, but that inevitably seduced the scientist into error. This false method of "hypothesis" exhorted the unwary scientist to make blind guesses at the hidden operations of nature. These two methods were con­ sidered antithetical; induction led to truth, hypothesis to prejudice and *Department of Philosophy, University of Leeds LS2 9JT, England.

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falsehood. In this paper I shall refer to the inductive view of scientific method as "Newtonian."1 In the late eighteenth century the inductive view was widely accepted, and one of its major channels of dissemination was the Scottish universi­ ties. Thomas Reid, the leader of the common-sense school of philosophy, did much to popularize the "Newtonian" methodology. He maintained that the "golden rule" of scientific method was Newton's first rule of philosophizing: "No more causes, nor any other causes of natural effects ought to be admitted, but such as are both true, and are sufficient for ex­ plaining their appearances." He claimed that unless a cause is both true and sufficient, "it is good for nothing." Railingagainst the use of theories, hypotheses, and conjectures, which he compared to "building a castle in the air," he warned the scientist to "treat with just contempt hypotheses in every branch of philosophy, and to despair of ever advancing real knowledge in that way."2 Reid's common-sense philosophy was based on the belief in a real material world external to man and in man's ability to perceive its true nature. Reid's methodological attitudes were widely disseminated in Scotland, in part through his teaching at Aberdeen and Glasgow. Among his disciples were several members of the Aberdeen Philosophical Society, notably James Beattie who obtained the chair of Moral Philosophy at Marischal College, Aberdeen in 1760. Reid's most influential student was Dugald Stewart, who held the chair of Moral Philosophy at Edinburgh from 1785 to 1810. Certain of his followers, like Stewart and Thomas Brown, con­ sidered hypotheses to have a limited use in science, but they maintained his sharp distinction between strict induction and ephemeral hypotheses which, if used, were to be treated with the utmost caution and not con­ fused with induction. The common-sense school's views on methodology were not confined to moral philosophers but were also shared by many Scottish natural philosophers.3 1 This view emphasized such statements as "whatever is not deduced from the phenomena is to be called an hypothesis; and hypotheses . . . have no place in experi­ mental philosophy" (General Scholium to the Principia). It should be noted that there were many views of Newton's position on methodology; the view discussed m this paper was the most common. 2 Thomas Reid, Essays on the Intellectual Powers of Man (Edinburgh, 1785), Essay 1, Chapter 3. See also L. L. Laudan, "Thomas Reid and the Newtonian Turn of British Methodological Thought," in The Methodological Heritage of Newton, eds. R. E. Butts and J. W. Davis (Oxford, 1970), pp. 103-131. 3 G. Cantor, "Henry Brougham and the Scottish Methodological Tradition," Studies in History and Philosophy of Science, 2 (1971), 69-89.

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Two protagonists in the optical debate of the early nineteenth century were Scots who had been educated at Edinburgh: David Brewster, who wrote extensively on science and particularly on optical subjects, and Henry Brougham, who had two optical papers read before the Royal Society of London in 1796 and 1797,4 but who apart from reviewing did not write again on optics until the late 1840's. Both Brewster and Broug­ ham followed the common-sense philosophers in considering induction to be the proper scientific method. Whereas Brougham frequently followed Reid in stating that hypotheses and conjectures have no legitimate role in science, Brewster followed Stewart in stating that hypotheses have a limited role. Brewster considered that "bold" hypotheses might assist the dis­ covery of the laws of nature; in this connection he referred to Huygens' law of double refraction in uniaxial crystals, which Huygens arrived at through his hypothesis of ellipsoidal wavefronts. Brewster demanded from Huygens' law what he demanded from any other law, whether or not it was deduced from hypotheses; namely, it must be true and therefore "con­ firmed by every subsequent inquiry." Furthermore, he emphasized that hypotheses, like the wave hypothesis of light, often led to novel predic­ tions which, if confirmed, further extended the frontiers of science. He argued that a perfectly confirmed, although not necessarily true, hypothe­ sis must contain a true law of nature among its assumptions. From this standpoint he rejected Comte's view that scientists should avoid all hy­ potheses that concern efficient causation. Despite his appreciation of the essential role of hypotheses, he distinguished between temporary, but use­ ful, hypotheses and the true laws that are the primary concern of the scientist. He particularly chastised those writers who confused or avoided this distinction; he took William Whewell to task for stating that the exis­ tence of a resisting medium in space is proven by the increase in the mean motion of Encke's comet. Brewster objected that this explanation was purely hypothetical and that the comet's motion could be explained equally well by an entirely different hypothesis, for example, by one Herschel suggested.5 Although in the early nineteenth century "Newtonian" views on scien4 Henry Brougham, "Experiments and Observations on the Inflection, Reflection, and Colours of Light," Phil. Trans., 86 (1796), 227-277; "Farther Experiments and Observations on the Affections and Properties of Light," ibid., 87 (1797), 352-385. 5 David Brewster, "Report on the Recent Progress of Optics," British Association Report, 2 (1832), 310-311; review of Comte's Cours de Philosophie Positive, in Edinburgh Review, 67 (1838), 304; review of Whewell's Astronomy . . ., ibid., 58 (1834), 455-456.

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tific method were particularly prevalent among Scottish and Scottishtrained natural philosophers, they were also held by others; Richard Potter and John Barton are cases in point. Potter's early education under John Dalton appears largely to have shaped his attitudes. Subsequently he at­ tended Cambridge University and later held the chair of Natural Philos­ ophy and Astronomy at University College, London. During the early 1830's he wrote a series of papers refuting the wave theory of light, which he followed up with another series of optical papers in 1840-1841. Barton, about whose background little is known, patented a process for making buttons and other ornaments that produced startling colors by the "inter­ ference" of reflected light, and wrote two or three papers on practical and theoretical optics shortly before his death in 1834. In the following discussion I shall refer to the four natural philosophers— Brewster, Brougham, Potter, and Barton—as the "objectors" to the wave theory.^All four initially worked in the Newtonian corpuscular tradition and based their methodology on the demand for true causes. Their meth­ odological rule that scientists should not be primarily concerned with ephemeral hypotheses was at the core of their objections to the wave theory. They contended that an hypothesis could never be proven true, despite its degree of empirical confirmation and its ability to predict; they considered that induction was the only method for attaining scientific truth. Potter, for example, claimed that in "our enquiries . . . our only safe and legitimate course is by induction from experiments." The four objec­ tors to the wave theory emphasized that the scientist should spend much of his time engaged in experimenting, a far more important activity than theo­ rizing: "every page of the history of science warns us against too much reliance on abstract reasoning." 6 Brewster placed "the greatest value on the results of observation, and on experimental laws. Theorists value these only when they are deducible from theory, and the Undulationists of this country are such fanatics that they have no faith in physical truth beyond their own [ideas?]." 7 In the early nineteenth century the method of hypothesis, which had been supported by few eighteenth-century natural philosophers, 8 was 6 Richard Potter, "An Account of Experiments to Determine the Refractive Powers of Crown, Plate, and Flint-Glass at Different Angles of Incidence . . .," Edinburgh Journal of Science, 4 (1831), 53. 7 David Brewster to Henry Brougham, 21 February 1849. University College, Lon : don, Brougham Correspondence, 26, 642. 8 For example, David Hartley and Joseph Priestley. Reid harshly criticized Hartley on methodological grounds in Essay 2, Chapter 3 of his Essays, op. cit. (note 2). L. L. Laudan discusses eighteenth-century methodologies in his "Theories of Scien­ tific Method from Plato to Mach," History of Science, 7 (1968), 1-63.

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championed by a number of leading scientists. Significantly, several of these scientists were educated at Cambridge University where little science was taught, but where mathematics was studied extensively as a major part of the highly competitive tripos examination. Of still greater impor­ tance was their familiarity with Continental analytical mathematics, which they helped introduce into Cambridge in the years following the forma­ tion of the Analytical Society in 1812. Among the Cambridge graduates who gained a high degree of competence in analytical mathematics were John Herschel, George B. Airy, and William Whewell. Herschel and Airy were active in optical research in the early 1830's, and Whewell cham­ pioned the wave theory of light in his History and Philosophy of the Induc­ tive Sciences at the end of the 1830's. 9 Outside Cambridge the two major supporters of the wave theory were Baden Powell, the Savilian Professor of Geometry at Oxford, and Humphry Lloyd, who held the chair of Na­ tural and Experimental Philosophy at Trinity College, Dublin. In the fol­ lowing discussion, the five natural philosophers—Herschel, Airy, Whewell, Powell, and Lloyd—will be referred to as the "supporters" of the wave theory of light. The supporters, who were trained primarily as mathematicians, applied the powerful tool of analytical mathematics to a wide range of problems in optics, astronomy, and the theory of tides. They formed the first genera­ tion of a new type of scientist in Britain: the mathematical-physicist or, more exactly, the cross between an applied mathematician and a mathematical-physicist. By contrast, the objectors to the wave theory considered that mathe­ matics should play a subordinate role in scientific investigation, an atti­ tude which reinforced their suspicion of the wave theory. At Edinburgh, where Brewster and Brougham were trained, the study of mathematics was closely related to the precepts of common-sense philosophy; in the first mathematics class there, great emphasis was placed on the philosophy of mathematics. Although Continental analytical mathematics was well known in Edinburgh in the late eighteenth century, the Scots were very cautious about applying it to the solution of physical problems. Their caution stemmed partly from the conflict between the concepts of analyti­ cal mathematics and the common-sense philosophy. Whereas the Cam­ bridge mathematicians learned analytical methods by rote and applied 'William Whewell, History of the Inductive Sciences . . . (London, 1837), Book IX; The Philosophy of the Inductive Sciences, Founded upon Their History (London, 1840). Walter B. Cannon has thrown much light on the "Cambridge faction" in his "Scientists and Broad Churchman: an Early Victorian Intellectual Network," Journal of British Studies, 4 (1964), 65-88.

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them to physical problems, the Edinburgh-trained natural philosophers, who were often well versed in analytical methods, remained philosophically sceptical about their value in scientific investigation. 10 The supporters of the wave theory, unlike its objectors, championed the method of hypothesis. Herschel, for example, maintained that an hypoth­ esis is "a most real and important accession to our knowledge" provided "it serves to group together in a comprehensive point of view a mass of facts almost infinite in number and variety, to reason from one to another, and to establish analogies and relations between them." 11 He did not de­ mand that an hypothesis contain only observables as long as it was testable and highly confirmed. Airy, who took a pragmatic position on scientific method and did not demand true causes, was willing to accept an hypoth­ esis provided it could explain and predict facts. When Brewster objected that the wave theory was defective as the true description of the physical nature of light, Airy replied "I imagine that any theory must be defective in this point." 12 Whewell, in his Philosophy of the Inductive Sciences, rejected the "New­ tonian" methodology, arguing that the scientist could not avoid hypotheses and showing that even Newton's major discoveries had involved their use. Furthermore, he showed that the generally received distinction between fact and theory was not tenable, thereby undermining the supposedly clear-cut distinction between the method of induction and that of hy­ pothesis. Following Whewell, Powell maintained that "every induction is seen essentially to involve a certain amount of hypothesis." 13 Whewell's use of the term "induction" therefore differed radically from that of Reid, Brewster, and the other objectors. Moreover, the supporters and ob­ jectors differed over the meaning of Newton's first rule of philosophizing. Whewell claimed that Reid's demand for "true causes" was injurious to 10 G. E. Davie, The Democratic Intellect, 2nd ed. (Edinburgh, 1964), pp. 105-200; and Richard Olson, "Scottish Philosophy and Mathematics; 1750-1830," Journal of the History of Ideas, 32 (1971), 29-44. 11 John Herschel, A Preliminary Discourse on the Study of Natural Philosophy (London, 1830), p. 262. Herschel's philosophy of science is discussed by David B. Wilson in his Ph.D. thesis, The Reception of the Wave Theory of Light by Cambridge Physicists (1820-1850): A Case Study of the Nineteenth Century Mechanical Philos­ ophy (The Johns Hopkins University, 1968); "Herschel and Whewell's Version of Newtonianism," Journal of the History of Ideas, 35 (1974), 79-97. 12 George B. Airy, "Remarks on Sir David Brewster's Paper 'On the Absorption of Specific Rays, . . .',"Phil. Ma s ., 2 (1833), 419-424. 13 Baden Powell, Essays on the Inductive Philosophy, the Unity of Worlds, and the Philosophy of Creation (London, 1855), p. 6.

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science because it limited the scientist to causes that were already known and prevented him from discovering those that were not. 14 Another basic difference between the two schools needs to be stated explicitly, for it was not clearly perceived by the protagonists. The ob­ jectors to the wave theory emphasized the logic of discovery, and their arguments centered on the distinction between induction as the proper method of scientific discovery and the useless feigning of hypotheses. The supporters were concerned with justifying the use of hypotheses, and they therefore stressed the role of testability.

2. THE DEBATE OVER THEORIES OF LIGHT As background to the optical debate of the early nineteenth century, we must briefly look at the state of optical science in the previous century. The most important publication was Newton's Opticks (1704-1730), which established the Newtonian corpuscular doctrine in Britain and ex­ cluded the forms of "wave" theory proposed by Descartes, Hooke, and Huygens. Most of the optical works of the eighteenth century were pri­ marily concerned with the interpretation of the Opticks and with slight extensions of it rather than with challenges to it. Probably the most im­ portant modification of Newton's optics resulted from the Scottish assim­ ilation of Boscovichian atomism during the 1780's. 15 The major objec­ tions to Newtonian corpuscular optics came from Euler and Franklin, both of whom subscribed to forms of the wave theory. Their objections found little support in Britain and were speedily "refuted" by orthodox Newtonians such as Samuel Horsley. 16 In a series of articles 17 beginning in 1799 Thomas Young put forward 14 Whewell, Philosophy, op. cit. (note 9), 2, 436-448. Whewell's interpretation of Newton's first rule was related to the "consilience of inductions." See Robert E. Butts, "Whewell on Newton's Rules of Philosophizing," in The Methodological Heritage of Newton, op. cit. (note 2), pp. 132-149. 15 Richard Olson, "The Reception of Boscovich's Ideas in Scotland," lsis, 60 (1969), 91-103. 16 S. Horsley, "Difficulties in the Newtonian Theory of Light, Considered and Removed,"ίώ. Trans., 60 (1770), 417-440. 17 Thomas Young's four early papers on optics, read before the Royal Society, were: "Outlines of Experiments and Inquiries Respecting Sound and Light," Phil. Trans., 90 (1800), 106-150; "On the Theory of Light and Colours," ibid., 92 (1802), 12-48; "An Account of Some Cases of the Production of Colours not Hitherto Described," ibid., 92 (1802), 387-397; "Experiments and Calculations Relative to Physical Optics," ibid., 94 (1804), 1-16. One of the best accounts of Young's work is C. C. Gillispie, The Edge of Objectivity (New Jersey, 1970), pp. 406-421.

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ideas relating to the nature of light, which considerably extended the earlier wave theories of Hooke, Huygens, and Euler. However, his theory was rather clumsy, marred by inconsistencies and ad hoc hypotheses. Es­ sential to Young's theory was the luminiferous ether, a rare, elastic medium pervading the universe and supporting the propagation of light waves. Consistent with his adoption of this hypothetical medium was his rejection of the demand for certainty through inductively derived knowledge. He believed that scientific knowledge was built on "plausible hypotheses . .. by which a great number of apparently heterogeneous phenomena are reduced to coherent and universal laws," and that such hypotheses were used "to connect facts in the memory" and to predict the outcome of ex­ periments. If an hypothesis were confirmed by a large number of experi­ ments and no counter examples were found, then it could be considered as one of the "fundamental laws of nature" or, as Young elsewhere called it, a "theory." Although he considered that hypotheses were essential to science, he realized that if a scientist held an hypothesis too strongly it could lead him astray and prejudice him against recognizing counter examples. Furthermore, he realized that a well-confirmed hypothesis is sufficient only "to attach a value and importance to our theory, but it is not fully decisive with respect to its exclusive truth, since it has not been proved that no other hypothesis will agree with the facts." 18 Young's use of the method of hypothesis contributed to the general rejection of his work, particularly in Scotland. One reviewer stated that "instances also occur of gratuitous assumptions, [and] of hypotheses too extensive." 19 Another reviewer complained that an hypothesis is "a work of fancy, use­ less to science, . . . it requires continual polishing, touching and retouch­ ing, in order to adapt it to the phenomena." 20 After Newton's wellfounded conclusions and his caution against the use of hypotheses, Young's work appeared tentative, even unscientific, to those imbued with "New­ tonian" methodology. 18 Young's early statements on methodology are in his MSS. Lecture Notebooks, 19/11 (University College, London); "On the Theory . . .," ibid., p. 12; "Dr. Young's Reply to the Animadversions of the Edinburgh Reviewers," Miscellaneous Works of the late Thomas Young . . ., ed. George Peacock (London, 1855), 1, 204. See also G. Cantor, "The Changing Role of Young's Ether," British Journal for the History of Science, 5 (1970), 44-62. 19 Review of Young, "On the Theory . . .," in Monthly Review, 39 (1802), 404. 20 [Henry Brougham], review of Young, "On the Theory . . .," Edinburgh Review, 1 (1803), 450-456. See also, id., Discourse on Natural Theology (London, 1835), p. 165. For a sidelight on the Young-Brougham controversy, see G. Cantor, "Henry Brougham . . .," op. cit. (note 3).

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In France during the second decade of the nineteenth century, Augustin Fresnel, who had been educated at the Ecole Polytechnique, proposed a mathematically sophisticated form of the wave theory with far greater internal consistency than Young's. Fresnel believed that nature is basically simple, producing the maximum number of effects by the minimum num­ ber of causes; accordingly, the scientist must aim to represent nature by employing the minimum number of hypotheses, even though he uses com­ plex methods of mathematical analysis. Fresnel rejected the Newtonian corpuscular theory, for it required separate and independent ad hoc hy­ potheses to explain different phenomena. He said that Newton, in explain­ ing the expansion of "interference" rings when viewed obliquely, had to assume that the length of the fits of easy reflection and transmission in­ creases with an increase in the length of the path traversed. Fresnel ob­ jected to this hypothesis as arbitrary. 21 He presented his own form of the wave theory as a simple and highly consistent hypothetical system that could explain a wide range of phenomena. It was this simplicity and con­ sistency, which Young's and Newton's theories lacked, that appealed to many of Fresnel's followers and that was frequently cited in support of the wave theory. Fresnel's theory also predicted a novel consequence that was sometimes quoted in support of the wave theory: his equations predicted a bright spot at the center of the shadow of an opaque disc which, contrary to general expectation, was confirmed. 22 John Herschel's treatise on light, published in 1830, provided the first extended account of Fresnel's theory in Britain together with a generous exposition of corpuscular optics.23 The second edition of Airy's Mathe­ matical Tracts 24 in 1831 contained a detailed discussion of the wave theory and a curt rejection of its rival. Thus, in the early 1830's a consis21 Augustin Fresnel, "Memoir sur la Diffraction de la Lumiere, couronne par 1'Academie des Sciences," Oeuvres Completes d'Augustin Fresnel, ed. Henri de Senurmont et al. (Paris, 1866), 1, 253-254. 22 D. F. J. Arago, "Rapport fait par M. Arago a l'Academie des Sciences, au Nom de la Commission (J.-B. Biot, D. F. J. Arago, L. J. Guy-Lussac, et S. D. Poisson] qui avait ete Chargee d'Examiner Ies Me'moirs Envoyes au Concours pour la Prix de la Diffraction," ibid., pp. 229-246. 23 John Herschel, "Light," in Encyclopaedia Metropolitana, 4, 341-586. Copies of this article, written in 1827, were privately distributed prior to publication. Signifi­ cantly, it later formed part of The Encyclopaedia of Mechanical Philosophy . . . (London and Glasgow, 1854). Herschel's conversion to the wave theory dated from about 1826. The significance of the Cambridge scientists' early interest in wave optics is discussed by Wilson in his thesis, op. cit. (note 11). 24 George B. Airy, Mathematical Tracts on the Lunar and Planetary Theories . . . and the Undulatory Theory of Optics, 2nd 1 ed. (Cambridge, 1831).

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tent form of the wave theory became generally available, heralding the revival of interest in optics among British scientists after decades of al­ most unquestioning acceptance of Newton's corpuscular theory. 25 The publication of Herschel's and Airy's works marked the beginning of the major confrontation between the supporters of the wave theory, who adopted the method of hypothesis, and the objectors, who held inductj/On to be the true scientific method. As soon as Fresnel's wave theory became known in Britain, the objectors argued that the wave theory was false if any one of its deductions was false. This argument, which was based on the assumption that all scientific statements were either true or false, was extensively used against the wave theory. Potter, for example, considered that a true description of natural processes, or a physical theory, should explain all phenomena, and he re­ jected the wave theory because it failed to explain certain ones. The ex­ periments he reported in his publications concentrated on just these anom­ alous phenomena. To test the wave theory of light, he suggested an "experimentum crusis," 26 which -related to the fringe pattern obtained by observing a small white light source in two plane mirrors inclined at a small angle to one another. The wave theory predicted that the center of this fringe pattern should always be white, yet Potter usually obtained a black central band, although at times he obtained a white one. He claimed that the failure of this prediction meant that the wave theory was not the true physical description of light. In other papers he used the same type of argument when he found that the predictions of the wave theory did not agree with experiment. After one such refutation he stated that "I consider the controversy, as to the undulatory theory being the [true] physical theory of light, to be nearly terminated . . . ." 27 Barton shared Potter's 2s The progress of the debate can be gauged from the number of articles on optics published in the Philosophical Magazine. Thisjournal carried only about three optical papers a year during the first three decades of the nineteenth century. A spate of papers on experimental and theoretical optics followed in the early 1830's. For example, in 1833 the journal carried seventeen papers on optics, most of which were concerned with the crisis in the subject. However, by the early 1840's the major crisis had passed; in 1841 the Philosophical Magazine only contained eight optical papers, most of which were concerned with extending the new wave paradigm to explain further phenomena. 26 Richard Potter, "On the Method of Performing the Simple Experiment of Inter­ ferences with Two Mirrors Slightly Inclined, so as to Afford an Experimentum Cruets as to the Nature of Light,"Phil. Mag., 16 (1840), 380-387. 27 Richard Potter, "On the Phenomenon of Diffraction in the Centre of the Shadow of a Circular Disc, Placed Before a Luminous Point, as Exhibited by Experiment," Phil. Mag., 19 (1841), 155.

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methodology, rejecting the wave theory because it did not satisfactorily explain the phenomenon of inflexion. Likewise, many of Brewster's papers and reviews emphasized the anom­ alous experiments that were not explained by the wave theory. One such experiment concerned the selective absorption of light by nitric acid gas, resulting in a spectrum that was crossed by about two thousand dark lines. 28 Brewster pointed out the inability of the wave theory to explain why vibrations of a given frequency were transmitted by the gas while vibrations differing only slightly in frequency were absorbed. In the face of such anomalies he could not assent to the wave theory as the true physical theory. Despite Brougham's claim in 1850 that he was unwilling to enter into the controversies over theories of light and despite his claim that he wished to present only experimental results, his later papers, 29 which were mostly concerned with diffraction experiments, were clearly intended to falsify the wave theory. He argued that his experiments could not be explained by the wave theory and instead indicated a new property of light. Brewster, too, wrote several papers dealing with a new property of light which, in his view, defied explanation on any theory. 30 Thus, one of the major methodological arguments used by Brewster, Brougham, Potter, and Barton against the wave theory was the failure of some of its predictions to be confirmed experimentally. Since Newton's corpuscular theory was also proved false by the same argument, the ob­ jectors to the wave theory behaved consistently when they abandoned the Newtonian corpuscular theory after its shortcomings had been clearly shown in the 1830's. Toward the end of their lives both Brewster and Brougham followed Biot in publicly claiming to be "rienistes," whom they considered to be the only unobjectionable philosophers. 31 Rejecting both theories, they concentrated on describing optical phenomena per se and delineating those phenomena that were not adequately explained by the wave theory. It should be noted that Brewster did not reject the wave theory out of hand, and even described himself as an admirer of the 28 David Brewster, "Observations on the Absorption of Specific Rays, in Reference to the Undulatory Theory of Light,"Phil. Mag., 2 (1833), 360-363. 29 See especially Henry Brougham, "Experiments and Observations upon the Prop­ erties of Light," PiiiL Trans., 140 (1850), 251-252. 30 For example, David Brewster, "On a New Property of Light," British Associa­ tion Report, 7 (1837), 12-13. Brougham, op. cit. (note 29), p. 236, and Brewster's review of three works con­ cerning F. Arago in North British Review, 20 (1854), 488.

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"beautiful theory of waves." As a competent experimentalist Ke was impressed by the power of the wave hypothesis to explain and predict facts, but he was willing to use it "only as a temporary auxiliary." 32 He objected to Airy, Whewell, and others who in his opinion dishonestly represented the wave theory as physical truth and glossed over its experi­ mental and philosophical limitations.

/

Unlike the objectors, the supporters of the wave theory considered anomalous facts to be relatively unimportant. Following one of Brewster's attacks on the wave theory, Airy charged Brewster with having paid inordinate attention to the phenomenon of absorption which, Airy readily admitted, could not at that time be accounted for by the wave theory. The anomaly was unimportant because in comparing the two theories, the corpuscular came off worse owing to its inability to explain not only absorption but also a great number of other phenomena. 33 Likewise, Powell, who believed that nature is basically uniform, proposed the "grand maxim" that "having once grasped firmly a great principle, we should be satisfied to leave minor difficulties to await their solution." 3 * These diffi­ culties would in time be resolved by altering some of the subsidiary hy­ potheses connected with the wave theory. We must now consider the criteria employed by the supporters of the wave theory in choosing between rival hypotheses. They frequently stated that they chose Fresnel's simple and consistent theory because it was able to explain a greater range of optical phenomena than its rival. For instance, at the British Association meeting in 1834 Lloyd proclaimed that "[vjaried and comprehensive classes of phnomena [sic] have been em­ braced by its [the wave theory's] deductions." 35 The corpuscular theory failed because it was less highly confirmed, and because it was not as simple and consistent owing to the ad hoc and even contradictory assumptions it employed. For Airy the power of the wave theory to explain and predict facts was a sufficient test of its truth. He stated that the corpuscular theory offered no simple explanation of destructive interference and polarization, and until it did he wished to hear nothing further of it. 36 32 [David

Brewster], review of Whewell's History, in Edinburgh Review, 66 (1837), 143; and ibid., 74 (1843), 304. See also his review of Comte's Cours de Philosophie Positive, ibid., 67 (1838), 305-306. 33 Airy, "Remarks . . .," op. cit, (note 12). 34 Powell,Essays, op. cit. (note 13), p. 94. 3s Humphry Lloyd, "Report on the Progress and Present State ofPhysical Optics," British Association Report, 4 (1834), 296. See also Whewell, History, op. cit. (note 9), 2, 428-429. 36 Airy, "Remarks . . .," op. cit. (note 12).

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Airy's optical papers extended the wave theory to explain complex and sometimes new phenomena. Being a competent mathematician he calcu­ lated some of the complicated integrals that occur in Fresnel's theory; for example, those expressing the intensity of the diffraction pattern pro­ duced in the shadow of a circular disc or aperture. 37 Airy considered that the outcome of these and similar investigations confirmed the "truth" and "correctness" of the wave theory, a reflection of his unsophisticated, pragmatic methodology. He found that the wave theory led to novel predictions that he later confirmed by experiment; one phenomenon he discovered by prediction, and which he considered inexplicable by the rival theory, was the Newton's rings obtained when a convex lens is placed on a polished metal plate and viewed by polarised light. 38 Lloyd and Powell were attracted to the wave theory in part because its "consistency" agreed with their approach towards natural theology. Lloyd believed that this consistency indicated the simplicity, "harmony, and unity, and order which must reign in the works of the One Supreme Author." He considered that the consistency of a true theory was matched by its high degree of confirmation. On the other hand, a theory that employed a superfluity of ad hoc hypotheses was "no longer a physical theory, whose very essence is to ascend in simplicity, in the same time that it arises in generality;—[instead] it is 'a mob' of individual laws, without connexion, order, or dependence." 39 He saw just this lack of consistency in the Newtonian corpuscular theory. Central to Powell's philosophy was a belief in the uniformity of nature. He conceived every generalizing principle to indicate the harmony and unity of nature and thus to be proof of "a presiding Mind, the supreme moral Cause of all things." He considered that the role of the inductive philosopher was to seek the great unifying principles in nature. Powell appears to have followed Whewell in adopting the antithesis between facts and theories and the view that the role of theories is to reduce facts to an ordered system. In his understanding of scientific progress, change takes place "from anomaly to regularity, . . . from confusion to order, . . . from artificial dogmatism to the simplicity of nature." He contended that a progressive theory can be extended to explain new classes of phenomena 37 George B. Airy, "On the Diffraction of an Annular Aperture," Phil. Mag., 18 (1841), 1-10. 38 George B. Airy, "On a Remarkable Modification of Newton's Rings," Trans. Cambridge Phil. Soc., 4 (1833), 279-288. 39 Humphry Lloyd, "Report . . . ," op. cit. (note 35), p. 296, and Lectures on the Wave-Theory of Light (Dublin, 1841), pp. 88-89.

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with increasing accuracy without having to alter any of its basic postu­ lates. 40 To show that the wave theory had this desirable characteristic, Powell cited Cauchy's extension of the theory to include the phenomenon of dispersion. Onseveral occasions Powelljustified his adherence to the wave theory by its ability to explain consistently a larger number of phenomena than the rival theory could. Following a challenge to the wave theory by Barton, Powell in 1833 drew up a table of twenty-three diverse phenomena and against each noted whether it was explained by the corpuscular or the wave theories. 41 He also requested that Barton add a further column to assess his own hypothesis. The result of this tabulation was a resounding victory for the wave theory; it explained "perfectly" eighteen phenomena, whereas the corpuscular theory did so for only five. Using this test he found that the wave theory was much more highly confirmed than the corpuscular theory and that therefore the former was the one that ratio­ nally should be adopted. Elsewhere 42 he stated that in deciding between two rival theories, individual anomalous facts should not be accorded high priority; the decision should favor the theory that "connects, by a common principle, and thus explains the greatest number of facts." Whewell cited the wave theory of light to illustrate several important aspects of his philosophy of science. For example, he considered that "one of the most decisive characteristics of a true theory" was revealed when an hypothesis which had been developed to explain one class of phenomena was found also to explain other initially unrelated classes; this he termed "the concilience of inductions." The development of wave optics provided Whewell with many examples of "concilience," such as Fresnel's laws of polarized light which were also found to account for the polarization, or "Brewster," angle. 43 A contentious issue between the two schools was the lupiiniferous ether, which was considered to be an essential part of the wave theory. Although no direct, independent evidence was available to confirm the ether, Airy accepted its existence as almost certain and supported his 40 Powell

op. cit. (note 13), pp. 132 and 59. Powell, "Remarks on Mr. Barton's Reply, Respecting the Inflection of Light ,"Phil. Mag., 3 (1833), 416-417. 42 Footnote in F. Arago, Biographies of Distinguished Scientific Men, eds. W. H. Smyth, Baden Powell, and Robert Grant (London, 1857), p. 443. 43 Whewell, Philosophy, op. cit. (note 9), 2, 232 and 447. This aspect ofWhewell's work is discussed in L. L. Laudan, "William Whewell on the Consilience of Induc­ tions," The Monist, 55 (1971), 368-391. 41 Baden

j Hssays,

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belief by the analogy between the propagation of light in the ether and the propagation of sound in air. Whewell, too, readily adopted the real exis­ tence of the ether, but Powell insisted that the ether was only an hy­ pothesis. The supporters of the wave theory offered many nonoptical pieces of confirmatory evidence; for instance, they regarded the ether as the cause of the observed retardation of Encke's comet. Herschel and Whewell considered that the ether provides the efficient cause of light, and they assumed that the ether obeys the same mechanical laws as do macro­ scopic fluids. Whewell even pictured God as an artisan, the maker of the ether, an image which contrasts sharply with Brewster's natural theology. 44 Brewster, by contrast, chastised those who stated dogmatically that the luminiferous or other ethereal fluid really exists. 45 He maintained that the ether was a purely hypothetical medium and thus that the wave theory was also an hypothesis and should be treated as such. He particularly ob­ jected to Airy's and Whewell's claims that the wave theory was nearly as certain as Newton's theory of gravitation. For Brewster the wave theory was based on a conjectural ethereal fluid, whereas the theory of gravitation expressed a true law of nature. The different methodological positions of the two schools determined not only their attitudes towards the ether but also their research problems. Airy believed that the wave theory might be reduced to purely mathe­ matical laws which, if discovered, would mark a considerable advance in science; he therefore encouraged James MacCullagh, James Challis, Philip Kelland, John Tovey, and others in their efforts to construct mechanical models of the ether. 46 Powell, too, acknowledged that these mechanical attempts belonged to an important although underdeveloped area of opti-

44 Brewster complained that in his Bridgewater Treatise Whewell had devalued natural theology by claiming that the wave theory of light and the luminiferous ether were proofs of divine wisdom and skilful adaptation. Whewell even claimed that without the mechanism of the ether, the whole world would be inert. This line of argument incensed Brewster who insisted that natural theology should not be founded on ephemeral hypotheses, but should be based on indubitable, inductively derived facts. ([David Brewster], review of Whewell's Astronomy and General Physics considered with reference to Natural Theology, in Edinburgh Review, SS [1834], 422-457.) 45 David Brewster, review of Whewell's Philosophy, in Edinburgh Review, 74 (1843), 304; review of Mary Somerville's On the Connexion of the Physical Sciences, ibid., 59 (1834), 164. 46 George B. Airy, "On the Equations Applying to Light under the Action of Magnetism," Phil. Mag., 28 (1846), 469-477, and his "Remarks on Dr. Faraday's Paper on Ray-Vibrations," ibid., p. 537.

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cal research, and in 1855 Ke conjectured that the ether might be reduced to a specific example of some more general principle. 47 Many attempts were made to build mechanical or dynamical models of the ether; one writer in 1849 counted fifteen different models that had been seriously discussed. 48 Not all of these models were purported to represent the true nature of the ether but, as Airy pointed out, they opened up the possibil­ ity of reducing optics to mechanical principles. On the other hand, the objectors to the wave theory maintained that building models of this conjectural fluid was not a legitimate scientific activity, but a waste of time. Brewster frequently attacked those who did not clearly distinguish be­ tween the wave hypothesis and the principle of interference. Certainly the latter could be deduced from the former, but the principle of interference, which he conceded to be a law of nature, neither proved nor confirmed the wave hypothesis. Young considered that the principle of interference "is wholly independent of any opinion respecting the nature of light," 49 and Brewster followed him in separating the principle of interference from the wave theory or any other hypothesis about the nature of light. Brewster claimed that Young had "declared that the law of interference may be reconciled to the doctrine of emission," which was possible if the particles of light were endowed with an hypothetical periodic motion. With this additional postulate the hypothesis of emission could be extended to ex­ plain periodic phenomena just as well as the wave theory. 50 Thus, he recognized that both the wave and corpuscular hypotheses could incorpo­ rate the principle of interference, and that although a law may logically be deduced from any number of different hypotheses, the converse is not true. Herschel gave equivocal support to Brewster on this point, but Powell, Airy, and Whewell claimed that destructive interference could not reasonably be explained by the impact of particles. They considered 47 Powell, Essays, op. cit. (note 13), p. 124. Powell was very impressed with William Grove's work on the correlation of forces. 4 8 R. Moon, Fresnel and his Followers. A Criticism. To Which Are Appended Out­

lines of Theories of Diffraction and Transversal Vibration (Cambridge, 1849), p. ix. The controversy between Moon and "Fresnel's followers" over the details of the wave theory, particularly over the structure of the ether, was originally published in journals. 49 Thomas Young's MSS. Lecture Notebooks, 16(15r (University College, London). 50 David Brewster, review of Somerville, op. cit. (note 45), pp. 163-164; David Brewster to Henry Brougham, 29 August 1848 (University College, Brougham Cor­ respondence, 26, 634); The Life of Sir Isaac Newton (London, 1833), p. 105; Treatise on Optics (Philadelphia, 1852), pp. 111-119.

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Brewster's attempt to explain interference on the corpuscular theory in­ admissible because it involved complex ad hoc hypotheses, whereas they regarded the principle of interference as a " necessary " consequence of waves that required no additional assumptions. Once the shortcomings of Newton's corpuscular theory were acknowl­ edged by its supporters, they suggested supplementary hypotheses to increase its explanatory power. Although they accepted that the true na­ ture of light was not known, they were willing to entertain these supple­ mentary corpuscular hypotheses that might contribute to the eventual discovery of truth; they considered the wave theory, however, to be patently false. Furthermore, these variations on the corpuscular theory helped combat the claim that the wave theory was unassailably superior. Thus, Brewster suggested that the particles of light might be endowed with a periodic motion. In order to explain inflection, Barton proposed that light is emitted from a luminous body in the form of a particulate stream that behaved like an elastic fluid of mutually repelling particles. 51 The repelling force explained why a beam of light was inflected into the shadow of an opaque body. Bearing in mind that sound vibrations are produced when a jet of air passes close to an obstacle, Barton suggested that similar vibrations were set up in the particles of the luminiferous fluid when it passed through an aperture or close to a material body, and that these vibrations determined the diffraction pattern. Some four years earlier Brewster, probably independently of Barton, had suggested the hypothesis that repulsive forces existed between the particles or rays of light. Even as late as 1855, however, Potter claimed that since the wave theory was "evidently false, the Science of Physical Optics requires now to be remodelled." 52 Four years later he published a novel form of the theory of emission by which he could explain both chemical reactions and peri­ odic optical phenomena. He believed that the true theory would have to account for the related thermal and chemical phenomena, and he con­ sidered that the failure of the wave theory to explain them was one of its major shortcomings. In this new theory Potter proposed that each luminous point emits "luminous particles" which "must be considered as flying off in surfaces, sheets or shells" at constant intervals whose separations de-

5 1 John Barton, "On the Inflexion of Light," Abstracts of Papers printed in the Philosophical Transactions, 3 (1838), 72-73; Phil. Mag., 2 (1833), 263-269, and 3 (1833), 172-178. 5 2 Richard Potter to Henry Brougham, 19 March 1855. Univeristy College, Broug­ ham Correspondence, 26, 199.

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pended on the color of the light. 53 This hypothesis, however, appears to have attracted little interest, and even Brewster did not understand how Potter could explain the fact that the velocity of light is less in water than in air. A further aspect of the debate having methodological significance con­ cerns the role of "crucial" experiments, which Herschel considered to be of "great importance" in deciding between the two theories. To illustrate this point, in his Preliminary Discourse on Natural Philosophy he described an experiment in which the wave theory predicted perfectly black stripes between a set of bright fringes, and in which the corpuscular theory pre­ dicted the same spaces to be "half bright." In conclusion Herschel reported that Fresnel had stated the outcome to be "'decisive in favour" of the wave theory. 54 Later in the debate the velocity of light in dense media was frequently cited as leading to a "crucial" test between the two theories. The wave theory predicted that the velocity of light is greater in air than in water or any other dense medium, whereas the opposite result was ex­ pected on the corpuscular theory. Lloyd believed that Arago's experiment, in which a thin transparent plate placed in one beam of an interferometer displaced the fringe pattern, was "conclusive in favour of the wave theory" and against the corpuscular theory. 55 Despite "crucial" experiments like Arago's, and like Foucault's in 1850, the objectors to the wave theory were not won over. Potter continued to propose a form of the corpuscular theory, and Brewster maintained that Arago had "proved nothing more than the displacement" of the fringes. Likewise, Brewster stated that Foucault's experiment certainly confirmed the wave theory, but for him this did not mean that the wave theory was a "universal and necessary truth." Brewster resented the manner in which "we are called upon by persons in Cambridge . . . to surrender our judgements, and to give our allegiance to a great speculation" following the outcome of the "crucial" experiments, concluding that "we can only express our wonder at the intolerance of the age." 56 53 Richard Potter, Physical Optics, Part 2 (Cambridge and London, 1859), partic­ ularly p.l. Brewster likewise considered that the failure of the wave theory to ex­ plain chemical phenomena was a major shortcoming (University College, Brougham Correspondence, David Brewster to Henry Brougham, 26 September 1847 [26, 632] and 9 September 1848 [26, 635]). 5 ^Herschel,Preliminary Discourse . . . , op. cit. (note 11), pp. 206-207. 55 Lloyd, Lectures, op. cit. (note 39), p. 38. 5 6 [David Brewster], review of three works concerning F. Arago, op. cit. (note 31), pp. 487-488.

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Some of the supporters of the wave theory, particularly Powell, advo­ cated a nontheoretical position similar to Brewster's. In an early work that gave a simple, yet comprehensive, account of all optical phenomena, Powell avoided any discussion of the competing theories of optics and instead "described facts, their mathematical laws, and the conse­ quences." 57 Following this nontheoretical approach he acknowledged that the periodicity of light "is established as an experimental fact entirely independent of any theory." Later he frequently stated that the wave theory was consistent with his empirically based postulates; indeed, he considered it a "necessary consequence from facts and observations" that light is some form of transverse vibrating motion. This "necessary" con­ clusion formed the basis of a pure mathematical system that was entirely independent of any physical explanation. Thus, to Powell, the wave theory was not an hypothesis, although the ethereal fluid was. He ac­ cepted the luminiferous ether as a legitimate, but unproven part of science; in his theory he therefore dissociated the "proven" wave theory from the purely conjectural ethereal medium. 58 In his Mathematical Tractss9 Airy, like Powell, divided the wave theory into two parts. He designated as "geometrical" the hypothesis that "light consists of undulations depending on transversal vibrations, and that these travel with certain velocities in different media according to laws." This hypothesis was "certainly true" because it adequately explained a con­ siderable variety of complicated phenomena. The other part of the wave theory he referred to as the "mechanical"; it concerned problems that had yet to be solved, including the problem of the structure of the ether. He warned his readers to approach these problems with caution since only tentative, though probable, solutions had so far been found. However, unlike Powell, Airy appears to have subscribed to the idea of efficient causation and to have been certain that the ether really exists. The "revolution" in theories of optics was accompanied by the institu­ tionalization of the wave theory. It became the new orthodoxy, and scientists holding heterodox opinions found great difficulty in having their works accepted for publication. In ] 840 Potter complained that 57 Baden Powell,/! Short Elementary Treatise on Experimental and Mathematical Optics Designed for the Use of Students in the University (Oxford, 1833), pp. viii— x. 58 Baden Powell, "Remarks on the Nature of the Evidence in Support of a Theory of Light," Edinburgh New Phil. ]., 18 (1835), 275-285. See also id., A General and Elementary View of the Undulatory Theory . . . (London, 1841), pp. iv-v. 59 Airy, op. cit. (note 24), pp. v-vi.

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members of the Cambridge Philosophical Society adhered to the wave theory of light without having carefully investigated it, being satisfied that it "merely showed a prima facie accordance with some known facts." 60 Likewise, he contended, their objections against the corpuscula? theory were either trivial or were based on false arguments. By the 1840's Brewster and Airy were disputing with one another at meetings of the British Asso­ ciation and the Royal Society, especially in connection with an experi­ ment that Brewster considered to indicate a new property of light. In the 1840 Bakerian Lecture 61 Airy attacked Brewster and argued that the new property of light was amenable to explanation by the wave theory. Brewster was incensed, privately describing the lecture as "a complete blunder from beginning to End." 62 At two subsequent meetings of the British Association he retaliated by pointing out some inconsistencies be­ tween Airy's theory and his own experimental results, objecting that Airy was not personally acquainted with the experiments he was trying to explain. In 1841 the Royal Society refused to print in the Philosophical Transactions one of Brewster's papers which, in his opinion, contained "results and views hostile to the Undulatory Theory." 63 Following these and other incidents Brewster became progressively antipathetic towards the wave theory and resented its institutionalization. He was aware that largely through the dogmatism of the "Cambridge faction" led by Airy and Whewell the wave theory had become the "creed" of the Royal Society. Furthermore, he believed that this "Cambridge faction" was "hostile to all Scotsmen." 64 After his paper had been rejected he com­ plained to P.M. Roget: "The Undulatory Theory is now to be the test of all Optical Papers submitted to the Royal Society. If the most important discoveries are made, they are considered of value only if the Undulationists can explain them. If not they are worthless." 65 In a letter dated 26 September 1847, Brewster requested that Brougham "take up the subject of the Emission versus the Undulatory theory of light,'' a cause for which "I have struggled single handed for the last 30 6 0 Richard Potter, "On Photometry in Connexion with Physical Optics," Phil. Mag., 16 (1840), 17. 6 1 George B. Airy, "On the Theoretical Explanation of an Apparent New Polarity of Light," Ρω. Trans., 130 (1840), 225-244. 6 2 David Brewster to P. M. Roget, 9 October 1841. RoyalSociety Archives, MC. 3. 189. 6 3 David Brewster to Henry Brougham, 14 December 1841. University College, Brougham Correspondence, 26, 624. 6 4 Ibid. 6 5 Brewster to Roget, 9 October 1841 (op. cit. [note 62]).

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years." 66 Subsequently Brewster tutored Brougham in the optical ad­ vances that had taken place during the previous few decades. He assured Brougham that the principle of interference had to be accepted as a law of nature and not as an hypothesis dreamed up by the supporters of the wave theory. In his early papers Brougham had explained diffraction in terms of a force emanating from the diffracting body, but in this later correspondence Brewster argued that such a force was inconsistant with experimental data. The outcome of this correspondence and the ensuing experiments was a series of papers read between 1849 and 1853 at the Royal Society of London, the British Association, and the Academie des Sciences. While Brougham's optical ideas were being courteously received in Paris, the "undulationists" in the Royal Society dealt them the final and crushing blow. The first of Brougham's later papers was printed in the Philosophical Transactions for 1850 despite Airy's protests. The next paper, read on 29 April 1852, was referred to Airy and G. G. Stokes, who regarded it as a feeble attack on the wave theory; it was finally rejected by Herschel. The referees claimed that not only were the experiments of little importance but they were also reconcilable with the "undulatory theory of interfer­ ences." They attributed Brougham's view that his experiments were inex­ plicable by the wave theory to "either his misconceptions of that theory, or his misconception of its principles." Finally, they stated that Broug­ ham's paper was twenty or thirty years out of date. Following this coup de grace, he withdrew his third and final paper. 67

3. CONCLUSIONS On several occasions Herschel stated that if as much research had gone into improving the corpuscular theory as in developing the wave theory, the former might be as advanced as the latter. However, Powell, Lloyd,

66 David Brewster to Henry Brougham, 26 September 1847. University College, Brougham Correspondence, 26, 632. 67 Brougham, "Experiments," op. cit. (note 29), and Abstracts of Papers Com­ municated to the Royal Society, 6 (1854), 172-174 and 312. Royal Society referees' reports in the Royal Society by G. G. Stokes (RR. 2.35), George B. Airy (RR. 2.36), and John Herschel (RR. 2.37). Letter in the Royal Society from B. C. Brodie to Charles Bell, 23 November 1853 (RR. 2.38). See also the paper by Baden Powell that was rejected by the Royal Society: "Remarks on Lord Brougham's 'Experiments and Observations on the Properties of Light',"Phtl Mag., 6 (1852), 1-8.

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and Whewell rejected this suggestion because they demanded more from a theory than just a high degree of confirmation. They stressed that the corpuscular theory was in a degenerate state, whereas the wave theory provided a consistent, unifying principle encompassing an increasing range of diverse phenomena. On the other hand, Potter, who rejected the wave theory, not only agreed with Herschel but even declared that given an equal opportunity the corpuscular theory would probably have been more successful than its rival. 68 Neither the corpuscular nor the wave theory remained static during the debate; both changed in response to criticism and new experimental data. Ultimately the corpuscular theory was judged inadequate, although its adherents initially tried to reformulate it and reconcile its deductions with experiment. The wave theory, on the other hand, exhibited great capacity for accommodating new phenomena. Paradoxically, Brewster aided the development of the wave theory, prompting through his criticisms new deductions from the theory. Another major difference between the supporters and objectors was the relationship they perceived between optics and other branches of science. The objectors demanded that optical theories should not be judged in isolation, but in the scientific and philosophical context of a wider natural philosophy; thus, they frequently stressed that the failure of the wave theory to explain optically related thermal and chemical phenomena was one of its major limitations. Furthermore, they wished to subsume optics within their corpuscular worldview, which was incommensurable with the wave theory in general and the luminiferous ether in particular. By con­ trast, the supporters of the wave theory developed optics mathematically in relative isolation from other branches of science: subsequently, how­ ever, it became the paradigm for further studies, such as the wave theory of heat. 69 The objectors to the wave theory placed greater emphasis on the role of experimentation in science than did their rivals who firmly advocated a mathematical approach towards physics. This latter approach, which was 6 8 See, for example, Herschel, Preliminary Discourse, op. cit. (note 11), p. 262; Powell, General and Elementary View, op. cit. (note 58), p. xvii; Lloyd, "Report," op. cit. (note 35), p. 296; Whewell ,History, op. cit. (note 9), p. 434; Richard Potter, "A Reply to the Remarks of Professors Airy and Hamilton . . . ," Phil. Mag., 2 (1833), 280. 6 9 Stephen G. Brush, "The Wave Theory of Heat: A Forgotten Stage in the Transi­ tion from the Caloric Theory to Thermodynamics," British Journal for the History of Science, 5 (1970), 145-167.

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not readily accepted at Edinburgh University, 70 came to dominate British physics for nearly a century. Thus, the initial disinterest in Einstein's special theory of relativity in the early twentieth century was largely due to the inordinate attention paid to mathematical models of the ether by Cambridge physicists. 71 In general, eighteenth-century natural philosophers adopted both the corpuscular theory of light and inductive "Newtonian" methodology as complementary facets of science. This methodology, particularly in Scot­ land, formed a strong, well-articulated intellectual tradition that related not only to epistemological problems in optics but also to a number of other fields of research; for this reason "Newtonian" methodology was of great importance to Brewster and Brougham. The wave theory, on the other hand, could not be assimilated to the "Newtonian" methodology, but instead required a different epistemology and methodology. The over­ throw of the corpuscular theory of light radically challenged the "New­ tonian" worldview held by the objectors to the wave theory. Although the latter had to abandon many of their views on the corpuscular nature of light, they retained their "Newtonian" position on scientific method and used it extensively in the optical debate, particularly when the corpuscular theory was faced with defeat. Since the wave theory was not commensurate with "Newtonian" meth­ odology, its supporters were forced to develop alternative epistemologies and sophisticated forms of the method of hypothesis. Thus, Herschel in his Preliminary Discourse on Natural Philosophy and Whewell in his Philosophy of the Inductive Sciences discussed in depth many of the methodological problems prompted by the optical debate; the problems in­ cluded the justification of hypotheses, the criteria for choosing between them, and the vindication of etherial fluids. Brewster, who remained totally unconvinced by the new methodology, wrote in 1843 that the wave theory's "doom, as the [true] physical 70 Airy introduced the wave theory of light into Cambridge during the late 1820'sprobably in 1828--and for several years he delivered mathematically sophisticated lectures before large audiences. By contrast, J. D. Forbes's first attempts to teach the wave theory of light at Edinburgh in 1835 were not well received, owing to his students' lack of knowledge of mathematical techniques. See Autobiography of Sir George Biddell Atry . . . , ed. W. Airy (Cambridge, 1896), pp. 73, 76, 87, 90, and 113. See also J. D. Forbes to John Herschel, 14 February 1837. Royai Society, Herschel Correspondence, 7.298. 71 Stanley Goldberg, "In Defense of Ether; The British Response to Einstein's SpeciaITheory of Relativity, 1905-1911," Historical Studies in the Physical Sciences, 2 (1970), 89-125.

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theory is sealed, and when it has lingered another century as a mathe­ matical hypothesis, the true cause of the phenomena of light will reward the diligence and genius of those who, in the spirit of genuine induction, have advanced in the straight and narrow way that leads to the Temple of Truth." 72 The century has now long passed, and we must disappoint Brewster not only because we have not found "the true cause of the phe­ nomena of light," but because we have not followed the "straight and narrow" way he advocated. Instead, we have come to recognize the validity of the method of hypothesis, which Brewster rejected because he believed it could never lead to the "Temple of Truth."

ACKNOWLEDGMENTS I wish to thank the librarians of University College, London and of the Royal Society of London for permitting me to quote extracts from archi­ val materials. I completed part of the research for this paper while working at Hendon College of Technology, now the Middlesex Polytechnic.

72 Brewster's review of Whewell's Philosophy, op. cit. (note 45), p. 306. See also his Newton, op. cit. (note 50), p. 110.

Origins and Consolidation of Field Theory in Nineteenth-Century Britain: From the Mechanical to the Electromagnetic View of Nature BY BARBARA GIUSTI DORAN* Introduction 1. Early Demechanization of the Aether

134 138

Intellectual Heritage

138

Distorting the Elastic Solid Luminiferous Aether

149

Faraday, Thomson, and the Electromagnetic Aether

162 170

2. Revolutionary Insights into Aether and Matter

Thomson's Field Theory of Matter: The Vortex-Atom and Its Heirs 179 Origins

179

Incompatability of Spectral Radiation and the Kinetic Theory of Gases

190

Undermining the Mechanistic Gravitational and Kinetic Theories

192

Vortex-AetherTheories

194

The Tradition of Field Theories of Matter

197

Maxwell's Models and the Electromagnetic Theory of Light 3. Effecting the New Synthesis: 1880-1894

198 207

Updating the Luminiferous Aether Theories

211

Correcting Maxwell's Theory of Electromagnetism

222

The Medium Plus the Source: Incorporating Charged Par­ ticles

222

The Vector Potential, Displacement Currents, and Moving Charges

226

*Mathematician-Physicist, Baylor College of Medicine, 5006 Wigton, Houston, Texas 77035.

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Problems in the Representations: Polarization versus Con­ tinuous Transmission

230

Implications of the Relation between Charge, Matter, and Aether

238

The Problem of Motion through the Aether

240

Atomic Structure, Spectral Radiation, and the Kinetic Theory of Heat

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The Culmination of a Tradition: Larmor's Electron Theory of Matter and Electromagnetic View of Nature Conclusions

254 257

INTRODUCTION In the electromagnetic view of nature, Western science experienced its greatest disjuncture since the seventeenth-century Newtonian synthesis.1 For the first time, numerous phenomena that could find no explanation in the context of the mechanical worldview had an alternative, encompassing metaphysic. By the end of the nineteenth century, the mechanical notions of "atoms in a void" and "forces acting between material particles" had been replaced by the notions of the electromagnetic field as a nonmaterial, continuous plenum and material atoms as discrete structural-dynamic products of the plenum. This revolution in worldviews germinated and matured in Britain during the nineteenth century, fed by a rich tradition of physical theories that sought to comprehend the nature of the field and the atom of matter within a peculiarly British conceptual and methodological perspective. Originating in the second quarter of the century in theories of the luminiferous aether and Faraday's lines of electric and magnetic force, the revolution developed at midcentury into a conscious rejection of the mechanical concepts of atom, void, and force in 1 Russell McCormmach, "H, A. Lorentz and the Electromagnetic View of Nature," Isis, 61 (1970), 459-497, on p. 496 concurs that "the most significant shift in the intellectual horizons of physicists in two hundred years . . . occurred within what, by convention, we have come to regard as nonrelativistic classical physics . . . in the electron theory and the associated electromagnetic view of nature." This paper is ?n outgrowth of Chapters 9-12 and segments of Chapters 13-15 of B. G. Doran, Contributions of British Physics to the First Electron Theory of Matter and the First Electromagnetic View of Nature—Sir Joseph Larmor's 1893 Theory of Aether and Matter (Ph. D. dissertation, The Johns Hopkins University, 1972). It also briefly summarizes some of the findings reported in Chapters 20 and 21 of my larger study, Sir Joseph Larmor and the Roots of Modern Physics (1972), an unpublished manuscript on file at The Johns Hopkins University.

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favor of the plenum and a field-theoretic notion of matter. The revolution culminated in the final decades in persistent efforts by a number of physicists to resolve the problems of optics and electromagnetics within the context of the new British view of the atom and its relation to the aether. Both the luminiferous aether and Faraday's lines of force had been demechanized in principle by midcentury. But both were beset with the problems, which would later encumber Maxwell's electromagnetic theory of light, of representing the transmission of action through a nonmaterial plenum in other than mechanical terms, and of explaining the relation and mode of interaction between the plenum and matter. In 1856, William Thomson, later Lord Kelvin, found in Faraday's experiment on magnetooptic rotation a hint that the relation between matter and the aether might be understood through vortical atoms in the plenum; in 1860, he explicitly endorsed this conception as an alternative to that of atoms in a void and interparticulate forces acting at a distance. When Helmholtz' hydro­ dynamics and Tait's smoke rings suggested that such vortical motions might have the permanence and indivisibility of material atoms, Thomson devoted his full efforts to developing the vortex-atom theory of matter. It was with revolutionary intent that Thomson presented his vortex-atom as the basis for a new kinetic theory of gases, asserting that it afforded an explanation of phenomena such as spectral radiation that are incompatible with the notion of the hard, impenetrable atom. This field-theoretic conception of the material particle as a structuraldynamic product of the aether gave direction and momentum to the search for a nonmechanical view of nature. The conception that Thomson put forward in 1856 directly motivated not only Thomson's vortex-atom but, as well, Maxwell's theory of electromagnetism, which misinterpreted Thomson somewhat, and Maxwell's later speculations about aether and matter, which correctly interpreted him. It motivated, too, Pieter Zeeman's initial search in 1892 for the effect of magnetism on spectral radiation, and Joseph Larmor's 1893 synthesis of optical, electromagnetic, and atomic theory into the first "electron theory of matter" in which mass is viewed as an electromagnetic phenomenon. Indeed Thomson's powerful conception spawned an entire tradition of aether and matter based on the continuous nonmaterial plenum. Larmor was but one of several British physicists in the 1880's who sought the physical relation and mode of interaction between the electric charge, matter, and aether in extensions of that tradition. The intellectual vitality of the period, witnessed in part by

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the intensity of the collective search for a synthesis, quickly made apparent the physical phenomena and conceptual difficulties that still precluded a comprehensive physical theory. Larmor resolved those difficulties, supplying what both the vortex-atom and Maxwell's electro­ magnetic theory lacked—an understanding of the relation between charge and matter—and thus providing the field-theoretic view with an electro­ magnetic basis. Emphasizing that the electromagnetic worldview involves modes of physical action not possible in the traditional theories of matter, Larmor further developed its implications for the electrodynamics of moving bodies and for equipartition, spectral radiation, and atomic structure. The British revolution advanced not in spite of the peculiar methodo­ logical approach to theoretical physics that motivated nineteenth-century British physicists, but as a consequence of it. The method itself derived in part from Fourier's revolt against the hypothetical deductive method of the French and German "mechanico-molecular" school, which deduced laws of phenomena from the universal hypothesis of forces between material particles. 2 Fourier's criticism made a deep impression on the Cambridge school of physics during the second quarter of the century. Following Fourier, British physicists acknowledged first that mathematical analysis must describe the laws governing phenomena independently of any hypotheses, and second that the universal applicability of mathematics may lay bare formal similarities between diverse phenomena in potent mathematical analogies. But the British physicists did not long accept Fourier's positivistic refusal to seek causes underlying these laws. Rather, they came to believe that physicists should begin with experimental obser­ vation and mathematical analysis of the laws and then deduce hypotheses as to the causes. The British school thus adopted an approach diametrically opposed to that of the molecular theorists, seeking a "dynamical theory" in which all the forces or causes may be deduced from the laws governing the phenomena. The methods by which the British physicist deduced causes from laws helped him conceive the elements of his physical theory. Since similar mathematical formulations of two phenomena reveal "hidden analogies which unite them," he used the method of "physical analogy" to reason 2 The revolt by nineteenth-century British physicists against the established methodology of mechanics is examined in Robert H. Kargon, "Model and Analogy in Victorian Science: Maxwell's Critique of the French Physicists," J. Hist. Ideas, 30 (1969), 423-436.

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from aspects of the more familiar phenomenon to aspects of the less familiar. 3 Maxwell consciously proposed this method of physical analogy as an adjunct to mathematical analysis; moreover, it underlay the diverse elastic solid and fluid models of Faraday's field that he devised following Thomson's demonstration of the mathematical equivalence of the laws of heat flow, fluid flow, elasticity, and electric and magnetic lines of force. 4 Thomson's method for seeking physical causes involved, too, the free creation of a mental image of the phenomenon followed by the construc­ tion of a mechanical model to demonstrate the "possibility" of the existence of that mental construct. 5 The British physicist after 1880 combined mathematical and physical analogy with mental imagery in his attempts to determine the mode of action of electromagnetic radiation, still finding it necessary to append to the theory a mechanical model that might help the audience comprehend such an action. Larmor appended such a model to his theory in order to gain reception, but, ironically, the model led some Continental physicists to mistake this first comprehensive theory of the nonmechanical aether for a mechanical theory during those early years of the twentieth century when the mechanical worldview was destined for oblivion. In this paper, I will discuss the interplay between experimentation and mathematical laws, physical analogy and mental images, and metaphysics and working models in the development of the new theory of aether and its elaboration into an electromagnetic worldview. Among the questions I will treat are the following. How did the British school arrive at the notion, which was essential for Larmor's 1893 synthesis, that the atom emits radiation in pulses and only when stable electron orbits of minimum total energy are violently disturbed? How did Larmor's speculations about aether and matter lead the British physicist to a new definition of "matter in motion through the aether," one which did not involve aether drags and 3 J. Fourier, Analytical Theory of Heat, trans. Alexander Freeman (Cambridge, 1878), pp. 7-8. Quoted by Kargon, ibid., p. 428. 4 Through his concern for the method of physical analogies, "Maxwell offered the scientific community a methodological pluralism rare in its history"; he offered a union of mathematical and physical thinking that stimulated the succeeding genera­ tion of British physicists, which included J. J. Thomson, R. T. Glazebrook, Larmor, Oliver Lodge, and Ernest Rutherford, and that underlay their contributions to modern physics. (Kargon, op. cit. [note 2], pp. 435-436.) 5 William Thomson, "Ether, Electricity and Ponderable Matter," Presidential Ad­ dress to the Institution of Electrical Engineers, January 1889; published for the first time in William Thomson, Mathematical and Physical Papers, 6 vols. (Cambridge, 1882-1911), 3, 485-511, 508.

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drifts? How, indeed, did the modern conception of the atom and the field arise out of this unique aether tradition in nineteenth-century British physics?

1. EARLY DEMECHANIZATION OF THE AETHER Although the mechanical worldview was not overthrown until the field notion had effected a superior synthesis, dissatisfaction with mechanical principles and attempts to find an alternative explanation for light and gravitation date from the earliest years of its success. Nonmechanical ideas arose out of the early polemics concerning atoms in a void, Cartesian fluids, and the Leibnizian force-plenum; new theories of force, powers, and matter found diverse expression in imponderable fluids, mechanical fluid aethers, and Boscovichian point-atoms. These seventeenth- and eighteenth-century speculations introduced concepts upon which the British physicists of the early and mid-nineteenth century consciously drew for their new conception of the nonmaterial aether and its relation to matter. What are some of those perplexing and discomforting problems and perspectives that lived on into the nineteenth century and that motivated the British physicist? Intellectual Heritage The field notion had its origins in attempts to render dynamic the con­ ception of nature. However, the desire to explain motion and change in a consistent physical theory was also the aim of the mechanical philosophy which the field replaced. 6 Atomists hoped to escape the implication of 6 Among the best interpretive studies and surveys of the conceptual development of the mechanical philosophy and the field metaphysic are: F. M. Cornford,Laws of Motion in Ancient Thought (Cambridge, 1951); K. Lasswitz 1 Geschichte der Atomistik, 2nd ed. (Leipzig, 1926); R. G. Collingwood, The Idea of Nature (Oxford, 1945); E. J. Dijksterhuis, The Mechanization of the World Picture, trans. C. Dikshoorn (Oxford, 1961); Alexandre Koyre, From the Closed World to the Infinite Universe (Baltimore, 1957); E. A. Burtt, The Metaphysical Foundations of Modern Science (Garden City, 1954); M. Mandelbaum, Philosophy, Science and Sense Perception (Baltimore, 1954); R. H. Kargon, Atomism in England from Hariot to Newton (Ox­ ford, 1966); A. J. Snow, Matter and Gravity in Newton's Physical Philosophy (Ox­ ford, 1926); A. Vartinian, Diderot and Descartes (Princeton, 1953); Mary B. Hesse, Forces and Fields (New York, 1959); Robert E. Schofield, Mechanism and Material­ ism: British Natural Philosophy in an Age of Reason (Princeton, 1970); P. M. Heimann and J. E. McGuire, "Newtonian Forces and Lockean Powers: Concepts of Matter in Eighteenth Century Thought," Historical Studies in the Physical Sciences, 3 (1971), 233-306; E. T. Whittaker, A History of the Theories of Aether and Elec­ tricity, 2 vols., revised and enlarged ed. (London, 1951 and 1953); Joseph Larmor,

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continuum theories such as Parmenides' theory and Zeno's paradox; namely, if substance is unchanging, then motion is impossible and the uni­ verse is static. In atomism, motion was made an external phenomenon, accidental to substance; atoms moved in the void according to the laws of mechanics, but they themselves were not changed. With atomism, one of the fundamental postulates of mechanical materialism was introduced: substance, the basic reality, consists of the immutable, permanent, homo­ geneous, and indivisible atoms of matter. The result was an absolute duality between substance and activity. From the question of how motion arises out of dead matter evolved the second, alternative postulate of the mechanical view; namely, the duality of force and matter. Without the postulate of force the mechanical view requires that God set the universe in, motion at the moment of creation, overcoming its otherwise passive and static nature. Descartes hoped to avoid the concept of force, and attempted to explain actions across a distance in terms of a material plenum, which he equated with extension and which involved the vortical motion of infinitely small parts; but he was not able to explain the phenomena. Newton, in his theory of gravita­ tion, introduced forces acting at a distance in addition to contact and impact as a possible explanation of certain motions. The natural philosopher had now to distinguish between passive, inert matter and the dynamic force that moves matter and to account for their interaction. He asked if force is a formless and immaterial reality, and if so, how it is capable of moving matter. Do the forces emanate from the hard material particles as in Newton's theory of matter? If so, does this mean that force inheres in matter, so that matter is a dynamic substance? Or is force itself a "material stuff" that acts upon ordinary matter by contact? Finding the hypothesis of action at a distance difficult, many natural philosophers tried to find a mechanical explanation for apparent distance action in terms of contact action. Material aethers, or all-pervading fluids Aether and Matter, subtitled "A Development of the Dynamical Relations of the Aether to Material Systems on the Basis of the Atomic Constitution of Matter: In­ cluding a Discussion of the Influence of the Earth's Motion on Optical Phenomena" (Cambridge, 1900); A. d'Abro, Decline of Mechanism (New Y ork, 1939), reprinted as The Rise of the New Physics—Its Mathematical and Physical Theories, 1 vol. in 2 (New York, 1952); Milic Capek, The Philosophic Impact of Contemporary Physics (Princeton, 1961); Max Jammer, Concepts of Space (Cambridge, Mass., 1954), Con­ cepts of Force: A Study in the Foundations of Dynamics (Cambridge, Mass., 1957), and Concepts of Mass in Classical and Modem Physics (Cambridge, Mass., 1961). Al­ though my study challenges crucial interpretive positions taken in some of the above studies (for example, see notes 14, 17, 18, 164, 212), their value as conceptual guides remains.

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capable of executing motions, were conceived to fill the space between planets and atoms so that action would be continuous. However, the only aethers consistent with a mechanical scheme had to have particles and the void to allow action by contact, and consequently they were not pervasive. Thus, in seeking to avoid action at a distance through the concept of a material aether, natural philosophers revived the original force-matter dualism. The problem of the cause of motion remained unsolved, but was relegated to the particles of aether. An infinite regress of aethers was the prospect so long as mechanical principles were forced upon the medium. Leibniz proposed an alternative to the mechanical philosophy that resolved the dualism. He argued that the basic substance is essentially dynamic rather than inert, that force is an intrinsic attribute of substance so that substance and activity are one. 7 Leibniz' proposal became the starting point of a philosophical tradition that both belonged to and sub­ verted the mechanical philosophy, and that touched the concerns of nineteenth-century British physicists. A summary of Leibniz' view of force and matter will be helpful in analyzing the many aspects of that tradition and how each contributed to the origins and consolidation of field theory. For Leibniz the logical difficulties of the dualistic view of force and matter were sufficient to demonstrate that it is not correct. He derived his concept of substance as "an intensive continuum of force" from the principle of unity, which any comprehensive view of nature must satisfy. 7 Major references supporting my interpretation of Leibniz include the following: Robert Latta's introduction and notes to Leibniz, The Monadology (Oxford, 1898); H. F. Rail, Der Leibnizsche Substanzbegriff mit besonderer Beziehung auf seine Entstehung und sein Verhaltnis zur Korperlehre (Leipzig, 1899); A. Hannequin, Essai critique sur I'Hypothese des Atomes dans la Science Contemporaine (Paris, 1899); J. Jalabert, La Theorie Leibnizienne de la Substance (Paris, 1947); M. Blondel 1 De vinculo Substantiali et de substantia composita apud Leibnitium (Paris, 1893); E. Wendt, Die Entwickelung der Leibnizischen Monadenlehre bis zum ]ahre 1695 (Berlin, 1885); G. Wernick, Der Begriff der Materie bei Leibniz in seiner Entwickelung und in seinen historischen Beziehungen (Jena, 1893); H. W. Carr,Leibniz (New York, 1960). Good sources for Leibniz'works are the translations by R. Latta, op. cit.; G. M. Duncan, The Philosophical Works of Leibniz (New Haven, 1908); and P. Costabel, Leibniz et la dynamique, Les Textes de 1692 (Paris, 1960). JosephAgassi, "Leibniz's Place in the History of Physics,"/. Hist. Ideas, 30 (1969), 331-344, notes the significance of Leibniz' ideas for modern physics and suggests that Leibnizian ideas might have influenced nineteenth-century elasticity theories, rather than non-Euclidean geometry, and through them Einstein's ideas of nonhomogeneous, anisotropic space. My study of British theories of the aether demon­ strates how Leibniz' new notion of substance provided the metaphysical foundations for the aether that became the modern conception of space long before Einstein's general theory of relativity.

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According to this principle, the whole of nature must be a continuum within which the parts exist not as quantitative units but as intensive units, or monads, indivisible from the whole. How can the whole and the parts be related such that each part "contains the whole within itself" and "includes an infinite manifold"? This relation is possible if "the whole stands not merely in a mechanical but in a dynamic relation to the part." The whole cannot be "merely other than the part, but in some way passes into it and expresses itself through it," and "the part must contain the whole in such a way that the whole might be unfolded entirely from it." Thus, substance must be force itself in order that both the parts and the whole have the "spontaneity or power of acting" naturally.8 Leibniz' universe is "at once continuous and not only infinitely divisible but infinitely divided, consisting of an infinity of real elements." How is this principle of continuity capable of effecting the changes that occur in the real world? It requires that both the smallest monad and the world monad, i.e., the substance pervading the whole universe, are a plenum, for only in a plenum can change affect every part and yet not disturb the continuity. The world monad is "not an extensive plenum of mass," as Descartes would have it, but "an intensive continuum of force" that can .

φ

·

9

give rise to extension.

Leibniz, then, gave a new meaning to the Aristotelian terminology of substance through his notion of the differentiation of the particles or atoms of matter out of the continuous plenum of force-substance. Every monad or substance consists of "force at once active and resistant." Every monad is a force-plenum, an entelechy or vis activa (primitive active force) combined indissolubly with materia prima or vis passiva (primitive passive force). Entelechy is "force or energy, activity of some kind, which is a potential activity, tending to realize itself, automatic and spontaneous, containing within itself the principle of its future condition." Materia prima is bare or "abstract matter," that which consists in passive resistance ("impenetrability or the need for space") and extension ("continuation through space, or continuous diffusion throughout a place").10 8 R. Latta, op. cit. (note 7), pp. 30-31; A. Hannequin, op. cit. (note 7), pp. 352357,376-387. 9 R. Latta, op. cit. (note 7), p. 40. 10 H. F. Rail, op. cit. (note 7), pp. 31-37; G. M. Duncan, "Review of Rail's Der Leibnizsche Substanzbegriff mit besonderer Beziehung auf seine Entstehung und sein Verhaltnis zur Kdrperlehre," Philosophical Rev., 10 (1902), 94-96; L. J. Russell, "Leibniz," Encyclopedia of Philosophy, ed. Paul Edwards, pp. 429-430; and R. Latta, op. cit. (note 7), pp. 93-97.

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Modifications of these primitive forces yield derived forces, both active and passive. Thus, the impenetrability of extended bodies is derived from the materia prima of monads; the inertia of extended bodies is derived from both the prime matter and the active force of monads; the energy of material bodies or vis viva is derived from primitive active force. A material body, therefore, is characterized by the combination of mass (impenetra­ bility and extension) and energy; it is materia secunda, secondary or derivative matter, since all the properties defining it are derived from the plenum of force-substance. 11 Leibniz' metaphysics attempted to reconcile the continuity of the primordial plenum with the discreteness of matter by conceiving of the atom as a structural modification of the force-substance. Only if the atom is a structure of the force-substance, he asserted, can the continuity of activity be guaranteed. The concept of substance as a continuous plenum of force provided an alternative explanation of motion to that of external contact of bodies in a void or of forces acting at a distance. A clear statement of Leibniz' vague metaphysical substance notion is important in itself for the history of the field concept, for the notion was undeniably the basis of a unified field

theory of matter. But Leibniz'

notion also inspired new theories of aether and force within the mechanical school and thereby contributed significantly, though indirectly, to the final demechanization of the aether. Furthermore, because the same phenomenon—magneto-optic rotation—that stimulated Thomson's new conception of material atoms and the aether also convinced him that Leibniz' plenum must replace atoms in a void, the question arises whether Leibniz' metaphysics contributed to Thomson's creation of the first scientific field theory of matter. Leibniz' correspondence with Clarke informed the scientific world of his alternatives to the Newtonian concepts of atoms in a void and forces act­ ing at a distance. 12 Although Leibniz admitted the reality of atoms, he insisted equally on the reality of a medium that is the locus of optical and gravitational action. In his fifth letter to Clarke, Leibniz noted that it is 11 Referencesin

note 10. Leibniz-Clarke debate centered on Leibniz' claim that Newton's mathemati­ cal theory of gravitational force was in contradiction with his mechanical conception of atoms and the void. H. G. Alexander, ed., The Leibniz-Clarke Correspondence (Manchester, 1955), includes a bibliography of several other published collections of the correspondence. See the study of the documents by A. Koyre and I. Bernard Cohen, "Newton and the Leibniz-Clarke Correspondence," Arch. Int. Hist. Sci., IS (1962),63-126. 12 The

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strange to simply state that "all bodies gravitate or attract according to their masses and distance." He believed that a physical explanation must be given for gravity; namely, that it "depends upon the medium."13 Granted that his notion of substance successfully reconciled the con­ tinuity of the force-plenum with the discontinuity of matter, the unity of the whole with the particularity of the atoms, could it also account for the phenomena of light and gravity? Leibniz never achieved a physical representation of either in terms of the medium, but he apparently sought it in the relation between the medium and matter. Like the nineteenthcentury British physicist, he was not satisfied with a mere mathematical description of the relations in nature and found the limiting conception of a continuous fluid a useful physical analogy for the activities of the nonmaterial force-plenum.14 It was only after the Leibniz-Clarke debate and Leibniz' death in 1716 that Newton groped for a physical explanation of gravitational action in his aether hypothesis.15 The aether of the 1717 second edition of Newton's Optics did not explain phenomena by contact action and thus was not mechanical in the sense of the first principle of mechanics. But it was mechanical in the sense of the second principle, for it incorporated forces acting between vanishingly small particles of passive matter to 13 Alexander,

ibid. demanded that Newton give Ά physical explanation of the gravitational force law. Furthermore, he correctly observed that for Newton to be consistent with his own principles, he would have to provide a mechanical explanation of force. See Snow, op. cit. (note 6), pp. 97-165, 225, et seq. Hesse, op. cit. (note 6), p. 163, and "Action at a Distance and Field Theory," Encyclopedia of Philosophy, ed. Paul Ed­ wards, 1, p. 11, concluded erroneously that Leibniz believed that all explanations must be mechanical and that the physical world is constituted entirely of matter in motion. I have shown that Leibniz' physics provided a consistent, nonmechanical ac­ count of force and matter. Yet, the erroneous interpretation of Leibniz as a confused mechanist has been propagated in most surveys of philosophy since the eighteenth century and is found also in Capek, op. cit. (note 6), p. 93; J. B. Stallo, The Con­ cepts and Theories of Modern Physics (New York, 1881); Russell, op. cit. (note 10), pp. 430 et seq., who confessed that Leibniz' physical conception is "difficult to understand," that "it does not seem that there is any way of making out Leibniz's view in detail," and that Leibniz had insisted that he was not properly understood. 15 Newfon iS first pronouncements on the aether occurred in Query 21 of his Optics or a Treatise of the Reflections, Refractions, Inflections & Colours of Light, 2nd ed. (London, 1717); see p. 325, where he assigned the attraction of gravitation to the pressure of an ambient medium. As Larmor observed, Newton's aether, ultimately given an active role in chemical, thermal, and electrical phenomena as well, affected his moving corpuscles of light "so as to adapt them for reflexion and transmission at equidistant intervals." Young and Fresnel got rid of "the extraneous machinery of corpuscles which Newton felt unable to avoid" by explaining how rectilinear propaga14 Leibniz

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explain gross properties of the aether. Newton emphasized that "aether" is different from "body" and proposed an aether which went beyond the "mechanical fluid aether" of the Cartesians. Newton once asserted that the gross properties of the aether are not like those of ordinary matter; the aether is "a substance in which bodies move and float without resistance and which therefore has no vis inertia, but acts by other laws than those that are mechanical," i.e., by laws other than those of contact action. 16 Rather, Newton based the action of the aether on repulsive forces between infinitesimal passive particles and thereby established this mode of action, its logical difficulties notwithstanding, as a viable concept for the mechanical explanation of chemical and electrical as well as gravitational actions of matter. But although Newton viewed force and space as categorically different from matter and sought to explain action at a distance by forces filling space and operating in space, the forces were "interstitial," repulsive forces between aether particles which retained the

tion depends on the shortness of the waves. Young's memoir, "On the Theory of Light and Colours," Phil. Trans. Roy. Soc., 92 (1802), 12-48, gives an account of "Newton's recorded pronouncements on the optical necessity of an aether." (Larmor, Aether and Matter, op. cit. [note 6], pp. 315-316.) On the changes made in the Queries of the Optics in the eighteenth century, see A. Koyre, "Etudes Newtoniennes. II-Les queries de IOptique," A rchs. Int. Hist. Sci., 14 (1960), 15-29; Henry Guerlac, "Francis Hauksbee, experimentateur au profit de Newton," ibid., 16 (1963), 113-128, and "Newton's Optical Ether," Notes and Records of the Royal Society, 22 (1967),45-57. !^Speculation in a draft letter to Leibniz, U. L. C. Add. 3965.17, fol. 257 r , quoted in J. E. McGuire, "Force, Active Principles and Newton's Invisible Realm," Atnbix, 15 (1968), 203, and cited in Heimann and McGuire, op. cit. (note 6), p. 244n. Forty years later, in Four Letters from Sir Isaac Newton to Doctor Bentley (London, 1756), p. 25, reprinted in Papers and Letters on Natural Philosophy and Related Documents, ed. I. Bernard Cohen (Cambridge, Mass., 1958), p. 302, Newton proposed that "some­ thing else, which is not material" may operate upon "inanimate brute Matter" in gravitational action. Quoted in A. R. Hall and M. B. Hall, "Newton's Theory of Mat­ ter," Isis, 51 (1960), 136-137. Hesse, op. cit. (note 14), p. 11, and Koyre, op. cit. (note 6), p. 209, observe that Newton's statement sounds like a statement of the field concept and accordingly credit Newton with its anticipation. Hall and Hall, ibid., pp. 136-144, argue that Newton actually filled the chasm between particles and forces acting at a distance with a nonphysical hypothesis, the Grand Sensorium, that created a bigger chasm, a leap to the First Cause, God. However, Heimann and McGuire, op. cit. (note 6), analyze the physics of Newton's aether, and suggest that Newton's aether was a "force aether" that was essentially different from matter and that acted by means of repulsive forces essentially different from the attractive forces of ordinary matter. Unlike the gravitational force, repulsive force is not proportional to the total quantity of matter, but increases in intensity with a decrease of particle size. See also notes 17 and 18.

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essential qualities of brute matter; namely, hardness, impenetrability, mobility, and inertia. 17 The problems of dualism and infinite regress remained. Nonetheless, Newton, by disregarding the infinitesimal aether particles and giving greater significance to the interstitial forces that act in void space, turned the attention of his followers to the medium of action. The eighteenth-century aether theories may be divided into mechanical fluid aethers, which attempt to explain gravitational phenomena in terms of both the aether particles and the forces between them, and force-aethers, which ignore the particles and seek the explanation of phenomena solely in terms of the forces or powers present in and emanating from them. In this way, Newton's force-aether fathered the imponderable fluid aethers of light, electricity, and heat; and it is not surprising that Boscovich, inspired by Leibniz' force-continuum, attempted to reduce Newton's interparticulate aethereal forces to "a single, monolithic repulsive force." 18 Boscovich and Kant attempted to reconcile Newton and Leibniz in con­ ceptions which, though they distorted Leibniz' essential meaning, regarded space as a continuum of force. Boscovich's reconciliation was to dematerialize the Newtonian atom and introduce point-centers of force that 17 Heimann and McGuire, ibid., pp. 245-246. On pp. 242-246, Heimann and McGuire argue that the difference between the repulsive force of the aether particles and the gravitational force is sufficient to make Newton's force aether free of the problem of infinite regress: the repulsive nonmechanical action of the aether particles gives rise to the differential density and elasticity of the aether that explains gravita­ tion. However, I believe that the remaining dualism between the matter-like aether particle and the interstitial force tied his aether theory to the regress dilemma. New­ ton's near escape from regress and material aether properties was completed when a number of eighteenth-century thinkers transformed the "active principle" of the repulsive interstitial force into an "active substance" that had no need for aether particles from which to emanate ( i b i d . ) . 18 Heimann and McGuire, ibid., p. 242, asserted on the basis of their liberal inter­ pretation of Newton's force aether that Newton himself sought such a monolithic force and was "never seriously troubled" by action at a distance. Here I disagree again, and again because Newton never discarded the aether particles and, more im­ portant, always insisted that they are no different in essential qualities than particles of brute matter. Nonetheless, Heimann and McGuire have penetrated to the core of eighteenth-century aether theories and their connections with the intellectual and philosophic thought of the period. This major contribution resolves the confusions between "active principles" and "forces," traces the transformation from "active principles"—powers which become manifest only when passive material entities are in specific relation to one another—into "active substances," or into "innate powers" that define the essence of an entity in terms of inherent activity, and demonstrates the conceptual relations and differences between the imponderable fluids and me­ chanical aethers (ibid., pp. 304-306).

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extend throughout space. 19 Although he retained Leibniz' conception of the continuous medium, he inverted Leibniz' fundamental postulate that matter, or mass, is derived from this force-medium and that the medium itself is the source or locus of force. Boscovich's was still an atomic theory with action at a distance, action emanated from the point-atoms, not the force-extensions, and was instantaneous. 20 Kant likewise made matter dynamic, but lost the Leibnizian notion that matter derives from force. Retaining Newton's concept of attractive forces acting at a distance, Kant introduced "enclosed" force-extensions; the atom of matter is neither a point nor an infinite extension, but a continuous, bound region of repul­ sive force. 21 Leibniz' idea that nature is dynamic and space a plenum of force also inspired Naturphilosophie. Schelling, influenced perhaps by Kant's metaphysic, supposed that nature exists as a basic polarity or tension of oppos­ ing forces filling space. But Schelling dematerialized or spiritualized repulsive force and substantialized attractive forces acting at a distance, arriving at a view akin to Leibniz'. 22 Schelling regarded the medium as filled with force or pure activity which realizes itself in finite matter; and he explained chemical, electrical, and mechanical activity in terms of the single underlying force. German Naturphilosophie, following Schelling, 19 Roger

Joseph Boscovich, A Theory of Natural Philosophy, trans. J. M. Child (Cambridge, 1966). Originally published 1763. 20 As Hesse observed, op. cit. (note 6), pp. 163-166, Boscovich's theory was a "philosophic justification for action at a distance." J. M. Child's "Introduction" in Boscovich, ibid., p. xiv, is explicit on the essential difference between Leibniz' and Boscovich's physical conceptions. Boscovich's theory was "totally different from the monads of Leibniz, which are true centres of force." ti Leibniz denies action at a dis­ tance; with Boscovich it is the fundamental characteristic of a material point." Thus, as J. B. Spencer demonstrated, Boscovich's force law, involving the interaction be­ tween point-atoms independent of the surrounding particles, was compatible with Faraday's view of gravity, which he allowed to be instantaneous, but not with Fara­ day's electromagnetic field ("Boscovich's Theory and Its Relation to Faraday's Re­ searches: An Analytic Approach," Arch. Hist. Exact Sci., 4 [1967], 184-202). 21 Hesse, op. cit. (note 6), pp. 170-180. L. Pearce Williams, Michael Faraday: A Biography (New York, 1965), pp. 60-62, and The Origins of Field Theory (New York, 1966), pp. 32-47. Kant's theory of action at a distance is developed inMetaphysische Anfangsgriinde der Naturwissenschaft (Riga, 1786; Leipzig, 1794), in Sammtliche Werke (Leipzig, 1839), pp. 5, 310, et seq. 22 Friedrich Wilhelm Joseph von Schelling, Ideen zu einer Philosophie der Natur (Leipzig, 1797); id, Von der Weltseele (Hamburg, 1798). In England, Ε. H. Coleridge independently transformed Kant's view into a similar conception of the essential polarity of the universe. See L. Pearce Williams, Michael Faraday, op. cit. (note 21), pp. 63-73.

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insisted that the activity of nature consists in the uniting of polar opposites, and explained all phenomena as a manifestation of the basic forces (Grundkrafte) under given conditions. Thus, polarity and the con­ vertibility of forces provided the essential mechanisms of change for the physical world. H. C. Oersted, by his own admission, was led in 1813 to envision the possibility of transforming electricity into magnetism "by the philosophical principle, that all phenomena are produced by the same original power." 23 Naturphilosophie expressed Leibniz' fundamental prop­ osition that nature's dynamism is innate in the force-plenum and that all particulars are aspects of one dynamic unity. The synthesizing program of Naturphilosophie was in part a response to the eighteenth-century proliferation of theories of subtle aethereal fluids to explain electricity, magnetism, heat, and gravity. There were other sources of synthesizing programs. By the middle of the eighteenth century, Franz Ulrich Theodor Aepinus had shown that electric atmospheres could be discarded and electric phenomena explained by forces acting at a dis­ tance. Joseph Priestley in 1767 speculated and Charles Augustin Coulomb in 1785 demonstrated that electrical attraction is subject to the same inverse square law of distance as gravitational attraction. 24 By 1777, Priestley conceived of attractive and repulsive forces together with exten­ sion as the essence of matter "in a substantive sense and not merely relationally or dispositionally as in seventeenth century thought," and he conceived of solidity and impenetrability not as essential properties of matter but as the result of powers or innate forces. 25 In Priestley's thought, the dualism between matter and force in the mechanical philosophy was transformed into a monism of dynamic force-matter in which action at a distance could become continuous action through forces extending across space. Through the work of Aepinus, Priestley, Coulomb, and others, action at a distance came to dominate electrical science. But the problem of multiple aethers or forces remained unsolved.

23 Oersted

described his discovery of electromagnetism in The Edinburgh Encyclo­ paedia (Edinburgh, 1830), reprinted in H. C. Oersted, Scientific Papers, 3 vols. (Co­ penhagen, 1922), pp. 356 et seq. See L. Pearce Williams, Origins, op. cit. (note 21), pp. 56-58, and Michael Faraday, op. cit. (note 21), pp. 137-140. 24 Franz Ulrich Theodor Aepinus, Tentamen Theoriae Electricitatis et Magnetismi (St. Petersburg, 1759). Joseph Priestley, The History and Present State of Electricity, with Original Experiments (London, 1767), p. 732. CharlesAugustin Coulomb, three memoirs in Mem. de.l'Acad. (1785), and four other memoirs presented to the Acad­ emy by 1789; reprinted in Collection de Memoires relatifs a la Physique (Paris, 1884). 25 Heimann and McGuire, op. cit. (note 6), pp. 268-275.

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Thomas Young's discovery of the interference of light in 1802 added another aether, one challenging both action at a distance and effluvial theories by giving credence to a new mode of transmission of action across a distance; namely, a step-by-step transmission by the undulatory motions of a medium. Building on the success of the wave theory of light, a wave theory of heat replaced the caloric theory during the second quarter of the nineteenth century. 26 Experiments on radiant heat by William Herschel, John Leslie, Macedonio Melloni, and others in the period 1800-1835 led to a widespread belief that light and heat are essentially the same phenomenon, that is, different manifestations of the same physical agent. Since the Young-Fresnel wave theory of light replaced the Newtonian particle theory between 1815 and 1830, the wave theory of heat was a logical development. Furthermore, the experiments of Rumford and Humphry Davy, which showed that heat lacks weight and can be generated without limit by mechanical processes such as friction, could be explained by the wave theory without a sharp break with the caloric theory. By first identifying caloric with aether, and then assuming that heat consists in the vibrations rather than the amount of this fluid, many of the explanations of the older theory could be preserved with only verbal modifications. In the early 1820's, Ampere attempted to explain electrodynamic actions by considering Fresnel's elastic solid luminiferous aether to be a combination of two electric effluvia, resurrecting the fluids and their innate powers. 27 But, having identified the electric and magnetic fluids with the luminiferous aether, Ampere easily incorporated the caloric fluid into his conception and ultimately developed the wave theory of heat in its most extensive form. 28 The electric fluids and caloric were not yet discarded, but were incorporated into the context of the luminiferous aether, the new foundation upon which theories of electromagnetic and 26 Stephen G. Brush, "The Wave Theory of Heat: A Forgotten Stage in the Transi­ tion from Caloric Theory to Thermodynamics," Brit. J. Hist. Sci., 5 (1970), 145-167. 27 Andri Marie Ampere, "Memoire sur la theorie mathematique des phenomenes electrodynamiques, uniquement deduite de l'experience," Mem. de I'Acad. (1822), reprinted in entirety in the second volume of Memoires sur Velectrodynamique, 2 vols. (Paris, 1885-1887). 28 Ampere, "Idees de M r Ampere sur la chaleur et sur la lumiere," Bibliotheque Universelle, Geneva, 49 (1832), 225-235. A subsequent article by Amperehadawider audience and associated his name with the theory: "Note sur la chaleur et sur la lumiere considerees comme resultant de mouvement vibratories," Annates de chimie et de physique, 58 (1835), 432-444; inBibliotheque Universelle, Geneva, 59 (1835), 26-37; English translation in Phil. Mag., ser. 3, 7 (1835), 342-349. See S. G. Brush, op. cit. (note 26), pp. 153-155.

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thermal phenomena would be based. The electric and magnetic effluvia were desubstantialized and considered actions in the luminiferous aether, a development which was to have an important early influence on Faraday's conception of the nature of electricity and magnetism. Similarly, the transition was easy from the concept of heat as motions of the luminif­ erous aether to the view that particles of matter in violent motion suffice to produce ordinary, nonradiant heat: the wave theory of heat inspired many of the early statements of the mechanical theory of heat between 1842 and 1850. But with the revival in 1848-1870 of the kinetic theory of gases and the associated conception of atoms in the void, the wave theory was eliminated from explanations of ordinary thermal properties of matter; and Maxwell's electromagnetic theory indicated that heat radia­ tion is a type of electromagnetic wave. By way of the wave theory of heat, the mechanical view of atoms in the void came to challenge the prevailing conception of the luminiferous aether. After 1870, the need to reconcile the wave theory of light and radiant heat with the kinetic theory of gases and ordinary thermodynamic phenomena stimulated speculation among British physicists regarding the nature of material particles and their mode of interaction with the aether. A rich intellectual heritage motivated the nineteenth-century physicist in his study of aether and matter; but what became a specifically British tradition in physics after midcentury drew especially upon two inde­ pendent, far-reaching investigations begun early in the second decade. The Cambridge school of physics, stimulated by the recent introduction of Leibniz' differentials at the University, 29 attempted to discern the nature of the optical aether. In London. Faraday, abhoring both action at a distance and aethereal fluids, began his probe of electric and magnetic force that led him to the notion of lines of strain or force existing in space devoid of matter. At issue were the nature of force, aether, and matter and the mode of transmission of action in the aether or space. Distorting the Elastic Solid Luminiferous Aether In their theories of the luminiferous aether, a number of nineteenthcentury British physicists broke completely with the tradition of particles and forces and established the conception of the aether as a continuous 29 F.

Cajori,y4 History of Mathematics (London, 1919), discusses the characteristics of Newton's fluxions and Leibniz' differentials on pp. 196-199, 205-209, and the introduction of the differential notation at Cambridge around 1820 on p. 272.1 dis­ cuss the influence of differentials on aether physics in the next section.

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entity ontologically different from ordinary matter. By midcentury, they had developed and debated alternative modes of representing its actions. The Iuminiferous aether theories later in the century sought a resolution of these problems in terms of the relation between a continuous aether and matter. A new tradition of physical speculation emerged from this con­ scious demechanization of the luminiferous aether, a tradition which was capable both of absorbing Faraday's lines of electric and magnetic force and of effecting a new conception of matter. The fundamental role played by the early theories of the luminiferous aether in the development from forces to the modern field concept has not been adequately acknowledged by historians of physics. 30 In his original speculations about the wave theory of light in 1800, Young recognized that the luminiferous aether would have to be a highly elastic substance. He reasoned that such elasticity in the pervading medium is possible since "the rapid transmission of the electrical shock shows that 30 In 1966, when I first undertook a study of the elastic solid luminiferous aether theories in a course at The Johns Hopkins University, many students were surprised to find that only one historical treatment of the British luminiferous aethers, exclud­ ing the many Maxwell studies, existed: Whittaker's two volume survey, op, cit. (note 6), which remains today an important and useful guide, perhaps because it was written in 1910 when the heritage of the nineteenth-century theories was still alive. It is even more surprising that today one can add only David Ball Wilson, The Recep­ tion of the Wave Theory of Light by Cambridge Physicists (1820-1850): A Case Study in the Nineteenth Century Mechanical Philosophy (Ph. D. dissertation, The Johns Hopkins University, 1968); id., "George Gabriel Stokes on Stellar Aberration and the Luminiferous Ether," Br. J. Hist. Sci., 6 (1972), 57-72; Geoffrey Cantor, "The Changing Role of Young's Ether," ibid., 5 (1970), 44-62; and Lloyd S. Swenson, The E thereat Aether: A History of the Michelson-Morley-Miller Aether-Drift Ex­ periments, 1880-1930 (Austin, 1972). In this paper, I will attempt to clarify the meaning of the British aether, to uncover the definitive characteristics of the aether theories obscured by nearly a century of scientifically and philosophically based mis­ conceptions, and to make this important era of physical thought more accessible to perceptive historical study. Specifically, I will examine the role of physical ideas and worldviews in the birth and early development of field theory and in its culmination in the electromagnetic view of nature—the history in large part of unique British conceptions of aether and matter. After 1880 the British tradition of the field acquired a broader base, both philosophic and geographic. British, French, and German scientists considered funda­ mental questions raised by Maxwell regarding dynamical explanation and the role of models in scientific explanation, contributing to the growing international preoccupa­ tion with scientific method and epistemology. Furthermore, the antimaterialist, neoidealist philosophic climate that spread throughout Europe undoubtedly con­ tributed to the proliferation of field theories of matter in Britain and the rise of the energetic worldview on the Continent. These broader currents must be treated in a separate study.

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the electric medium is possessed of an elasticity at least as great as is necessary to be supposed for the propagation of light." 31 At that date Young thought of the elasticity of the aether in terms of that of a fluid, using the analogy of waves in air and water to derive the principle of optical interference; thus, like Newton, he was unable to encompass polarization within the wave conception. To explain reflection and refrac­ tion, Young assumed further that the aether's density is greater in refract­ ing bodies than in a vacuum, whereas its elasticity is the same. 32 On the hypothesis of a fluid aether, he reasoned that aberration might be accounted for if the aether is able to pervade "all material bodies with little or no resistance," passing through the interstices of bodies "like the wind through a grove of trees." 33 Young considered the fluid aether different from ordinary fluids only in degree and concluded that an aether wind would blow over the earth's surface. That no such aether wind could be found experimentally decided later physicists against either a fluid aether or Young's explanation of aberration. Augustin Fresnel's explanation of diffraction in terms of the wave theory of light in 1816 gave further credibility to the existence of the luminiferous aether. 34 His discussion of the influence of the earth's motion on light modified Young's hypothesis somewhat; to insure that the laws of reflection and refraction are the same to first order approximation 31 Thomas Young, "Outlines of Experiments and Inquiries Respecting Sound and Light," Phil. Trans. Roy. Soc,, 90 (1800), 106-150. Whittaker, op. cit. (note 6), 1, 100-101. 32 Young, ibid. 33 Thomas Young, "Experiments and Calculations Relative to Physical Optics," Phil. Trans, Roy. Soc., 94 (1804), 1; reprinted in Miscellaneous Works of the Late Thomas Young, eds. George Peacock and John Leitch (London, 1855), 1, 188. Whittaker, op. cit. (note 6), 1, 108-109. 34 Augustin Fresnel, "Sur la diffraction de la lumiere,"Annates de Chimie, 2nd ser., 1 (1816), 239; reprinted in Oeuvres Completes d'Augustin Fresnel, ed. Henride Senarmont et al. (Paris, 1868), 1, 89-128. See also the supplement to the paper in Oeuvres, 1, 129-170. During the next two years, Fresnel developed these ideas further and presented them in a major memoir in 1818 to the French Academy for its prize competition on diffraction theories. The stronghold of the caloric theory and the emission theory of light, the Academy chose diffraction for the competition to stimu­ late research within the particle framework. Fresnel's calculations suggested to S. D. Poisson that a bright spot would exist at the center of the shadow of a circular screen. When this and other consequences were experimentally confirmed, Fresnel was awarded the prize, and the wave theory gained ascendance over the particle theory of light. The memoir was not published until 1826, however, because of a massive backlog ("Sur la diffraction de la Lumiere,"Mem de I'Acad., 5 [1826], 339; reprinted in Oeuvres, 1, 247-382).

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in a body in motion and at rest, Fresnel hypothesized that moving dielectrics carry along part of the aether—the excess density—in their interior. 35 Young's aether drift is compensated by this partial aether drag. 36 Fresnel discussed the problem in terms of motion relative to the stationary aether, or to that part of the aether which is impervioils to the mechanical motion of bodies through it and which consequently is not dragged. Although the bulk of his "fluid" aether was stationary, part of it was susceptible to mechanical motion, i.e., change of position in space and time. 37 Intrigued by the experiment of F. Arago and Fresnel in which light that was polarized in perpendicular planes showed no interference, Young in 1817-1818 suggested the "imperfect explanation" that light consists of 35 Augustin Fresnel, "Sur Tinfluence du mouvement terrestre dans quelques phenomenes d'optique," Annates de Chimie t 9 (1818), 57; reprinted in Oeuvres, ibid., 2, 627-636. See Whittaker, op. cit. (note 6), 1, 108-110. Fresnel's formula expressed the following relation: the absolute velocity of light in a moving body is equal to the velocity of light in the body at rest plus the velocity of the aether that is dragged by the moving body. The latter velocity is a function of the relative densities of the body and the aether. 36 In 1845, G. G. Stokes expressed Fresnel's theory in terms of aether drift: the ab­ solute velocity of light in a moving body is equal to the velocity of the body in the direction of propagation of light plus the velocity of light in the body at rest and minus the drift velocity of the aether within the body relative to the body. This drift velocity is the velocity of the body times the ratio of aether density to the density of the body; the last two terms represent the velocity of light relative to the body. Stokes challenged Fresnel's formula and proposed instead the hypothesis of total drag, according to which the moving matter pulls all the contained and surrounding aether with it. ("On the Aberration of Light," Phil. Mag., 3rd ser., 27 [1845], 9-15; re­ printed in Stokes, Mathematical and Physical Papers, 5 vols. [Cambridge, 18801905], 1, 134-140). See Wilson, "George Gabriel Stokes," op. cit. (note 30), p. 63n; Whittaker, op. cit. (note 6), 1, 110. 37 FresnePs formula was first experimentally confirmed in 1851 by H. Fizeauwho measured the displacement of interference fringes formed by light passing through a column of moving water ("Sur Ies hypotheses relatives a l'ether lumineux, et sur une experience qui parait demontrer que Ie movement des corps change la vitesse avec laquelle la lumiere se propage dans Ieur interieur," Comptes Rendus, 33 [1851], 349-354; translated in Ann. d. Phys., Erganzungsband, 3 [1853], 457; reprinted in Annates de Chimie, 57 [1859], 385). In other words, the change of phase produced by motion is null to the first order as predicted by Fresnel's formula. Albert A. Michelson and Edward W. Morley, "Influence of Motion of the Medium on the Velocity of Light," Am. J. Sci., 3rd ser., 31 (1886), 377-386, demonstrated that the change of phase is null even to the second order. Larmor argued on general principles based on thermodynamic exchanges of radiation that the laws of reflection and re­ fraction of moving bodies are the same to all orders as those for bodies at rest; the change of phase anticipated for moving matter does not occur at all. The distribution of energy and thus the concentrations of radiation transmitted by a unit of trans-

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transverse vibrations like undulations of a plucked cord.38 Fresnel recognized that this hypothesis both solved the problem of polarization for the wave theory and made untenable an elastic fluid aether in which the direction of vibration was parallel to the direction of propagation. He introduced into the luminiferous aether theory the concept of rigidity, a power that resisted distortion of shape and that gave rise to transverse vibrations; with conviction, he then set out to demonstrate that the results of geometrical optics could be obtained from the dynamics of this unique elastic solid medium.39 Young found the notion of a solid aether "per­ fectly appalling" and insisted in 1823 that it is yet "open for discussion" whether fluids

might be able to support transverse vibrations.40 For the

next twenty years, however, the concept of the luminiferous aether as an elastic solid dominated physical speculation. Fresnel bequeathed to the study of the luminiferous aether both the concept of an elastic solid aether and the general method of dynamical justification. However, his elastic solid, devised to fulfill the requirements of optics, was not a true elastic solid, since it assumed that forces of restitution depend on absolute displacements rather than relative displace­ ments or strains.41 The mathematical theory of the propagation of waves

parent matter must be the same whether the matter is at rest or in motion, for other­ wise the equilibrium of radiation would be vitiated (Joseph Larmor, "A Dynamical Theory of the Electric and Luminiferous Medium, Part I ,"Phil. Trans. Roy. Soc., 185 [1894], 719-822, on p. 775; reprinted in Joseph Larmor, Mathematical and Physical Papers [Cambridge, 1927-1929], 2 vols., 1, 414-535, on p. 477. Whittaker, op. cit. [note 6], 1, llln). Larmor further emphasized that the invariance to all orders of the amount of radiation transmitted from a body at rest or in motion is further proof that Fresnel's law does not express aether drifts or aether drags. Rather, what was thought to be a first order compensation for aether drift via aether drag is a "unilateral change of effective elasticity somehow produced by the motion through the quiescent medium of the vortices constituting matter." (Larmor, ibid.) Larmor's development of the first correct second order transformation equations is analyzed in detail in Doran, Sir Joseph Larmor, op. cit. (note 1), pp. 486-492, and in summary form in Section III.3 below. 38 Letter from Young to F. Arago, 12 Jan. 1817, and letter from Young to Arago, 29 April 1818, in Young, Works, op, cit. (note 33), 1, 380 et seq. 39 Augustin Fresnel, "Sur Ie calcul des teintes que la polarisation developpe dans Ies lames cristallisees," Annates de Chimie, 17 (1821), 180; reprinted in Oeuvres, op. cit. (note 34), 1, 609-653, 629. See Whittaker, op. cit. (note 6), 1, 115 et seq. 40 Thomas Young, "Theoretical Investigations Intended to Illustrate thePhenomena of Polarization: Being an Addition Made by Dr. Young to M. Arago's 'Treatise on the Polarization of Light,'" in Works, op. cit. (note 33), 1, 415-417. Quoted by Wilson, "George Gabriel Stokes," op. cit. (note 30), p. 57. 41 Whittaker, op. cit. (note 6), 1, 119.

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in ordinary elastic solids originated only in 1821, when C. L. Navier con­ sidered the elastic solid to be composed of point-centers of force. 42 Cauchy avoided all molecular hypotheses in his first study of elastic solids in 1828, but later based his analysis of crystalline bodies on particles and forces. 43 The first application of the theory of ordinary elastic solids to the optical aether was Cauchy's 1830 study of crystal optics. 44 In Cauchy's work particles and forces replaced contiguous action as the mechanism of wave propagation in an elastic solid aether. Cauchy's approach was similar to Fresnel's, but he replaced Fresnel's quasi-elastic solid with a true one. Taking the differential equations of motion of an ordinary elastic solid to be the equations of the propagation of light, and making initial assumptions about whether the vibrations constituting light are parallel or at right angles to the plane of polarization and whether or not the aether is equally dense in all material bodies, Cauchy tried to deduce the principles of optics. 45 He invariably found that the boundary conditions that yield the optical laws are not those of an ordinary elastic solid; he thus dealt with types of elasticity not en­ countered in ordinary matter and a set of elastic constants difficult to explain physically. He could give no justification for either the initial assumptions or the unusual conclusions about the nature of the aether that entered his first and second theories of reflection in 1830 and 1836, respectively. 46 Cauchy had been unable to justify or account for the laws of optics using the dynamics of an ordinary elastic solid. Did this mean that a new method of dynamical justification was needed, or perhaps that the luminiferous aether was not an ordinary elastic solid? During the next few years British physicists raised both questions and gave an affirmative answer to each. 42 Claude

L. Navier, "Sur Ies Iois de l'equilibre et du mouvement des corps solides elastiques," Mem. de I'Acad., 7 (1827), 375; presented 14 May 1821. It must be noted that the "forces" in Navier's analysis are mathematically very different from New­ tonian forces. Forces in an elastic body are manifest as stresses and strains subject to the constraints of the body. Whereas a Newtonian force is a vector with three com­ ponents, stresses and strains act on a surface element through a point and constitute mathematically a so-called tensor with either six or nine components. I am indebted to Solomon Bochner for this distinction. 43 Augustin Louis Cauchy, Exercises de Mathematiques (Paris, 1828), 3, 160. 44 Augustin Louis Cauchy, "Memoire sur la theorie de la Iumiere," Mem. de I'Acad., 10 (1830), 293-316. 45 Whittaker, op. cit. (note 6), 1, 133-138. 46 Cauchy, op. cit. (note 44). See also "Notes de M. Cauchy sur l'optique,"Comptes Rendus, 2 (1836), 341-349.

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In 1837, the Dublin physicist James MacCullagh used the converse of the Fresnel-Cauchy procedure in his theory of reflection and refraction; he began with the principles of optics and sought by essentially geometrical reasoning the equations of motion for a medium in which Fresnel's formulas of reflection hold. 47 He could not, however, escape from making initial assumptions similar to Cauchy's, although he chose the assumptions for their agreement with the requirement of continuity. Criticizing Cauchy's second theory because it did not guarantee continuity of the displacement at the interface between two media, MacCullagh and Franz Neumann, who constructed a similar theory at the same time, 48 chose the assumption of his former theory that the vibrations are parallel to the plane of polarization. 49 The type of elasticity that MacCullagh's optics described likewise contradicted that of an ordinary elastic solid, and MacCullagh had no more justification than Cauchy for his elastic constants. He admitted that "the constitution of this [highly elastic] aether, and the laws of its connexion (if it has any connexion) with the particles of bodies, are utterly unknown. The peculiar mechanism of light is a secret which we have not yet been able to penetrate . . . but perhaps something might be

47 James MacCullagh, "Short Account of Some Recent Investigations Concerning the Laws of Reflexion and Refraction at the Surface of Crystals," Brit. Assoc. Rep. (1835), p. 37; "On the Laws of Crystalline Reflexion," Phil. Mag., 10 (1837), 42-45; "On the Laws of Crystalline Reflexion and Refraction," Proc. Roy. Irish Acad., 18 (1837). Larmor observed in 1893-1894 that MacCullagh's insight was essentially geometrical and that the substance of his theory was provided by the experiments of Brewster and Seebeck on the polarization of light by a crystal. MacCullagh's "simple geometric theorems" stand in stark contrast with the complex analytical solutions of F. Neumann and G. R. Kirchoff (Joseph Larmor, "Abstract, A Dynamical Theory of the Electric and Luminiferous Medium," Proc. Roy. Soc., 54 [1893], 438-461; re­ printed in Larmor, Papers, op. cit. [note 37], 389-413, on p. 393. Id., op. cit. [note 37], on p. 424.) 48 F. E. Neumann had arrived at the same principles from the basis of an elastic solid aether, but, as Larmor later demonstrated, Neumann's reasoning was invalid, "so that the solution as stated by him might be considered to be the result of a fortu­ nate accident" (Larmor, "The Action of Magnetism on Light; with a Critical Correla­ tion of the Various Theories of Light-Propagation," Report of the Brit. Assoc. [1893], 335-372; reprinted in Larmor 1 Papers, op, cit. [note 37], 1, 310-355, on pp. 348353; id., op. cit. [note 47], on pp. 392-394',id., op. cit. [note 37], on pp. 421-422). F. E. Neumann, "Theoretische Untersuchung der Gesetze, nach welchen das Licht an der Grenze zweier vollkommen durchsichtigen Medien reflectirt und gebrochen wird," Abhandlungen Berlin Akademie aus dem Jahre 1835, Math. Klasse (1837), pp. 1-160. 49 Whittaker, op. cit. (note 6), 1, 138.

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done by pursuing a contrary course; by taking these laws for granted and endeavouring to proceed upwards from them to higher principles." 50 In the same year, 1837, the Cambridge mathematical physicist George Green presented a theory of reflection that was at once a regression and a radical innovation in the physics of the aether. Considering the aether to be an ordinary elastic solid, Green determined by general dynamical principles the correct boundary conditions for ordinary bodies, but ob­ tained formulas of reflection disagreeing with Fresnel's. 51 MacCullagh concluded that Green irrefutably demonstrated that the luminiferous aether is not an ordinary elastic solid. 52 But in the process Green had introduced into optical theory a particular type of dynamical justification, a new method by which the physicist might prove that the peculiar elastic properties required by optical phenomena are conformable to dynamical laws. His method was to establish the potential energy function of Lagrange on which the action of the medium depends and then to derive the laws of optics directly from it. In 1839 MacCullagh was completely successful in accounting for Fresnel's laws by Green's pure dynamical method. 53 Green's theory of reflection also inspired Cauchy's third theory of re­ flection in 1839, which assumed negative compressibility to make the velocity of longitudinal vibrations vanish; 54 this theory was the contractile

50 MacCullagh, "On the Laws of Crystalline Reflexion and Refraction," op. cit. (note 47). Quoted in Larmor, op. cit. (note 37), p. 425. 51 George Green, "Memoir on Ordinary Refraction," Trans. Camb. Phil. Soc., 7 (1838), 1, 113 (read 11 December 1837); reprinted in The Mathematical Papers of the Late George Green, ed. Ν. M. Ferrers (London, 1871), p. 245. See also George Green, "On the Propagation of Light in Crystallized Media," Trans. Camb. Phil. Soc., 7 (1839), read 20 May 1839; reprinted in Green, Papers, p. 293. Larmor observed in 1893 that Green "made a magnificent failure of his attempt to explain optical phenomena" on the basis of an ordinary elastic solid (Larmor, op. cit. [note 47], pp. 394-395). 52 James MacCullagh, "An Essay Towards a Dynamical Theory of Crystalline Re­ flexion and Refraction," Trans. Roy. Irish Acad., 21 (1840), read 9 December 1839; reprinted in The Collected Works of James MacCullagh, eds. John H. Jellet and SamuelHaughton (Dublin, 1880), p. 145. 53 Ibid. 54 Augustin Louis Cauchy, "Memoire sur la polarisation des rayons reflechis ou refractes par la surface de separation de deux corps isophanes et transparents," Comptes Rendus, 9 (1839), 676-691 (read 25 November 1839); and "Note sur Ies milieux dans lesquels un rayon simple peut etre completement polarise par reflexion," ibid., 9 (1839), 726-730 (read 2 December 1839).

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or labile aether theory that Thomson corrected and expanded in the 1880's.55 But Green's greatest contribution was his new general principle for dynamical justification, which Maxwell, Thomson, Helmholtz, FitzGerald, and Larmor all made productive use of. In MacCullagh's dynamical theory, the elasticity of the aether and thus the potential energy do not depend on distortion or compression, as the elasticity and potential energy of ordinary matter do, but only on the absolute rotational displacements of its elements by strain from their equilibrium position. The resulting strain vector has a meaning inde­ pendent of any system of axes to which the motion is referred. From the equations of the energy of this "rotationally elastic aether," MacCullagh then deduced "in natural and easy sequence, without a hitch, or any forc­ ing of constants, all the known laws of propagation and reflexion for transparent isotropic and crystalline media.56 The boundary conditions that he derived from purely dynamical analysis are, as he was fully aware, different from those of an ordinary elastic solid. This method of dynamical justification apparently was not yet suf­ ficiently attractive to warrant acceptance by British physicists as late as 1862. In that year George Gabriel Stokes, the Lucasian Professor of Mathematics at Cambridge, objected that the vector representing the light disturbance in MacCullagh's analysis cannot possibly be the displacement in a medium with elasticity like that of an ordinary elastic solid. Stokes said that the vector is incompatible with the form deduced by Green "from the very same supposition of the perfect transversality of the transversal vibrations . . . [by] perfectly straightforward and irreproach­ able [reasoning] ." 57 He objected further that "MacCullagh's form leads to consequences absolutely at variance with dynamical principles," an objec­ tion which was based on the mistaken hypothesis that the potential energy in MacCullagh's equation is due entirely to the elasticity of simple de­ formation of the medium. Shortly thereafter Stokes recognized that a dynamical basis might be found for MacCullagh's theory by going beyond that hypothesis and considering perhaps that "a couple [proportional to 55 This assumption implies that no work is required to give the medium any small irrotational disturbance, so that one may specify the behavior of transverse waves at the interface without considering the irrotational part at all (William Thomson, "On the Reflection and Refraction of Light,"Phil. Mag., 26 [1888], 414-425, 500-501). 56 Larmor, op. cit. (note 37), pp. 425-426. 57 G. G. Stokes, "Report on Double Refraction," Brit. Assoc. Rep, (1862), pp. 253282-,reprinted in G. G. Stokes, Papers, op. cit. (note 36), 4, 157-202, 178.

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the element of surface] is supposed to act on each element to which there is no corresponding reacting couple."58 But as yet there was no known mechanical model that might illustrate the mode of action of the rotationally elastic aether. Because of these objections, the rotationally elastic aether was generally ignored—although it crucially influenced Rankine's theory of elasticity—until FitzGerald rediscovered it in 1878. Did Stokes actually believe that the luminiferous aether was equivalent to an ordinary elastic solid, or was his first objection merely that its elasticity with respect to the transmission of light must be like that of an ordinary elastic solid? I will demonstrate that the latter is the case, for Stokes twenty years previously had presented a theory of the luminiferous aether that accentuated the aether's distinct ontological status. With respect to his second objection, Stokes required a model only to enhance our understanding of the aethereal actions by proving that the conse­ quences are dynamically justified. Nonetheless, he based the dynamical justification ultimately on a deduction from the dynamics of the model rather than from the fundamental dynamical equation of least action. This method of justification introduced further confusion into the already overly complex physics of the aether; many physicists took the difference between the model and the aether to be one merely of degree rather than of kind.59 Stokes intended his aether to be completely different from matter in its nature and activities, with the exception of mechanical aether drag. Im­ pressed by Euler's mathematical theory of the "ideal" fluid—which re­ jected the molecular theory of fluids, considered the elements of a con­ tinuous body as mathematical points, and derived the equations of motion of this perfectly continuous fluid—Stokes proposed that the motion of "ordinary" fluids can be determined from the equations of an ideal fluid "without making any hypothesis as to the molecular constitution of fluids."60 He said that we can "calculate according to the hypothesis of perfect fluidity" some cases of ideal fluid motion that can be accurately compared with experimental observations of ordinary "imperfect" fluids, and thereby "estimate the extent to which the imperfect fluidity of fluids may modify the laws of their motion."61 Fluidity, thus, is not a macroS&Ibid., p. 197. "See, for instance, notes 197 and 212 and Larmor's position in III.4 below. 60 G. G. Stokes, "On Some Cases of Fluid Motion," Trans. Camb. Phil. Soc., 8 (1843), 105 (read 29 May 1843); reprinted in Stokes, Papers, op. cit. (note 36), 1, 17-68, 18. 61 Ibid.

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scopic effect of constituent particles, but a condition that attains perfect expression only in a perfectly continuous substance and is defined by the equations of the ideal fluid. Likewise, Stokes reasoned, an "ideal" continuous solid medium perfectly expresses the essential properties or conditions of solid bodies, notably their elasticity. 62 He accordingly set forth the mathematics of an ideal continuous solid parallel to Euler's hydrodynamic field equations. Again he looked to experimental evidence to demonstrate how actual solid bodies deviate from the perfect elasticity of the ideal continuous solid. Although Stokes always interpreted the equations applicable to fluid and solid matter in terms of the particles constituting them, he consciously avoided a molecular hypothesis in explaining the elasticity involved in the transmission of light through the aether: "It is easy to imagine that the relative displacement of the particles of the ether may be so small as not to reach, nor even come near to the greatest relative displacement which could exist without the molecules of the medium assuming new positions of equilibrium, or, to keep clear of the idea of molecules, without the medium assuming a new arrangement which might be permanent" (italics added). 63 Stokes dissociated the luminiferous aether from ordinary matter, allowing it the privileged status of a perfectly continuous substance. The continuity of the aether, which constituted its difference from ordinary matter, was in turn essential to Stokes's solution to a major problem facing an elastic solid theory of light. The problem was to explain how a single medium can resist attempts to distort its shape and yet allow the easy motion of the planets through it. This apparent contradiction led many, among them James Challis, the Plumian Professor of Astronomy at Cambridge, to postulate hydrodynamical theories of a fluid aether. 64 But it made Stokes doubt Fresnel's hypothesis that the aether offers no resistance to the moving planets and reject the idea of the aether as an ordinary fluid. Convinced by experiment that a body moving through a viscous fluid entails enough friction to pull part of the surrounding fluid with it, 65 Stokes argued on theoretical grounds and from the principle of continuity that elasticity defined as "the tangential force called into action by a displacement of continuous sliding" may be present to some 62 G. G. Stokes, "On the Theories of the Internal Friction of Fluids in Motion and of the Equilibrium and Motion of Elastic Solids," Trans. Camb. Phil. Soc., 8 (1849), 287 (read 14 April 1845); reprinted in Stokes,Papers, op. cit. (note 36) 1, 75-129. 63 Ibid., p. 127. 64 Wilson, "George Gabriel Stokes," op. cit. (note 30), pp. 60-71. 65 Ibid., pp. 61-62.

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degree in all substances, so that "there seems no line of demarcation be­ tween a solid and a viscous fluid."66

The ideal continuous solid and the

ideal continuous fluid may indeed be one ideal continuous substance in which viscosity and elasticity attain their perfect form. Thus, the property of elasticity of the type required for the transmission of light may be "quite insensible in ordinary cases of fluid motion." Stokes concluded that the luminiferous aether may be such a medium, acting like an elastic solid regarding the small vibrations constituting light and like a viscous fluid regarding translational motions of material bodies through it. 67 Three years later he compared this solid-fluid aether to a glue-water jelly, the first of the "working models" that for two generations would play a significant role in the creation and explication of the British aether theories. 68 Stokes's hesitancy to hypothesize a particulate aether was undoubtedly related to the classical difficulties of infinite regress and force-matter dualism. Further, by attributing elasticity and viscosity to the aether with­ out interpreting them as macroscopic effects of microscopic particles in motion, Stokes's theory suggested that these properties are ultimate, irreducible characteristics of the aether. Here indeed was his greatest contribution to the British tradition of the aether: the conception of the aether as a continuous substance ontologically different from matter, and the related conception of the transmission of strain through a continuous medium as a possible alternative to the conceptions of a step-by-step transmission along a chain of material particles and the transmission of force across a distance. The debate over the nature of the aether intensified in the British school during the decade after 1845. Is the aether represented by Fresnel's quasielastic solid, or Cauchy's ordinary elastic solid, or Challis's fluid, or Stokes's continuous medium having both solid and fluid properties? Central to the debate was the possibility of a continuous medium and continuous transmission of action. In this connection, the question of the nature of the "continuity" described by differentials once again attracted the attention of mathematicians and physicists. W. R. Hamilton and Augustin DeMorgan's polemics over the existence of finite differential 66 Stokes,

op. cit. (note 62), p. 126. p. 127. 6 8 G. G. Stokes, "On the Constitution of the Luminiferous Ether, Viewed with Reference to the Phenomenon of the Aberration of Light," Phil. Mag., 29 (1846), 6-10; reprinted in Stokes,Papers, op. cit. (note 36), 1, 153-156. 6 7 Ibid.,

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limits reflected a serious concern with the possibility of a truly continuous medium and its representation by the differential and integral calculus.69 Furthermore, many physicists, most notably Maxwell, attempted to ex­ plain continuous transmission in terms of the limiting case of a chain of material particles, an analogy which led Continental physicists and later historians erroneously to conclude that the British aether was molecular.70 To be sure, many physicists in Britain, such as S. Tolver Preston, Osborne Reynolds, and J. J. Thomson, retained the mechanical concep­ tion of a particulate aether acting according to contact action.71 But the conception that dominated the second half of the century and matured in the 1880's was that of a continuous aether which is different from matter and within which action is transmitted by a redistribution of strain, not of parts, throughout the whole. It was on the question of continuous versus discontinuous action that physicists in the 1820's first found grounds for conceptually comparing the theories of the luminiferous aether and con­ temporaneous discoveries in electromagnetics. Faraday, Maxwell, and William Thomson each attempted to determine whether the "ideal fluids" and "quasi-elastic solids" of optics might account as well for electricity, 69 See Robert Graves, Life of Sir William Rowan Hamilton (Dublin, 1882-1889), 3, 571-575. Henri Poincare, Hermann Weyl, and Ernst Cassirer later called continuity a "disguised discontinuity" since it is mathematically a process of infinite divisibility. See Capek, op. cit. (note 6), pp. 316, 331. Thus, even the differential analysis of the aether is amenable to atomistic interpretation, another ground for historical con­ fusion. But to the British physicist, the continuity of the aether was unequivocally real. 70 See, for example, note 212. 71 On Preston, see note 162. Theories of mechanical, corpuscular aethers were still current in the twentieth century. As late as 1902 Osborne Reynolds claimed to have "revealed the prime cause of the physical properties of matter" in an analysis "so contrary to previous conceptions as to entail an inversion of ideas hitherto advanced," by which he meant ideas that had made the structure of the universe "approximate to empty space." Noting that this nonmaterial concept of the structure of the universe had prevailed "for the last hundred years," Reynolds then presented his alternative conception of the aether: the aether is a concrete, mechanical "arrangement, of in­ definite extent, of uniform spherical grains generally in normal piling so close that the grains cannot change their neighbors, although continually in relative motion with each other; the grains being of changeless shape and size; thus constituting to a first approximation, an elastic medium with six axes of elasticity symmetrically placed." (Osborne Reynolds, On an Inversion of Ideas as to the Structure of the Universe [Cambridge, 1902]; also published as the third volume of his Collected Scientific Papers [Cambridge, 1903] under the title Sub-Mechanics of the Universe; quotations on pp. 3-5, 15.) Reynolds' theory was a reversion to a strict mechanical materialism in which distance actions are to be explained by continuous mechanical contact action.

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magnetism, magneto-optics, and spectral radiation. Two distinct pathways to understanding aether and matter were taken, one ultimately helping to clarify the mode of action of a continuous electromagnetic and optical aether, the other accelerating the movement towards a new conception of matter and the relation between aether and matter. In the 1880's these pathways joined: the new conception of the aether was found superior to the mechanical postulates of atoms in a void and forces between particles in explaining electric, magnetic, and optic phenomena involving the inter­ actions of aether and matter, and the resulting synthesis into the electro­ magnetic view of nature completed the revolution prompted in part by the early demechanization of the luminiferous aether. Faraday, Thomson, and the Electromagnetic Aether In Faraday's theory of electromagnetism, as Larmor observed in 1900, "the modern theory of the aether obtained a start from the electric As professor of engineering at Owens College, Reynolds was one of the earliest of J. J. Thomson's mentors. Thomson also required a mechanical, particulate aether, even after 1903 when he attempted a "field theory of matter." The "mechanical mo­ mentum" in the aether that gave rise to mass was in fact mechanical; it was the "kinetic energy" of moving aether in tubes of force. He was insistent that in his bound-aether theory of matter, the potential energy of the visible universe is actually "the kinetic energy of portions of the [invisible] aether attached to the system"; the "invisible" aether thus provided the "hidden masses" and "hidden motions" required for his unquestionably mechanical theory. (Presidential Address, Sect. A, British As­ sociation for Advancement of Science, 78 [1909], 16-20, especially p. 20.) In 1910 he admitted that his use of "the conception of tubes of electric force for representing the state of the electric field" requires that "the electric field is made up of a number of discrete units," "the electric field itself, as well as the electric charges in it, being molecular in constitution." ("On a Theory of the Structure of the Electric Field and its Application to Roentgen Radiation and to Light,"Phil. Mag., 6th ser., 19 [1910], 301-313, 302.) Thomson always called the electric charge a "corpuscle," identifying it as the true atom and emphasizing its rigidity and immutability in analogy with Newton's corpuscle. To J. J. Thomson, matter and the aether consisted of hard mechanical particles. See, for example, his article "Matter" in Encyclopaedia Britannica (1904), pp. 891-895, and his Presidential Address to the British Association (this note), pp. 16-17. Robert Andrews Millikan, The Electron (Chicago, 1966), pp. 221222, 229, has suggested that Einstein's equation for light quanta "was designed to be the symbolic expression" of Thomson's hypothesis of the fibrous aether, but that Ein­ stein later gave it up because it was "found so untenable." However, it is more likely that Einstein's equation was merely the "symbolic expression" of Thomson's experi­ mental observations on the absorption and emission of electromagnetic radiation by electrons. See Doran, Contributions of British Physics, op. cit. {note 1), pp. 135-140; see also pp. 27-60 for the fate of the aether in the first decades of the twentieth cen­ tury. Id., Sir Joseph Larmor, op. cit. (note 1), Chapter 19, analyzes Einstein's concep­ tion of a continuous nonmaterial field plenum and its relation to material particles.

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side." 72 His experimental studies of electricity and magnetism led Faraday after 1845 away from contiguous particles and forces acting at a distance to the hypothesis that space devoid of matter is capable of physical action, But this transformation to the modern field concept did not occur solely in one man's mind; nor did Faraday initiate it. Indeed, shortly after Faraday's thoughts on matter and force first began to take form circa 1844, he entered into an interchange of ideas with Thomson that guided him to the field concept. By 1848 Faraday had turned to the British notion of a nonmaterial continuous aether, drawing upon it for clues and in turn enriching the store of knowledge about the nature and functions of that aether. In this section I will reevaluate the changes in Faraday's posi­ tion regarding the aether between 1820 and 1855. 73 It is my thesis that Faraday's notion of the field, which he first enunciated in 1852, was inspired in part by the idea, which was already deeply rooted in the Thomson-Stokes Cambridge circle, that the luminiferous aether is a unique physical entity different from matter in essence and activity. Furthermore, I will show that Thomson had arrived at the field concept by 1850 based on Faraday's experiments and his own mathematical-physical conceptual­ ization of the lines of force. Between June 1847 and June 1850, Thomson communicated to Faraday both verbally and in writing the various notions going into that concept, thus stimulating Faraday's conversion to the "field" of electromagnetic action and the new British conception of the aether. Faraday's thought on the luminiferous aether began with his earliest speculations on electricity and magnetism and ran the gamut of interpre­ tations regarding its nature. In his opposition to Ampere's theory of electrodynamics during the early 1820's, Faraday wrestled with the notion that Fresnel's undulating medium is a combination of two electric effluvia mutually saturating one another. 74 At that date Faraday already ques7 ^J. Larraor, "The Methods of Mathematical Physics," Address to the Mathematical and Physical Section of the British Association (Bradford, 1900); reprinted in Larmor,Papers, op. cit. (note 37), 2, 193-216, on p. 207. 73 It is in part because Faraday scholars have not been aware of the extent to which the luminiferous aether had been demechanized in Britain by midcentury that they have had difficulty distinguishing between that which was original with Faraday and that which was part of a general movement. Williams'Michael Faraday, op. cit. (note 21) is a case in point. The radical change that occurred in Faraday's views on the aether between 1845 and 1848 also has not been appreciated. Thus, Williams'judg­ ment, ibid., pp. 454-457, and Origins, op. cit. (note 21), pp. 113-115, 131-137, is open to question; I offer a reinterpretation here. 74 Williams, Michael Faraday, op. cit. (note 21), pp. 140-157, 164-175, 197-202.

FIELD THEORY IN 19A-CENTURY BRITAIN

tioned "the materiality of electricity" and "the existence of any current through the wire," suggesting that "the cause which is active within the connecting wire" may be instead "the induction of a particular state of its parts." 75 His search for this "electrotonic" state, or state of strain, by passing polarized light through an electrolytic solution was spurred by his desire to find an alternative to the effluvial aether. Although it is possible that the Naturphilosophie conception of a web of conflicting forces manifesting themselves as various physical conditions may have influenced Faraday's notion of a state of strain, 76 he nonetheless identified Oersted's "conflicting forces" of electricity and magnetism with the two fluid theory that he hoped to replace by strains. Faraday's discovery that same year of circular forces in electromagnetic rotation challenged his notion of strain by seeming to require that the electric current be a movement rather than a static arrangement of par­ ticles. Within a few years, however, Faraday found in another conception of the luminiferous aether an analogy that comprehended motion and arrangement as a single phenomenon and that did not demand the transfer of matter. From 1827 to 1829 he studied Fresnel's nonmathematical account of the undulatory theory of light. 77 The luminiferous aether, no longer burdened with Ampere's effluvia, was now in Faraday's mind a medium composed of contiguous particles that transmit vibrations in the same way as strings, rods, and air. After assimilating John Herschel's 1830 treatise on natural philosophy, which stressed the analogy between sound

75 Zbid.,

p. 154. Williams, Origins, op. cit. (note 21), pp. 32-63, summarizes possible in­ fluences of Naturphilosophie on electromagnetism, which he documents in Michael Faraday, op. cit. (note 21), pp. 53-94. As Williams admits in the preface to Origins, his view is not widely accepted. See, for instance, T. S. Kuhn, review of Williams' Michael Faraday, in Br. J. Phil. Sci., 18 (1967), 148-154; Robert Siegfried, "Boscovich and Davy: Some Cautionary Remarks," Isis, 58 (1967), 236-238, who sees Davy's ponderable atoms as inconsistent with both Naturphilosophie and Boscovich's theory; Τ. H. Levere, "Faraday, Matter and Natural Theology—Reflections on an Un­ published Manuscript," Br. J. Hist. Sci., 4 (1968), 95-107, who juxtaposes Davy's "adolescent enthusiasms" for idealist Naturphilosophie around 1800 with his revul­ sion to it around 1808. D. M. Knight, "Steps Towards a Dynamical Chemistry," Ambix, 14 (1967), 179-197, especially pp. 181-182, agrees with Williams on the role of Naturphilosophie in Davy's chemistry but observes that it was not necessary for Davy to think of chemical processes in terms of forces. Levere, ibid., pp. 95-96, makes the same observation. 77 FresnePs "Elementary View of the Undulatory Theory of Light" appeared in a series of articles in the Quarterly Journal of Science between 1827 and 1829 (Williams, Michael Faraday, op. cit. [note 21], pp. 176-177). rj6 Ibid.

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and light vibrations, Faraday successfully explained a number of acous­ tical phenomena in terms of the surrounding medium, experimentally varying the medium to further test the analogy. 78 It is not clear whether the theory of optical transmission stimulated his view of acoustical trans­ mission through the medium or whether it was the other way around. At any rate, he immediately took the analogy one further step and set up an experiment in which he might detect a wave in electric and magnetic action: in this experiment Faraday discovered that a current can be induced by an electromagnet, proving the inverse of Oersted's phe­ nomenon. The elastic solid theory of the luminiferous aether that led Faraday to view the medium as the locus of action also suggested to him that that medium is particulate. The aether had become in his mind's eye a medium that transmits force or motion between its subtle particles. During the 1830's, Faraday expanded his theory of electricity to include such an aether; he transferred the locus of electric and magnetic action from the charges and magnetic poles to lines of force in the medium, and explained the action as the ordering of a chain of contiguous polarized particles of the medium." In a defense of the effluvial theory of electricity in 1839, Robert Hare accused Faraday of harboring action at a distance between his contiguous particles and noted the absurd conclusion to which the matter-and-void hypothesis must lead Faraday's electric theory: empty space must act as both a conductor and a nonconductor. 80 Thus, the old force-matter dualism threatened to undermine Faraday's view of action in the medium. In January 1844, following five years of silence couched as positivist un­ concern, Faraday announced that Boscovich's hypothesis of point-centers of force extending throughout space offered a solution to Hare's dilemma: he would resolve the force-matter dualism with a monism of force-atoms. 81 " js Ibid., pp. 178-181. J. F. W. Herschel, A Preliminary Discourse on the Study of Natural Philosophy (London, 1830). 79 Williams, Michael Faraday, op. cit. (note 21), pp. 274-319; id., Origins, op. cit. (note 21), pp. 76-91. 80 Robert Hare, Professor of Chemistry at the University of Pennsylvania, argued that Faraday's action was still action at a distance in a letter of January 1839; pub­ lished in Phil. Mag., 17 (1840), 44; reprinted in Faraday's Experimental Researches in Electricity, 3 vols. (London, 1839-1855), 2, 251-261. Faraday responded on 14 April 1840, offering no solution (ibid., pp. 262-274). 81 Michael Faraday, "Speculation Touching Electric Conduction and the Nature of Matter," a letter of 25 January 1844 to Richard Taylor, published in Phil. Mag., 24 (1844), 136-144; reprinted in Faraday, op. cit. (note 80), 2, 284-293.

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Although Faraday had been exposed to Boscovich's theory through Davy, he apparently was not aware of the specifics of that theory or of the peculiar meaning Boscovich had given his force-atoms.82 In fact, Faraday discussed Boscovich's theory in the terminology of the eighteenth-century British philosophical tradition in which Newtonian forces acquired Lockean powers as part of their essence.83 The interparticulate forces of that tradition and Boscovich's monism merged to form Faraday's view that matter fills all space: "Matter will be continuous" throughout all space so that "in considering a mass of it we have not to suppose a distinction between its atoms and any intervening space."84 Yet Faraday's conception was never a consistent or true Boscovichianism: Faraday opposed Boscovich's central tenet of action at a distance. In addition, Faraday's own experimental researches gradually led him to the inescapable conclusion that the medium is different from matter in both its nature and its activities, forcing him to discard the monism of the Boscovichian view as well as to search for a new conception of the nature and mode of action of the medium. Within two years after his statement on Boscovich's theory, Faraday had dismissed the concept of the discon­ tinuous aether, whether composed of Boscovich's atoms or particles of ordinary ponderable matter. This turning point occurred in 1845 when Thomson's fertile physical and mathematical imagination made its first mark on Faraday's conception of the aether.

82 Williams, in his two studies, op. cit. (note 21), and R. H. Kargon, in "William Rowan Hamilton, Michael Faraday and the Revival of Boscovichian Atomism," A m, J. Phys., 32 (1964), 792-795, have demonstrated Faraday's familiarity with Boscovich's views and his use of them for his own ends. Siegfried, op. cit. (note 76), and Spencer, op. cit. (note 20), have emphasized that Faraday misinterpreted Boscovich's views. The historical and analytical studies disagree; Faraday adopted what he thought was Boscovich's view only to transform it shortly to meet the needs of his developing conception. 83 Heimann and McGuire, op. cit. (note 6), pp. 304-306, observe that Faraday dis­ cussed Boscovich's theory within a significant tradition of eighteenth-century British natural philosophy. That tradition rejected "the fundamental principles of late seven­ teenth-century natural philosophy—the primary and secondary qualities distinction and Newton's notion of essential qualities, the connection of unobservables to observables," and it established the doctrine that "the essence of matter is constituted by powers." P. M. Heimann, "Faraday's Theories of Matter and Electricity," Br. J. Hist. Sci., 5 (1971), 235-257, examines Faraday's "Speculation" in detail and shows that Faraday's views contained only those aspects of Boscovich's theory that Priestley had incorporated in his Disquisitions Relating to Matter and Spirit (Birmingham, 1777). He thus shows that the distinguishing features of the "Speculation" derive from a "native British tradition [of forces] exemplified by Priestley." 84 Faraday, op. cit. (note 81), pp. 289-291.

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In 1841, at the age of eighteen and "inoculated with Faraday fire," 85 Thomson published under the name P.Q.R. a mathematical demonstration that the formulas of electricity deduced from the laws of action at a distance are identical with the formulas of heat distribution deduced from the ideas of action between contiguous particles. 86 Although Thomson first conceived this analogy when pondering the problem of Faraday's curved lines of force and was now convinced by it that Faraday's view of action in the medium must be taken seriously, he did not note this pos­ sible implication of Faraday's theory of electricity in this paper. But thereafter all of his thoughts about Faraday's theory were guided by the view that a medium may have a conducting power for lines of electric force just as it has a conducting power for stream lines of heat flow. 87 By January 1845, Thomson had discovered Green's physico-geometrical notion of a potential function and immediately used it to demonstrate that Coulomb's electrical action at a distance and Faraday's notion of action by contiguous particles in the intervening medium lead to the same mathematical theory. 88 In June 1845, Thomson met Faraday for the first 85 Silvanus P. Thompson, The Life of William Thomson, Baron Kelvin of Largs, 2 vols. (London, 1910), 1, 19. s6 Ibid., p. 42. Thomson frequently noted that Fourier had had the greatest in­ fluence on his thought (ibid., 1, 13-20). See also Whittaker, op. cit. (note 6), 1, 130. Thomson's paper was "On the Uniform Motion of Heat in Homogeneous Solid Bodies, and Its Connection with the Mathematical Theory of Electricity," Camb. Math., /., 3 (1842); reprinted in Phil. Mag., 7 (1854), and in William Thomson, Re­ print of Papers on Electrostatics and Magnetism (London, 1872), pp. 1-14. 87 Thompson, op. cit. (note 85), 1, 143-144, 210-216. ss Ibid., 1, 134. The potential function was crucial in the development of an alterna­ tive to action at a distance. It was a mathematical apparatus that applied to both continuous media and Newtonian discrete mass points, making possible a conception of continuous action encompassing all branches of mechanics. With the potential function, the mechanical worldview became inappropriate even for Newtonian me­ chanics. In a personal communication, Salomon Bochner explained succinctly how the potential function explains forces between mass points in terms of continuous ac­ tion: "In a so-called conservative system—and a gravitational system, without 'fric­ tion, 1 always is conservative—the components of the resultant force acting on a mass point are partial derivatives of their 'potential,' which is a scalar function. It has level surfaces, on which the potential function has the same value, and lines of force which intersect the level surfaces perpendicularly. Now, one of these lines of force goes through our mass point on which the forces act, and our mass point moves along this line of force from surfaces of higher level to those of lower level. Thus the mass point is being pushed by a continuous push, as if by 'immediate' contact, from one level of the potential to the 'immediately' lower one. Thus the behavior of the potential function in the immediate vicinity of a point brings about the motion of the point from this position to the immediately neighboring one." Bochner also observed that potential functions were already fully introduced by Poisson in electrostatics and magnetostatics in 1811-1812 under the French appelation "une expression."

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time at the British Association meeting at Cambridge, where Thomson presented a paper demonstrating this equivalence and suggesting experi­ ments that might reveal something of the nature of the relation between light, electricity, and magnetism. 89 Faraday discussed the paper with Thomson and a month later initiated a correspondence that would change the direction of his experimental researches and both his and Thomson's thoughts on the nature of action in the medium. Faraday wrote to Thomson asking him to explain a mathematical memoir by Avogadro that incorporated Faraday's curved lines of inductive action. 90 In his reply, after summarizing Avogadro's physical hypothesis, mathematical formulation, and calculated results, Thomson discussed his own attempt to determine mathematically Faraday's curved lines of induc­ tion. He explained his geometrical model and noted that he had first been able "to perceive the relation which the lines of inductive action have to the mathematical theory" from the mathematical theory of heat. 91 This letter, dated 6 August 1845, would have been a valuable historical docu­ ment even had it ended at that point, for it was Faraday's first introduc­ tion to the analogy with heat and the mathematician's geometricization of lines of heat flow. Faraday adopted that analogy and formulation in late 1848 and by 1850 had transformed it into the field conception of lines of force in empty space independent of any magnet, conductor, or dielectric. But Thomson went on to ask Faraday whether experiments had been made on three specific actions that the theory predicted and that must be clarified before a complete mathematical theory of electricity and magnetism could be formulated. 92 The question regarding the third action, that of a transparent dielectric on polarized light, evoked a series of ex­ periments by Faraday that uncovered many new phenomena. One in particular—the action of magnetism on polarized light 93 —appeared to depend less on the action of a chain of polarized particles than on the polarization of the chain or line of force as a whole. In the action of magnetism on light, a magnetic field rotates the plane of polarization of light passing through certain transparent substances. The s 9 Ibid.,

1, 145. 1 Michael Faraday, op. cit. (note 21), p. 383. 91 Ibid., pp. 383-385. Thomson's letter to Faraday is printed in full in Thompson, op. cit. (note 85), 1, 146-149. 92 This part of Thomson's letter is also quoted in Williams, Michael Faraday, op. cit. (note 21), p. 383. 93 Williams' discussion of this problem is superb (ibid., pp. 386-394). See also id., Origins, op. cit. (note 21), pp. 92-97. 90 Williaras

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direction of rotation depends only and in an absolute sense upon the direction of the magnetic lines of force, not at all upon the direction of the incoming polarized ray; the rotation of the ray will change only if the polarity of the electromagnet is reversed. The power of rotating polarized light is directly proportional to the intensity of the magnetic force. Al­ though Faraday recognized that the polarity here is not that of the particles of the dielectric but of the entire line of magnetic force and the ray of light, he had not yet dissociated the lines of force from matter. He interpreted the phenomenon as indicating a "new magnetic condition" in the transparent substance; he called the "new magnetic force or mode of action of matter" "diamagnetism."94 When he found that gases do not act upon polarized light in a magnetic field and that a decrease in the number of gas particles by rarefaction has no effect on magnetic action, he dis­ missed as nonsense the implication that "mere space" has magnetic prop­ erties and retained his notion that diamagnetism is "a specific action antithetically distinct from ordinary magnetic action." 95 By 1846, Faraday had used the conception of a continuous polarized curve of force as an argument against the need for a particulate aether to transmit optical force. In his "Thoughts on Ray-Vibrations," he attempted to replace waves in a material aether with vibrations in the lines of force as the mode of propagation of light.96 Since 1839, Faraday could not accept a particulate aether because of the force-matter dualism it entailed. He now reasoned that perhaps the conception of continuous lines of force can account equally well for the luminiferous vibrations, so that no hypothesis need be made about the transmission of light by aether particles. Faraday summarized the difference between the aether hypothesis and his alterna­ tive force conception: forces replace the molecular aether as the pervading medium, forming a true plenum, and continuous lines of force replace contiguous particles in effecting the activities in the medium. He wrote: "The aether is assumed as pervading all bodies as well as space: in the view now set forth, it is the forces of the atomic centres which pervade (and 94 Michael Faraday, "Nineteenth Series. On the Magnetization of Light and the Il­ lumination of Magnetic Lines of Force," Phil. Trans. Roy. Soc., 136 (1846), 1-20; re­ printed in Faraday, op. cit. (note 80), 3, 1-26, on p. 21. ' 5 Michael Faraday, "Twenty-first Series. On New Magnetic Actions, and on the Magnetic Condition of all Matter—Continued," Phil. Trans. Roy. Soe., 136 (1846), 41-62; reprinted in Faraday, op. cit. (note 80), 3, 54-82, on p. 77. Williams, Michael Faraday, op. cit. (note 21), p. 395. 96 Michael Faraday, "Thoughts on Ray-vibrations,"Phil. Mag., 28 (1846); reprinted in Faraday, op. cit. (note 80), 3, 447-452, especially pp. 449-450.

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make) all bodies, and also penetrate all space. As regards space, the difference is, that the aether presents successive parts or centres of action, and the present supposition only lines of action." 91 Faraday had com­ pletely "dismissed the [particulate] aether," whether considered as com­ posed of subtle material particles or Boscovichian point-centers of action. The medium penetrating all space was a continuum of force-extension: the point-atoms now existed for Faraday only in matter and defined its essence. With his lines of force capable of existing within the interior of matter and between its particles, and his force-plenum devoid of any particulate connotation, Faraday had a conception of a medium that might replace that of the particulate luminiferous aether. Inverting Boscovich's essential meaning, Faraday here explicitly required that the force-extensions filling space act by means of the lines connecting the force-atoms of material bodies: "As regards matter, the difference is, that the aether lies between the particles and so carries on the vibrations, whilst as respects the supposition, it is by the lines of force between the centres of the particles that the vibration is continued." 98 Faraday dismissed the particulate aether, but not the vibrations it ex­ plained. Experimental philosophy, he asserted, can imagine "various kinds of lines of force . . . partaking of a dynamic character . . . [such as] a shake or lateral vibration." 99 Here, then, was Faraday's alternative to transmission by aether particles: "The occurrence of a change at one end of a line of force easily suggests a consequent change at the other. The propagation of light, and therefore probably of all radiant action, occupies time; and, that a vibration of the line of force should account for the

phaenomena of radiation, it is necessary that such vibration should occupy time also." 100 Faraday wondered if "such a lateral disturbance" of the lines of force would "require time or .. . of necessity be felt instantly at the other end." He speculated further that gravitation might also require time for its transmission and be a disturbance of the lines of force. 101 While Faraday was immersed in his thoughts on a continuous forceplenum and action across time and space by the vibration of continuous lines of force, Thomson was expanding his earlier comparison of the dis­ tribution of electrostatic force with the distribution of heat flow in 91 Ibid.,

pp. 450-451. pp. 451-452. 99 Ibid., p. 449-450. 100 Ibid., p. 451. i 0 i Ibid. 9 %Ibid.,

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homogeneous solid bodies.102

171 Then, in November 1846, Thomson

presented a new physical analogy; he examined mathematically the "sug­ gestion" of Faraday's researches that "there may be a problem in the theory of elastic solids corresponding to every problem connected with [electric, magnetic, and galvanic forces] ." 103 He represented the electric force as a state of distortion resulting from the "absolute displacement of a particle, in any part of the solid," and the magnetic force as an angular displacement as indicated by Faraday's experiments in magneto-optic rotation. In June 1847, Thomson discussed the paper with Faraday at the Royal Institution and immediately sent him a copy, explaining that Faraday's magneto-optic rotation experiment had stimulated his attempt to explain electric and magnetic forces in terms of the physical theory that currently encompassed optical phenomena.104 Thomson's analogy for the propagation of electric and magnetic forces by means of strains in an elastic solid was a conscious first step towards a synthesis of the optical aether and Faraday's forces. During the summer of 1847 Thomson was also working with Stokes on "various interesting pieces . . . connected with some problems in electricity, fluid motion, etc., that I have been thinking on for years."105 Immersed in the problems of electricity, fluid motion, the elasticity of solids, and Stokes's solid-fluid continuous aether, Thomson met with Faraday in Tuly at the British Association meeting held at Oxford.106 This meeting was an occasion for continued discussion of ideas of mutual interest. The summer of 1847 was a turning point in both Thomson's and Faraday's developing conceptions, and I believe that a significant exchange of ideas occurred that provided the new direction for each. Thomson was enthusiastic about the analogy of Faraday's electric and magnetic forces with elastic displacement when he gave Faraday the paper in June. It is possible that, at the July meeting or soon after, 102 Thomson,

op. cit. (note 86). Thomson, "On a Mechanical Representation of Electric, Magnetic and Galvanic Forces," Camb. and Dublin Math. J,, 2 (1847); reprinted in Thomson, Papers, op. cit. (note 5), 1, 76-80. 104 Letter from Thomson to Faraday, 11 June 1847 (Thompson, op. cit. [note 85), 1, 203-204). On 11 June, Thomson wrote his brother of his conversations with Faraday and plans to "see a good deal more of him at Oxford, and afterwards, as his lectures end tomorrow, he will have some time to spare" (ibid., 1, 202). On visits to London, Thomson "seldom failed to call at the Royal Institution to see Faraday in his laboratory, and discuss with him the latest investigations" (ibid., 1, 211-212). los Ibid., 1 204-205. Quotations from a letter to his father dated 20 June 1847. l06 Ibid., 1, 205, 211. 103 William

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Faraday informed Thomson of his own recent abandonment of the particulate elastic solid aether for a continuous medium, which squelched Thomson's enthusiasm to carry further the analogy with elastic displace­ ment based on action between aether particles; he did not returji to the analogy until 1889. This was Thomson's first struggle with the problem of representing continuous action that had troubled Faraday for almost a decade; the impact of that problem on Thomson's thought was profound. In a major study of magnetism dated June 1849, Thomson eagerly accepted the magnetic character of the "medium occupying space" before Faraday himself did and spoke of the magnetic force as an "imaginary" substance different from ordinary solids or fluids. Furthermore, Thomson attempted to explain optical phenomena by analogy with a fluid rather than a solid when he again addressed the question during the period 18671880. After his July 1847 meeting with Faraday, Thomson's preference for a continuous medium over a solid, particulate aether was as persistent as it was pervasive. I suggest also that Thomson informed Faraday of recent attempts to develop a conception of continuous transmission through the luminiferous aether. Specifically, he informed Faraday of Stokes's hypothesis that the aether need not be molecular to transmit light waves, and that the propaga­ tion of strain through an ideal elastic solid-fluid may be considered a mode of continuous transmission. That this exchange of ideas did occur at some time during the next several months is supported by the suddenness'with which Faraday made a complete about-face. By 1848, Faraday had de­ scribed the action of rays of light as an alternative to the action of contiguous particles, reversing his prior interpretation of the transmission of light. By 1850, he again had looked to the "aether" as a possible means for transmitting the electric and magnetic force, speaking of it then as a continuous fluid that transmits action in a manner analogous to a stretched spring. His studies of magneto-optics ultimately forced him to acknowledge that the lines of force are independent of the force-atoms and express actions occurring in the medium occupying space, returning him to the aether concept. The conceptual interaction between Faraday and Thomson through the former's discoveries in magneto-optics and the latter's new conception of continuous transmission in the nonmaterial luminiferous aether was crucial to the development of the modern field notion. I will here trace the main paths of that interaction. Faraday strove since 1845 to encompass the new phenomena he had discovered—the action of magnetism on polarized light and the dia-

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magnetic force—within a comprehensive theory of electric, magnetic, and optic forces and their relation to material bodies. On 31 August 1848 he discussed the nature of the two forces he postulated to explain magnetooptic rotation.107 The first, the diamagnetic force, was a "natural magnetooptic force" present in matter itself, existing even when neither light nor magnetic force is present. The second was an "optical force" induced by the magnetic field that rotated polarized light. Afterwards, in looking for currents that might be induced by the optic force, Faraday found instead the relation between a magnetic field and crystalline bodies. Continuing his earlier line of reasoning, Faraday concluded that crystals may have a new "magnecrystallic" force, "being the resultant of the action of all the molecules" and aligning itself along the magnetic lines of force.108 Unable to deny the "extraordinary character of the [magnecrystallic] force—not polar, for [there is] no attraction or repulsion"—Faraday noted two al­ ternative interpretations open to him: either polarity exists in the new force but is masked by other forces, or magnetic forces themselves are "like lines of gravitating force or rays of light," rather than like polar forces or "lines of contiguous acting particles."109 By September 1848 he had recognized that the transmission of light through the luminiferous aether is a continuous action and not an action communicated by con­ tiguous particles. That Thomson had some influence in making Faraday aware of this new conception of the aether is suggested by Faraday's reference in September 1848 to the analogy between light and heat that Thomson had made in 1842 and had reported to Faraday by letter on 6 August 1845. Indeed, Faraday now acknowledged that the notion that bodies may have varying power to conduct lines of magnetic force as well as heat and light may be the correct one: 1 cannot resist throwing forth another view of these phenomena which may possibly be the true one. The lines of magnetic force may perhaps be assumed as in some degree resembling the rays of light, heat, etc.; and 107 Faraday's Diary, Being the Various Philosophical Notes of Experimental Investi­ gation Made by Michael Faraday, D.C.L., F.F.S. During the Years 1820-1826 (London, 1932-1936), #9440-9443. Williams, Michael Faraday, op. cit. (note 21), pp. 414-416. los Ibid., pp. 416-419. Michael Faraday, "Twenty-second Series. On the Crystalline Polarity of Bismuth (and Other Bodies) and on Its Relation to the Magnetic Form of Force," Phil. Trans. Roy. Soc., 139 (1849), 1-45; reprinted in Faraday, op. cit. (note 80), 3, 83-136, on p. 90. 109 Faraday'sDiary, op, cit. (note 107), #9910-9919.

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may find difficulty in passing through bodies, and so be affected by them, as light is affected. They may, for instance, when a crystalline body is interposed, pass more freely, or with less disturbance, through it in the direction of the magnecrystallic axis than in other directions. In that case, the position which the crystal takes in the magnetic field with its magnecrystallic axis parallel to the lines of magnetic force, may be the position of no, or of least resistance; and therefore the position of rest and stable equilibrium.110 But before he could accept this new conception of lines of force and its implications for the magnetic nature of empty space, Faraday had to have proof that the magnecrystallic force was not polar and thus that polarity did not underlie the electric and magnetic forces of nature.111 He looked for but could not find evidences of polarity; yet, in early 1850 he still rejected the magnetic character of space. He said that the idea that lines of magnetic force exist in a vacuum "is difficult to comprehend according to the Ampere theory, . . . or with any other generally acknowledged, or even any proposed view or even any trial speculation that I am aware of."112 Thomson, however, had already asserted the magnetic nature of empty space in his major study of magnetism dated June 1849.113 He there observed that it was "convenient" to conceive of magnetic force as due to "attractions and repulsions mutually exerted between portions of an imaginary matter." It was convenient because the analogy enabled him to use the potential function of Laplace and Green in defining the "resultant magnetic force at any point in space," whether or not that point was occupied by magnetized matter. He stressed that the imaginary matter of the analogy "possesses none of the primary qualities of ordinary matter, and it would be wrong to call it either a solid, or the 'magnetic fluid' or 'fluids'" (italics added).114 He found no difficulty accepting the meaning of magnetic force in empty space, but he thought that "the resultant force at a point situated in space occupied by magnetized matter, is an expres­ sion the signification of which is somewhat arbitrary." He speculated that an "infinitely small" portion of the imaginary substance may be con110 Faraday, op. cit. (note 108), #2591, pp. 122, 123. Williams, Michael Faraday, op. cit. (note 21), pp. 436-438. l l l Ibid., pp. 420-435. 11 ^Ibid., p. 434. Faraday's Diary, op. cit, (note 107), #10834. 113 William Thomson, "Mathematical Theory of Magnetism," Abstract in Proc. Roy. Soc., June 1849 and June 1850; reprinted in entirety in Thomson, Papers on Electrostatics (note 86), pp. 340-405. 114 Ibid., pp. 361, 351-352.

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sidered removed without producing a "finite effect upon any point," so that the polarity of the real magnet determines the magnetic force at a point.115 In a footnote he alternatively suggested that the resultant force is always determined by the imaginary substance. In June 1850 he added another note in which he chose the latter definition because of "some subsequent investigations of the comparison of common magnets and electro-magnets." 116 Thus, by June 1850 Thomson had concluded that the magnetic substance determines the total force in the magnet, and that the magnetic action lies in the imaginary matter and not in the ordinary matter. In June 1849 Thomson wrote Faraday in support of diamagnetic forces, placing them within the framework of his own ideas of magnetic force: "After our conversation today I have been thinking again on the subject of a bar of diamagnetic non-crystalline substance, in a field of magnetic force which is naturally uniform, and I believe I can now show you that your views lead to the conclusion I had arrived at otherwise, that such a bar, capable of turning round an axis, would be set stably with its length along the lines of force." 117 Fearing that he "may not have another opportunity of seeing [Faraday] again before [he] left town," Thomson decided to "continue" their "conversation by writing a few lines on the subject." In this letter, dated 19 June 1849, Thomson diagrammed "a field of force naturally uniform, but influenced by the presence of a ball of diamagnetic substance," and he discussed the difference between diamagnetic sub­ stances and iron in terms of their "conducting power" or ability to conduct lines of magnetic force. 118 Thomson thus provided Faraday with a pictorial representation of lines of force in terms of Thomson's mathe­ matical conception of a field. After further meetings through early July, Thomson sent Faraday a letter suggesting experiments that might provide more data on the nature of the magnetic force and its conduction by matter.

119

During the next three years, Faraday gradually assimilated Thomson's view of lines of magnetic force and the aether into his own conception of force. In the summer of 1850 he finally accepted what he had been unwill­ ing to in 1845 and still questioned as "difficult to comprehend" only a lisIbid.,

pp. 360-362. p. 362. n7 Thompson, op. cit. (note 85), 1, 214-216. Letter dated 19 June 1849. l l s I b i d . , i , 215. 1 1 9 Ibid., 1, 216-218. Letter dated 24 July 1849. ll6Ibid.,

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few months previously; namely, that the magnetic lines of force exist in empty space: "It seems manifest that the lines of magnetic force can traverse pure space, just as gravitating force does, and as static electrical forces do; and therefore space has a magnetic relation of its own, and one that we shall probably find hereafter to be of the utmost importance in natural phaenomena" (italics added). Furthermore, the magnetism of space is fundamentally different from the magnetism of matter: But this character of space is not of the same kind as that which, in relation to matter, we endeavour to express by the terms magnetic and diamagnetic. To confuse them together would be to confound space with matter, and to trouble all the conceptions by which we endeavour to understand and work out a progressively clearer view of the mode of action and the laws of natural forces. It would be as if, in gravitation or electrical forces . . . one were to confound the particles acting on each other with the space across which they are acting, and would, I think, shut the door to advancement. Mere space cannot act as matter acts. . . . 120 Thus, not only are matter and space different in nature or character, but space also "comports itself independently of matter, and after another manner. > , 1 2 1 In the following year, 1851, Faraday found that the lines of force do not end on the poles of the magnet and do not move with the magnet. He thus finally recognized that the lines of force not only can exist in empty space but exist only in space and are independent of the magnet. In October, while speculating on how magnetic force is transmitted, he discarded the possibility of action at a distance: "How the magnetic force is transferred through bodies or through space we know not:—whether the result is merely action at a distance, as in the case of gravity; or by some inter­ mediate agency, as in the case of light, heat, the electric current, and (as I believe) static electric action. . . . I am more inclined to the notion that in the transmission of the force there is such an action, external to the magnet, than that the effects are merely attraction and repulsion at a distance." His view of magnetic and electric action demanded an interven­ ing medium which he thought might be the luminiferous aether: "Such 120 Michael Faraday, "Twenty-fifth Series. On the Magnetic and Diamagnetic Con­ dition of Bodies,"Phil. Trans. Roy. Soc., 141 (1851), 7-28; reprinted in Faraday, op. cit. (note 80), 3, 169-199, on p. 194. l ^ l Ibid., on p. 195.

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an action may be a function of the aether; for it is not at all unlikely that, if there be an aether, it should have other uses than simply the conveyance of radiations." 122 This aether was the continuous force-plenum within which action is transmitted continuously. Faraday, like Thomson at this stage, chose to think of the aether as a fluid rather than a solid, since Stokes had shown that an ideal fluid may have the elasticity required for the transmission of light. In an unpublished manuscript entitled "The Hypothetical Ether," Faraday asked several questions about the nature of the aether. 123 Is it a homogeneous fluid as optics appears to demand? Mathematically speaking, can a homogeneous fluid support lateral vibra­ tions more easily than direct ones? What, indeed, in the continuous aether accounts for transmission? He asked: "If a stretched spring represents by its lateral vibrations the ether and its vibrations—what is there in the ether that represents the strong cohesion in the line of the spring particles on which however the lateral vibration(s) essentially depend?" Having acknowledged that the continuous aether is fundamental to electromagnetic science, Faraday in June 1852 finally made the transition to the field concept. In asserting "the physical character of the lines of magnetic force," he asserted the reality of the lines of force in empty space. The magnetism of matter depends essentially and totally on the surrounding space void of matter: I conceive that when a magnet is in free space, there is such a medium (magnetically speaking) around it. . . . What that surrounding magnetic medium, deprived of all material substance, may be, I cannot tell, per­ haps the aether. [Italics added.] I incline to consider this outer medium as essential to the magnet. 124 The relation between bodies externally appears to me to be through the space around the magnet. . . . The magnet could not exist without a 122 Michael

Faraday, "Twenty-eighth Series. On Lines of Magnetic Force; their Definite Character; and their Distribution within a Magnet and through Space," Phil. Trans. Roy. Soc., 142 (1852), 1-56; reprinted in Faraday, op. cit. (note 80), 3, 328-370, on pp. 330-331. 123 Michael Faraday, "The Hypothetical Ether," unpublished manuscript, contained in the eighth folio volume of the manuscript copy of Faraday's Diary at the Royal Institution. Reproduced in entirety in Williams, Michael Faraday, op. cit. (note 21), pp. 455-456. I completely invert Williams'interpretation of Faraday's note. Faraday was not scorning the aether but seeking, together with his British colleagues, new modes of representing transmission through the continuous aether plenum. 124 Michael Faraday, "On the Physical Character of the Lines of Magnetic Force," Phil. Mag., 3 (1852), 401-427; reprinted in Faraday, op. cit. (note 80), 3, 407-437, on p. 425.

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surrounding medium or space, and would be extinguished, if the space be occupied adversely by the dual power of a dominant magnet of suffi­ cient force.125 Faraday de'/ised four criteria for the physical reality of the lines of force: they must be modified by the presence of matter, exhibit a limited capa­ bility of action, be propagated in time, and be independent of the body on which they Urminate.126 These criteria would guide Maxwell's mathematization of Faraday's conception. In summation, the modern concept of the magnetic field was largely created by Thomson. Indeed, it was not until late 1850 that Faraday adopted Thomson's early notion of magnetic conductibility and acknowl­ edged the magnetic nature of empty space. By June 1850 Thomson had already gone beyond that notion to argue that the magnetic action lies completely in the force-field pervading empty space and not within matter. Only in 1852 did Faraday reach essentially the same position; he recog­ nized that the medium is essential to the action of the magnet and that all of the energy of the magnet lies in the field of force or, as Thomson and Faraday both called it, the aether. The complete dichotomy between Fsraday's pre- and post-1850 conceptions—his 1846 dismissal of the aether and his return to it a few years later—is explained in terms of his rich interaction with Thomson after 1845. Faraday's lines of force and the luminiferous aether entered Thomson's mathematical analysis of a mag­ netic field of force, from which Faraday derived his field conception. Through Thomson, Faraday's theory became a theory of the field and merged with the tradition of the continuous luminiferous aether whose continuous actions could be described by the differential calculus. During the next decade Thomson's speculations on the nature of the electromagnetic and luminiferous aether and its relation with matter led him to discard the traditional mechanistic views of matter for new views consistent with a continuous dynamic medium filling space. He enriched the field tradition with the possibility of a new metaphysic based on the continuous plenum; that possibility fired the imagination of many British physicists. On the other hand, James Clerk Maxwell continued the tradi­ tion of the field in terms of Faraday's early views, groping for a representa­ tion of its activities by analogies Thomson and Faraday had already abandoned, but nonetheless introducing into that tradition the relation 1 2 5 Michael Faraday, "On Some Points of Magnetic Philosophy," Phil. Mag., 9 (1855), 81-113; reprinted in Faraday, op. cit. (note 80), 3, 528-565, on p. 564. 1 2 6 Faraday, op. cit. (note 124).

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between optic and electromagnetic phenomena that made possible a new synthesis.

2. REVOLUTIONARY INSIGHTS INTO AETHER AND MATTER Thomson's Field Theory of Matter: The Vortex-Atom and Its Heirs The "new conception" that replaced the traditional views of matter in nineteenth-century British physics was demanded by magneto-optic rota­ tion. This conception was unique both because it was a field theory of matter and because it led to implications regarding spectral radiation and atomic structure. The numerous field theories of matter that appeared in the last quarter of the century 127 were rooted in Thomson's early specula­ tions on the aether, and the modern quantum atom was an immediate descendent. Origins In the opening paragraph of his "Mathematical Theory of Magnetism" (1849-1850), Thomson said that he was led to inquire into "the physical nature of magnetism and its connexion with the general properties of matter" by Faraday's recent discoveries of "the operation of magnetism with reference to polarized light." 128 But he said that we must consider the investigation of the mathematical, not the physical, laws regulating magnetic action as "primary." 129 Still under the influence of Fourier's positivism, Thomson demonstrated that the hypothesis of two magnetic fluids and of action at a distance is not necessary to the mathematical theory of magnetism. Thomson, who had urged Faraday to undertake the magneto-optic ex­ periment, finally speculated on its physical meaning in a highly influential paper that he delivered on 10 May 1856 to the Royal Society of London. He proposed an image of the relation between the continuous luminiferous aether, Faraday's electric and magnetic lines of force, and the atomic con­ stituents of matter. Thomson explained magneto-optic rotation as an elastic reaction in the aether to innate spiral structures that are also in orbital rotation. Innate spirals are required, Thomson argued, because the existence of structural rotation is inconsistent with a completely homo­ geneous medium and "must be due to elastic reactions dependent on the 127 See

notes 190-192. op. cit. (note 113), p. 341. 129 Ibid., p. 341.

128 Thomson,

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heterogeneousness of the strain through the space of a wave, or to some heterogeneousness of the luminous motions* dependent on a heterogene­ ousness of parts of the matter of lineal dimensions not infinitely small in comparison with the wave length" (italics added).130 Thomson thought it "more probable that the matter of transparent bodies is really hetero­ geneous from one part to another of lineal dimensions not infinitely small in comparison with a wave length, than that it is infinitely homogeneous and has the property of exerting finite direct 'molecular' force at distances comparable with the wave length." Should the former be the case and either right-handed or left-handed spirals predominate in the vibrating medium, "a finite rotation of the plane of polarization of all waves of which lengths are not infinitely great multiples of the structural spirals" would result. The condition for this rotation to take place is that the spiral elements of the matter be innate in the vibrating medium, or aether, and influence its elasticity by the strain they create in it. But spiral heterogeneity in the vibrating medium is not sufficient to ex­ plain magneto-optic rotation. Thomson continued: "The magnetic influ­ ence on light discovered by Faraday depends on the direction of motion of moving particles. For instance, in a medium possessing it, particles in a straight line parallel to the lines of magnetic force, displaced to a helix round this line as axis, and then projected tangentially with such velocities as to describe circles, will have different velocities according as their motions are round in one direction (the same as the nominal direction of the galvanic current in the magnetizing coil), or in the contrary direction [italics added]." Thomson noted that since "circularly polarized light transmitted through magnetized glass parallel to the lines of magnetizing force, with the same quality, . . . is propagated at different rates according as its course is in the direction or is contrary to the direction in which a north magnetic pole is drawn," 130 William Thomson, "Dynamical Illustrations of the Magnetic and Helicoidal Rotary Effects of Transparent Bodies on Polarized Light," Proc. Roy. Soc., 8 (1856); reprinted in Phil. Mag., 25 (1857), and in William Thomson, Baltimore Lectures on Molecular Dynamics and the Wave Theory of Light, rev. ed. (London, 1904), in Ap­ pendix F, pp. 569-577, on p. 569. The asterisk refers to a footnote in which Thom­ son gave as one example of "heterogeneousness of the luminous motions" Rankine's "important hypothesis . . . that the vibrations of luminiferous particles are directly af­ fected by pressure of a surrounding medium in virtue of its inertia." But he proposed in the same sentence in the text, as he did throughout the article, an example that does not depend on luminiferous particles at all. This footnote caused many physicists erroneously to identify Thomson's view with Rankine's and to misinterpret the article.

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the elastic reaction of the medium must be the same for the same dis­ placements, whatever be the velocities and directions of the particles; that is to say, the forces which are balanced by centrifugal force of the circular motions are equal, while the luminiferous motions are unequal. The absolute circular motions being therefore equal or such as to trans­ mit equal centrifugal forces to the particles initially considered, it fol­ lows that the luminiferous motions are only components of the whole motion; and that a less luminiferous component in one direction, com­ pounded with a motion existing in the medium when transmitting no light, gives an equal resultant to that of a greater luminiferous motion in the contrary direction compounded with the same non-luminous motion [italics added] .131 In other words, Thomson interpreted magneto-optic rotation as the re­ sult of the interaction between the vibrating system of the aether and the material system that rotates. He described the rotation of the light ray as an elastic reaction to the spiral or vortical structure of particles of matter innate in the aether combined with their orbital motion around an axis. He believed that "it can be demonstrated that no other explanation is possible." Thomson concluded that "Faraday's optical discovery affords a demonstration of the reality of Ampere's explanation of the ultimate nature of magnetism [as due to small electric currents in the molecules of the magnetic matter]; and gives a definition of magnetization in the dy­ namical theory of heat." After speculating on the relation between aether and matter implicit in this explanation, Thomson appended a dynamical illustration of the "two kinds of effect on the plane of polarization."132 The influence of the kinetic theory of heat on Thomson's explanation of magneto-optic rotation is apparent in his summary statement: "The explanation of all phenomena of electromagnetic attraction or repulsion, and of electromagnetic induction, is to be looked for simply in the inertia and pressure of the matter of which the motions constitute heat."133 In 131 Ibid,,

p. 570. append the solution of a dynamical problem for the sake of the illustrations it suggests for the two kinds of effect on the plane of polarization referred to above. Let the two ends of a cord of any length be attached to two points at the ends of a horizontal arm made to rotate round a vertical axis through its middle point at a constant angular velocity, u>, and let a second cord bearing a weight be attached to the middle of the first cord. The two cords being each perfectly light and flexible, and the weight a material point, it is required to determine its motion when infinitely little disturbed from its position of equilibrium." Ibid. 133 Thomson op. cit. (note 130), p. 571. 1 132 "I

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1872 Thomson noted that after he had "learned from Joule the dynamical theory of heat" at the British Association meeting in 1847, he "was forced to abandon at once many, and gradually from year to year all other, statical preconceptions regarding the ultimate causes of apparently statical phenomena." In this connection he referred to his 1856 jpaper on magnetooptic rotation in which he had analyzed the phenomenon as due to the rotatory motion of matter in the aether. 134 But in his 1856 paper he had gone beyond the kinetic theory in his conception of the particles of matter: "Whether this matter is or is not electricity, whether it is a con­ tinuous fluid interpermeating the spaces between molecular nuclei, or is itself molecularly grouped; or whether all matter is continuous, and molec­ ular heterogeneousness consists in finite vortical or other relative motions of contiguous parts of a body; it is impossible to decide, and perhaps in vain to speculate, in the present state of science" (italics added). 135 On the one hand, Thomson suggested that the particles of matter in motion that cause heat may also be electricity. On the other hand, he offered three possible physical relationships between matter and aether: first, matter itself is a pervasive continuous fluid surrounding molecular nuclei; second, matter as well as aether consists of groupings of discrete particles; third, matter exists as vortical motions of finite portions of the continuous aether filling space. Although Thomson's 1856 paper influenced Maxwell's model of an aether filled with contiguous spiral molecules and consequently has gen­ erally been interpreted as making a case for a discontinuous aether, I be­ lieve that Thomson's intent was to reconcile a continuous aether with the molecules of matter demanded by the kinetic theory of heat. Thomson suggested that the particles of matter in motion that cause heat exist as heterogeneities in the continuous plenum and produce all the phenomena of electromagnetism and light. It is evident that he envisioned vortical motions to occur in particles of matter which, being structures in the aether, effect by strain the rotatory momentum in the aether observed by Faraday. Did Thomson deduce this field-theoretic

conception of matter solely

from Faraday's experiments, or did he respond to other influences as well in 1856? Although the kinetic theory of heat stimulated him to consider the particles of matter in a dynamic sense, it did not lead him to the 134 Note added January 1872 to Thomson Paperi on Electrostatics, op. cit. (note 1 86), p. 419. 1 ^ 5 Thomson, op. cit. (note 130), p. 571.

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vortical motions by which he explained magneto-optic rotation nor to his conception of particles as heterogeneous structures in the continuous aether. A clue to the origin of Thomson's field conception of matter is contained in his Royal Institution Friday Evening Lecture of 18 May I860.136 In his brief account of the development of physical theory from the eighteenth century to the present, he scorned Boscovich's theory as having misguided physicists and mathematicians until Faraday demon­ strated its absurdity: The eighteenth century made a school of science for itself, in which, for the not unnatural dogma of the earlier schoolmen, "matter cannot act where it is not," was substituted the most fantastic of paradoxes, con­ tact does not exist. Boscovich's theory was the consummation of the eighteenth century school of physical science. This strange idea took deep root, and from it grew up a barren tree, exhausting the soil and overshadowing the whole field of molecular investigation, on which so much unavailing labour was spent by the great mathematicians of the early part of our nineteenth century. If Boscovich's theory no longer cumbers the ground, it is because one true philosopher required more light for tracing lines of electric force.137 Thomson said that Faraday's experiments discarded nor merely Boscovichian action at a distance but also Newtonian atoms acting by external contact in a vacuum: "Mr. Faraday's investigation of electrostatic induc­ tion influences now every department of physical speculation, and consti­ tutes an era in science. If we can no longer regard electric and magnetic fluids attracting or repelling at a distance as realities, we may now also contemplate as a thing of the past that belief in atoms and in vacuum, against which Leibnitz so earnestly contended in his memorable corre­ spondence with Dr. Samuel Clarke." This statement reveals that Thomson was familiar with the Leibniz-Clarke debate and agreed with Leibniz' posi­ tion against atoms and the void, and that he identified Faraday's influences on physical speculation with Leibniz' position. "We now look on space as full [italics added]" were Thomson's next words, and they were the conclusion Leibniz had drawn in his letter to Clarke in his argument against atoms and the void and for the plenum. Thomson did not believe in "atoms," because the concept implied New136 William Thomson, "Royal Institution Friday Evening Lecture," 18 May 1860, published in Papers on Electrostatics, op. cit. (note 86), 208-226, on p. 224. 137 Ibid. This and the following quotations are from p. 224.

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tonian corpuscles acting by contact in the void or at a distance.138 He had abandoned the mechanical philosophy for the Leibnizian concept of the plenum. There is no contradiction between Thomson's disbelief in atoms at this date and his equally strong faith in the molecular theory of matter or in his own intense effort later to develop the vortex-atom theory of matter. Indeed, Thomson saw in the vortex-atom a concept that could replace particles acting at a distance or by contact in the void. Although it is not known if Thomson was influenced by Leibniz' ideas before he conceived of the physical hypothesis of rotational structures in a continuous plenum to explain magneto-optic rotation, in 1860 he referred to Faraday's magneto-optic experiment and reiterated the message of his 1856 paper: Faraday's experiment proves that electricity is "an essence of matter": "If electric force depends on a residual surface action, a resultant of an inner tension experienced by the insulating medium, we can con­ ceive that electricity itself is to be understood as not an accident, but an essence of matter [latter italics added]. Whatever electricity is, it seems quite certain that electricity in motion is heat; and that a certain alignment of axes of revolution in this motion is magnetism. Faraday's magneto-optic experiment makes this not a hypothesis, but a demonstrable conclu­ sion."139 This quotation is further proof that in his 1856 paper Thomson envisioned vortical motions only in that part of the aether that constitutes the particles of matter; these motions in turn create rotational strain in the immediately proximate aether and rotational elasticity throughout the aether. In concluding his 1860 lecture, Thomson asked if we are "to fall back on facts and phenomena, and give up all idea of penetrating that mystery which hangs round the ultimate nature of matter." "It does seem," he answered, that the unparalleled train of recent discoveries is tending to­ ward a stage of knowledge "in which laws of inorganic nature will be understood in this sense—that one will be known as essentially connected with all, and in which unity of plan through an inexhaustibly varied execu­ tion, will be recognised as a universally manifested result of creative wis­ dom."140 This idea, echoed in the twentieth century in the unified field 138 Consider Thomson's statement, Proc. Manchester Lit. and Phil. Soc., (1862): "This of course gives a definite limit for the size of atoms, or rather as I do not be­ lieve in atoms, for the dimensions of molecular structures" (quoted by Larmor in Ap­ pendix D to Aether and Matter, op. cit. [note 6], p. 319). 139 Thomson, op. cit. (note 136), pp. 224-225.

i4 OIbid.,

p. 225.

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program, is the central postulate of Leibniz' metaphysics: a dynamic sub­ stance underlies the unity of nature and differentiates itself into the varied particulars of nature. After 1860, Thomson was a Leibnizian in his accep­ tance of the continuous plenum as an alternative to atoms acting by con­ tact in the void or at a distance. His vortex-atom theory, which he first pre­ sented in 1867, was a Leibnizian conception of materia secunda deriving from materia prima or force-substance. The "new conception" of the rela­ tion between aether and matter—between continuous substance and dis­ continuous material atoms—was a Leibnizian differentiation of the dy­ namic unity. I have suggested that Leibniz' conception of matter and force may have contributed to Thomson's new view of the relation between matter and aether. Robert Silliman has pointed to W. J. M. Rankine's hypothesis of "molecular vortices" as another possible influence on Thomson's 1856 "interpretation of magnetism" and, by implication, on his conception that molecules may exist as vortical motions in a continuous medium.141 But, as I will demonstrate, Rankine's influence on Thomson was confined to the concept of vortical motion and did not extend to that of the con­ tinuum. The influence of Rankine's hypothesis on the vortex-atom was limited to what Thomson himself admitted in 1867; namely, to the "mere title [molecular vortices]," which was "a most suggestive step in physical theory."142 From 1850 on, Rankine's hypothesis of molecular vortices143 assumed "that each atom of matter consists of a nucleus or central point enveloped 141 Robert H. Silliman, "William Thomson: Smoke Rings and Nineteenth Century Atomism," Isis, 54 (1963), p. 468, asserts that Rankine's hypothesis of "molecular vortices" "inspired" the "new interpretation of magnetism" that Thomson published in 1856. 142 William Thomson, "On Vortex Atoms," read before the Royal Society of Edin­ burgh, 18 February 1867, published inProc. Roy. Soc. Edinburgh, 6 (1867), 94-105; reprinted in Phil. Mag., 34 (1867), 15-24, and in Thomson 1 Paperi, op. cit, (note 5), 4 (1910), 1-12. Quotation on p. 3. 143 W. J. M. Rankine, "On the Centrifugal Theory of Elasticity, as Applied to Gases and Vapours," read before the Royal Society of Edinburgh, 4 February 1850, published in Phil. Mag., 2 (1851), 226-239; "On the Mechanical Action of Heat, Es­ pecially in Gases and Vapours," read same day and published in Trans. Roy. Soc, Edin., 20 (1852), 147-190; "On the Vibrations of Plane-Polarized Light," read to same society on 15 December 1851, published in Phil. Mag., 2 (1851), 441-446. All reprinted in W. J. M. Rankine, Miscellaneous Scientific Papers, ed. W. J. Millar (London, 1881), pp. 16-48, 234-281, 150-155, respectively. Quotation from "On the Centrifugal Theory of Elasticity" on p. 17.

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by an elastic atmosphere, which is retained in its position by attractive forces, and that the elasticity due to heat arises from the centrifugal force of those atmospheres, revolving or oscillating about their nuclei or central points." 144 Rankine attributed the hypothesis to "many natural philoso­ phers from a very remote period," to Davy for its first ''intelligible" state­ ment, and to Joule for having made it more distinct in 1845. 145 Rankine's peculiar contribution to the hypothesis was to suppose "that the vibration which, according to the undulatory hypothesis, constituted radiant light and heat, is a motion of the atomic nuclei or centres, and is propagated by means of their mutual attractions and repulsions. . . . [Thus] absorption of light and of radiant heat consists in the transference of motion from the nuclei to their atmospheres; and conversely, . . . the emission of light and of radiant heat is the transference of motion from the atmospheres to the nuclei.146 These definitions of absorption and emission reveal the unique­ ness of Rankine's conception. It is, as he admitted, the exact "converse of the idea hitherto adopted, of an ether surrounding ponderable par­ ticles."147 Rather than considering particles of matter as somehow situated in an imponderable aether, he proposed that the aether itself consists of atomic centers, or particles, whose atmospheres are matter: "the luminiferous aether is a system of atomic nuclei or centers of force, whose office it is to give form to matter; while the atmospheres by which they are surrounded give, of themselves, merely extension."1** Rankine thus proposed to replace the mechanical philosophy's concep­ tion of hard-core particles of matter with the idea that matter is neither hard-core nor fundamental. For him the medium is the basic reality, and so he may have contributed to Thomson's notion that matter is derived from the fundamental medium. But Rankine's hypothesis was the converse of Thomson's in that it was essentially a modification of Boscovichian point-centers of force. It considered the force-centers or nuclei to belong to the undulatory medium and the force-extensions to be "an essential

w Ibid. 145 Ibfci.

J. P. Joule, "On the Changes of Temperature Produced by the Rarefaction and Condensation of Fluids,"Phil. Mag., 26 (1845),369-383. 146 Rankine, "On the CentrifugalTheory of Elasticity," Papers, op. cit, (note 143), p. 18. 147 Rankine, "On the Mechanical Action of Heat," Papers, op. cit. (note 143), p. 236. 148 Rankine, "On the Vibrations of Plane-Polarized Light," Papers, op. cit. (note 143), p. 155.

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part of the atom" of matter, indeed the real locus of matter: 149 "the luminiferous medium consists of particles forming the nuclei of atmo­ spheres of ordinary matter." 150 Like Boscovich's theory, Rankine's had the advantage of suggesting a mode of relation between the atoms and the medium not found in the atoms and void of the mechanical philosophy: "motion can be communicated between the nuclei [aether] and their atmospheres [matter], and between the different parts of the atmo­ spheres." 151 Although Rankine hoped to avoid the difficulties of the mechanical philosophy by making matter secondary to the medium, he was not able to escape the particulate hypothesis in conceiving the nature of the basic medium. Atomism was now the property of the aether. The mechanical philosophy could not account for the difference between atoms of matter and atoms of aether; Rankine altered the conception of matter but re­ tained "luminiferous atoms" which give polarity to the medium: The hypothesis now to be proposed as a groundwork for the undulatory theory of light, consists mainly in conceiving that the luminiferous medium is constituted of detached atoms or nuclei distributed through­ out all space, and endowed with a peculiar species of polarity, in virtue of which three orthogonal axes in each atom tend to place themselves parallel respectively to the corresponding axes in every other atom; and that plane-polarised light consists in a small oscillatory movement of each atom round an axis transverse to the direction of propagation. 152 149 Rankine, "On the Mechanical Action of Heat," Papers, op. cit. (note 143), p. 234. W. J. M. Rankine, "Laws of the Elasticity of Solid Bodies," read before the British Association at Edinburgh, 1 August 1850, published in Camb. and Dublin Math. J., 6 (1851),47-80, 178, 185; reprinted in Rankine,Papers, op. cit. (note 143), pp. 67-101, admitted that "almost all the investigations of the laws of elasticity which have hitherto appeared, are founded on the hypothesis of Boscovich" (p. 81); but "the great and obvious deviations from the laws of elasticity as deduced from the hypothesis [Boscovich's] of atomic centres, which many substances present, render some modification of it essential." Rankine said that he had presented such a modifi­ cation with his hypothesis of molecular vortices that allowed two parts to the elastic­ ity of a body (pp. 84-85). 150 W. J. M. Rankine, "General View of an Oscillatory Theory of Light," read be­ fore the British Association at Hull, 10 September 1853, published in Phil. Mag., 3 (1853), 404-414; reprinted in Rankine, Papers, op. cit. (note 143), pp. 156-167, on p. 158. 151 Rankine, "On the Mechanical Action of Heat," Papers, op. cit. (note 143), p. 236. 152 Rankine, op. cit. (note 150), p. 159.

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Rankine proposed oscillating luminiferous atoms to explain the elasticity of the medium required by the undulatory theory of light. The peculiar species of polarity that he attributed to it was "a kind of force which [according to MacCullagh's analyses] must be absolutely destitute of direct influence on resistance to change of volume or change of figure in the parts of that medium."153 The fundamental difference between Thomson's and Rankine's concep­ tions is by now clear: Rankine's aether was particulate, Thomson's con­ tinuous. Thomson's atoms of matter were vortical nuclei or structures in a continuous fluid, not atmospheres around oscillating force-centers.154 Rankine admitted that his theory could not answer the questions of "whether the elastic molecular atmospheres are continuous or consist of discrete particles" and whether "elasticity is . . . a primary quality of matter, or is wholly the result of repulsions of discrete particles [consti­ tuting the atmospheres] ."15S Nor could he say whether the luminiferous nuclei were "distinct from" the atmospheres like "real nuclei" or "merely . . . centres of condensation of the atmosphere, and of resultant attractive and repulsive forces."156 In addition, his hypothesis retained attractive forces at a distance for the atomic centers of the medium, but explained repulsive forces in terms of "the elasticity of their atmospheres."157 Thus, not only did Rankine's theory fail to escape the logical difficulties of the mechanical postulates, but it left unanswered the fundamental ques­ tions as to the nature of both aether and matter. We may wonder if this was one of the objections, which Rankine acknowledged, that Thomson had raised against the theory in 1850.158 The likeliest immediate influence of Rankine's molecular vortices on Thomson's thought during the 1850's was their suggestion that alternatives may be found to the mechanical pos­ tulates. But Thomson's 1856 idea of vortical motion in a continuous ple­ num was no direct heir to Rankine's idea of aether and matter. Thomson was careful to distinguish between Rankine's and his own ideas in his spec­ ulation in 1856 about three possible conceptions of the relation between i s Ilbid.,

pp. 159-160. can readily see how Leibniz' plenum and Rankine's "suggestive" title of "molecular vortices" could combine in Thomson's mind to become what he would later call the "vortex-atom theory of matter." 155 Rankine, "On the CentrifugalTheory of Elasticity," Papers, op. cit. (note 143), p. 17. i s 6 Ibid. l s Ilbid., p. 18. i s g Ibid., p. 16. 154 One

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matter and aether.159 The first conception of the relation of aether and matter was Rankine's notion of matter permeating the spaces between the aether's nuclei; the second was the mechanical view in which matter and aether consist of particles; the third was Thomson's alternative to Ran­ kine's molecular-vortex aether and to any particulate aether concept. It was the third conception, Thomson's own, that became the vortex-atom. Neither the kinetic theory nor Rankine's molecular vortices provided the definitive aspects of Thomson's new conception. His hypothesis, an alternative to both atoms in a void and action at a distance, must have been influenced by some other source, if there was any in addition to Faraday's experiments. In a lecture in 1860, Thomson asserted that Fara­ day's experiments demanded Leibniz' view of the plenum. Leibniz' con­ ception alone contains the ideas necessary to Thomson's ultimate choice of the continuous plenum and of the peculiar derivative nature of matter. The vortex-atom represented the relation between material particle and field that was a necessary consequence of the influence of a magnetic field on the propagation of light. Dating from 1867,160 the vortex-atom was only one possible example of the physical conception that Thomson had demanded since 1856. Thomson's "exceedingly important remark" regard­ ing vortical structures in the aether, which Maxwell said "must form the basis of the relation of light to magnetism,"161 appeared two years before Helmholtz' memoir on the dynamical theory of vortex motion in fluids. Thus, the vortex-atom had a more complex origin than Tait's smoke-rings and Helmholtz' hydrodynamics and a much more fundamental place in physical theory than has been recognized.162 Helmholtz' mathematical analysis showed that vortex-rings in a perfect fluid may satisfy the proper­ ties of material atoms; Tait's demonstration that smoke-rings elastically bounded off one another and were impossible to "cut" convinced Thom­ son that vortex-rings could relate the discrete atom to the continuous plenum.163 Had Thomson not replaced Newtonian atoms with Leibniz' 159 Thomson,

op. cit. (note 130), p. 571. op. cit. (note 142). 161 James Clerk Maxwell, A Treatise on Electricity and Magnetism, 2 vols. (Oxford, 1873),2, #831. 162 See Silliman, op. cit. (note 141), pp. 461-474, for references to the primary sources and a concise statement of the respective roles of Helmholtz' hydrodynamics and Tait's experimental demonstration in 1867 of smoke rings; John Theodore Merz, A History of European Thought in the Nineteenth Century, 4 vols. (Edinburgh, 1896-1914), 2, 57-66; Whittaker, op. cit. (note 6), 1, 293-303. 163 Silliman, op. cit. (note 141), pp. 463-464. See also Peter Guthrie Tait, Lectures on Some Recent Advances in Physical Science, 2nd ed. (London, 1876), pp. 290-300. 160 Thomson,

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continuous plenum, the vortex-atom theory, indeed any field theory of matter, may never have been born.164 As it happened, Thomson demanded the plenum, created the vortex-atom, and initiated revolutionary specula­ tions about the kinetic theory of gases and spectral radiation that culmi­ nated in the modern atom. Incompatibility of Spectral Radiation and the Kinetic Theory of Gases

In his paper "On Vortex Atoms" in 1867, Thomson sought to replace atoms in a void with vortex-atoms in a plenum as the basis for a "new kinetic theory of gases." Vortex-rings, he argued, may satisfy all the thermodynamic properties of gases that have heretofore required assump­ tions of "mutual forces between two atoms and kinetic energy acquired by individual atoms or molecules." The "kinetic elasticity of form" of vortex-rings in a plenum "is at least as good a beginning as the 'clash of atoms' to account for the elasticity of gases." His mathematical investiga­ tion of the mutual actions between vortex-rings would "become the foun­ dation of the proposed new kinetic theory of gases."165 Problems in the dynamical theory of spectral radiation demanded Thomson's new kinetic theory. Developed in the 1850's and 1860's by Clausius, Maxwell, Thomson, and Boltzmann, the kinetic theory of gases 164 The nineteenth-century historian of atomism Kurd Lasswitz argued that vortex theories of atoms did not necessarily entail the abandonment of discontinuity be­ cause they made the infinitesimal particles of the aethereal medium the true atoms. ("Uber Wirbelatome und stetige Raumerfiillung," Vierteljahrsschr. f. wissenschaftl. Philosophie, 3 [1879], 206-215, 275-294, especially pp. 279 ff.; reference and dis­ cussion of this work in Capek, op. cit, [note 0], pp. Ill, 120.) Lasswitz' argument, however, does not hold for Thomson's vortex-atom. Yet Capek's entire interpretation of the Thomson-Larmor tradition is based on the assumption that vortex-atoms were not an alternative to atoms in a void, and that atomism and mechanical laws were relegated to the aether. Although he admits that Thomson and many other physicists took the expression "continuity of the aether" literally (p. 110), he either refuses to allow that they were seeking an alternative to a mechanical conception in the vortexatom theory or fails to appreciate that it could explain motion in a plenum. Capek's own "pulsational becoming" requires a plenum and explains motion in it in the same way that vortex-atoms and strain-centers did; namely, by structural-dynamic discon­ tinuities arising out of a continuum and interacting through it. The aether was not discontinuous to Thomson, Lodge, or Larmor, and yet it did allow motion. Further support for my view is gained by contrasting Capek's claim that Thomson's theory, like any hydrodynamical theory of gravitation, is different "in detail rather than sub­ stance" from mechanical theories of the seventeenth century with Preston's opposi­ tion in 1883 to the Lodge-Thomson aether because it was different from matter "in kind or essence" rather than "in degree." (Ibid., p. 111;S. Tolver Preston, "Letter to the Editor, Regarding Lodge's Lecture 'The Ether and its Functions,' " Nature, 21 [1883], 579.) It is this error of historical interpretation that distorts Capek's other­ wise discerning analysis of the meaning of twentieth-century physical theory. 165 Thomson, op. cit. (note 142), p. 2.

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encouraged the notion that vibrating molecules are the source of spectral radiation. 166 R. B. Clifton proposed in 1866 a "classical" model of the vibrator; he argued that "the vibrations in the ether which constitute radiant heat and light, are due to the vibrations of the atoms in the mole­ cule, and not of the motion of the molecule as a whole." 167 In 1868 G. J. Stoney described gaseous molecules as highly complex systems con­ sisting of inter- and intra-molecular motions. The former account for the kinetic energy but are irregular and too "coarse" to absorb or emit vibra­ tions in the aether; the internal motions are regular and produce the spec­ tra. 168 In his Theory of Heat in 1870, Maxwell proposed a molecular theory of radiation according to which "the small vibrations of a con­ nected system [molecule] may be resolved into a number of simple vibra­ tions, the law of each of which is similar to that of a pendulum." Maxwell argued that at a collision a molecule is "roughly shaken," and that during its subsequent free path it vibrates with an amplitude determined by the nature of the collision and with a period depending on its constitution; the molecule emits radiation by communicating these vibrations to the aether. 169 Thomson accepted the dynamical theory of the spectrum which "re­ quired that the ultimate constitution of simple bodies should have one or more fundamental periods of vibration." 170 This theory in turn necessi­ tated that the atom have "flexibility and elasticity," and thus provided a major argument for the concept of vortex-atoms in a plenum and against that of "atoms and vacuum"; the latter concept had originally been thought "necessary to account for the flexibility and compressibility of tangible solids and fluids." The ultimate or basic constituents of matter must themselves be elastic, and "the vortex-atom has perfectly definite fundamental modes of vibration, depending solely on that motion the existence of which constitutes it." Finally, a vortex-atom model of the sodium atom "would act precisely as incandescent sodium-vapor acts—that is to say, would fulfill the 'spectrum test' for sodium." 171 166 William McGucken Nineteenth Century Spectroscopy: Development of the 1 Understanding of Spectra 1802-1897 (Baltimore, 1969), pp. 35-47. 167 R. B. Clifton, "An Attempt to Refer Some Phenomena Attending the Emission of Light to Mechanical Principles," Proc. Lit. and Phil. Soc. Manchester, 5 (1866), 24-28, 24. McGucken, ibid., p. 41. 168 G. J. Stoney, "The Internal Motions of Gases Compared with the Motions of Waves of Light," Phil. Mag., 36 (1868), 132-141. 169 James Clerk Maxwell, Theory of Heat (London, 1870), pp. 285, 306. 170 Thomson, op. cit. (note 142), pp. 3-5. See also McGucken, op. cit. (note 166), pp. 166-167. 171 Thomson, op. cit. (note 142), pp. 3-5.

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Thomson was isolated during the early years of his vortex-atom theory when he opposed the Lucretian atom and challenged the foundations of the kinetic theory of gases. As late as 1873 Maxwell agreed with Democritus, Epicurus, and Lucretius' view that the atom is "only the bare and utter hardness of utter impenetrability."172 Only in 1875, after August Kundt and Emil Warburg had experimentally verified that mercury vapor consists of monatomic molecules, did Maxwell discard his molecular theory of spectra for Thomson's vortex-atom theory.173 He asserted in his article "Atom" in the Encyclopaedia Britannica that neither Lucretian nor Boscovichian atoms can account for spectra and that vortex-atoms alone are capable of internal motion or vibration.174 Earlier Maxwell had re­ garded Thomson's criticisms of the foundations of the kinetic theory as brash, if not heretical. Thomson had to proceed with circumspection in his criticisms of the kinetic theory. Undermining the Mechanistic Gravitational and Kinetic Theories In 1871 Thomson briefly discussed Georges-Louis LeSage's gravitational theory in view of the "modern science" of the kinetic theory of gases.175 He noted that the postulate of hard atoms in a void underlying both the kinetic theory of gases and LeSage's theory was open to doubt: "This much is certain, that if hard indivisible atoms are granted at all, his principles are unassailable; and nothing can be said against the probability of his [additional] assumptions. The only imperfection of his theory is that which is inherent to every supposition of hard, indivisible atoms. They must be perfectly elastic or imperfectly elastic, or perfectly inelastic. Even Newton seems to have admitted as a probable reality hard, indivisible, unalterable atoms, each perfectly inelastic." (Italics added.)176 After argu­ ing that the modern theory of energy conservation forbids inelasticity in the ultimate atoms, Thomson tried to show that "modern thermodynam­ ics" and "perennial gravity" may be consistent with LeSage's theory on the assumption of perfectly elastic atoms: "All that is necessary to complete LeSage's theory of gravity in accordance with modern science, is to 172 James Clerk Maxwell, "Molecules," Nature, 8 (1873), 437-441, 338, Reprinted in The Scientific Papers of James Clerk Maxwell, ed. W. D. Niven, 2 vols. (Cambridge, 1890), 2, 361-367, 363-364. See McGucken, op. cit. (note 166), p· 45. 173 James Clerk Maxwell, "Atoms," Encyclopaedia Britannica, 9th ed. (Edinburgh, 1875), 2; in Maxwell, Papers, op. cit. (note 172), 2, 445-484, 470. McGucken, op. cit. (note 166), pp. 157-163. 174 Maxwell, ibid. 175 William Thomson, "On the Ultramundane Corpuscles of Le Sage," read 18 De­ cember 1871, published in Proc. Roy. Soc. Edin., 7 (1872), 577-589; reprinted in Phil. Mag., 45 (1873), 321-322, and in Thomson 1 Paperi 1 op. cit. (note 5),5, 64-76. 176 Ibid., pp. 70-71.

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assume that the ratio of the whole energy of the corpuscles to the translational part of their energy is greater, on the average, after collisions with mundane matter than after inter-collisions of only ultramundane cor­ puscles. This supposition is neither more nor less questionable than that of Clausius for gases, which is now admitted as one of the generally recog­ nised truths of science" (italics added). Thomson's paper was more a critique or warning of the limitations of the assumption of hard indivisible atoms in a void underlying the kinetic theory of gases than it was a demonstration of the "truth" of the corpuscular theory of gravity: "The corpuscular theory of gravity is no more difficult in allowance of its funda­ mental assumptions than the kinetic theory of gases as at present received; and it is more complete, inasmuch as, from fundamental assumptions of an extremely simple character, it explains all the known phenomena of its subject, which cannot be said of the kinetic theory of gases so far as it has hitherto advanced" (italics added).177 Thomson's message was that it may be less questionable to explain gravity than the kinetic theory of gases on the basis of atoms and the void. He had already challenged the assumption of atoms and the void and pro­ posed a new kinetic theory of gases based on vortex-atoms in a plenum. He did not consider his kinetic theory to be in final form, couching his conclusions in terms that recognized the temporary, limited stage of the theory. Even as late as 1881 he had not given up his hope of replacing atoms in a void with vortex-atoms in a plenum as the foundation of the kinetic theory: he demonstrated that "in the statistics of vortex-impacts the pressure exerted by a gas composed of vortex-atoms is exactly the same as is given by the ordinary kinetic theory, which regards atoms as hard elastic particles."178 Ironically, the effect of Thomson's discussion of LeSage's theory was to identify him in the eyes of some contemporary and future physicists and historians as a proponent of atoms in a void and of a particulate aether.179 However, the LeSage theory of an ultramundane particulate aether could have no place in Thomson's new kinetic theory of gases whose basis was a " 7 Ibid., pp. 73,75. 178 William

Thomson, "On the Average Pressure Due to Impulse of Vortex-Rings on a Solid," Proc. Roy. Soc. Edin., read 17 April 1881; notice in Nature, 24 (1881), 47; reprinted in Thomson,Papers, op. cit. (note 5), 4, 188. 179 My analysis counters the interpretation by Samuel Aronson, "The Gravitational Theory of Georges-Louis Le Sage," The Natural Philosopher, 3 (1964), 53-71, es­ pecially pp. 64-65, in which he uses the same quotations from Thomson's paper to identify Thomson as a proponent of LeSage's mechanical theory of gravity. Aronson notes that LeSage's theory today is often called the "Thomson-Le Sage Theory" (p. 62).

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continuous aether. Oliver Lodge insisted in 1883 that the vortex-atom theory had introduced a continuous medium to avoid hard-core atoms in interaction, so that "we cannot go back to the impact of hard bodies" in the form of an "artificial battery of ultramundane corpuscles" to explain gravity. 180 In response, S. Tolver Preston, the true advocate of the LeSage theory in its original form, protested that Thomson's notion of a contin­ uous aether was in contradiction with the atomic theory of matter as well as with the LeSage theory of gravity. 181 But Thomson modified the LeSage theory to make it consistent with his notion of the continuous plenum. Having demonstrated to the critics of LeSage's theory of gravity that it stands on stronger grounds than the "generally recognized truth" of the kinetic theory, Thomson allowed the possibility of LeSage's theory only within the context of his vortex-atom theory of matter, and only be­ cause ultramundane vortical motions within the continuous aether plenum cannot be excluded from possible explanation of the "relation [of gravity] to inertia of masses." 182 G. F. FitzGerald's and W. M. Hicks's continuous vortex-aethers were "full" of such vortices seeking to explain gravita­ tion. 183 The vortex-aether theories of late nineteenth-century British physics introduced a new approach for understanding electromagnetic and optic as well as gravitational phenomena. Vortex-Aether Theories I must emphasize first that the vortex-atom theory of matter and the later vortex-aether theories cannot be considered separate developments. Faraday's discovery of the rotation of light was the stimulus to both. They are actually two different viewpoints of the same physical conception of the relation between aether and matter; whereas the vortex-atom theory conceived of material atoms as molecular vortices in the aether and sought 180 Oliver

Lodge, "The Ether and Its Functions, Part II," Nature, 27 (1883), 328330, 329. 181 Preston op. cit. (note 164), p. 579. Preston revealed his strong adherence to the 1 theory in "On Some Dynamical Conditions Applicable to Le Sage's Theory of Gravi­ tation, No. 1," Phtl Mag., 4 (1877), 206-213; and m "On Some Dynamical Condi­ tions . . . , No. 2," ibid., p. 365. 182 William Thomson, "Elasticity Viewed as Possibly a Mode of Motion," Roy. Institution Proc., 9 (1881), 520-521; reprinted in Thomson, Papers, op. cit. (note 5), 4, 472-474. 183 See Whittaker, op. cit. (note 6), 1, 284-285, 294-296, 300-303. G. F. FitzGerald, "On a Model Illustrating Some Properties of the Ether," Proc. Roy. Dublin Soc., 4 (1885), 407; reprinted in Scientific Writings of the Late George Francis I'itzGerald, ed. Joseph Larmor (London, 1902), p. 154. Id., "On a Hydrodynamical Hypothesis as to Electromagnetic Actions," Proc. Roy. Dublin Soc., 9 (1889), 5054; reprinted in FitzGerald, Writings, pp. 472-477.

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to explain the properties of matter, vortex-aether theories considered the effects of such vortical singularities on aethereal activity through the rota­ tional elasticity they introduced into the aether. The vortex-aethers of the 1880's were strictly continuous in the manner of Thomson's 1856 plenum; the complex structures attributed to the aether were models by which British physicists sought to explain its activities. Because the vortex-atom theory of matter required an associated vortexaether theory, and vice versa, the viability of one theory depended on the success of the other. In fact, problems in the theories of the vortex-aether accelerated the demise of the vortex-atom. In November 1889 Thomson wrote to FitzGerald that the various vortey-aether theories of the 1880's, which considered the aether filled with either rotational vortex cores or coreless vortices, seem "to promise at present but little towards explaining universal gravitation or any other property of matter; so you may imagine I do not see much hope for chemistry and electro-magnetism." 184 As he suggested in a paper in 1907, the year he died, he had discarded the simple vortex-atom in a perfect fluid as early as 1877 because a fluid

aether

proved incapable of explaining optical phenomena: "We sometimes hear the 'luminiferous ether' spoken of as a fluid. More than thirty years ago I abandoned, for reasons which seem to me thoroughly cogent, the idea that [the luminiferous] ether is a fluid presenting appearances of elasticity due to motion, as in collisions between Helmholtz vortex rings. Abandoning this idea, we are driven to the conclusion that ether is an elastic solid, capable of equi-voluminal waves in which the motive force is elastic re­ sistance against change of shape." 185 Thus, Thomson had discarded the theory of vortex-atoms and the associated concept of a fluid aether not only because it could not explain the properties of matter, but also, indeed mainly, because it did not admit a viable luminiferous aether. The hydrodynamical analogy presented other difficulties that could not be reconciled with a field theory of electricity and matter. Helmholtz, in his 1858 researches on vortex motion, had considered the analogy between electricity and the flow of an incompressible fluid. 186 In his view, if the 18i William Thomson, "On the Stability and Small Oscillation of a Perfect Liquid Full of Nearly Straight Coreless Vortices," Proc. Roy. Irish Acad., read 30 November 1889; reprinted in Thomson, Papers, op. cit. (note 5), 4, 202-204. 185 William Thomson, "On the Motions of Ether Produced by Collisions of Atoms or Molecules, Containing or Not Containing Electrons,"Electrician, 59 (1907), 714716; Phil. Mag., 14 (1907), 317-324; reprinted in Thomson, Papers, op. cit. (note 5), 6 (1911), 235-243, 236. 18 ®H. von Helmholtz, "Uber Integrale der hydrodynamischen Gleichungen, welche den Wirbelbewegungen entsprechen," Journal fur die reine und angewandte Mathematik, 55 (1858), 25-55. Thomson, op. cit. (note 142).

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vector for the magnetic field produced by electric currents is represented by the fluid velocity so that electric currents correspond to the vortex filaments in the fluid, the charged particles creating the currents would have to be the sources and sinks in the fluid where the fluid is continually being created and destroyed. 187 On the other hand, Riemann viewed matter as a place where aether is destroyed, requiring that aether flow into this sink to replace the destroyed aether; but this view could not account for the continual creation of new aether. 188 A fluid was inadequate as a vortex-aether both because it could not ex­ plain light propagation and because its vortex-atoms could not explain the existence of particles and the phenomena of electricity. Because the fluid aether failed to provide a synthesizing theory of electric, magnetic, and optical phenomena and material particles, Thomson once again attacked the basic question of the nature of the aether. In his review of optical theory in the 1884 Baltimore lectures, Thomson drew directly upon Rankine's elasticity studies, attempting to explain the aether's activities in terms of complex material atoms and related aether structures. But then, as in 1856, Thomson's aether was in essence a continuum, the ideal limit­ ing case of the infinitesimal aether structures. Nonetheless, it was through Rankine's attempt to explain MacCullagh's elasticity that Thomas arrived in the 1880's at the conception of matter as a gyroscopic atom in a rotationally elastic aether. Although Rankine's molecular vortices were no ancestor to Thomson's vortex-atoms, their use in explaining the aether's elasticity guided Thomson's efforts in the 1880's to revise the vortex-atom theory to account for all of the phenomena of optics and electromagnetics. The numerous theories of an elastic aether which were proposed in the 1880's must be recognized as alternatives to the ideal fluid aether of vortex-atomism that had proven incapable of explaining optical and elec­ tromagnetic phenomena. Although Thomson had discarded the theory of vortex-atoms in a perfect fluid, he did not discard or even question the particle-field relationship that the vortex-atom represented. It remained 187 See Whittaker, op. cit. (note 6), 1, 293. Mathematically, sources and sinks of hydrodynamical flow are singular points where the condition of continuity of flow, du/dx ~ dv Idy - dwldz = 0, breaks down and becomes infinite. 188 Georg Friedrich Bernhard Riemann, "Fragmente philosophischen Inhalts," Gesammelte mathematische Werke (Leipzig, 1892), p, 529. C. V. Burton, "Notes on Aether and Electrons," Phil. Mag., 13 (1907), 694, believed that Helmholtz was the first to point out that Riemann's theory could not account for the creation of aether. Whittaker, op. cit. (note 6), 1, 240, notes that Reimann's paper is believed to have been written in 1853.

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in his vortex-sponge aether of the early 1880's, in his gyrostatic aether of the Baltimore lectures, and in his ideal rotationally elastic solid aether of 1889. In each he sought to determine initially the nature of the continuous aether to develop a more adequate field theory of atomic matter. The Tradition of Field Theories of Matter The vortex-atom notion, conceived by 1856 and widely discussed by 1867, had introduced to the physicists of the late nineteenth century the idea that matter is not the basic substance, but is derived from a primordial medium, the physical field of action. In 1883 Sir Oliver Lodge described the vortex-atom theory as the simplest conception of the material universe which has yet occurred to man. The conception that is of one universal substance, perfectly homogeneous and continuous and simple in structure, extending to the furthest limits of space of which we have any knowledge, existing simply everywhere. Some portions either at rest or in simple irrotational motion transmitting the undulations which we call light. Other portions in rotational motion, in vortices that is, and differentiated permanently from the rest of the medium by reason of this motion. These whirling portions constitute what we call matter; their motion gives them rigidity, and of them our bodies and all other material bodies with which we are acquainted are built up. One continuous substance filling all space: which can vibrate as light; which can be sheared into positive and negative electricity; which in whirls constitutes matter; and which transmits by continuity, and not by impact, every action and reaction of which matter is capable.189 The program for a field theory of matter—a theory that derived matter from the aether—was widely subscribed to in Britain by 1880. W. L·. Clifford's space theory of matter in 1876, which proposed mat space is the "ultimate and exclusive building material of physical re­ ality,"190 must be considered a product of the British tradition of field theories of matter established by Thomson's vortex-atom. Developed from purely geometrical principles, the theory proposed that matter is a struc­ tural, rather than a structural-kinetic, modification of physical space: "In the physical world nothing else takes place but this variation [of the 189 Lodge,

op. cit. (note 180), p. 330. K. Clifford, "On the Space Theory of Matter," Proc. Camb. Phil. Soc. (1876); reprinted in The Mathematical Papers of William Kingdom Clifford, ed. RobertTucker (London, 1882), pp. 21-22. 190 W.

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curvature of space] ."191 Other British concepts developed within field theories of matter include Charles V. Burton's strain-figures in 1891, Joseph Larmor's strain-center electrons in 1891 and 1894, Karl Pearson's "ether-squirts" in the 1890's, John Fraser's "ether bubbles" in 1901-1905, Alfred North Whitehead's Leibnizian "persistence of relative motions of points of space" in 1906, and S. B. MacLaren's "sources" in a fluid aether in 1913.192 Maxwell's Models and the Electromagnetic Theory of Light Hertz's pronouncement that Maxwell's theory is Maxwell's system of equations was his response to the difficulties of "representing" in a model l9i Ibid.

Jammer, Concepts of Space, op. cit. (note 6), pp. 162-16.3; id., Concepts of Mass, op. cit. (note 6), pp. 217-218; id., The Conceptual Development of Quan­ tum Mechanics (New York, 1966), pp. 241-242. Clifford accepted the British aether and its functions; see W. K. Clifford, "Ether; the Evidence for Its Existence and the Phenomena It Explains," in Lectures and Essays, eds. Leslie Stephen and F. Pollock (London, 1901). He united the tradition of the aether and the vortexatom field conception of matter with Riemann's conception of the inhomogeneity of space. Although space was still considered isotropic and a container of a subtle material medium within the mechanical worldview, the British aether theorists had long established the anisotropy of the nonmaterial plenum and specifically its in­ homogeneity due to the existence of matter within it. Riemann's attempt to de­ velop a quasi-elastic aether (see note 188) is believed to have been written before or simultaneously with his geometrical work, "Uber die Hypothesen welche der Geometrie zu Grunde liegen" (Habilitationsschrift, 1854), in Riemann, Gesammelte mathematische Werke, op. cit. (note 188), p. 272. On p. 286, Riemann observed that "the basis of metrical determination must be sought outside the manifold in the binding forces which act on it," as it was in his aether theory. C. V. Burton, "A Theory Concerning the Constitution of Matter," read 20 November 1891 before the Physical Society and published in Phil. Mag., 5th ser.,33 (1892), 191-204; op. cit. (note 188); "On the Faraday-Maxwell Mechanical Stress; and on Aethereal Stress and Momentum in General," Phil. Mag., 6th ser., 17 (1909), 641-654; and "On the ApparentDispersion of Light in Space, and the Minuteness of the Structure of the Aether," Phil Mag., 6th ser., 18 (1909), 872-877. Karl Pearson, The Grammar of Science (London, 1900), pp. 265-267. John Fraser, "A Theoretical Representation Leading to General Suggestions Bearing on the Ultimate Constitution of Matter and Ether," Proc. Roy. Soc. Edin., 17 (November 1901 to July 1903), 2664 (read 6 January 1902); "Suggestions Towards aTheory of Electricity Based on the Bubble Atom," op. cit., 25 (1905), 680-715 (read 15 May 1905). Alfred North Whitehead, "On Mathematical Concepts of the Material World," Phil. Trans. Roy. Soc., 205 (1906), 465-525. Samuel Bruce McLaren, Phil. Mag., 6th ser., 26 (1913), 636-673; reprinted in Samuel Bruce McLaren, Scientific Papers (Cambridge, 1925), pp. 34-40. Joseph Larmor, "The Equations of Propagation of Disturbances in Gyrostatically Loaded Media, and the Circular Polarization of Light," Proc. London Math. Soc., 23 (1891); reprinted in Larmor,Papers, op. cit. (note 37), I, 248-255. Id., op. cit (note 47). Id., op. cit. (note 37).

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the activities of aether and matter that the theory expresses. 193 However, in 1869 Ludwig Lorenz had independently achieved an electromagnetic theory of light aitd the fundamental equations of Maxwell's theory from a reverse perspective; he viewed the hypothesis of an aether as unnecessary since space presumably contains enough matter for the electromagnetic propagation to occur. 194 Maxwell's theory is a mathematical statement of Faraday's continuous aether—the lines of force and the electrotonic state. Maxwell's "double s)stem of differential equations in which the electric and magnetic fields appear as the dependent variables" 195 established the reality of energy in the aether: the magnetic energy is the kinetic energy of the continuous aether plenum, and the electric energy is its energy of strain. It was this physical conception c-f the active plenum that led Max­ well to his fundamental principle that the total current is closed by a dis­ placement current within the dielectric (which includes the aether). In addition, Maxwell deduced his equations from his models for Faraday's field actions. Thus, Maxwell's equations are Maxwell's theory of the aether and must be studied as such. To what extent did Faraday and Maxwell attain the modern view of the field? Two postulates of modern field theory are that force or energy exists in the medium, and that the medium is different from ordinary matter. Faraday discarded his early theory of polarized particles in the medium in favor of his conception of continuous lines of force. When he briefly endorsed Boscovich's view that matter consists of force-extensions throughout space, he identified matter with the field. Influenced in part by Thomson's conception of the magnetic character of space, he ulti­ mately distinguished aether from matter and thus attained the modern field concept. Maxwell began with Faraday's lines-of-force representation of the state of the aether, imagining the aether as a fluid moving in tubes bounded by the lines of force, but reintroduced polarization as a possible explanation of the state of the aether. In seeking a representation of the physical processes involved in electromagnetic phenomena, Maxwell came to the electromagnetic theory of light; he also reinstated inapplicable 193 P. M. Heimann, "Maxwell, Hertz and the Nature of Electricity," Isis, 62 (1971), 149-157, has shown that Hertz not only repudiated Maxwell's use of models but also rejected central concepts in Maxwell's equations: "For Hertz, the equations which expressed the essentials of Maxwell's theory were his own equations rather than Maxwell's" (p. 157). 194 Whittaker, op. cit. (note 6), 1, 270 et seq. 195 A. Einstein, "Maxwell's Influence on the Evolution of the Idea of Physical Reality" (1931), in A. Einstein, Ideas and Opinions (New York, 1954), p. 268.

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mechanical corpuscular notions that led to fundamental errors and hindered physicists in their search for a comprehensive theory of the field. The difficulties physicists faced in attaining the modern theory of the field were threefold: first, how to conceive of the aether as "something" different from matter; second, how to conceive of the transmission of action across the continuous aether plenum; and third, how to represent the relation and mode of interaction between aether and matter. On all three counts, the search for a field theory was hindered at first by the de­ termined bias of physicists to describe all phenomena mechanically; the early elastic solid luminiferous aethers and Faraday's polarization were cases in point. Later, as Faraday's and Maxwell's early researches show, the search was hindered by the lack of a physical conception of aether activities to replace the Newtonian conception of particles in motion. Even after Thomson had attained this new conception, the search was hindered by the habit of physicists such as FitzGerald, Lodge, and J. J. Thomson of thinking in mechanical terms. Maxwell, like Faraday, was ex­ plicit on the existence of force in the medium, the first postulate of a field theory; but, like Faraday again, he did not have an adequate representation of the difference and mode of interaction between aether and matter. Maxwell's mechanical model of the aether in 1862 was an attempt to conceptualize Faraday's continuous transmission of force across a me­ dium. 196 He represented aether as a series of vortices and rolling particles transmitting continuous action by contact. It was a mechanical model in­ corporating Thomson's 1846 suggestion that electric phenomena are analogous to displacements in an elastic solid, and that magnetic phenom­ ena are analogous to rotations. Maxwell derived the details of his model, however, from his interpretation of Thomson's 1856 analysis of magnetooptic rotation. Indeed, Maxwell's model erroneously labeled Thomson's plenum as molecular, a misinterpretation that originally hindered Maxwell and continued to confuse other physicists. 197 Confusion arose either be196 James Clerk Maxwell, "On Physical Lines of Force," Phil. Mag., 21 (1861), 161-175, 338-348, and 23 (1862), 12-24, 85-95; reprinted in Maxwell,Papers, op. cit. (note 172), 1, 451-513. Gears that mesh, representing parts of the aether that actually touch, supposedly would escape the problem of action at a distance, so that the action or transmission would be continuous. Maxwell's commitment to continouous action became more evident by 1862, and he made it explicit several times subsequently. 197 It confused Helmholtz, for instance; see note 285. Hertz adhered to Thomson's plenum of vortex-atomism, but attributed the infinitesimal molecular vortices of the Maxwell-Helmholtz electric theory to it rather than seeking a new dynamics in terms of a strict continuum that is not merely the limit of a discontinuous medium; see note 295.

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cause they did not see the identity of the aether of magneto-optic and electrical theory and the continuous plenum of the vortex-atom theory of matter or they were biased towards the particulate representation. Maxwell's "electric displacement" was generally interpreted mechani­ cally; it was done so not only by Continental physicists unfamiliar with the British notion of continuous action in the plenum, but also by British physicists groping to explain its meaning. Taken literally, the term means that the "elements" of the aether have changed position. Maxwell's model incorporated the literal meaning: an induced force urges a change of posi­ tion of the electric particles in the model, and by a chain reaction effected through the elastic force between vortices and particles "a general dis­ placement of the electricity in a given direction" occurs.198 As late as 1892 Poincare' introduced a "fluid inductuer" as "the name of a thing displaced in the dielectric" when an electric displacement occurs.199 Although Max­ well ultimately abandoned his mechanical model and sought a new repre­ sentation for aetheral transmission, his electric displacement remained an integral part of the theory, which created a fundamental confusion that prevented him from attaining the correct equations for the electrody­ namics of moving bodies. Maxwell emphasized in his dynamical theory of 1864 that the mechani­ cal analogy and terminology of the paper were "illustrative, not. . . ex­ planatory"; they were meant to assist the reader "in understanding the electrical" phenomena: "In speaking of the Energy of the field, however, I wish to be understood literally. . . . [It] is mechanical energy . . . [which] resides in the electromagnetic field, in the space surrounding the electrified and magnetic bodies, as well as in those bodies themselves, and is in two different forms, . .. the motion and strain of one and the same me­ dium."200 Maxwell retained polarized particles as a possible representation of the medium, but the aether particles were now a limiting case and the medium was essentially continuous. It appeared to him that there is an aethereal medium pervading all bodies, and modified only in degree by their presence; that the parts of this medium are capable of being set in motion by electric currents and magnets; that this motion is communicated from one part of the medium to another by 198 Maxwell,

op. cit. (note 196), pp. 491-492. '"Noted by G. F. FitzGerald in his discussion of Poincare's Electricite et optique ("M. Poincare and Maxwell," Nature, 45 [7 April 1892], 532-533; reprinted in FitzGerald, Writings, op. cit. [note 183], p. 284). 2 ^ lo James Clerk Maxwell, "A Dynamical Theory of the Electromagnetic Field," Phil. Trans. Roy. Soc., 155 (1865), 459-512; reprinted in Maxwell, Papers, op. cit. (note 172), 1, 526-697, 564.

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forces arising from the connexions of those parts; that under the action of these forces there is a certain yield depending on the elasticity of these connexions; and that therefore energy in two different forms may exist in the medium, the one being the actual energy of motion of its parts, and the other being the potential energy stored up in the con­ nexions, in virtue of their elasticity. 201 Maxwell implied and later made explicit that the "elasticity of these connexions" is possible even in media that are strictly continuous; for the equations of the model merely reflect transmission /6wing to elasticity and stand "without the aid of hypothesis" as to the connections or parts. 202 Nonetheless, in Maxwell's model, although the medium and the action were theoretically continuous, the "representation" was still particulate. Maxwell already realized that this model was not acceptable because the particle representation invariably mechanized the field and made no real distinction between aether and matter. To Maxwell the aether or field was a real physical substance; he contin­ ued Faraday's attempt to describe the actions of this fundamental sub­ stance which was not the matter of the mechanical philosophy. Maxwell often stated that the aether permeated the spaces occupied by the mole­ cules of matter as well as those between them; the aether was no accident of matter, but a unique and independent substance capable of interacting with matter. 203 His attempts to describe electromagnetic phenomena in­ corporated representations of the state of the aether, and although in his earliest representations the field appeared merely as an "accident" of dielectric substances, in his later ones the field gradually acquired its inde­ pendence from such substances. But the ultimate solution to the problem 201 ZWd.,

pp. 532-533. Clerk Maxwell, "Ether," Encyclopaedia Britannica, 9th ed., (Edinburgh, 1878), 8; reprinted in Maxwell, Papers, op. cit, (note 172), 2, 763-775, 774. 203 Maxwell left no' question that the aether ft "distinct from gross matter, distinct from the transparent medium known to us, though it interpenetrates all transparent bodies and probably opaque bodies too" (ibid., p. 768). Tetu Hirosige, "Origins of Lorentz' Theory of Electrons and the Concept of the Electromagnetic Field," Historical Studies in Physical Sciences, 1 (1969), 151-209, 159, 172, argues that one of Lorentz' major innovations that ultimately resolved the difficulties of Maxwell's theory was to consider the aether and ponderable matter to be different from one another and thereby establish the independence of the electro­ magnetic field. This innovation was accomplished, he correctly perceives, by suppos­ ing that intermolecular spaces are also filled with aether, so that electromagnetic phenomena are due mainly to the aether and very little to the molecules. I will demonstrate that Maxwell had already made these assumptions about the indepen­ dence of the aether and the small degree of influence of matter on field activities. Thus, Lorentz' and Larmor's innovation was to determine the electrical connection between material bodies and the aether. 202 James

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of aether and matter was not possible even then because Maxwell still ignored the question of the nature of the electric charge. Maxwell could not provide an adequate account of the respective roles of material dielec­ trics and aether only because he had no conception of the mode of con­ nection between aether and matter. Dissatisfied with the particulate conception in which there was only a difference of size between particles of aether and matter but determined to represent the nature of the aether, Maxwell returned to the concept of force in 1868. 204 What representation might establish aether as different from matter and yet explain the transmission of action across the aether? In his search for an answer to this question, Maxwell looked for an analogy from the side of electromagnetism alone, ignoring optics. In his Treatise in 1873, he again introduced polarized particles, but emphasized that they were not a true representation of the aether and were intended only as an aid for understanding the theory. 205 In the first edition, he stated that he could not accept as an explanation of both matter and aether Faraday's force extending throughout space. He thought that a mere difference in the size of particles of matter and aether as in the polarization conception provided a better representation than one that recognized no difference at all between matter and aether. 206 Because Maxwell could not describe the activities of an aether that is qualitatively different from matter, he avoided any further representation of the aether in the Treatise. 207 Rather, he returned to the approach he 204 James Clerk Maxwell, "On a Method of Making a Direct Comparison of Elec­ trostatic with Electromagnetic Forces; with a Note on the Electromagnetic Theory of Light," Phil. Trans., 158 (1868), 643-657; reprinted in Maxwell, Papers, op. ctt. (note 172),2, 125-143. 205 Maxwell, Treatise, op. cit. (note 161), #831. Maxwell here explicitly abandoned the mechanism of his model of 1862 and, at the same time, he continued to accept Thomson's argument that "some phenomenon of rotation is going on in the mag­ netic field." But he still could only conceive of such rotation as being "performed by a great number of very small portions of matter" filling the field. 206 Ifeiti., #529. See P. M. Heimann, "Maxwell and the Modes of Consistent Rep­ resentation," Archive Htst. Exact Sci., 6 (1970), 171-213, 181-183. 207 Maxwell, Treatise, op. cit. (note 161), #110-111, #645, emphasized that while he postulated the existence of the stress, he was not making suggestions about the nature of the stress or about "the mode in which this state of stress is originated and maintained in the medium"; he was merely showing that a representation of such a stress was possible. Larmor observed in 1928 that "although a main object of the Treatise was to transcend the model, it may well have been this that kept him [Max­ well] away from the electron" (Larmor, Papers, op. cit. [note 37], 2, 19n). Larmor arrived at the concept of the electron from a model based on the new conception that Thomson had hypothesized to explain how the stress in the continuous medium is maintained by its connection with matter.

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had used in his dynamical theory in 1864, asserting that the development of the equations of electromagnetism from the Lagrangian formalism enables one to ignore the nature and laws of internal forces. Because the causes for the phenomena remained unknown, he did not regard the theory as complete. 208 His demand for an understanding of the underlying physical events responsible for electric and magnetic actions continued to guide his developing conception of the relation between aether and matter. During the next decade, Maxwell resolved some of his earlier questions regarding the nature of the aether. In 1875 he applied "the molecular theory of gases to test the hypotheses about the luminiferous aether which assume it to consist of atoms or molecules." He reasoned that "a molecular aether would be neither more nor less than a gas," and would "be subject to the ordinary gaseous laws as to pressure and temperature." If it were no different from matter, "its presence . . . could not fail to be detected in our experiments on specific heat." He concluded that "the constitution of the aether is not molecular" (italics added). The aether is a continuum and thus ontologically different from particulate matter. 209 Maxwell insisted that such properties as elasticity or compressibility of the continuous medium must not be considered equivalent to those same properties of particulate matter. He suggested that "new conceptions" were needed to explain how the medium could be strictly continuous and yet able to propagate action. Until then "we may regard Faraday's conception of a state of stress in the electromagnetic field as a method of explaining action at a distance by means of the continuous transmission of force, even though we do not know how the state of stress is produced." 210 In his Treatise and his article "Ether" in 1878 in the Encyclopaedia Britannica, Maxwell stated that perhaps the theory of structural rotation in a rotationally elastic aether that Thomson had proposed in 1856 to explain magneto-optic rotation was the new conception of the aether-matter rela­ tion. He thought it might ultimately explain the relation between light and 208 Heimann Op. cit. (note 206), pp. 210-213, discusses the omissions from the 1 second edition and Maxwell's recognition that the state of stress still lacked an ade­ quate representation. 209 James Clerk Maxwell, "On the Dynamical Evidence of the Molecular Constitu­ tion of Bodies,"Nature, 11 (1875), 357-359, 374-377; reprinted in Maxwell, Papers, op. cit. (note 172),2,418-438,437-438. WehereseethatMaxwellwasnotheading blindly into an "ultraviolet catastrophe," but, on the contrary, was convinced of the continuity of the aether because the aether did not share the ordinary thermal prop­ erties of gases. 210 James Clerk Maxwell, "On Action at a Distance," Proc. Roy. Instn. Gr. Br., 7 (1876); reprinted in Maxwell, Papers, op. cit. (note 172),2, 311-323, 321.

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electric and magnetic phenomena and the continuous transmission of action through the aether. He reiterated that the elasticity of the aether is not incompatible with its continuity: "It is often asserted that the mere fact that a medium is elastic or compressible is a proof that the medium is not continuous, but is composed of separate parts having void spaces be­ tween them. But there is nothing inconsistent with experience in supposing elasticity or compressibility to be properties of every portion, however small, into which the medium can be conceived to be divided, in which case the medium would be strictly continuous." He then considered the relation between a continuous aether and the material molecules of Thomson's vortex-atom conception: "A medium, however, though homo­ geneous and continuous as regards its density, may be rendered hetero­ geneous by its motion, as in Sir W. Thomson's hypothesis of vortexmolecules in a perfect liquid. . . . The aether, if it is the medium of electromagnetic phenomena, is probably molecular, at least in this sense."211 Maxwell referred here to Thomson's magneto-optic rotation paper of 1856. This statement was interpreted by many of Maxwell's con­ temporaries and by subsequent scholars as an indication that Maxwell and Thomson ultimately required a molecular aether.212 On the contrary, Max­ well's meaning here was that the aether is molecular only in that molecular vortices or vortex-atoms arise out of it as required by magneto-optic rota­ tion. Maxwell recognized that Thomson's conception overcomes the prob­ lems of the mechanical, discontinuous aether which cannot represent aether as different from matter. Thomson's aether-matter conception, which had become Maxwell's new representation of the aether, supplied a continuous medium for electromagnetic propagation, and it explained how to obtain structural-dynamic particles from a continuous field. Whereas Maxwell in his 1862 model had interpreted Thomson's 1856 in211 Maxwell,

op. cit. (note 202), p. 774. op. cit. (note 6), pp. 207-208, uses Maxwell's statement as an example of the evasion of the question of action at a distance by infinite regress. See M.Hesse, "Action at a Distance in Classical Physics," Isis, 46 (1955), 337. Capek, op. cit. (note 6), pp. Ill, 120, refers to this quotation and Hesse's analysis for his assertion that Maxwell explicitly "conceded, though hesitatingly and with a great deal of caution, the discontinuous" particulate aether. Whittaker, op. cit. (note 6), 2, 247249, says Maxwell's article on the aether regarded the aether as "composed of cor­ puscles, moving in all directions with the velocity of light." Whittaker notes that this article inspired two new representations of electromagnetism by E. Cunningham and Leigh Page in 1914. But, as Whittaker admits, Page's ideas are reminiscent of J. J. Thomson's corpuscular aether; J. J. Thomson always insisted that Maxwell's aether must be particulate (note 71). 212 Hesse,

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sights on magneto-optic rotation in terms of a mechanical chain of vortices filling the medium, in 1878 he recognized that the rotational "structure" is a fundamental property of the continuous medium and that the mag­ netic rotation of light is a reaction of the aether to strains created in it by the particles of matter existing as structures within it. Yet Maxwell, like Thomson and the other British physicists, called the aether a "material substance" because it had one of the properties of matter; namely, inertia. But British physicists conceived of the aether's "inertia" in a nonmechanical sense; it was different from the inertia of matter. Moreover, the aether was essentially different from ordinary matter because matter was secon­ dary and had additional properties. Maxwell's death in 1879 prevented him from contributing to the development of Thomson's continuous aether representation, but his suggestions prompted FitzGerald and Hicks to adopt Thomson's vortex-aether conception of a nonmaterial aether and Larmor to relate it to matter. The electric displacement, the product of Maxwell's particulate model, remained a problem for Maxwell's followers. The electric displacement made no real distinction between the roles of the aether and the material dielectric, substances which Maxwell recognized as different. Not only did this residue of his initial model attribute the mechanical property of dis­ placed elements to the aether, but it attributed to matter along with the the aether the role of being the seat of electromagnetic phenomena. In Maxwell's theory the electromagnetic field was both the state of the mate­ rial medium and the state of the aethereal medium. Maxwell hesitated to speculate further; he was aware of the confusions that already burdened his theory, and he had no conception of a relation between electricity, aether, and matter that would distinguish between the activities in the material dielectric and those in the aether. Until the seat of electromagnetic phenomena was restricted to the aether, the electric displacement could not be consistently incorporated into the theory. But, until the connection between aether and matter was recognized, this restriction would be difficult because of the presence of electrical activity in ponderable media. The resolution of these difficulties in Maxwell's concept of electric displacement demanded a deeper probe into the nature of aether and matter. Physicists gained crucial insights from optical as well as electrical analyses. Larmor observed that Maxwell's models and his theory attacked "the problem of the aether. . .from the side of electrical phenomena," and accordingly was strongest in "the elec­ tromotive part which gives an account of electric radiation and of the

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phenomena of electromagnetic induction in fixed conductors." But be­ cause "our notions of what constitute electric and magnetic phenomena are of the vaguest as compared with our ideas of what constitutes radia­ tion," Maxwell's ideas understandably "involve difficulties, not to say contradictions, and in places present obstacles" that may be surmounted "by beginning at the other end"; namely, by explaining electric actions on the basis of the optical activities of the aether. 213 The existence of contradictions and problems in Maxwell's notions of electric displacement and continuous transmission stimulated Maxwell's followers to probe deeper into his views of aether and matter than they otherwise might have. Maxwell contributed the electromagnetic theory of light which made possible the ultimate synthesis of optical and electric phenomena. His attempts to explain Faraday's lines of force and strain were equally significant, however, for attaining a consistent and compre­ hensive theory of field and matter. The substance of British physics after 1880 consisted of a complex interaction between Maxwell's electromag­ netic theory, vortex-aether theories, new insights into the nature of the electric charge, and modified vortex-atom conceptions of matter. The method of British physics during these years was in a state of flux in which dynamical justification and mathematical formalism vied with mechanical models. The tradition of field physics begun by Faraday and Thomson at midcentury was continued after 1880 in the context of persistent physical conceptions and wavering methods.

3. EFFECTING THE NEW SYNTHESIS: 1880-1894 The vortex-atom theory was a field theory of matter, explaining matter as a structural-dynamic product of a homogeneous fluid plenum. The theories of the aether of the 1880's were mechanical in the sense that they offered complicated explanations of the aether in terms of mechanical models. The electron theory of matter, born in 1894, was once again a field theory that accounted for the properties of matter in terms of funda­ mental aether relations. The progession from field theories of matter to mechanical models of the aether and back to field theories of matter was not an inconsistency in the British school. The vacillation between aetheral explanations of matter and mechanical models of the aether's actions was an essential aspect of the search for a new field theory of matter and occurred several times within the development of a single theory. The 2 1 3 Larmor,

op. cit. (note 47), p. 397.

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mechanical explanations of the aether were necessary to determine an appropriate representation of field activities and hence the true connection between the field and the atomic constituents of matter. From the simple hypothesis of a continuous aether of which matter is a product, and from the complex mechanical models of the effect of mate­ rial atoms on optical, magneto-optic, and electric aethereal activities, Thomson concluded that the aether is an "ideal" substance that possesses a rotational elasticity and that is strained in its intimate relation with matter. Recognizing that Thomson's aether plenum required new modes of physi­ cal action in order to explain Faraday's lines of force and Maxwell's dis­ placement, Larmor reinterpreted vortex-atoms as nuclei of aetheral strain which he considered as charged particles constituting matter. For Larmor matter interacts with the aether through the strain-centers in and of the aether. By the use of mechanical models of the aether, British physicists attained their long-sought goal: an understanding of the phenomena of aether and matter within the framework of a continuous plenum. The mechanical postulates of atoms and the void or action at a distance finally gave way to a new field-theoretic synthesis and metaphysic: the electro­ magnetic view of nature. Before tracing some of the major steps by which that synthesis was effected, I will emphasize the definitive characteristics of British concep­ tions of the aether in the 1880's, for they are often overlooked or mis­ interpreted. In his 1883 discussion of the functions of the ether, Lodge declared that the aether is "one continuous substance filling all space." The hypothesis of a continuous aether plenum had been made not to support a vortex-atom theory of matter; on the contrary, the vortex-atom theory was conceived because optics and electromagnetics demanded a continuous aether. In 1883 Stokes likewise argued that the luminiferous aether must be considered continuous. When Huygens speculated in the seventeenth century on the ultimate constitution of the aether and imag­ ined it to consist of molecules whose actions on one another produce optic phenomena, he had "abandoned the simplicity of the fundamental conceptions of the theory of undulations and adopted a mode of reasoning not strictly allowable." For the transmission of regular undulations, of which the period is arbi­ trary, at least within wide limits, requires us to suppose that the trans­ mitting medium is either continuous or may be treated as such;. . .and we have no right to extend to the medium treated as a whole, and re­ garded as continuous, a mode of communication of motion applicable

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only to the communication from one to another of a set of discrete molecules. Newton's discovery of the compound nature of white light showed that there must be in light an element of some kind susceptible of con­ tinuous variation. [On] the theory of undulations, . . . one element. . . might serve for the purpose, namely wave length, or what comes to the same thing, periodic time.214 In 1884 Thomson observed that while we consider matter to be molecular, "we regard ether as utterly continuous and structureless. It may be found in some future time that ether too has molecular structure, perhaps much finer than any structure of ponderable matter; but at present we neither see nor imagine any reason for believing ether to be other than continuous and homogeneous through infinitely small contiguous portions of space void of other matter than ether."215 Maxwell noted that the elasticity or compressibility of the aether is not inconsistent with its "strictly con­ tinuous" nature. As late as 1907 Thomson continued that argument. With­ out proposing to "enter on any atomic theory of ether," he said that "it seems to me indeed most probable that in reality ether is structureless; which means that every portion of ether however small has the same elastic properties as any portion however great. There is no difficulty in this con­ ception of an utterly homogeneous elastic solid, occupying the whole of space from infinity to infinity in every direction."216 The aether of the dominant British tradition was continuous. Another property of the nineteenth-century British aether was "inertia." This property is generally taken as proof that the British aether was not a "pure" or true field but a mechanical substance. However, in 1884 Stokes made explicit the meaning of the aether's inertia: "The theory of undulations. . .requires us to suppose that the interplanetary and inter­ stellar spaces are not, strictly speaking, a vacuum but a plenum; that though destitute of ponderable matter they are filled with a substance of some kind, constituting what we call a medium, or vehicle of transmission of the supposed undulations. When I speak of this medium as a substance, or as material, I mean that it must possess that distinctive property of matter, inertia; that is to say a finite time must be required to generate in 214 G. G. Stokes, On Light, Burnett Lectures, delivered at Aberdeen in November 1883, December 1884, and November 1885 (London, 1892); quotation from lecture "On the Nature of Light" (1883), pp. 19-21. 215 Thomson, op. cit. (note 130), Lecture XVII, p. 279. This lecture had been "altered (1901, 1902), to extension of Lecture XVI." 216 Thomson, op. cit. (note 185), p. 236.

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a finite portion of it a finite velocity" (latter italics added).217 The inertia of the aether is that property which makes transmission through it take place in finite time rather than instantaneously. (Larmor referred to Thomson's Baltimore lectures for a statement that the inertia of the aether is different from the inertia of matter. 218 ) Finite propagation is one of Faraday's criteria for the physical reality of transmission in space void of matter; it is a criterion of the physical reality of the field. Einstein, like the British physicists, rejected action at a distance and demanded a field through which action is transmitted in time.219 The British aether, even with its inertia, was no more mechanical than Einstein's field. The elas­ ticity and inertia of the aether were ultimate, irreducible properties; they were not in contradiction with its nonmaterial continuous essence, and indeed distinguished it from a particulate mechanical medium. Already completely demechanized and equivalent to the modern field, the British aether of the 1880's was acknowledged as the basis for a new worldview. After 1880 field theory continued to develop along the two paths established by Thomson and Maxwell. Dissatisfied with the simple vortexatom in a perfect fluid, Thomson sought a satisfactory mode of connection between the continuous aether plenum and innate material particles by considering various models of the aether. His search led many physicists and historians, including Larmor, to see theoretical eclecticism where in reality there was an unwavering commitment to a field-theoretic view of matter. The development of Maxwell's theory after 1880, however, was certainly eclectic. Action in the electromagnetic field was described by Helmholtz in terms of polarized particles, by Poynting and J. J. Thomson in terms of tubes of force, by FitzGerald and Larmor in terms of elastic stress and strain. Heaviside and Hertz each sought and found a direct and simple formalism for electromagnetic theory, helping establish mathe­ matically and conceptually the nature of the electromagnetic field. FitzGerald, Larmor, and Lorentz attempted to reconcile Maxwell's theory with earlier luminiferous aether theories, to incorporate the charged particle, and to establish the difference and mode of interaction between aether and matter. Together with Lodge and a number of British spectroscopists and thermodynamicists, FitzGerald and Larmor found in the vortex217 Stokes,

op. ctt. (note 214), p. 15. op. cit. (note 37), p. 531. 219 See, for instance, A. Einstein, "The Mechanics of Newton and Their Influence on the Development of Theoretical Physics" (1927), in Einstein, op. cit. (note 195), p. 259; and "Relativity and the Problem of Space" (1954), ibid., pp. 375-376. Doran, Sir Joseph Larmor, op. cit. (note 1), Chapter 19. 218 Larmor,

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atom a connection between aether and matter that provided new insight into perplexing problems in electrodynamics and spectral radiation. In this section, I deal with the field-theoretic synthesis of aether and matter—a major episode in nineteenth-century intellectual history—in a way that attempts to capture both its internal complexity and its co­ herence. I shall first identify the dominant problems that confronted the British physicist, and then trace the development of new concepts and explanations in response to each problem and their elaboration by differ­ ent British physicists at different times. I shall divide the problems into three broad categories. Under the first category of problems, I shall discuss critical evaluations of earlier theories of the luminiferous aether and the attempts to incorporate them into a vortex-aether, field-theoretic frame­ work. Under the second category, I shall discuss attempts by both British and Continental physicists to incorporate the notion of electric charge into Maxwell's theory, to remove all confusing and inconsistent concepts, and to determine the appropriate representation of electric action in the field. The third category comprises the two unsolved problems involving inter­ actions between matter, aether, and electric charge; namely, the influence of the motion of matter through the aether on the propagation of electro­ magnetic waves, and the relation between spectral radiation, atomic struc­ ture, and the kinetic theory of heat. Because the problems were closely related and solutions to one problem helped solve another, I cannot avoid all overlap and repetition in discussing them. However, I hope that my organization will clarify the development and culmination of the British tradition of the field.

Updating the Luminiferous Aether Theories In the 1880's, British physicists took stock of their theories, noting their failures and seeking ways to overcome them. The number and variety of luminiferous aether theories were bewildering. In his "Report on Double Refraction," communicated to the British Association in 1862, Stokes observed that in most theories "the direct action of the ponderable mole­ cules is neglected, and the ether treated as a single vibrating medium." He went on: "It was, doubtless, the extreme difficulty of determining the motion of one of two mutually penetrating media that led mathematicians to adopt this, at first sight, unnatural supposition; but the conviction seems by some to have been entertained from the first, and to have forced itself upon the minds of others, that the ponderable molecules must be

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taken into account in a far more direct manner."220 However, those few theories that attempted to account for the effect of matter on the aether— Cauchy's theory of mutually penetrating media and Challis' theory of re­ sisting masses in an ordinary elastic fluid—had been unsuccessful in ac­ counting for the phenomena. During the next decades, British physicists sought to develop a theory of refraction that takes into account the manner in which matter interacts with the aether. By 1877, Thomson had discarded the theory of vortex-atoms in a per­ fect fluid. He did so not merely because the theory could not explain material mass or because he could not demonstrate the nondissipation of vortex-rings; vortex-rings in a perfect fluid aether could not explain the totality of optical, electric, and magnetic phenomena. In 1880 Thomson sought to describe a medium that had both the properties of a fluid that vortex-rings required and the properties of an elastic solid that the propa­ gation of light required.221 The vortex-sponge—an aether admitting a mix­ ture of differential rotational and irrotational motions—became the first of Thomson's vortex-aethers. Although other physicists immediately seized upon the vortex-sponge concept to synthesize electromagnetic and gravita­ tional actions, Thomson first undertook a critical review of the wave theory of light and was led to other, more promising models of the aether's activities. Thomson's Baltimore Lectures on Molecular Dynamics and the Wave Theory of Light delivered at The Johns Hopkins University in 1884 record a crucial development in his ideas.222 The title reveals his major concern at the time, which was to determine the effect on optical phenomena of motions of material molecules. Since 1856 he had considered the main problem of physics to be the relation and mode of interaction between material particles and the continuous aether. The difficulties of the wave theory, he suggested, could perhaps be resolved if the mode of interaction between molecules and the aether is found. In his Baltimore lectures he attempted to gain knowledge of the aether through a dialectic between molar dynamics, by which he determined the points on which the wave theory currently floundered, and molecular dynamics, by which he ex­ amined the possible influence of the dynamic structure of molecules of matter on optical and electromagnetic phenomena. This most fascinating and critical period in scientific theory demands intensive study, but we can 220 Stokes,

op. cit, (note 57), p. 180. Thomson, "On Maximum and Minimum Energy in Vortex Motion," Brit. Assoc. Rep. (1880), pp. 473-476. 222 ThomsOn Op. cit. (note 130). 1 221 William

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here indicate a few general characteristics of the path by which Thomson arrived at an alternative to the vortex-atom. Even the structure of the Baltimore lectures reflects the dialectical process of Thomson's thought; he passed easily between molar and molec­ ular considerations within each lecture. In the first lecture he highlighted the limits of given elastic-solid theories of the aether and his plan for seek­ ing a reconciliation between them. It appeared that an elastic-solid aether could not allow the transmission of optical and electromagnetic phenom­ ena and at the same time be uninfluenced by the motion of the planets through it. Elastic-solid theories were also incapable of explaining three optical phenomena: dispersion, refraction and reflection, and double re­ fraction. Thomson thought that the phenomena might be explicable in terms of his conception of the intimate connection between aether and matter: We have now this interesting point to consider, that if we would work out the idea of dispersion at all, we must look definitely to times of vibration, in connection with all ponderable matter. To get a firm hy­ pothesis that will allow us to work on the subject, let us imagine space, otherwise full of the luminiferous ether, to be partially occupied by something different from the general luminiferous ether. That something might be a portion of denser ether, or a portion of more rigid ether; or we might suppose a portion of ether to have greater density and greater rigidity, or different density and different rigidity from the surrounding ether.223 He thought that similarly refraction and reflection may be explained in terms of variations in density and rigidity of the aether in different mate­ rial media. It is apparent that Thomson had not given up his Leibnizian fieldtheoretic conception, but sought a new representation of the material atom as a product of the continuous aether to replace that of vortex-rings in a perfect fluid. He said that this new representation must be consistent with the historical successes of theories of the luminiferous aether and overcome their difficulties. It must explain how either of two diametrically opposed assumptions about the nature of the aether is able to satisfy all of the conditions of the problem of optical reflection and lead to the same energy equation. The Fresnel-Cauchy and Stokes-Rankine-Rayleigh theory of reflection, 213Ibid.,

p. 8.

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which postulated an aether with the isotropic elasticity of an ordinary elastic solid in all media and with aeolotropic effective inertia, required, as Thomson demonstrated, only the additional assumption that there be no resistance to laminar compression. The MacCullagh-Neumann type of aether, which postulated aeolotropic rotational elasticity and isotropic ef­ fective inertia in all media, solved the problem of reflection without any assumption regarding the degree of its compressibility.224 Several explana­ tions had been offered for the failure of the choice of the model to affect the energy equation. Perhaps the aether has a mixed elastic-solid and rota­ tional elasticity, or perhaps a more general type of elasticity. Or perhaps it is a homogeneous medium, and all optical properties of material bodies are due to the nature of the connection and mode of interaction between the aether and matter. In 1867, Joseph Boussinesq, assuming the latter ex­ planation, postulated that one homogeneous aether fills all space and that it has the same inertia and rigidity in all material bodies; he sought an in­ teraction between material particles and the aether to explain optical properties.225 Neumann and Matthew O'Brien also made a distinction be­ tween aether and matter, suggesting that the aether surges around material particles and is modified by their presence.226 In the Baltimore lectures, Thomson observed that the hypothesis of aeolotropic elasticity needs some conception of the action of molecules of matter upon the aether in producing the initial strain. He suggested that perhaps the aether pervades material atoms, occupying the same space jointly with them, and that material atoms are differentiations of the aether continuum. He proposed that the labile aether demands this new conception of the relation between aether and matter; the continuous aether can be condensed or rarified in the atoms, but it can never be totaEy absent. He noted further, that the unrestrained motion of the 224 Whittaker, op. cit. (note 6), 1, 159. Larmor, op. cit. (note 48), pp. 419-429; op. cit. (note 37), pp. 419-429. 225 Joseph Boussinesq, "Theorie nouvelle des ondes lumineuses," Journal de Math., 13 (1868), 313-339; id., "Addition sur memoire intitule: Theorie nouvelle des ondes lumineuses," ibid., 13 (1868), 425-438; id., "Introduction naturelle de termes proportionelies aux displacements de l'ether (ou termes de Briot) dans Ies equations de mouvement des ondes lumineuses," Comptes Rendus, 117 (1893), 80-86; id., "Ex­ pression de la resistance opposee par chaque molecule ponderable au mouvement vibratoire de l'ether ambian," ibid., 117 (1893), 138-144; id., "Considerations diverses sur la theorie des ondes lumineuses," ibid., 117 (1893), 193-199. See Whittaker, op. cit. (note 6), 1, 167. 226 F. E. Neumann, Abhandlungen. Berlin. Akademie aus dem Jahre 1841, Zweiter Teil (Berlin, 1843), p. 1. Matthew O'Brien, Trans. Camb. Phil. Soc., 7 (1842), 397. Whittaker, op. cit. (note 6), 1, 166-167.

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planets through the aether requires that any optical theory make the addi­ tional assumption that material atoms move through space without dis­ placing the aether. All of these assumptions about the relation between aether and matter were already present in his 1856 analysis of magnetooptic rotation and, with the exception of the assumption that an elastic connection creates aethereal strain, in his original vortex-atom conception. Thomson argued that whether one postulates the properties of isotropic elasticity and aeolotropic inertia or their inverse, some field-theoretic con­ ception of the relation between aether and matter is required to explain them. During the next six years, he expanded both views of the properties of the aether, hoping that one would yield the relation of electricity to aether and matter; he nearly effected the synthesis in 1889 with a rotationally elastic model. The insights that went into those later efforts were drawn from his Baltimore lectures. Starting from the general proposition of a field-theoretic view of the material particle, Thomson examined many possible kinetic models of molecules that might produce the requisite influences on the aether in which they are "imbedded." He rejected Helmholtz' "singly vibrating particle connected with the luminiferous ether" as incapable of accounting for the phenomena, and considered a "multiple vibrating heavy elastic atom imbedded in the luminiferous ether." 227 The particles of gases must, in their detached particles, somehow or other act on the luminif­

erous aether, have some sort of elastic connection with it. . , [italics added]. By taking enough of these interior shells [of the multiple mole­ cule], and by passing to the idea of continuous variation from the den­ sity of the ether to the enormously greater density of the molecule of grosser matter imbedded in it, we may come as it were to the kind of mutual action that exists between any particular atom and the luminifer­ ous aether. It seems to me that there must be something in this molecu­ lar hypothesis, and that as a mechanical symbol, it is certainly not a mere hypothesis, but a reality. 228 Disillusioned by the failure of the vortex-atom to account for the phenom­ ena of the aether, but convinced that atoms in interaction with the aether are the real cause of those phenomena, Thomson attempted several types of linked vibrating atoms, all of which were unable to account for the facts. 229 227 Thomson, op. cit. (note 130), Lecture II, p. 30. ^Ibid., Lecture I, pp. 13-14. 229 Ibtd., Lecture II.

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In passing on to the "condition of the aether" in liquids and solids that rotate the plane of polarized light, Thomson introduced the gyroscopic molecular model. In the twentieth Baltimore lecture, he attempted to "illustrate or explain" Faraday's magneto-optic rotation with a gyroscopic molecule, and in an appendix with an "improved gyroscopic molecule" he defined the elastic connection with the aether. 230 Helmholtz' view of the "vibrating particle" as the source of radiation, which Thomson had discarded, continued to dominate the Continental school, influencing Lorentz' theory of the electrically charged ion as the means of interaction between matter and the aether. 231 But Helmholtz and Lorentz did not explain how the vibrator excites or is excited by the aether. Lorentz' theory accepted the dualism of matter and aether; other Continental theorists such as Max Abraham, Gustav Mie, and Einstein sought to reject that dualism through a conception of the particle as a field structure. Such a conception Thomson had already arrived at by 1856 and had developed in his vortex-atom theory of matter, and he retained it in his modifications of the vortex-atom in the Baltimore lectures. Only the gyroscopic model, he concluded, could explain the phenomena of mag­ neto-optic rotation, and it was able to account for the other interactions between aether and matter as well. Thomson was dissatisfied with the "molecule" as he presented it in the Baltimore lectures, and continued to improve on the model throughout the 1880's; he showed, for instance, how the rotational rigidity required by several phenomena of electricity and magnetism can exist in a continuous medium. But in his conception of matter and aether he had forever replaced the vortex-atom and vortexaether with the gyroscopic-atom and gyroscopic-aether. Having concluded in 1884 that optics requires a quasi-elastic solid aether and a gyroscopic molecule, Thomson set out to discover the precise na­ ture of the elasticity and its possible relation to electric and magnetic phenomena. In November 1888, "in endeavouring to explain results of observation regarding the refraction and reflection of light," 232 he was led "from Green's original theory [and his own IabHe elastic solid aether] by 230 Ifaici.,

Lecture XX, "written afresh, 1903," pp. 436-467. T. Hirosige, op. cit. (note 203) for a discerning account of the origins of Lorentz' electron theory. 232 William Thomson, "On the Reflexion and Refraction of Light," Phil. Mag., 26 (1888), 414-425. Extracts reprinted in Thomson, Baltimore Lectures, op. cit. (note 130), pp. 174, 351-354, 407. Quotation is from William Thomson, "On a Mechanism for the Constitution of Ether," Proc. Roy. Soc. Edin., 17 (1890), 127-132; reprinted as "On a Gyrostatic Adynamic Constitution for 'Ether'," in Thomson, Papers, op. cit. (note 5), 3, 466-472, on p. 472. 231 See

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purely optical reasons" to a medium having gyrostatic quasi-rigidity. His Presidential Address to the Institution of Electrical Engineers in January 1889 considered the relation between "ether, electricity, and ponderable matter."233 Inthesepapers in 1888 and 1889 Thomson finally re-addressed the question he had raised in his 1846 paper, "On a Mechanical Representa­ tion of Electric, Magnetic and Galvanic Forces." He had only the outlines for the representation: electric phenomena give a turning motion to the aether, and the aether is a medium "which has the properties of an incom­ pressible fluid, and no rigidity except what is given to it gyrostatically."234 He noted that this aether is also expressible as a quasi-elastic solid: "There you have a body, then, that you could not distinguish from an ordinary elastic solid in respect to any irrotational distortion, or in respect to translational motion of the whole, but which if you try to turn it, will re­ sist."235 He preferred to call the medium a solid rather than a fluid because the latter term implied nonelasticity, notwithstanding Stokes's notion of the indistinguishability of solids and liquids on the basis of elasticity. Arguing that a model can help our minds "think of possibilities"—of things which may have real existence—and thus show that the hypothesis is not "merely playing at theory," Thomson produced a "skeleton" model of a rotationally elastic solid aether.236 Such an aether is not homogeneous, but has the aeolotropic "structure" of rotational elasticity together with a struc­ tural strain created by the particles of matter. Thomson's 1888 aether was no ordinary elastic solid but an updated version of MacCullagh's, now supplied with the skeleton of a model. He said of it that although we know that the rotational rigidity of the aether exists and must be enormously less in magnetic bodies than in nonmagnetic bodies and nonconductors, we have no explanation of how the strains arise in the medium and why they do not balance out into an equilibrium condition. He asked: "how can there be a solid capable of giving rise to that wonderful condition which we have in the air between the poles of an electro-magnet?" He asked further: "how can it be that these prodigious forces are developed in ether, an elastic solid, and yet ponderable bodies be perfectly free to move through that solid?"237 In July 1889, Thomson attempted to answer the first question. In the 233 William

Thomson, "The Relation between Ether, Electricity, and Ponderable Matter," published for the first time in Thomson, Papers, op. cit. (note 5), 3, 484511. 234Ibid., p. 5 0 5. 235jbtd., p. 509. 236Ibid; p. 508. 2,37ibid., pp. 509-510.

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"Molecular Constitution of Matter," he emphasized again that the explana­ tion of electrostatic force consisting in a strained condition of the medium was to be found in the relation of the aether to matter. In his search for anew field-theoretic conception to replace the vortex-atom, he now turned his attention to the Boscovichian idea of atoms as point-centers of force extending throughout space. But he insisted that atoms must be considered as having finite dimensions and structure. 238 Atoms of matter are neither hard-core particles nor points of force, but force-regions that extend throughout space. Indeed, he incorporated Boscovich's hypothesis into his conception of matter as a product of the aether; Thomson's aether had become a pervasive force-substance. The strains or lines of force in this force-aether could perhaps be explained in terms of motions and struc­ tures of the atoms and molecules of matter; Thomson proposed models to explain the properties of the elastic solid aether in terms of Boscovichian attractions and repulsions, propagated through the aether in finite time, exerted by finite vibratory, rotational atoms. For Thomson the nature of both the aether and the atoms of matter had become force. The strain in the aether produced by matter would in this and in all of Thomson's subsequent models explain optical and electro­ magnetic phenomena. Between July and September 1889, Thomson con­ sidered electrodynamics and magnetism in more detail and was led again to a rotationally elastic aether. 239 In a series of connected articles, he ex­ amined the "motion of a viscous liquid," the "equilibrium of motion of an elastic solid" or jelly, the "equilibrium of motion of an ideal substance called for brevity ether," and finally the "mechanical representation of magnetic force." 240 The ideal substance again had no intrinsic rigidity, but a quasi- or "gyrostatic" rigidity "depending on an inherent quasielastic resistance to absolute rotation." 241 It was the marvelous exigencies of an attempt to include inductive mag­ netisation, in the mechanical representation, that compelled the assump­ tion of a quasi-elastic force, depending on absolute rotation, and not 238 William Thomson, "The Molecular Constitution of Matter," Proc. Roy. Soc. Edin., 16 (1889), 693-724, read 1 and 15 July 1889; reprinted in Thomson, Papers, op. cit (note 5), 3, 395-427. 239 Thomson, op. cit. (note 232). 240 William Thomson, "Motion of a Viscous Liquid; Equilibrium or Motion of an Elastic Solid; Equilibrium or Motion of an Ideal Substance Called for Brevity Ether; Mechanical Representation of Magnetic Force," published for the first time in May 1890 in Thomson, Papers, op. cit. (note 5), 3, 436-465. 2 ^ l Ibid., p. 463.

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otherwise on distortion; and this compelled the introduction of the new ideal substance which we have been calling "ether". . . . The magnetic force being in our analogy the rotation of the jelly, or ether, we see . . . that the proper interfacial condition between substances of different rigidity . . . is not fulfilled by the jelly, and is fulfilled by the ether. 242 Thomson insisted that he had discarded the ordinary elastic solid: "It need scarcely be said that the 'ether' which we have assumed, is a merely ideal substance. It seems to me highly probable however, that the assumed dependence of its forcive on absolute rotation, is at all events analogous to the truth of real ether." 243 The rotational elasticity of the aether is brought into play only by activity on the atomic or molecular level. Gross matter does not cause any rotational movement of the aether. Thus, Thomson concluded, by considering only magnetic susceptibility we are led to the conception underlying Stokes's explanation of aberration: the earth and other heavenly bodies give only irrotational motion to the ether by their motions through it," if, that is, they move the aether at all. 244 Thomson almost effected the synthesis of optics and electromagnetism by means of his conception of aether and matter when he briefly considered Maxwell's electromagnetic theory of light in terms of his rotationally elastic aether. After demonstrating that Maxwell's use of his own 1846 elastic displacement analogy did not account for the electro-static force, or the generation of heat in a conductor according to Ohm's law, or the fact that the velocity of light in aether "is the number of electro-static units in the electro-magnetic unit of electric quantity," Thomson argued that the relation between aether and matter on the atomic scale must play a crucial part in the physical representation of Maxwell's theory. "All of this essentially involves the consideration of ponderable matter permeated by, or imbedded in ether, and a tertium quid which we may call electricity, a fluid go-between, serving to transmit force between ponderable matter and ether and to cause by its flow the molecular motions of ponderable matter which we call heat." 245 Thomson's hypothesis, dating from 1856, that electricity is an essence of matter was expressed here in terms of a tertium quid between aether and matter, a "fluid go-between." Thomson

said nothing here or elsewhere about incorporating a discrete charge into his synthesis. It was FitzGerald who introduced the concept of a discrete charge into British field 242 Ibid.,

theory in the early 1880's, laying the foundation for the

p. 462 . 244 Ibid., p. 464.

243ibid., p . 463. 2^Hbid., pp. 464-465.

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synthesis of the Maxwell and Thomson traditions into the electron theory of matter. FitzGerald further paved the way for the synthesis with his electromagnetic interpretation of MacCullagh's optical theory. In 18791880, he demonstrated that if the magnetic force is visualized as the velocity in MacCullagh's rotationally elastic aether and if the aether is assumed incompressible, then MacCullagh's theory is formally equivalent to Maxwell's electromagnetic theory of light. 246 FitzGerald believed that this representation was superior to Maxwell's because electric displacement, or polarization, refers to "changes in structure of the elements of the ether" and not to a displacement or movement of the elements of the medium. 247 In his vortex-sponge and vortex-filament models, FitzGerald imagined structural changes that might represent the electric displacement in the context of MacCullagh's rotationally elastic aether. 248 Following the research program Thomson had established with his vortex-atom, FitzGerald sought a solution in terms of the relation and mode of interaction between the aether and matter. In 1879 he suggested that electric disturbances may originate from "the relation of matter and ether, and this is probably an atomic interaction, as spectroscopic phe­ nomena also seem to show, and will be explained only when some work­ able hypothesis as to the nature of this interaction has been sufficiently investigated." 249 In 1882 he noted that "it seems further probable that, contrary to what I have stated in my first paper, the interactions between the molecules of matter and the ether are of the same character as the electromagnetic actions with which we are acquainted." 250 By 1885 he 246 G. F. FitzGerald, "On the Electro-Magnetic Theory of the Reflection and Re­ fraction of Light," read 9 January 1879, published in Phil. Trans. Roy. Soc., 171 (1880), 691-712; reprinted in FitzGerald, Writings, op. cit. (note 183), pp. 41-73. 247 G. F. FitzGerald, "Sir William Thomson and Maxwell's Electromagnetic Theory of Light," Nature, 32 (1885), 4; reprinted in FitzGerald, Writings, op. cit. (note 183), pp. 170-173, on p. 173. Also see p. 162. 248 G. F. FitzGerald, "On a Model Illustrating Some Properties of the Ether," Proc. Roy. Dublin Soc., 4 (1885), 407-412; and "On the Structure of Mechanical Models Illustrating Some Properties of the Ether," Phil. Mag., 19 (1885), 438. Reprinted in FitzGerald, Writings, op. cit. (note 183), pp. 142-156 and 157-162, respectively. 249 G. F. FitzGerald, "On the Possibility of Originating Wave Disturbances in the Ether by Means of Electric Force," read 17 November 1879, published in Trans. Roy. Dublin Soc., 1 (1879), 133-134; reprinted in FitzGerald, Writings, op. cit. (note 183), pp. 90-92, on p. 92. 250 G. F. FitzGerald, "On the Possibility of Originating Wave Disturbances . . . — Corrections and Additions," read 5 May 1882, published in Trans. Roy. Dublin Soc., 1 (1883), 325-326; reprinted in FitzGerald, Writings, op. cit. (note 183), pp. 99-101, on p. 101.

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had presented a "crude mechanism in order to show that it is possible to represent by a mechanism the connexion between the ether and matter, and also to illustrate how electrostatic attractions depend entirely on the way the ether is connected with matter."251 That same year he insisted that "in order to represent the rotation of the plane of polarization of light by magnetism, it would be necessary to introduce some mechanism connecting this ether with matter."252 In 1893, after a ten-year dialectical study of Maxwell's electromagnetic theory and Thomson's analyses of magneto-optic rotation, Larmor dis­ carded the polarization representation of the dielectric displacement for "some more continuous mechanism such as an elastic displacement in an aether loaded with the molecules of the dielectric." When he discovered FitzGerald's analysis of MacCullagh's theory, Larmor immediately under­ took a critical comparison of the various theories of light with reference to the action of magnetism on light.253 Examining the multitude of aether models, both optical and electric, Larmor showed that they led to the same energy equations for the aether. He then restricted his attention to Mac­ Cullagh's rotationally elastic aether, because "for the explanation of elec­ trical phenomena, MacCullagh's energy function possesses fundamental advantages for which none of the other possible optical schemes appears to be able to offer any equivalent."254 These fundamental advantages were twofold. First, since FitzGerald had already translated the rotationally elastic model into the language of the electromagnetic theory, all details of Maxwell's theory could more easily be incorporated into it. Second, and at that stage of his synthesis more important, Thomson had already explained how purely rotational elasticity could exist in an otherwise ho­ mogeneous medium, how vortical motions of finite portions of this me­ dium might constitute matter, and how the strains that they create in the surrounding aether might explain magneto-optic rotation. By examining electrical phenomena in terms of this model of the relation between aether and matter, Larmor deduced that the electric charge, or straincenter, is the fundamental constituent of matter, that Maxwell's equations must be modified for matter in motion through the aether, and that the radiation that matter emits and absorbs may reveal something about atomic structure. 251

FitzGerald, "On a Model . . . ," op. cit. (note 248), p. 144. "On the Structure . . . ," op. cit. (note 248), p. 161. 253 Larmor, op. cit. (note 48). 254 Larmor, op. cit. (note 37), p. 436. 252 FitzGerald,

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Correcting Maxwell's Theory of Electromagnetism The conception of the aether as a new type of physical reality different from matter was essential to Faraday's, Thomson's, and Maxwell's the­ ories. The difficulties that Faraday and Maxwell shared related to that difference. They sought ways of representing activities within the nonmaterial aether, and of representing the interactions between the aether and matter. Faraday's conceptions progressed from polarized particles to a Boscovichian monism, neither of which conception admitted a difference between aether and matter, to an acknowledgement of the dualism of aether, or space void of matter, and matter. Having arrived at the field con­ cept, Faraday represented its unique mode of action in terms of a con­ tinuous transmission of strain through the aether plenum. Maxwell accepted Faraday's notion of the uniqueness of the aether and continued groping for a conception that would reflect both the difference and mode of connection between aether and matter. In this Maxwell failed: neither his model nor his equations reflected the difference between aether and matter because he could not conceive of their mode of interaction. Thomson's vortex-atom theory of matter succeeded in representing the difference and one mode of interaction between aether and matter, but it could not encompass electric phenomena. Maxwell's theory, like the wave theory of light, was essentially molar. But whereas Maxwell's theory emphasized the role of the medium in elec­ tric and optical actions, its limitations could only be overcome by con­ sidering the source of action, the electric charge, and the relation between the molecular structure of material bodies and electric and optical phe­ nomena within them. During the 1880's physicists turned their attention to the nature of the electric charge, and found a clue to resolving the paradoxes and inconsistencies in Maxwell's electromagnetic theory and Thomson's vortex-atom theory. By incorporating the discrete electric charge into Maxwell's theory, both the representations and the equations could more consistently incorporate the uniqueness of the aether as a reality unlike matter.

The Medium Plus the Source: Incorporating Charged Particles Throughout the century two hypotheses about the transmission of elec­ tric action prevailed: one identified the transmission with the movement of particles of electricity, the other with changes in the physical state of

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the aether. 255 Although the British school concentrated heavily on the aether hypothesis, Maxwell analyzed electrolytic conduction as the pas­ sage of charged particles. 256 But he never attempted to incorporate charged particles into the foundations of his electromagnetic theory. By contrast with the British, Continental theorists such as Gustav Fechner, Wilhelm Weber, 257

Bernhard Riemann, Gustav Robert Kirchhoff, 258

Rudolf Clausius, and Helmholtz emphasized the movement of charged electric particles endowed with mass and forces acting at a distance. 259 Helmholtz tried to combine the concepts of electric particles and the transmission of electric force in the medium; an advocate of Maxwell's theory, he popularized the notion that Maxwell's electromagnetics is not contradicted by the assumption of electric particles. 260 Thus, the particle hypothesis was not inherently foreign to Maxwell's theory, but had merely been ignored. Indeed, Faraday's quantitative laws of electrolysis had been interpreted by both Maxwell and Helmholtz as demonstrating that "electricity is distributed in an atomic manner, that each atom of matter has its definite electric equivalent, the same for all kinds of atoms"; and even the expressive phrase "an atom of electricity" was imported into

255 See,

for example, Hesse, op. cit. (note 6), pp. 216-222, for the Continental ac­ tion at a distance school; for the field theories, see pp. 189-215. Forcorresponding discussions, see Whittaker, op. cit. (note 6), 1, 198-236, 171-194, and 240-303. 256 Maxwell, Treatise, op. cit. (note 161), #768-770. 257 See A. E. Woodruff, "Action at a Distance in Nineteenth Century Electrody­ namics," lsis, S3 (1962), 439-459; and J. R. Ravetz, "Action at a Distance," Br. J. Hist. Sci., 1 (1962), 78-82. J. Larmor, "A Dynamical Theory of the Electric and Luminiferous Medium.—Part II. Theory of Electrons," Phil. Trans. Roy. Soc., 186 (1895), 695-743, read 20 June 1895; reprinted in Larmor, Papers, op. cit. (note 37), 1, 543-597, on pp. 578-579, compares Weber's molecular theory, described in #846860 of Maxwell's Treatise, with his own theory of electrons. Larmor writes that in Weber's theory "electric molecules act on one another directly at a distance accord­ ing to a law of force which involves their relative velocity," whereas "on the present theory actions are transmitted from one moving electron to another solely by the intervention of the aether" (ibid.). 258 Larmor, op. cit. (note 48), pp. 346-353; id., op. cit. (note 37), pp. 422-424, argues that Kirchhoffs optical aether theory of 1876 is "in its elementsjust the same as the labile elastic solid optical aether," but that it arrived at different results for reflection because of faulty mathematical procedures. 259 Whittaker, op. cit. (note 6), 1, 198-236. 2(0 Ibid., pp. 354-355. H. von Helmholtz, u On the Modern Development of Faraday's Conception of Electricity," J. Chetn, Soc., 39 (1881), 227. See also A. E. Woodruff, "The Contributions of Hermann von Helmholtz to Electrodynamics," lsis, 59 (1968), 300-311.

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the theory by Maxwell.261 By the 1880's British physicists were also seek­ ing to assimilate the hypothesis of charged particles of electricity into Maxwell's theory. In 1881, in his paper "On the Electric and Magnetic Effects Produced by the Motion of Electrified Bodies," J. J. Thomson argued that Maxwell's displacement current causes the magnetic effects of moving conductors and showed that the resistance that a moving electrically charged body experiences as it moves through a dielectric "must be equivalent to an increase in the mass of the charged moving sphere."262 Max Jammer states that Thomson "envisioned the possibility of reducing inertia to electromagnetism," but no suggestion of this is found in the paper itself.263 It is with hindsight that Thomson's paper takes on this additional significance. Indeed, Thomson had to consider these magnetic effects of moving charges merely "equivalent to" an increase in mass of the charges because he had not yet made any physical connection between the electric field and mat­ ter in motion: alterations in the electric field, or displacement currents, incited by the moving charges provided the total current, and the moving charges contributed no direct electric effect. As FitzGerald demonstrated that same year, Thomson's equations do not satisfy Maxwell's circuital condition, and the term that must be added to provide a closed circuit is physically explicable only on the assumption that "a moving quantity of electricity acted like an element of an electric current." In fact, only the convection current of the moving charged body, not Maxwell's displace­ ment current, gives rise to magnetic effects; the terms implying an in­ crease of mass arise from the convection current alone.264 In 1889 Oliver Heaviside derived a more exact form of the Thomson-FitzGerald formula for the increase in mass of a charged moving sphere and, guided perhaps by vortex-atomism, considered the increase of mass a real inertial effect.265 Although, from hindsight, the development stemming from J.J. Thom261 Larmor ,Aether

and Matter, op. cit. (note 6), p. 25. J. Thomson, "On the Electric and Magnetic Effects Produced by the Motion of Electrified Bodies," Phil. Mag., 11 (1881), 229-249. 263 Jammer, Concepts of Mass, op. cit. (note 6), p- 136. 2m G . F. FitzGerald "Note on Mr. J. J. Thomson's Investigation of the Electromag­ 1 netic Action on a Moving Electrified Sphere," Proc. Roy. Dublin Soc., J (1881), 250; reprinted in FitzGerald, Writings, op. cit. (note 183), pp. 102-107. 265 Oliver Heaviside, "On the Electromagnetic Effects Due to the Motion of Elec­ trification Through a Dielectric," Phil. Mag., 27 (1889), 324-339; reprinted in Oliver Heaviside, Electrical Papers, 2 vols. (Boston, 1925), 2, 504. Jammer, Concepts of Mass, op. cit. (note 6), pp. 138-141, and Whittaker, op. cit. (note 6), 1, 307-309, give modernized versions of Heaviside's solution. 262 J.

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son's 1881 paper may appear to be the foundation for the electromagnetic view of matter, it was but one of several elements contributing to it. In fact, it was not among those factors that directly stimulated the first explicit statement of the electromagnetic theory of mass by Larmor in 1893. Whereas Thomson in 1881 did not even allow the moving charge a direct electric effect, by 1893 Larmor had concluded from his dialectical study of electric and optical theories that the convection of electric charges is the sole cause of the phenomena of the electric field; from this result Larmor concluded that Maxwell's hypothesis that the total current is circuital "involves and is equivalent to the magnetic influence of moving charges." 266 The major sources of Larmor's electromagnetic view of nature were the considerations by several physicists of the nature of the charge and its mode of interaction with both aether and matter, and Larmor's own considerations of the relations between charges, matter, and aether within the context of the vortex-atom, field-theoretic conception. The return to the charge, the source, enabled the physicists of the 1880's and 1890's to correct Maxwell's theory. They asked how the electric charge interacts with the field and proposed many answers. J. Willard Gibbs imagined an interaction between the electromagnetic wave and "the free vibrations of the atomic electric charges." 267 Helmholtz, and Lorentz after him, examined the effect on radiation of "a charged harmonic oscil­ lator within a molecule." 268 After progressing from Helmholtz' polariza­ tion version of Maxwell's field to Hertz's purified version, Lorentz made the electric charges of Hertz's analysis more than mere starting points of changes occurring in the medium. In Lorentz' theory, moving electric charges influence the medium, and new equations of the electromagnetic field are required to describe the situation. Larmor continued the attempts of Maxwell, Helmholtz, and Hertz to represent electromagnetic phenomena within the framework of Maxwell's theory. He developed the first consis­ tent representation of both the difference and the interrelation between aether and matter by incorporating the electric charge into a theoretical 266 Larmor, ed., Scientific Writings of . . . FitzGerald, op. cit. (note 183), pp. xlviii-xlix. 267 J. Willard Gibbs, "On the General Equations of Monochromatic Light in Media of Every Degree of Transparency," Am. J. Sci., 25 (1883), 107-118; reprinted in The Collected Works of J. Willard Gibbs, 2 vols. (New York, 1928), 1, 211-222. J. Lar­ mor, "The Singularities of the Optical Wave-Surface, Electric Stability, and Magnetic Rotatory Polarization," Proc. London Math. Soc., 24 (1893), 272-290; reprinted in Larmor, Papers, op. cit. (note 37), 1, 292-309, on p. 300; id., op. cit. (note 47), p. 410 268 T. Hirosige, op. cit. (note 203), pp. 173-179.

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complex that included William Thomson's vortex-atom conception and his related explanation of magneto-optic rotation, MacCullagh's rotationally elastic optical aether theory, and Maxwell's theory of electromagnetic radiation. The Vector Potential, Displacement Currents, and Moving Charges Although Maxwell's purpose was to distinguish between aether and mat­ ter, his theory only superficially attained this end. All of the electro­ magnetic energy or force was in principle located in the medium. But, perhaps because he worked from the side of electricity and magnetism which involved material dielectrics and magnets for the media, Maxwell spoke of the aether as the limit of a dielectric of polarized particles, so that there was only a blurred distinction between the aether and the mate­ rial dielectrics. Consequently, he did not include an independent variable to represent the electromagnetic field when he put the theory in Lagrangian form. 269 In addition, he considered certain quantities involved in the equa­ tions for material dielectrics to be fundamental quantities of electromagnetism; he alternatively identified these quantities as the vector potential of the electric current, the electromagnetic momentum at a point, and Faraday's electrotonic state. 270 In the mid-1880's physicists in trying to obtain standard terminology, units, symbols, and formulas for electromagnetic theory questioned Max­ well's use of the scalar and vector potentials as fundamental quantities. 271 Heaviside argued that the potentials, "if given everywhere, are not suffi­ cient to specify the state of the electromagnetic field." There was "nothing absolutely wrong," but the potentials were not applicable to the "general" case. Instead, a "mathematical expression of the Faraday law of induc­ tion," obtained "immediately and independently" of the potentials, also led to the equations of the potentials "as its consequence." Having abol­ ished the "highly artificial quantities" from the fundamental equations, and using them only "for special purposes," he argued that we are brought into immediate contact with the electric force and the magnetic force, which "have physical significance in really defining the state of the me­ dium anywhere . . . which [the potentials] do not, and cannot, even if given over all space." 272 269 Zbid 210 See

1 p. 192. Alfred M. Bork, "Maxwell and the Vector Potential," his, 58 (1967), 210-

222. 2 ^ 1 Ibid. See also Alfred M. Bork, "Physics Just Before Einstein," Science, 152 (1966), 597-603. 272 Oliver Heaviside, "On the Self-Induction of Wires," Phil. Mag., 22 (1886), 118137; reprinted in Heaviside, Papers, op. cit. (note 265), 2, 168-185, on pp. 172-173.

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Heaviside's formulation of electromagnetic theory in terms of two funda­ mental quantities, the electric and magnetic forces, specified the nature of the free aether and thereby helped establish its mathematical and con­ ceptual independence from matter. Maxwell had originally used this formulation, "being the simplest and most direct formal expression of the theory," but he left it aside "in favour of a conception of electrodynamic momentum or vector potential that was intended to connect the equa­ tions directly with dynamical principles." 273 Nearly simultaneously with Heaviside, FitzGerald and Hertz also concluded that the potential function did not apply to the free field. Whereas Heaviside and Hertz made use of the potential functions of the vector electric current and the scalar elec­ tric distribution and then eliminated them, no such potentials occurred in FitzGerald's dynamical procedure based on the energy function; he merely began from the pair of circuital relations between the fundamental vectors that result when the potentials are eliminated. On the other hand, Hertz did not go so far as Heaviside and FitzGerald in denying physical meaning to the potential and allowing its use only as a mathematical tool in com­ plex calculations. Rather, Hertz admitted that Maxwell had introduced the potential because the "distance forces which appeared discontinuously at particular points were replaced by magnitudes which at every point in space were determined only by the conditions at the neighbouring points." But, he continued, we now "have learnt to regard the forces themselves as magnitudes of this latter kind," so that "there is no object in replacing them by potentials unless a mathematical advantage is thereby gained." 274 It was necessary for physicists to recognize that the potential function is not required to express the state of the aether. That state is defined solely in terms of the electric and magnetic forces and associated energies. Physicists like Heaviside and J. H. Poynting were able further to mathematize the activity of the field in terms, for instance, of fluxes of this energy. 275 Hertz was able to accept Maxwell's essential principle that the 273 Joseph Larmor, "Abstract, A Dynamical Theory of the Electric and Luminiferous Medium.—Part III: Relations with Material Media," Proc. Roy. Soc., 61 (received 21 April and read 13 May 1897), 272-285; reprinted in Larmor 1 Paperi, op. cit. (note 37), 1, 625-639, on p. 626. 274 Heinrich Hertz, Electric Waves, trans. D. E. Jones, preface by William Thomson, Lord Kelvin (London, 1900), pp. 195-196. 275 J. H. Poynting, "On the Transfer of Energy in the Electromagnetic Field," Phil. Trans. Roy. Soc., 175 (1884), 343-362; "On the Connection between Electric Current and the Electric and Magnetic Inductions in the Surrounding Field," ibid., 176 (1885), 277-306. Oliver Heaviside, for example, "On Resistance and Conduc­ tance Operators, and Their Derivatives, Inductance and Permittance, Especially in Connection with Electric and Magnetic Energy," Phil. Mag., 24 (1887), 479-502;

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field is a real physical entity. Yet the purely formal attitude towards the potential function could not resolve the paradoxes and problems involved in establishing the difference between aether and matter. Maxwell and Hertz believed the potential function represented reality in the me/dium, but they lost sight of the concept of charged particles that led to the mathematical function and that therefore may otherwise influence the field. 276 The presence of matter in the aether was thought not to alter the equations of the aether. Hertz and Heaviside made no change in Maxwell's equations for charged conductors in motion in the aether; they thought that matter pulls the surrounding aether along with it. 277 The role of the source of the field was obscured by the formal attitude. When the electric charge and its relation to the medium were considered, as in Larmor's electron and Lorentz' ion theories, the potential function found its true physical interpretation and the correct equations for moving conductors were derived from it. As Larmor observed, what Maxwell, FitzGerald, Heaviside, and Hertz lacked for the "satisfactory accomplish­ ment of [placing 'the fundamental formal equations of the aether itself on a dynamical basis'] . . . was a definite and consistent idea of how the elec­ tric charges and currents in the matter establish a hold on the aether." 278 Although FitzGerald was first to note that the magnetic action of moving electric charges is just as necessary as displacement currents in order to make all circuits closed, his dynamical method eliminated the potentials altogether and thus was "limited expressly to the case of transparent media, in which there are no wandering electric charges." 279 Larmor sought a conception for the mode of interactions between electric charges and aether within the context of the electromagnetic theory of light and the vortex-atom theory of matter; he arrived at the concept of the electron and with it resolved the problems in Maxwell's potential function and equations for moving media. For Larmor the potential function was not merely a mathematical tool "On the Forces, Stresses, and Fluxes of Energy in the Electromagnetic Field," Phil. Trans. Roy. Soc., 183 (1892), 423-480. Reprinted in Heaviside, Papers, op. cit. (note 265), 2, 355-374 and 521-574, respectively. 276 More precisely, Hertz saw "electricity"—the positive and negative charges—as merely the starting point of the seeming distance forces, so that they have no influ­ ence on the field. 277 Hertz, Electric Waves, op. cit. (note 274), pp. 241 ff. Heaviside, "On the Forces . . . in the Electromagnetic Field," op. cit. (note 275), pp. 524-525. 278 Larmor, ed., op. cit. (note 183), introductory and biographical statement, pp. xliv-xlv. 279 Larmor, op. cit. (note 273), p. 627.

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but a representation of the physical situation: its great "complication" is "of the essence of a more thorough analysis" that considers the conditions imposed by the presence of the "wandering electric charges" that consti­ tute matter.280 Moving electric charges alter the state of the aether, and the vector potential defining that state must be interpreted in terms of these currents. When the potential function is recognized as "a physical entity as distinct from a mathematical expression," the effect of a moving

charged conductor on the state of the aether can be incorporated into Maxwell's equations. Many times in his papers, and again in editing them in 1927-1928, Larmor observed that confusions still surrounded Maxwell's notion of the vector potential. "One of the main sources of the obscurity said to inhere in Maxwell's formulation" was that there are two ways of looking at the vector potential in terms of currents.281 The potential function may be considered as a potential propagated "from the seats of the true electric disturbances"; namely, from the "true current" of moving electrons. Al­ ternatively, the potential function may be interpreted as "an instantaneous mathematical potential of the total circuital current which includes ethe­ real displacement as well as electric." The latter interpretation, which incorporates Maxwell's view of the reality of the potentials in the medium, appeared to many physicists to contradict both Maxwell's theory of pure propagation in time and the interpretation of potentials in terms of the true current. Larmor said that this misconception can be cleared up if one recognizes that "the potential [of the total current] is in part that oiethe­ real displacement, which is not electric disturbance but merely a result thereof like the potential itself."282 Maxwell's formulation was incorrect until the magnetic action of moving charges was added to that of displace­ ment currents. Ironically, once this correction was made, physicists tended to ignore the physical meaning of the displacement current and its relation to the true current. Thus, the confusions surrounding Maxwell's notion of the vector poten­ tial were related to the confusions surrounding his notion of electric dis­ placement. In his attempt to find a consistent representation for Maxwell's electric displacement that would comprehend phenomena involving the interactions between aether and matter, Larmor determined that the total electric displacement consists of the movement of discrete charges, or 280 Larmor,

Aether and Matter, op. cit. (note 6), p. 22. ed., op. cit. (note 183), pp. 90-91n. 282 Larmor, op. cit. (note 37), pp. 511, 512n.

281 Larmor,

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centers of rotational strain, plus an aethereal "displacement" representing transmission of rotational strain. That is, Larmor interpreted Maxwell's electric displacement and vector potential as physical entities within the context of a field-theoretic view of aether and matter. In the 1850's Maxwell and Thomson took diverging paths to develop the recently emer­ gent concept of the field; when the insights gained along each path were combined, the field attained its first consistent and comprehensive state­ ment. By 1900, however, it had already become popular to say that the poten­ tial function is only an auxiliary mathematical apparatus which does not represent physical quantities. 283 The attitude that the potential function serves only as a tool for calculation was in line with the current movement against models. Larmor's physical interpretation, which explained the rela­ tion between electric displacement, true and total currents, and the vector potential, was soon ignored.

Problems in the Representations: Polarization versus Continuous Transmission The emphasis by British physicists on the medium of action had di­ verted their attention from the source of that action, the electric charge. Larmor arrived at his conception of the relation between charge, matter, and aether, and thereby at his unique explanation of Maxwell's displace­ ment current and the true current, through a study of the several represen­ tations that had been proposed to explain Maxwell's electric displacement. The representations or models played a fundamental role in the creation of the first electron theory of matter. Helmholtz in 1870 "translated" Maxwell's theory of electromagnetism into the Continental mode of analysis which considered electricity as the motion of charged particles acting at a distance. 284 He incorporated the British conception of the essential role of the medium in electromagnetic phenomena, but he regarded the aether as a polarized dielectric. The 283 Larmor acquiesced in the new attitude toward the potential function; see Lar­ mor's statement in Bork, op. cit. (note 270), p. 222. Larmor there observed that the potential function "can now if it is thought fit be dispensed with" since its use was to facilitate integration by parts. Yet, Larmor qualified the statement by saying that "these auxiliary functions" do not "directly represent physical quantities" that "are propagated" {Aether and Matter, op. cit. [note 6], pp. 93, 112). 284 Helmholtz, "Uber die Bewegungsgleichungen der Elektricitat fur ruhende leitende Korper," Journal fur die reine und angewandte Mathematik, 72 (1870), 57-129; reprinted in Helmholtz, WissenschaftUche Abhandlungen, 3 vols. (Leipzig, 1882-1895), 1, 545-628. See Woodruff, op. cit. (note 257), pp. 439-459.

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polarization was a fundamental characteristic of the medium, it is true, but it again was explained in terms of a particulate structure of the me­ dium with forces acting at a distance. Helmholtz recognized that whereas Maxwell had tried to eliminate action at a distance by means of his con­ ception of polarization in a dielectric, his own polarization theory would only "diminish" action at a distance: The two theories are opposed to each other in a certain sense, since ac­ cording to the theory of magnetic induction originating with Poisson, which can be carried through in a fully corresponding way for the theory of dielectric polarization of insulators, the action at a distance is diminished by the polarization, while according to Maxwell's theory on the other hand the action at a distance is exactly replaced by the polar­ ization. . . . It follows . . . from these investigations that the remarkable analogy between the motion of electricity in a dielectric and that of the light aether does not depend on the particular form of Maxwell's hypoth­ eses, but results also in a basically similar fashion if we maintain the older viewpoint about electrical action at a distance.285 In an early paper in 1875, Lorentz retained Helmholiz' polarization conception of the aether, and simultaneously with other physicists in Britain and on the Continent, he sought to establish the aether as a sub­ stance different from matter.286 But he did not succeed until 1892 after additional clues had come from Britain through Hertz's advocacy of Max­ well's plenum to replace action at a distance. Helmholtz also adhered to action at a distance until around 1894 when he acknowledged in his pref­ ace to Hertz's Principles of Mechanics that Maxwell's theory had indeed introduced a new concept, a continuous field, which could explain action in the medium without recourse to action at a distance between aether molecules.287 In his "Introduction" to Electric Waves, Hertz related how he had been led prior to the actual discovery of the waves to give up Helmholtz' notion of action at a distance and to adopt in its place the conception that all 285 Helmholtz, ibid., pp. 556-558. Quoted by Woodruff, op. cit. (note 260), pp. 307-308. 28 ^H. A. Lorentz, doctoral thesis, Over de Theorie der Terugkaatsing on breking vanhet licht (Leiden, 1875); reprinted in Lorentz, Collected Papers, 9 vols. (The Ha^ue, 1935-1939), 1, 1-92. The French translation of his thesis appears in the same volume. See the discussion of this work by Hirosige, op. cit. (note 203), pp. 159-173. 287 Woodruff, op. cit. (note 257), p. 459.

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action occurs within the continuous medium. 288 After discovering the electric waves, Hertz became a staunch believer in the reality of the field and sought to understand Maxwell's theory more fully. He observed that although Maxwell at times, like Helmholtz, conceived of the aether with the aid of an analogy of a material dielectric, Maxwell's equations apply only to the limiting conception of the dielectric in which all the energy be­ longs to the medium. Hertz adopted the "pure conception of action through a medium"; he believed that the "changes in space are . . . actually present" and that neither the distance forces nor "the electricities from which these forces are supposed to proceed" really exist. Although the electricities—the positive and negative charges—are the "starting points" of the changes in space, they have no influence on the medium. 289 Hertz had joined the British school, which hypothesized a plenum in intimate rela­ tion with matter. 290 His analyses rested entirely on the supposition that there is "only one medium filling the space" and that "air and empty space behave like all other dielectrics," so that "the gist and special signifi­ cance of Faraday's, and therefore of Maxwell's, view" is that "space is nowhere empty" and is the only means by which "material bodies act upon one another." 291 Hertz's, like Maxwell's, view of electricity could not adequately represent either mathematically or conceptually the commonly observed phenomena involving both aether and matter. Although based on a "pure conception of electricity," Hertz's theory failed to distinguish between aether and matter; the electromagnetic field existed in both media. 292 In 1892 288 Hertz

also noted there that Lodge had already observed oscillations and waves in wires, and "inasmuch as he entirely accepted Maxwell's views, and eagerly strove to verify them, there can scarcely be any doubt" that he eventually would "have suc­ ceeded in observing waves in air and thus also in proving the propagation with time of electric force." FitzGerald, another believer in Maxwell's theory, also "had some years before [1883] endeavoured to predict, with the aid of theory, the possibility of such waves, and to discover the conditions for producing them." (Hertz, Electric Waves, op. cit. [note 274], p. 3.) Wlbid., pp. 20-28, 25, 27. 290 In the preface to the English edition of Hertz, Electric Waves, op. cit. (note 274), p. xv, William Thomson included Hertz in the group of "many workers and many thinkers [who] have helped to build up the nineteenth-century school of plenum, one ether for light, heat, electricity, magnetism." 291 Ibid, pp. 241, 6, 7, 25. 292 Heinrich Hertz, "On the Fundamental Equations of Electromagnetics for Bodies in Motion," Ann. d. Phys., 41, (1890), 369-399. Id., Electrical Waves, op. cit. (note 274), pp. 240 et seq.; see pp. 240-242. Einstein characterized Hertz's theory as a dualism because in it the field exists both in matter and aether; however, he also characterized Lorentz' theory, which restricted the field to the aether, that way be-

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Lorentz combined Hertz's purified version of Maxwell's aether, according to which all force is in the medium and none acts at a distance, with the Continental postulate of electric charges associated with matter to arrive at the modern theory of the differences and relation between field and matter. Lorentz thus owed more than has generally been acknowledged to the British school for which the role of the medium had become a first prin­ ciple by midcentury. Hertz had explicitly advocated Maxwell's interpreta­ tion that the state of the aether, however described, is a fundamental physical reality. Like Maxwell, he wanted to be "understood literally" in speaking of the energy of the field. Hertz refused, however, to allow that a mechanical model of the aether, which British physicists continued to use as a tool for understanding, was necessary to explain Maxwell's theory. In this way, it has been argued, Hertz implied that the aether need not be mechanical.293 But I argue that Hertz had only eliminated the belief that a mechanical model of the aether is necessary to aether theory; he did not demechanize the aether. The nonmechanical aether was actually merely a consistent statement of the British conception. Hertz remained more of a mechanist than the British with their complex models; while the British were using a "new conception" in their models of the aether, Hertz retained the mechanical postualtes in his attempts to represent the continuous, pure aether. Even in his last work of 1894, he proposed, perhaps because of his monistic identification of aether and matter in his electric theory, that the aether had to be different from matter only in size. To Hertz the basic and suffi­ cient concepts of physics were space, time, and matter in motion; he pos­ tulated "concealed masses" undergoing "concealed motions" to explain apparent actions at a distance such as gravity, just as Helmholtz had hy­ pothesized "concealed polarization" as the cause of electricity.294 Hertz considered his theory of mechanics, which was the foundation of his elec­ tric theory, to be merely a modified version of Thomson's vortex-atom cause it did not account for the relation between aether and matter. The word "dual­ ism" is generally used in this latter sense. Thus, Hertz's theory was a monism because it made no distinction between aether and matter in either their natures or activities. Lorentz and Larmor distinguished between aether and matter in both senses. ^ 93 See, for example, Hesse, op. cit. (note 6), p. 214. 294 Heinrich Hertz, The Principles of Mechanics, trans, D. E. Jones and J. T. Walley (London, 1899), pp. 25-26. Note that Hertz there attributed this understand­ ing of the basic concepts of physics to Maxwell and his electromagnetic theory and to Thomson and his theory of vortex-atoms.

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theory of matter, but he misinterpreted that theory as one in which the all-pervasive medium consists of infinitely small "inextensible nuclei" in vortical motion. 295 Because Maxwell's electric theory had been appended ad hoc to the Continental analyses and because the continuity of Thom­ son's plenum in the vortex-atom theory had not been appreciated fully there, physicists on the Continent were faced with the same dilemma that Thomson had noted at midcentury: the aether could not be matter in motion and it could not be represented by even the limiting conception of a particulate medium. The continuity of the plenum can be interrupted only where a material body has arisen out of its structure. Certain German physicists including the young Einstein, who drew on some concepts familiar from mechanical pictures in his early discussion of the electromagnetic field, followed the Continental postulates. 296 But by 1897 the position of the energeticists, combined with the wide acceptance of Maxwell's theory as corrected by Larmor and Lorentz, had forced upon the majority of the German physicists the recognition of what Ludwig Boltzmann called the equally important "advantage of deriving the whole science of mechanics from conceptions which anyhow are indispensihle for the explanation of electromagnetism." 29 ' These conceptions were foreign to the German school and had been imported from Britain and developed by Helmholtz, Hertz, Boltzmann, and Lorentz. History must not propagate the error that the modern field as a nonmaterial entity is a German 295 Hertz expounded what he believed to be the similarities and differences be­ tween his aether-matter theory and Thomson's: the theory of vortex-atoms "presents to us an image of the material universe which is in complete accord with the princi­ ples of our mechanics. And yet our mechanics in no wise demands such simplicity and limitation of assumptions as Lord Kelvin has imposed upon himself. We need not abandon our fundamental propositions if we were to assume that the vortices re­ volved about rigid or flexible, but inextensible, nuclei; and instead of assuming simply incompressibility we might subject the all-pervading medium to much more complicated conditions, the most general form of which would be a matter for further investigation. Thus there appears to be no reason why the hypothesis ad­ mitted in our mechanics should not suffice to explain the phenomena" (ibid., pp. 3738). 296 See A. Korn, Eine Theorie der Gravitation und der elektrischen Erscheinungen auf Grundlage der Hydrodynamik (Berlin, 1894); second and third editions in 1896 and 1898. See Whittaker, op. cit. (note 6), 1, 289. For the transformation that oc­ curred in Einstein's conception from a mechanistic preference to an insistent prefer­ ence for unifying field theory concepts by 1909-1911, see R. McCormmach, "Einstein, Lorentz, and the Electron Theory," Historical Studies in the Physical Sciences, 2 (1970), 41-87. 297 Ludwig Boltzmann, Vorlesungen uber die Prinzipe der Mechanik (Leipzig, (1897), pp. 138-139. Quoted by Jammer, Concepts of Mass, op. cit. (note 6), p. 142.

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phenomenalist contribution, a correction of the misguided British mechanists. On the contrary, it was within the British school that the modern field concept was developed. In fact, Boltzmann emphasized that Lorentz' theory "does not intend to explain the concepts of mass and force, the law of inertia, and so forth, from something more simple and something that can be comprehended more easily." That was the program Larmor had established for his electron theory;298 the first electron theory of matter and electromagnetic view of nature were uniquely British. Larmor continued the British tradition of probing the relation between charge, matter, and aether and seeking a consistent representation of Max­ well's electromagnetic theory. In one of his earliest papers, dated Novem­ ber 1885, he examined Clausius' "well-known molecular theory" of galvanic polarization. The close agreement of several independent esti­ mates of molecular distance derived from considerations of galvanic po­ larization, Larmor reasoned, is strong evidence for the independent exis­ tence of ions or charged atoms of matter which are polarized by the action of an electric force. But, like Thomson in his earliest papers, Larmor temporarily put aside speculations "on the deeper question of the relation of the material atom to its electrical charge."299 A study of rotary polar­ ization in terms of Thomson's gyroscopic illustration, dated 12 June 1890, redirected his thoughts to the relation of charge, matter, and aether.300 In May 1891 he attempted to obtain a generalized theory of electrodynamics that would reconcile Helmholtz' polarization theory, which allows condensational waves, and Maxwell's elastic medium, which does not, concluding that the theory of electrodynamics "appears to be, on all sides, limited to Maxwell's scheme, which has also so much to rec­ ommend it on the score of intrinsic simplicity."301 Larmor noted in June 1892 that although Helmholtz' polarization model is valid only in the limiting case, it is more general and easier to follow than Maxwell's mechanical model of an elastic medium. Because Maxwell's electrodynamic equations "involve nothing directly of the elastic structure of this medium," but "involve simply the assumption of displacement 298Ibid. 299 Larmor, "On the Molecular Theory of Galvanic Polarization," Phil. Mag., 22 (1885), 422-435; reprinted in Larmor, Papers, op. cit. (note 37), 1, 133-145. 300 Larmor, "Rotary Polarization, Illustrated by the Vibrations of a Gyrostatically Loaded Chain," Proc. London Math. Soc., 21 (1890), 423-432; reprinted in Larmor, Papers, op. cit. (note 37), 1, 205-213. 301 Larmor, "On a Generalized Theory of Electrodynamics," Proc. Roy. Soe., 49 (1891), 521-536; reprinted in Larmor, Papers, op. cit. (note 37), 1, 232-247, on p. 247.

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across dielectrics with such properties as to make all electric currents circuital," it is possible to escape the elastic solid model and make use of other modes of representation, such as polarization. 302 LarmA questioned whether or not the polarization representation could explain the ponderomotive properties of the electric field.

He answered that although the

limiting polarization theory is "complete as regards electromotive proper­ ties," it "fails to include the static ponderomotive phenomena of elec­ trification." Thus, "some dynamical theory of displacement of a more continuous character" must replace the limiting polarization theory; Larmor suggested "some more continuous mechanism such as an elastic displacement in an aether loaded with the molecules of the dielectric." 303 He stated the major problem for any contending theory of aether and matter: the mode of interaction between aether and matter must con­ form to the proven principle that all energy is located in the aether and is transmitted by a pure, continuous action or strain. He considered and rejected Rayleigh's idea of a compound medium of aether and matter in which a molecular web of matter is imbedded in a refined particulate aethereal substratum. That conception is unable to explain the charging and discharging of a dielectric: "when a dielectric is excited, we find our­ selves in the presence of a strain of an aethereal origin somehow produced; it would relax on discharge of the system with the velocity of light." 304 The nature of the connection of aether with matter must account for the origin of the stress. Larmor considered at length the question of the connection of aether and matter in a paper of December 1891 which analyzed the circular polar­ ization of light in terms of Thomson's gyrostatically loaded media. Larmor compared the "purely dynamical influence" of gyrostatic cells with various hypotheses "based on assumptions wholly electrical" that had been offered to explain the rotation of the plane of polarization of electrical waves (the Hall and Rowland effects for conducting and insulating media, respec­ tively). To make the analogy complete, he had to replace the dynamical conception of rotary inertia with "some formal quality of rotational type, associated with the electric displacement." 305 In more extensive analyses 302 Larmor "On the Theory of Electrodynamics, as Affected by the Nature of the 1 Mechanical Stresses in Excited Dielectrics," Proc. Roy. Soc., 52 (1892), 55-66; re­ printed in Larmor,Papers, op. cit. (note 37), 1, 274-287. 303 J(bid., p. 284. 304 Ibid., p. 286. 305 Larmor, "The Equations of Propagation of Disturbances in Gyrostatically Loaded Media, and the Circular Polarization of Light," Proc. London Math. Soc., 23 (1891), 127-135; reprinted in Larmor ,Papers, op. cit. (note 37), 1, 248-255, on p. 253.

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of magneto-optic rotation, Larmor accepted the insight of Thomson's 1856 paper that the vibrating system (aether) must be linked to another system that rotates around the lines of magnetic force.306 Meanwhile, his studies of magneto-optic rotation from the perspective of geometrical optics led him to speculate in April 1893 that the singularities in the light wave that guide its propagation in free space may indicate that the radia­ tion "is modified or dominated by the inertia and the free periods" of the material molecules in its substance.307 When Larmor discovered MacCullagh's rotationally elastic aether, which was already interpreted in terms of Maxwell's electromagnetic theory, he quickly adopted it as the new rep­ resentation of the aether's actions and undertook to explain the relation and mode of interaction between it and matter. Larmor adopted Thomson's vortex-atom conception as the necessary relation between matter and the rotationally elastic aether. He noted that it provides in addition a solution to the "great puzzle of radiation"; namely, how an elastic solid medium could "yet be so yielding as to admit of the motion of the heavenly bodies through it absolutely without resistance."308 Larmor assumed that the atom could have no other prop­ erty than vortex motion or intrinsic aethereal elastic twist, or possibly both. The latter property, representing the electric charge, was required to explain induction in a steady magnetic field and the permanence of elec­ tric currents. But, in attempting to work out the details of the new rep­ resentation and to explain material mass, Larmor was forced to discard the vortex motion and declare that the atom, or elementary constituent of matter, is nothing but a strain-center in the rotationally elastic aether plenum. Hence, the total electrical displacement consists of the movement of discrete charges as well as an aethereal displacement representing the transmission of rotational strain. The physical relation between the aethe­ real displacement and the movement of the discrete charges guarantees the continuous, circuital nature of the total current. The new electron theory thus showed that there is a difference between the electric displacement of the aether and the electric displacement or current due to moving elec­ trons, a difference of crucial significance for the study of bodies in motion. With this conception of a continuous rotationally elastic aether and straincenter electrons, Larmor sought to resolve the contradictions between 306 Larmor,

op. cit. (note 48), esp. p. 314. op. cit (note 267), pp. 294, 299. 308 In Part I of Larmor's "Dynamical Theory," op. cit. (note 37), pp. 389-535. This paper was received by the Royal Society on 15 November and read on 7 December 1893. 307 Larmor

1

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spectral radiation and the kinetic theory of gases and the problems of the electrodynamics of moving bodies. Implications of the Relation between Charge, Matter, and Aether In his Friday Evening Lecture delivered to the Royal Institution on 27 April 1900, forty years after the lecture in which he announced that the Leibnizian plenum must forever replace atoms in a void and action at a distance, Thomson identified two "clouds" that obscured "the beauty and clearness of the dynamical theory which asserts heat and light to be modes of motion."309 The first cloud concerned the relative motion of the aether and ponderable bodies. Thomson said that cloud was still "very dense," even though FitzGerald and Lorentz had suggested a contraction effect that could explain the problematical null results of the Michelson-Morley experiment on the influence of the motion of the earth on the velocity of light. The second cloud, which concerned the Maxwell-Boltzmann equipartition theorem, appeared irreconcilable with the dynamics of atoms and molecules required to explain spectral radiation; Thomson recommended that the theorem be abandoned. Thomson, an independent thinker, had not yet resolved these two prob­ lems within a comprehensive field theory of the atom; he apparently was not aware of the new electromagnetic synthesis by which Larmor dispersed these clouds and, with sharpened vision, developed the implications of that synthesis for atomic structure and electrodynamics. The method that Thomson now suggested for overcoming these problems was the method he had proposed long before and that had inspired Larmor's solution. Re­ garding the first cloud, Thomson said that "it has occurred to me that, without contravening anything we know from observation of nature, we may simply deny the scholastic axiom that two portions of matter cannot jointly occupy the same space, and may assert, as an admissible hypothesis that ether does occupy the same space as ponderable matter, and that ether is not displaced by ponderable bodies moving through space oc­ cupied by ether" (italics added).310 This, indeed, had been the hypothesis of the vortex-atom. Still seeking a modified field theory of the atom that could account for the breadth of electromagnetic phenomena and yet allow the atom to move freely through the aether, Thomson proposed "a 309 WiIliam Thomson, "Nineteenth Century Clouds over the Dynamical Theory of Heat and Light," Phil. Mag., 2 (1901). Reprinted as Appendix B in Thomson, Balti­ more Lectures, op. cit. (note 130), pp. 486-527, on p. 486. 310 Ibid.

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spherical atom producing condensation and rarefaction, with concentric spherical surfaces of equal density, but the same total quantity . . . of free undisturbed aether"; however, he noted that such an atom required the ad hoc contraction hypothesis. 311 At any rate, he emphasized that we can make the first cloud less dense "if we have a satisfactory fundamental relation between ether and matter, instead of the old intractable idea that atoms of matter displace ether from space before them, when they are in motion relatively to the ether around them." 312 To be satisfactory, the relation between matter and aether must not be hypothesized ad hoc to explain the results of the Michelson-Morley experiments; it must be an essential property of atoms demanded also by other phenomena. Because of its characteristic of moving freely through the aether, the original vortex-atom was a popular alternative in the 1880 ! s to both the Fresnel aether drift with partial aether drag and the Stokes total aether drag. The British physicist was fully aware that the physical relation be­ tween aether and matter held the key to the resolution of the problem of the motion of bodies through the aether. In 1892 Oliver Lodge analyzed the question of aberration and the electrodynamics of moving bodies, and concluded that physicists had been hindered in answering it by the limited extent of their "knowledge of the connection between ether and mat­ ter." 313 Heaviside in the same year identified "the connection between matter (in the ordinary sense) and ether" as "a really difficult and highly speculative question, at present," one that bore on the problem of motion through the aether. 314 It was apparent by 1892 that the simple vortexatom hypothesis was not able to solve the problem. The British physicist then sought a modified atom-plenum conception that would retain the successes but overcome the limitations of the vortex-atom conception. With respect to the second cloud, Thomson wanted merely to dispel the confusion surrounding the equipartition theorem, because he had not yet found an atomic model capable of explaining it. However, during the 1890's a number of British physicists, stimulated by Thomson's view that the vortex-atom must replace Lucretian atoms as the basis for the kinetic theory of heat and the cause of spectral radiation, incorporated the elec311 Ibid.,

pp. 487-488, 492. Quotation on p. 488. p. 491. 313 Oliver Lodge, "On the Present State of our Knowledge of the Connection be­ tween Ether and Matter: an Historical Summary," Physical Society, 27 May 1892. See the detailed summary of the lecture in Nature, 46 (1892), 164-165. 314 Heaviside, "On the Forces . . . in the Electromagnetic Field," op. cit. (note 275), p. 524. 312 Ibid.,

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trie charge into the vortex-atom conception in an attempt to reconcile the difficulties of the equipartition theorem. The result of that attempt, another element in Larmor's synthesis, was a complete development of the modern view of atomic structure and radiation, one that would be trans­ lated by Bohr in 1913 into the language of Planck's quantum constant.

The Problem of Motion through the Aether In his attempt in 1893 to represent the phenomena of aether and matter in terms of the rotationally elastic aether, Larmor noted that that represen­ tation would have "to be in accord with what is known on the subject of the connection between aether and matter, both from the phenomena of the astronomical aberration of light, and from recent experimental re­ searches [by A. A. Michelson and E. W. Morley in 1881, 1886, 1887] on the motion of the aether relative to the Earth, and relative to transparent moving bodies." 315 Before discussing Larmor's representation in this con­ nection, it will be useful to indicate how nineteenth-century British physi­ cists attacked the problem of motion through the aether. In 1728 James Bradley discovered a yearly displacement in the period of the stars towards the direction of the earth's motion in its orbit and interpreted this aberration as a phenomenon of relative motion. Larmor probed and summarized the issue of aberration in 1898. 316 He said that Bradley's explanation is valid if light travels with finite speed and is unaf­ fected by the motion of the earth. In the undulatory theory this requires either that the aether is not disturbed at all by the earth's motion through it, or else that some special adjustment of its motion gives the same result. Thus, the explanation of aberration "immediately opens up the whole question of the disturbance of the aether by the motion through it of material bodies like the Earth," and also the question of the manner in which the reflection or refraction of light in observing instruments is af­ fected by their motion with the earth. Other optical phenomena, however, were found not to depend on the direction of the earth's motion. F. Arago and A. Fresnel demonstrated that the motion of the earth does not affect the laws of reflection and refraction of light. Further experiments revealed that dispersion and crys315 Larmor, op. cit. (note 37), p. 476. The experiments were reported in A. A. Michelson, op. cit. (note 37); A. A. Michelson and F. W. Morley, "Influence of Motion of the Medium on the Velocity of Light," Am. J. Sci., 31 (1886), 377-386; id., "On the Relative Motion of the Earth and the Luminiferous Ether," ibid., 34 (1887), 333-345. The latter paper was also published in Phil. Mag., 24 (1887), 449463. 31 ^Larmor Aether and Matter, op. cit. (note 6), pp. 1-29. 1

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talline interference are also uninfluenced by the earth's motion in space. Fresnel concluded that the aether is "unaffected by the motion of matter which it permeates"; i.e., the aether is not dragged by the earth but is stagnant. This conclusion implied that an aether wind blows over the earth, passing through the interstices of material bodies like the wind through a grove of trees. Why, then, had experiments failed to detect the aether wind or drift? Fresnel showed mathematically that the velocity of light along a moving course shared a fraction of the velocity of the source. This result suggested that if dielectrics carry part of the aether along in their interior, then all of the negative results, accurate to the first order in the ratio of the velocity of light to the velocity of the earth, would be explained. The drift exists, Fresnel asserted, but it has not been detected because of the compensating effect of the partial drag of the enclosed aether by moving dielectrics.317 Stokes opposed this interpretation, preferring the hypothesis of total aether drag at the earth's surface; but in order to explain aberration, he had to assume that whirlpools were not created in the aether dragged by the moving earth and that the aether was not incompressible. H. Fizeau's experimental test of Fresnel's hypothesis found the change in the velocity of propagation of light through running water precisely equal to the con­ vection coefficient predicted by Fresnel.318 Also Fresnel's assumptions of aether drift and partial aether drag provided a complete and satisfactory explanation of aberration. Since Fresnel's second, more implausible hy­ pothesis seemed to have been verified by Fizeau, physicists believed that the first assumption likewise is true and anticipated that experiments of a more refined order ought to be able to measure the aether drift and, thus, the earth's velocity relative to the aether. By an interference experiment on the difference of the times of propa­ gation around two cyclic paths, originally suggested by Maxwell as a test for the existence of a relative velocity between the earth and the aether, Michelson and Morley showed in 1887 that even the most refined experi317 Larmor reprinted in Appendix D of Aether and Matter Fresnel's classic letter to Arago, "On the Influence of the Earth's Motion on Optical Phenomena," which ap­ peared originally in Annates de Chimie, 9 (1818), 57-66. 318 For Fizeau's paper, see note 37. Fresnel's formula was also validated by Michelson in his 1881 study, op. cit. (note 37); see the discussion by Swenson, op. cit. (note 30), pp. 54 et seq. Swenson has presented an excellent historical treatment of the Michelson-Morley experiments, but his broader analysis of the problem is based on an interpretation of the British aether, and thus of the significance of the experi­ ments and of the fate of the British theories, which is in fundamental disagreement with my findings.

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mental arrangements could not detect any significant optical evidence of a relative velocity. 319 The time of propagation of light is independent of the earth's motion not merely to a first approximation as Fresnel had shown but to a higher order, so that Fresnel's explanation must be questioned. Michelson and Morely, who viewed the experiment as a test of Fresnel's hypothesis of a stationary aether with a partial aether drag inside a moving dielectric, concluded that only if the aether is completely pulled along can the "null" change in the velocity of light be explained. Their conclusion, however, challenged the interpretation of all the laws of optics and astro­ nomical aberration; it would require "some special adjustment" of the aether's motion to explain all the phenomena that the stagnant aether hypothesis had. In effect Michelson and Morley had abandoned Fresnel's stationary aether for Stokes's "adjusting" hypothesis of an aether drag at the earth's surface. Michelson and Morley noted in their discussion that the vortex-atom hypothesis of the free motion of matter through the aether, creating neither an aether drift nor an aether drag, might reconcile their experiment with other optical phenomena. In 1891 Lodge undertook an experiment to test whether or not matter drags the surrounding aether with it when it moves; his negative results further challenged Michelson and Morley's con­ clusion. In a paper on aberration and the motion of the ether near the earth, read before the Royal Society on 31 March 1892, Lodge argued that all phenomena and all experiments, except Michelson and Morley's, are explicable in terms of the vortex-atom theory of matter. Although Lodge observed that Michelson and Morley's experiment "may have to be ex­ plained away," he implied that perhaps the vortex-atom must be modified to encompass the puzzling results of that experiment. 320 This implication Larmor drew from Lodge's paper. Both Larmor and Lorentz challenged Michelson's conclusion of total aether drag; they returned to the stationary aether, the simplest and most logical theoretical basis for the given facts. 321 Once the immobile aether is accepted, the theory need account for only one apparently contradictory phenomenon: the null results of the attempts to measure velocity relative 319 Michelson

and Morley's 1887 study, op. cit. (note 315). Lodge, "Aberration Problems: A Discussion Concerning the Motion of the Ether Near the Earth and Concerning the Connexion between Ether and Gross Mat­ ter, with Some New Experiments," Phil. Trans. Roy. Soc., 184 (1893), 727-804. This argument was also made in Lodge, op. cit. (note 313). 321 Swenson, op. cit. (note 30), p. 95, observes that neither Michelson nor Morley "had much confidence in his ability to theorize." 320 Oliver

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to the aether. Rather than allowing an aether drag, FitzGerald, Lorentz, and Larmor looked at the moving matter, seeking what "special adjust­ ments" resulting from the matter's motion might account for the null re­ sults of the interferometer experiments. Lorentz and FitzGerald allowed an aether drift and proposed an ad hoc adjusting hypothesis. Larmor, on the other hand, had modified the vortex-atom into a strain-center electron and deduced that an anisotropy of energy propagation will result from the motion of the electrons in the rotationally elastic aether; there was no need for either an aether drift or an aether drag. Larmor's conception of the relation between aether and matter, by giving a new meaning to the motion of matter through the aether that was foreign to the Continental school and absent from post-1905 analyses, enabled him to obtain by 1897 the first correct second-order (indeed exact) transformation equations of space and time standards for reference frames in uniform motion. 322 Unlike Lorentz and Poincare, 323 Larmor did not reason from the null results of the Michelson-Morely experiment to the contraction hypothesis, to the transformation equations, and ulti­ mately to the electromagnetic view of nature. Rather, he began with the theory of the purely electromagnetic origin of matter and the peculiar conception of the particle as a strain-center in a rotationally elastic aether, which he had already introduced into his synthesis to explain induction in a steady magnetic field, the permanence of the atomic current, and the origin of material mass, and he then deduced the first-order transforma­ tion equation and the contraction-dilation phenomenon that explained the Michelson-Morley results. In brief, the free motion of the material particle through the aether, analogous to the motion of a knot along a rope, slightly alters the effective elasticity of the aether in the direction of motion, an effect physically represented by an anisotropy of energy propagation within the moving frame and a contraction-dilation of the space-time measures of the moving bodies. Larmor calculated this effect from the hypothesis that the velocity of light is the maximum velocity possible in an aether not subject to rupture, and from the proposition that each frame must represent a single event in such a way that the

322 Doran, Sir Joseph Larmor, op. cit. (note 1), Chapter 20, relates Larmor's devel­ opment of the equations of the electrodynamics of moving bodies. See also note 37. 323 Kenneth F. Schaffner, "The Lorentz Electron Theory of Relativity," Am. J. Phys., 31 (1969), 506-508. Stanley Goldberg, "Henri Poincare and Einstein's Theory of Relativity," ibid., 35 (1967), 941-943. Id., "The Lorentz Theory of Electrons and Einstein's Theory of Relativity," ibid., 37 (1969),982-994.

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particles constituting that event are uniquely determined (the postulate of the unique cosmos). Because of this new conception of the motion of a material particle through the aether, Larmor's electrodynamics of moving bodies satisfies the demands of both the theorists who see the need for a nonmaterial plenum and those who deny that an aether drift occurs when matter is in motion. Thus, when Einstein's special theory of relativity destroyed the concept of "velocity relative to the aether" in 1905, "it left Larmor's theory [and only his] quite unscathed." 324 Lorentz, beginning with the assumption that the aether is stationary, had to append ad hoc the con­ traction-dilation hypothesis because he had no physical conception of the mode of connection between particles and the aether. Einstein, opposing the absurdities of the hypothesis of the Fresnel aether drift, 325 conceived of the universal principle of the relativity of observations of motion that required a symmetric contraction-dilation effect; but he then had no explanation for the asymmetry of that effect when considering absolute physical events rather than mere observations of them. Indeed, Einstein presented the epistemological aspects of the electrodynamics of moving bodies, whereas Larmor developed the ontotogical meaning of this phe324 A. S. Eddington, "Obituary Notice: Joseph Larmor," Obituary Notices of Fellows of the Royal Society, 11 (1942), 199. 325 Einstein was led to his postulates by a paradox upon which he "had already hit at the age of sixteen": "If I pursue a beam of light with the velocity c (velocity of light in a vacuum), I should observe such a beam of light as a spatially oscillatory electromagnetic field at rest." Because "there is no such thing, whether on the basis of experience or according to Maxwell's equations," Einstein found it "intuitively clear that, judged from the standpoint of such an observer, everything would have to happen according to the same laws as for an observer who, relative to the earth, was at rest"; otherwise the observer would not be able to determine that he is in a state of fast uniform motion. (A. Einstein, "Autobiographical Notes," in Paul Arthur Schilpp, ed., Albert Einstein: Philosopher Scientist [Evanston, Illinois, 1949], p. 53.) To resolve this paradox, Einstein showed that the classical conctpts of space and time, distance and duration, and simultaneity are relative and established his theory of relativity with exactness to all orders. He had conceived his theory inde­ pendently of the aether hypothesis and thus questioned the aether's existence. How­ ever, the paradox existed only for an aether that was subject to mechanical motion, to drifts and drags; Einstein was unaware that the British had long ago arrived at a conception of matter and aether that escaped this paradox through vortex-atomism and that culminated in the same mathematical theory some seven years before he presented the relativistic solution. By 1909, Einstein had come to understand the nature and role of the nonmechanical aether and saw it from then on as the founda­ tion of all physical theory. See R. McCormmach, op. cit. (note 296), and my con­ clusions below.

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nomcnon.326 This distinction between levels of meaning underlies the asymmetry Einstein demanded in the traveling twin "paradox."327 Re­ cently, S. J. Prokhovnik has emphasized the need to distinguish between the epistemological and ontological levels of description in special rela­ tivity; he showed that Einstein's measurement criteria are not inconsistent with the aether hypothesis, which is demanded by electromagnetic, cosmological, and kinematic phenomena, when one takes into account the "anisotropy consequence" of that hypothesis.328 Prokhovnik's notion of the anisotropy of energy propagation with respect to reference frames moving relative to the substratum or aether is the same physical hypoth­ esis which Larmor developed in 1893 in his attempt to transform the vortex-atom into a more consistent and comprehensive field theory of matter.

Atomic Structure, Spectral Radiation, and the Kinetic Theory of Heat Larmor's study in April 1893 of magneto-optic rotation from the per­ spective of geometrical optics led him to suggest that the conception of a singularity guiding the propagation of the wave may indeed be a physical reality. He suggested that the connection of the material atom with the 326 Doran, Contributions of British Physics, op. cit. (note 1), and Sir Joseph Lar­ mor, op. cit. (note 1), pp. 27-52, discuss the similarities and differences between the theories of Einstein, Poincare, Lorentz, Larmor, and various schools of twentiethcentury physics. The theories are examined most closely in Chapters 19 and 20 of the latter work; Chapters 23-28 study, from both philosophic and scientific view­ points, the epistemological and ontological meaning of the modern theories. 3z7 Ibid., pp. 48-52. 328 S. J. Prokhovnik, The Logic of Special Relativity (Cambridge, 1967), discusses on p. 39 the demise and reinstatement of the aether hypothesis within special rela­ tivity: special relativity had purported to banish the aether and with it space and time. "Yet the banishment of the absolute was not absolute. The theory also seemed to imply that the uniform motion of matter was linked with physical effects [as in the traveling twin paradox]; and to explain this space-time was given an absolute signifi­ cance and treated as a basic substratum. General Relativity defined further properties of this substratum, and so in effect, was resurrected a new and more sophisticated aether." S. J. Prokhovnik, "A Note on Relativistic Phenomena in an Ether Theory," Brit. J. Phil. Sci., 17 (1966-1967), 322-323, summarizes on p. 322 the "anisotropy consequence" of the aether hypothesis, which he notes went beyond the meaning of Lorentz' and Poincare's aether theories: "A substratum provides a basis for the propagation of light (and of other forms of energy), such that its velocity is inde­ pendent of the velocity of its source and has the same value in every direction relative to a basic reference frame associated with this substratum. In other words, the prop­ agation of electromagnetic and other forms of energy is isotropic with respect to this basic reference frame . . . and therefore . . . anisotropic with respect to any refer­ ence system moving relative to the substratum or basic reference frame."

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aether may be such that radiation is emitted in pulses. 329 By November, in the first part of his "Dynamical Theory," he announced his hypothesis of the relation between atomic structure and the discontinuous emission and absorption of radiation, noting that it resolved the equipartition diffi­ culty facing the kinetic theory of heat. 330 His transformation of the vortex-atom into the strain-center electron enabled him to achieve the goal that motivated Thomson's development of the vortex-atom theory of matter: a new basis for the kinetic theory of gases capable of encompass­ ing spectral radiation as well. Larmor was aided by crucial insights con­ tained in Thomson's 1856 explanation of magneto-optic rotation. The phenomenon of magneto-optic rotation was perhaps the single most important influence of the modern field concept. I have already shown its importance in guiding Faraday and Thomson to recognize the magnetic nature of empty space and to locate all the energy of the magnet in space or aether. I have also indicated how Thomson's interpretation of the phe­ nomenon in 1856 led to the field-theoretic view of matter in general and the vortex-atom in particular, and how it was fundamental in Maxwell's original model of electric displacement and in his later attempts to de­ scribe continuous action in the aether. Thomson's explanation of magnetooptic rotation made an equally significant contribution to the development of field theory through its direct influence on theoretical and experimental researches in spectral radiation. Thomson's view that magneto-optic rotation involves an interaction be­ tween a vibrating system and another system in rotation suggested to Peter Guthrie Tait during the years 1875-1878 that there must exist a new, specific effect which can be found by experiment: The explanation of Faraday's discovery . . . requires, as shown by Thomson, molecular rotation of the luminiferous medium. The plane polarized ray is broken up, while in the medium, into its circularlypolarized components, one of which rotates with the ether so as to have its period accelerated, the other against it in a retarded period. Now, suppose the medium to absorb one definite wave-length only, then- if the absorption is not interfered with by the magnetic action—the portion absorbed in one ray will be of a shorter, in the other of a longer, period than if there had been no magnetic force; and thus, what was originally a 329 Larmor, 330 Larmor,

op. cit. (note 267), p. 294. op. cit. (note 37).

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single dark absorption line might become a double line, the components being less dark than the single one.331 Tait anticipated on theoretical grounds the effect Zeeman discovered in 1896.332 In 1892, while repeating experiments on the Kerr effect, Zeeman was led by a specific "train of reasoning" to consider "whether the light of a flame, if submitted to the action of magnetism, would perhaps undergo any change." Zeeman noted in his report of the discovery in 1896 that his "train of reasoning" began with the hypothesis of Thomson and Maxwell of the rotational character of magnetism and with the conception that radiation is caused by the motion of atoms revolving in orbits in a mole­ cule. If the hypothesis is true that in a magnetic field a rotatory motion of the ether is going on, the axis of rotation being in the direction of the mag­ netic forces (Kelvin and Maxwell), and if the radiation of light may be imagined as caused by the motion of the atoms, relative to the centre of mass of the molecule, revolving in all kinds of orbits, suppose for sim­ plicity, circles: then the period, or what comes to the same, the time of describing the circumference of these circles, will be determined by the forces acting between the atoms, and then deviations of the period to both sides will occur through the influence of the perturbing forces be­ tween ether and atoms. The sign of the deviation of course will be deter­ mined by the direction of motion, as seen from along the lines of force. The deviation will be the greater the nearer the plane of the circle ap­ proximates to a position perpendicular to the lines of force.333 Zeeman "got a clearer insight into the subject" from Thomson's suggestive illustration in 1856 of the "influence exercised on the period of a vibratory system if this is linked together with another in rapid rotatory motion." Although Thomson's ideas were "at most of any value as indications of 331 Peter

Guthrie Tait, "On a Possible Influence of Magnetism on the Absorption of Light, and Some Correlated Subjects," Proc. Roy. Soc, Edin., 9 (1875-1878), 118. 332 J. Brookes Spencer, "On the Varieties of Nineteenth-Century Magneto-Optical Discovery," Isis, 61 (1970), 34-51, on pp. 41-44. 333 Pieter Zeeman, "On the Influence of Magnetism on the Nature of the Light Emitted by a Substance," published in Dutch in Zittingsverslag, Akademie Amster­ dam, J (1896), 242-253, and in English in Phil. Mag., 5 (1897), 226-239. Id., Re­ searches in Magneto-optics (London, 1913), quotes in entirety on pp. 25-30 the English version. Quotations on pp. 25 and 29, respectively.

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somewhat analogous cases," Zeeman reported them "because they were the first inducement to me to undertake my experiments." 334 In September 1893 Larmor examined the effects of magnetism on light and their explanations in various optical theories. 335 Larmor emphasized that Thomson's 1856 explanation of magneto-optic rotation involves a compound medium of aether and matter. On reversing the light the magnetic rotation is not reversed; therefore, it depends on some outside influence of a vector character, exerted on the system which transmits the light. This influence makes the free period of a circular motion differ, according as it rotates in one direction or the opposite one. . . . There must be another dynamical system present, linked with the one which transmits the light, and possessing motion of rotation round the lines of magnetic force, or some other motion directed with respect to those lines; and the kinetic reaction between these two systems will account for the magnetic rotation. 336 Larmor felt he must emphasize that two systems are in interaction because many physicists still interpreted Thomson's statement in terms of Max­ well's notion that magnetic force is a rotation of the luminiferous medium. The next year, 1894, Larmor stated that various authors besides himself had come to recognize that this view is "too narrow an interpretation" of magneto-optic rotation; for instance, FitzGerald informed him "that he has for some time doubted the view that the magnetic force can be solely a rotation in the medium" and that he now favored the view that magnetic rotation is "a purely material phenomenon [and hence] must be of a sec­ ondary character." 337 In his 1893 study, Larmor also considered Thom­ son's dynamical illustration of the influence "exerted on the free periods of a vibrating system by linking it to another system which is in rotation," the same analogy which helped Zeeman to clarify his understanding of the problem. 338 During the early 1890's many physicists adopted the view that radiation is caused by the orbital revolution of material atoms, a view deduced at least partly from Thomson's explanation of magneto-optic rotation. Larmor continued to probe the nature of spectral radiation and was led to a theoretical anticipation of the Zeeman effect. 339 More impor334 Ibid.,

33 SLarmor, op. cit. (note 48). pp. 29-30. See note 132. 337 Larmor, op. cit. (note 37), p. 485. p. 314. 338 Larmor, op. cit. (note 48), p. 314. 339 Whittaker, op. cit. (note 6), 1, 411, and Jammer ,op. cit. (note 191), p. 121, note that Larmor had anticipated the existence of the Zeeman effect as early as 1894 but thought it would be unobservable since he considered the electron to have a mass 336 Tbid,

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tant was his resulting electromagnetic view of spectral radiation and atomic structure and its solution to the equipartition problem. Larmor was not alone in effecting the transformation of the vortexatom explanation of spectra into the electromagnetic explanation. Other advocates of the vortex-atom had isolated the electric charge as the con­ nection between the aethereal and material actions. Arthur Schuster, one of the leading British spectroscopists, originally opposed the notion that atoms of any type produce the spectrum. Observing that the kinetic theory, of gases predicted a nonrotating, nonvibrating monatomic sodium atom whereas spectroscopy showed that the sodium atom radiates, he argued that "molecules" must give rise to the spectra.340 In 1891 G. Johnstone Stoney, one of the originators in the 1860's of the molecular theory of spectra and later an advocate of vortex-atomism, argued against the Con­ tinental idea that spectral radiation is emitted by a Hertzian oscillator consisting of charged molecules and for the idea that orbiting electrons produce the spectral radiation. Likewise, FitzGeraldin 1893 objected that Hermann Ebert's analogy in 1891-1893 of a "simple Hertzian oscillator of the size of an atom" would produce many thousand times too much radiation, so that "sodium atoms must be complex Hertzian oscillators if they are Hertzian oscillators at all." Thomson had drawn the same conclu­ sion with respect to Helmholtz' vibrating particles in the Baltimore lec­ tures. At the 1893 meeting of the British Association, Lodge suggested that "radiation is due to the motion of the electrified parts of molecules— not to the molecules as a whole," but he did not suggest how or why this was so.341 However, it was only after Part I of Larmor's "Dynamical Theory" had appeared—it was read in December 1893 and published in August 1894—that real interest in the electromagnetic theory of spectra arose, for Larmor had argued there that the electromagnetic conception of the spectral radiation may be reconciled with the kinetic theory of heat. comparable to that of the hydrogen atom. However, J. Brookes Spencer, op. cit. (note 332), p. 48, has questioned the extent to which Larmor foresaw this implica­ tion of his theory of aether and matter. In Sir Joseph Larmor, op. cit. (note 1), Chapter 21, I demonstrate that Larmor's early papers do predict this effect, and I show how this theoretical anticipation was directly stimulated by Thomson's 1856 explanation of magneto-optic rotation. 3*>A. Schuster, "The Teachings of Modern Spectroscopy," Popular Scientific Monthly, 19 (1881), 466-482, on p. 469. See McGucken, op. cit (note 166), p. 171. Schuster did not advocate the vortex-atom, but he became a firm believer in Larmor's electron theory of matter. 341 Oliver Lodge, "On the Connection between Aether and Matter," Reports of the British Association, 61 (1893), 688. McGucken, op. cit. (note 166), pp. 188-190.

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Even before he had replaced the vortex-atom with the electron, Larmor noted that the spectral lines "depend only on the relative positions and motions of the vortex atoms in the molecule." He said that radiation oc­ curs in pulses and only "in so far as the molecules are dissociated or their component atoms violently displaced with respect to each other"; it does not occur under ordinary translatory motion or other less violent distur­ bances. But, he observed, in the vortex-atom theory a rise in temperature increases the energy of the isolated vortex-atoms, so that each ring ex­ pands and suffers both a diminution of its velocity of translation and an alteration in the periods of its electric vibrations; therefore, the electric vibrations of a molecule must depend only on its configuration and the relative motion of its parts: "The configuration of a molecule, which de­ termines its electric periods, would also be independent of the movements of translation and rotation, which constitute heat and are the concern of the kinetic theory of gases." 342 When other phenomena required Larmorin June-August 1894 to discard the vortex-atom and make the electron the sole constituent of matter, his image of atomic structure became the modern view of spectral radiation and electron orbits. The exact permanence of the wave-lengths in spectra, under various physical conditions, may be ascribed to the influence of radiation on the molecule, which keeps it in, or very close to, a constant non-radiating condition of steady motion, of minimum total energy corresponding to its pre-determined constant momenta. 343 If we consider a molecule to be made up of, or to involve, a steady configuration of revolving electrons, it will follow that every disturbance of this steady motion will involve radiation and consequently loss of energy. The only steady configuration of which we can assert that it will remain permanent under all circumstances is, therefore, that one which possesses least total energy. Thus by extending the conception of abso­ lute stability, which already plays a part in the theories of material systems which lose sensible energy by viscosity, to systems which lose energy by radiation, we obtain a possible mode of accounting for the uniqueness of the atom configuration and the invariability of its spectral lines. 344 342 Larmor,

op. cit. (note 37), pp. 486, 488. Larmor, "Abstract, A Dynamical Theory of the Electric and Luminiferous Medium.—Part II: Theory of Electrons," Proc. Roy. Soc., 58 (1895), 222-228; reprinted in Larmor, Papers, op. cit. (note 37), 1, 536-542, on p. 541. 344 Larmor, op. cit. (note 257), p. 596. 343 Joseph

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Several of the participants at the 1894 British Association meeting con­ tinued their discussion of the equipartition problem in letters to Nature over several months. George H. Bryan, like Larmor, argued that the kinetic theory is not incompatible with the spectra of gases: electromagnetic oscillations "determined by surface harmonics of different orders" may account for the spectra "without interfering with the assumptions required for explaining the specific heats of gases." In response to FitzGerald's confession that he, unlike Larmor and Bryan, could not see how "any help can be got by supposing spectral lines to be due to electromagnetic vibrations," Schuster explained how Larmor's theory of the spectral radia­ tion can get along with a "very restricted" number of degrees of freedom. He pointed out that the radiating molecule emits only one or a few of the spectral wavelengths at a given instant, and the entire spectrum is produced by the whole group of molecules emitting different rays simultaneously. 345 A distinction is often made between the "classical atom," in which "the electron emits continually a whole series of frequencies which moreover are harmonics of a certain number of fundamental frequencies determined by the harmonic analysis of the motion of the electron," and the "quan­ tum atom," in which "the electron in stationary motion does not radiate, but. . . is capable of undergoing transitions which will give rise to radiation whose frequency is definitely determined by Bohr's rule." 346 According to these definitions, the modern "quantum atom" had been born before the quantum itself. Indeed, Bohr followed J. W. Nicholson's definition of the minimum energy levels in terms of predetermined constant mo­ menta; 347 Nicholson in turn was trying to fix the relation between radia345 G. H. Bryan, "Professor Boltzmann and the Kinetic Theory of Gases," Nature, 51 (1894-1895), 21; G. F. FitzGerald, "The Kinetic Theory of Gases," ibid., p. 127; A. Schuster, "The Kinetic Theory of Gases," ibid., p. 293. McGucken, op. cit. (note 166), pp. 190-192. 346 Louis de Broglie, The Revolution in Physics, A Non-Mathematical Survey of Quanta, trans. Ralph W. Niemeyer (New York, 1953), pp. 123-156, on p. 150. 347 John L. Heilbron and Thomas S. Kuhn, "The Genesis of the Bohr Atom," Historical Studies in the Physical Sciences, 1 (1969), 211-290, gives a full account of Neils Bohr's debt to J. W. Nicholson. Leon Rosenfeld's accounts ignored the impor­ tance of Nicholson's work for Bohr's model: "Introduction" to On the Constitution of Atoms and Molecules (Copenhagen, 1963), a reprint of Bohr's three papers of 1913; and L. Rosenfeld and E. Ruedinger, "The Decisive Years, 1911-1918," in S. Rozental, ed., Neils Bohr: His Life and Work as Seen by His Friends and Colleagues (Amsterdam and New York, 1967), pp. 38-73. "Published records to which Rosenfeld attached little weight," revealing the crucial role of Nicholson in the creation of the Bohr atom, were uncovered by T. Hirosige and S. Nisio, "Formation of Bohr's Theory of Atomic Constitution," Jap. Stud. Hist. Sci., No. 3 (1964), pp. 6-28; J. L.

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tion and atomic structure, as developed by Larmor between 1893 and 1895, in terms of Planck's constant, as suggested by Larmor in the Adams Prize essay topic announced in December 1911.348 The explanation of spectral radiation and equipartition was an important element of Larmor's synthesis. In Part III of his "Dynamical Theory" in 1897, he restated that "the kinetic theory of gases is considerably affected by the view here taken of the constitution of a molecule." It is affected not in those features that are concerned only with the translatory motion of the molecules, but in features "like that of the ratio of the specific heats which involve the internal energy." According to the usual hypothesis of the theory of gases, all the internal kinetic energy of the molecule is taken to be thermal and in statistical equilibrium, through encounters, with the translatory energy. But on the present view, the energy of the steady orbital motions in the molecule (including therein slow free precessions) makes up both the energy of chemical constitution and the internal thermal energy; while it is only when these steady motions are disturbed that the resulting vibration gives rise to radiation by which some of the internal energy is lost. The amount of internal energy can however never fall below the mini­ mum that corresponds to the actual conserved rotational momenta of the molecule; this minimum is the energy of chemical combination of its ultimate constituents, while the excess above it actually existing is the internal thermal energy.349 Larmor saw the question of equipartition as one of reconciling the external thermal energy required for the kinetic theory of heat with the internal thermal energy reflected in the ratio of specific heats and involved in the Heilbron, A History of Atomic Models from the Discovery of the Electron to the Be­ ginning of Quantum Mechanics (Ph. D. dissertation, University of California, Berkeley, 1964); and R. McCormmach, "The Atomic Theory of John William Nichol­ son,"Arch. Hist. ExactSci., 3 (1966), 160-184. 348 Doran, Sir Joseph Larmor, op. cit. (note 1), Chapter 24, details Larmor's atomic model and its influence on Nicholson and Bohr. Larmor's announcement of the prize topic is printed in entirety in his preface to The Scientific Papers of S. B. McLaren, op. cit. (note 192), p. v. McLaren, who won the prize, wrote to Bohr in February 1913, in answer to a letter from Bohr which has been lost, that he was "inclining to the belief that the old mechanical notions are past mending" (Rosenfeld and Ruedinger, op. cit. [note 347], p. 57). McLaren was Larmor's student and proposed a Larmor-type theory of a gravitational and electromagnetic aether and its relation to matter (McLaren, op. cit. [note 192]). 349 Joseph Larmor, "A Dynamical Theory of the Electric and Luminiferous Me­ dium.—Part III: Relations with Material Media," Phil. Trans. Roy. Soc., 190 (1898), 205-300; reprinted in Larmor,Papers, op. cit. (note 37), 2, 11-132, on pp. 28-29.

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emission and absorption of radiation. The British school viewed the ques­ tion as one involving atomic structure and the connection between the atom and aether. Radiant heat had become a type of electromagnetic radiation that influences external thermal energy when absorbed or emitted by matter. Maxwell had by 1875 concluded that the aether is not molecular because it is not "subject to the ordinary gaseous laws as to pressure and temperature." Rayleigh's 1900 application of equipartition to low frequencies, though not to high frequencies, was in contradiction with both the continuous aether and the new conception of radiant and ordi­ nary heat.350 When Larmor learned in 1902 of Planck's quantum theory of radiation, developed from thermodynamic concepts in response to the problems of heat radiation, he immediately recognized its significance. For Larmor, Planck's constant expresses the nature of the relation between matter and the aether, between the strain-centers and their aethereal atmospheres, between the source of radiation and its subsequent propagation in the free State as singularities guiding the wave front. Larmor suggested to the British

Association that year how to avoid the "naive conception of an oscillator" and derive Planck's law of radiation by a method later called quantification of the phase-space.351 Planck attempted to exploit the method in 1906.352 Planck's quantum was not strange to Larmor because it was demanded by his own theory of the particle-aether relation for matter and light. Larmor's electron was a product of its field and thus necessarily capable of both wave and particle characteristics. The electron is a "freely mobile singular point in the specification of the aethereal strain"; the "field of physical activity is inseparably associated with the nucleus" of intrinsic strain in the aether. With justice he saw a resurrection of his own ideas in the physical theories of Bohr, de Broglie, Schrodinger, and Dirac.353 350 Brush, op. cit. (note 26), p. 147n, notes that scientists writing on the develop­ ment of quantum theory continue to state incorrectly that Planck was trying "to re­ solve a paradox discovered by Rayleigh, that the total energy of the ether would be infinite if each mechanical degree of freedom had an equal share of energy." Martin J. Klein, "Max Planck and the Beginnings of Quantum Theory," Arch. Hist. Exact Sci., 1 (1962), 459-479, shows that Planck did not view the question in this way when he was developing his distribution law based on the quantum constant. See note 209 for Maxwell's views in 1875. 351 Joseph Larmor, "On the Application of the Method of Entropy to Radiant Energy," Brit. Assoc. Rep. (1902), p. 546; reprinted in Larmor, Papers, op. cit. (note 37),2, 699. 352 Klein, op. cit. (note 350), p. 27. 353 The quotations are from Larmor, Aether and Matter, op. cit. (note 6), p. 26, and Joseph Larmor, "Aether," Encyclopaedia Britannica, 1902 supplement to Ilth

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The Culmination of a Tradition: Larmor's Electron Theory of Matter and Electromagnetic View of Nature I have elsewhere traced systematically and in detail the steps by which Larmor effected his synthesis, culminating a half-century long tradition of seeking a theory of aether and matter to replace the mechanical view of forces, atoms, and the void. 354 What I am concerned with here is the na­ ture of that synthesis; namely, its role as an "electron theory of matter" and an "electromagnetic view of nature," replacing the dualism of force and matter and the notions of atoms and the void of the mechanical worldview. Larmor and Lorentz developed simultaneously and independently the theory of electrons. The charged particles constituting matter were called "ions" in Lorentz' theory until 1899, two years after the discovery of electrons by J. J. Thomson, who always called them "corpuscles." Larmor in 1894 was first to identify the charged particles of matter with the basic unit of electric charge or "electron," as J. Stoney had termed it in 1881, and by which FitzGerald was referring to it. Indeed, Lorentz' was not an electron theory of matter; it did not postulate structural atoms or elec­ trons, "but only continuous volume densities which in unknown way hap­ pened to condense themselves into quasi-atomic accumulation."355 In fact, he had to add the concept of electodynamic force to the molecular scheme as an additional hypothesis. Lorentz never used the phrase "electron theory of matter" until 1902; Larmor introduced it in 1894 and popu­ larized it throughout the next decade. Larmor introduced the phrase to make more explicit the physical mean­ ing of the theory he had developed by November 1893. In that theory he addressed the problem of deriving the inertia of matter from the aether. It was the inability of the vortex-atom to explain the inertia of matter, which Maxwell and others objected to, that first induced Larmor to regard the strain-center as the sole constituent of matter. He defined mass as "a coefficient in the kinetic part of the energy function" in the least action formulation, and regarded all mass as aethereal in origin,356 The electrons or "monad elements out of which a magnetic molecule . . . is built up are electric centres or nuclei or radial rotational strain"; the electrons are "the ed., p. 294. When Larmor edited his own collection of papers in 1927-1929, he com­ mented on the recent developments by Einstein and by the quantum theorists in notes and extensive appendices. 354 Doran, Contributions of British Physics, op. cit. (note 1), Chapters 13-15, and Sir Joseph Larmor, op. at. (note 1), Chapters 20-22. 355 Joseph Larmor, "Addenda and Corrigenda," Papers, op. cit. (note 37), 2, xxi35 GLarmor, op. cit. (note 37), pp. 501-503. xxxiii, on p. xxxi.

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sole ultimate and unchanging singularities in the uniform all-pervading medium." 357 In notes added to his theory on 14 June and 13 August 1894, Larmor expanded on his electromagnetic definition of mass; he stated that the electronic inertia is purely aethereal, and that the electric inertia of an ion must be associated with the "inertia of matter to which the ion belongs." He assumed that the "nucleus of the electron has no other intrinsic inertia of its own." 358 Larmor then undertook to determine whether or not "the non-electric properties of matter may also be deducible from a simple theory of free electons in a rotationally elastic aether," 359 and he proposed the atomic model that ultimately became the Bohr atom. Larmor's was an electron theory of matter because it con­ tained an electromagnetic definition of mass. The program for a field theory of matter, which Thomson has envisioned in 1856 and had made widely acceptable to British physicists through his vortex-atom, finally achieved a formulation that could completely replace the mechanical worldview. Long after the field-theoretic conception had become popular in Britain and a few months after Larmor had proposed his electromagnetic theory of mass, the possibility of an electromagnetic view of mass was hinted at in Germany. EmilWiechert suggested that the "electromagnetic aether," which the luminiferous aether was now called by proponents of Maxwell's theory, might be the only reality, that electric particles might be excitations in the aether, and that matter might consist of aggregates of electric particles. 360 After Wiechert, no one discussed the possibility of such a view until the 1895 Liibeck conference, which was dominated by energeticists seeking to escape the constrictions of mechanical notions. But, as Boltzmann stated in 1897, the energeticists did not want to explain mass in terms of the aether, but only to derive the laws of mechanics from the laws of electromag­ netics. 361 By 1900 Paul Drude and Wilhelm Wien had proposed a purely electromagnetic mass as a possible implication of Lorentz' electron theory. 362 Lorentz, however, did not adopt the electromagnetic view until 351 Ibid.,

pp. 515-517 pp. 474-475, 514-525, 530-532, quotation on p. 522. 359Jbid., p. 530. 360 McCormmach, op. cit. (note 1), p. 460. Emil Wiechert, "Bedeutung des Weltathers," Physikalisch-okonomische Gesellschaft zu Konigsberg, 35 (1894), 4-11. 361 LudwigBoltzmann, op. cit. (note 297). 362 See McCormmach, op. cit. (note 1), pp. 459-497; T. Hirosige, "Electrodynamics before the Theory of Relativity, 1890-1905," Jap. Stud. Hist. Sci., No. 5 (1966), pp. 1-49; id., "Theory of Relativity and the Ether," ibid., No. 7 (1968), pp. 35-53. Paul Drude, "Zur Elektronentheorie der Metalle," Ann. d. Phys., 1 (1900), 566-613. Wilhelm Wien, "'Ober die Moglichkeit einer elektromagnetischen Begriindung der 35 *Ibid.,

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1903, and then only with, caution. Indeed, in 1913 he still distinguished "three parts" of nature: atomic matter, which has "no direct interaction" with the aether; the aether; and "some kind of 'vibrators,' each having a frequency of its own," and each carrying electric charges that enable it to interact with the aether in addition to interacting with the material par­ ticles through energy exchanges.363 Lorentz had not abandoned the Con­ tinental charged vibrator for the British electromagnetic theory of matter and the associated Larmor-Bohr theory of atomic structure and radiation. Historians must acknowledge that Larmor's definition of mass as a coeffi­ cient in the action of an electromagnetic medium underlay the first elec­ tromagnetic theory of matter, indeed perhaps the first of several attempts to deduce material concepts from electromagnetic ones. From the first, Larmor emphasized that "the centre of rotational strain which represents an electron is possible without a discrete structure of the medium." He said that although a gyrostatic model like Thomson's is "an important corroboration of our faith in the possibility of such a medium," we must not "infer that a rotational free aether is necessarily discrete or structural in its ultimate parts, instead of being a continuum." 364 Here, indeed, was Larmor's most difficult task, a task also most pressing for correct historical and scientific interpretation: to demonstrate how the nature and activities of his continuous aether are different from those of a mechanical, discrete medium. In Part III of his "Dynamical Theory in 1897 and in his 1900 Presidential Address to the British Association, Larmor noted that his theory had been misinterpreted by physicists who tried to understand it in terms of me­ chanical notions of physical action. For instance, Poincare had argued that since the intensity of the magnetic field represents the "velocity" of the aether at each point, the displacement of each point of the aether will in­ crease without limit over time in a constant magnetic field. 365 On the Mechanik," Archives Neerlandaises Sci., S (1900), 96-104; also in Recueil de travaux offerts par Ies auteurs a H. A. Lorentz (The Hague, 1900), pp. 96-107; and in Ann. d. Phys., S (1900), 501-513. 363 H. A. Lorentz, from "A Discussion on Radiation," Section A of the British Association Meeting, Birmingham, 1913, following Bohr's presentation of his quan­ tum atom (Brit. Assoc. Rep. [1913], p. 381). 364 Larmor, op. cit. (note 37), p. 521. 36s Henri Poincare, "A propos de la theorie de M. Larmor," L'eclairage electrique, 3 (1895), 5-13, 289-295, and S (1895), 5-14, 385-392; reprinted in Oeuvres de Henri Poincare, 9 vols. (Paris, 1954), 9, 369-426, on p. 412. Poincare's article was incorporated into his treatise Electricite et optique (Paris, 1900) as its final chapter; and the arguments were included in his Science and Hypothesis (Paris, 1900), English edition prefaced by Larmor (reprinted, New York, 1952), p. 170. See the discussion by Hirosige, "Electrodynamics . . . ," op. cit. (note 362), pp. 20-22.

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contrary, Larmor responded, the velocity does not apply to the aether substance but to the aether disturbance or strain; the aether is not com­ posed of particles having definite locations in absolute space or progressing through time. 366 Larmoremphasized in every statement of his theory that the theory involves a complete break from the long-standing conception of matter and physical action, and he took great care to show how and why it did. Material atoms in motion acting either "by contact" or "by step-bystep transmission" or "at a distance" had proven inadequate to deal with the aether or with the interactions of aether and matter. 367 His theory of strain-centers in a rotationally elastic continuous aether replaces those con­ ceptions and thus cannot be interpreted in their terms. 368 He underscored that every aspect of his theory is based on the conception of the aether as a continuous nonmaterial plenum, the primordial medium that is the source of material particles, and that this new notion of substance involves modes of physical action not possible in the traditional theories of matter. With this synthesis, though poorly comprehended and insufficiently acknowledged by Larmor's contemporaries, the revolution in physical theory had been completed.

CONCLUSIONS In May 1920, fifteen years after his special theory of relativity allegedly banished forever the aether from physics, Einstein delivered a speech at the University of Leiden in which he made explicit his views on the aether. 369 In summation, Einstein declared: "According to the general theory of relativity, space is equipped with physical qualities; an aether in this sense therefore exists. Space without aether is unthinkable with respect 366 Larmor responded to Poincare's criticisms in "The Methods of Mathematical Physics," an address to the Mathematical and Physical Section of the British Associa­ tion in Bradford in 1900. Reprinted in Larmor,Papers, op. cit. (note 37), 2, 192216, on pp. 211-212. See Doran, Sir Joseph Larmor, op. cit. (note 1), pp. 538-545. In his introduction to the English translation of Poincare's Science and Hypothesis, ibid., pp. xi-xxvii, on p. xvii, Larmor made no mention of the three gross misinterpre­ tations of his own work there. Rather he questioned Poincare's distinction between French and British theoretical methods, argued for the useful role that mechanical models had played in the development of crucial physical concepts, and emphasized that "the study of the historical evolution of physical theories is essential to the complete understanding of their impact." 367 Larmor, op. cit. (note 273), pp. 628-629. 368 Jfeid., pp. 628-632. Also id., op. cit. (note 349), pp. 12-28. 3® Einstein's speech was delivered on 5 May 1920 at the University of Leiden, published as Aether und Relativitatstheorie (Berlin, 1920).

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to the general theory of relativity. . . ." 370 Einstein was not merely trying to "salvage the aether concept on behalf of Lorentz" in whose honor the speech was made, 371 but had "seized this opportunity to underscore the increasing harmony he felt between his and Lorentz' thought," and to make explicit the functions and properties of the aether that are essential to his mature conception. 372 Without an aether, Einstein continued, "not only is there no light propagation but there is no possibility for the existence of measuring rods and clocks, hence there are also no space-time distances in the sense of physics." To Einstein, the aether of modern physics is, first, the physical medium of electromagnetic propagation. That had been the meaning of the "aether" since Thomson and Maxwell had given that name to Faraday's medium. Einstein's attempts after 1915 and to the end of his life to construct a field theory of the material particle and to unify the electromagnetic and gravitational fields demanded as a second function of the aether its necessity for the existence of measur­ ing rods and clocks. Here we see the primordial medium of Thomson's vortex-atom and Larmor's strain-center electron: the aether is the physical, nonmaterial substance which is the source of material particles and hence all material bodies. Third, Einstein's aether does not merely yield the kinematical properties of space, but it also has the physical property necessary to establish absolute physical standards of space and time (in the particles of matter) that underlie our relativistic measurements of them; this aethereal role was precisely stated and extensively developed by Larmor in his original papers and again in the 1920's. 373 370 The concluding paragraph, which I have translated into English in the text, reads as follows:

Zusammenfassend konnen wir sagen: Nach der allgemeinen Relativitatstheorie ist der Raum mit physikalischen Qualitaten ausgestattet; es existiert also in diesem Sinne ein Ather. Gemass der allgemeinen Relativitatstheorie ist ein Raum ohne Ather andenkbar;denn in einem solchen gabe es nicht nur keine LichtfortpRanzung, sondern auch keine Existenzmoglichkeit von Mass-staben und Uhren, also auch keine raumlichzeitlichen Entfernungen im Sinne der Physik. Dieser Ather darf aber nicht mit der fur ponderable Medien charakteristischen Eigenschaft ausgestattet gedacht werden, aus durch die Zeit verfolgbaren Teilen zu bestehen; der Bewegungsbegriff darf auf ihn nicht angewendet werden (ibid.). 371 I disagree with the interpretation of Einstein's speech proposed by L. S. Swenson, op. cit. (note 30), p. 187, and "The Michelson-Morley-Miller Experiments Be­ fore and After 1905,"/. Hist. Astronomy, 1 (1971), 64. 372 McCormmach, op. cit. (note 296), p. 86, put this speech into the perspective of the change in Einstein's understanding of the aether that occurred between 1905 and 1909 and that underlay his mature thought. 373 SeeDoran SZr Joseph Larmor op. cit. (note 1), Chapter 27. 1 t

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Einstein then summarized the properties of such an aether: it "must not be thought equipped with the characteristic property of a ponderable medium of consisting of particles which can be traced through time; the concept of motion must not be applied to it." The aether is ontologically different from matter. It is a nonmaterial physical medium, which is not composed of particles and thus is continuous; these are the properties of the aether that were established in Britain during the middle years of the nineteenth century. Finally, whereas Einstein's "special relativity" rested on the notion that motion relative to the aether has no meaning, the British physicists sought and Larmor ultimately effected a new, nonmechanical meaning of matter in motion through the aether. That meaning in turn enabled Larmor to establish the ontological aspects of the electrody­ namics of moving bodies. Einstein's speech revealed his lifelong desire to go beyond the epistemological statement that his theory of relativity ex­ pressed to develop a unified theory encompassing the ontology of the phenomena as well. History, to be sure, is contemporary thought about the past. The neglect of Larmor's theory, in part the result of confusions about which functions and characteristics of the aether had been discarded in 1905, contributed to the view that the Michelson-Morley experiment had dealt the final blow to the mechanically encumbered British theories in which aether drags and drifts were thought to accompany bodies moving through it. This myth continues to pervade recent historical references to Thomson's and Larmor's theories. Historians have had difficulty reconciling the ac­ complishments of Larmor's theory with its seemingly mechanical charac­ ter, mistakenly perceiving them as the result of a formal view of the aether or a development of Lorentz' ideas. 374 However, "non-classical retrospec­ tion," benefitting from a clearer understanding of the role of the aether in the modern theories, has in recent years begun to demonstrate that "Victorian science was not so Victorian," and that several nonclassical ideas were present in the British theories of aether and matter. 375 As Mary Hesse discerned from her study of forces and fields, "in spite of the in­ creasing mechanization of physics, the notion of 'reality' was seldom

374 Stanley Goldberg, "In Defense of Ether: The British Response to Einstein's Special Theory of Relativity, 1905-1911," Historical Studies in the Physical Sciences, 2 (1970), 111. Swenson, op. cit. (note 30), p. 124. 375 Boris Kuznetsov, "Quantum-Relativistic Retrospection and the History of Clas­ sical Physics: Classical Relationalism and Nonclassical Science," Historical Studies in the Physical Sciences, 3 (1971), 117-135, on p. 118.

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wholly restricted to matter-in-motion." 376 The present study shows the extent to which the modern conception of the field and the atom was the culmination of a dominant tradition in the British physics of the aether; it shows the extent to which the nonclassical viewpoint was the result of a conscious attempt to develop a new metaphysic.

ACKNOWLEDGMENTS I wish to thank Robert Kargon, Russell McCormmach, Salomon Bochner, Radoslav Tsanoff, and an anonymous reviewer for helpful comments and discussion. 3 ^ 6 Hesse,

op. cit. (note 212), p. 347.

Hertz's Researches on Electromagnetic Waves BY SALVO D'AGOSTINO*

1. Theoretical and Experimental Problems of Electrodynamics in the 1870's 2. The Helmholtz-Hertz Relationship

263 276

3. Hertz's First Approach to Electrodynamics and His 1884 Theoretical Paper

284

4. Hertz's Experiments on Electromagnetic Waves in Wires and in Air

5. Conclusions

296 321

In the preface to Heinrich Hertz's Principles of Mechanics, Helmholtz eulogized his former student as the ideal scientist who uniquely combined theoretical insight with experimental skill. 1 In his electrodynamic re­ searches Hertz revealed especially clearly the quality of physicist Helmholtz alluded to. These researches culminated in one of the masterful achieve­ ments in the history of modern physics: his renowned experimental proof of finitely propagated electric waves in air. Moreover, these researches placed Maxwell's theory on extended experimental foundations and thereby established it as the leading electrodynamics in Europe. The ulti­ mate theoretical and philosophical consequence of Hertz's researches was the replacement of the concept of action at a distance in electrodynamics *Istituto di Fisica "Marconi," Universita, P. Scienze 5, Roma, Italy. 1 Hermann von Helmholtz, preface to Heinrich Hertz, The Principles of Mechanics Presented in a New Form (New York, 1956). The Principles is the translation of the third volume of Heinrich Hertz, Gesammelte Werke, 3 vols. (Leipzig, 1895). The translations of the first two volumes are, respectively, Miscellaneous Papers (London, 1896) and Electric Waves, Being Researches on the Propagation of Electric Action with Finite Velocity through Space (New York, 1962). Throughout this article I have checked quotations from the above translations with the German originals, and 1 have inserted expressions in square brackets wherever I preferred a different render­ ing. E.g., I have often preferred the German "Elektrodynamik" to the English "electromagnetism."

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by that of contiguous action in the electromagnetic field. In this study I treat the historical problem of the genesis of Hertz's experiments on elec­ tric waves and his successive interpretations of them. I am especially con­ cerned to bring forward the complex interplay between theory and experiment

that underlay this, his most famous and characteristic,

achievement. Hertz's own account of that interplay in the introduction to his Electric Waves is highly illuminating and I draw heavily on it, but it is incomplete in the way of all autobiographical reconstructions. 2 Recent interpretative historical studies by Robert Cohen, 3 Tetu Hirosige, 4 Le'on Rosenfeld, 5 A. E. Woodruff, 6 and others have illuminated important problems relating to Hertz's electrodynamic researches. There remain problems, however, that have been insufficiently studied. One such problem is Hertz's role in bridging the largely distinct traditions of research on electric propagation in wires and in space. A related problem is the bearing of Hertz's purely theoretical critique of competing electrody­ namic theories in 1884 on his experimental researches on electric waves in 1888. Another is the role of Helmholtzian electrodynamics in Hertz's elec­ trodynamic researches. 7 Still another is the reasons for Hertz's replace­ ment of the concept of action at a distance by that of the field as the theoretical context of his progressing experimental researches on electric waves. I am aware of what may be considered a defect in the structure of this study. In the early parts I mention Hertz in connection with Helmholtz and others, which presupposes that the reader already knows Hertz's work. To overcome this difficulty I suggest that the study should be read and understood as a whole. Its four parts aim at a partial reconstruction of the development of Hertz's electrodynamic researches, based on an analy­ sis of several historical problems at several levels of technical complexity. I am aware of the limitations of this study, and I would like to see other Hertz scholars add to and improve on it. I would especially like to see 2 Hertz,

"Introduction, B Theoretical," in Electric Waves, pp. 20-29. S. Cohen, "Hertz's Philosophy of Science: An Introductory Essay," in Hertz, The Principles of Mechanics, pp. i-xx. 4 Tetu Hirosige, "Origins of Lorentz' Theory of Electrons and the Concept of the Electromagnetic Field," Historical Studies in the Physical Sciences, 1 (1969), 151209. 5 Leon Rosenfeld, "The Velocity of Light and the Evolution of Electrodynamics," Supplemento al Volume IV, Serie X delNuovo Cimento, 4 (1956), 1630-1669. 6 A. E. Woodruff, "The Contributions of Hermann von Helmholtz to Electrody­ namics," Isis, 59 (1968), 300-311. 7 Rosenfeld, op. cit. (note 5), and Woodruff, ibid., discuss this problem. 3 Robert

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further work done on Hertz's theoretical articles on electrodynamics in 1890 and his masterpiece of theoretical and philosophical insight, the Principles of Mechanics.8

1. THEORETICAL AND EXPERIMENTAL PROBLEMS OF ELECTRODYNAMICS IN THE 1870's Electrodynamics in the 1870's was a highly mathematized discipline. German electrodynamics was still developing along the lines laid down by the mathematical physicists of the middle of the century: Franz Neumann, Wilhelm Weber, and Gustav Kirchhoff. Following George Green, William Thomson, and James Clerk Maxwell, British electromagnetism was devel­ oping -Vith the aid of the mathematical tools of elasticity, hydrodynamics, and thermodynamics. To outline the situation of German electrodynamics in the 1870's, 9 I have to refer back to the years around 1850. At that time the most success­ ful development in mathematical physics in Germany was the various derivations from fundamental principles of Michael Faraday's electromag­ netic induction law of 1831. Faraday's law posed a theoretical problem within the two research traditions that are most relevant to Hertz's electrodynamic contributions: theories and experiments on propagation in wires on the one hand and theories of space, or free, propagation on the other. Together with its capacitance, the inductance of a wire was considered the cause of propagation in the wire itself, and the process of induction in space was fundamental to the free propagation of electric disturbances in Maxwell's theory. Franz Neumann in 1845 and 1848 derived the electro­ motive force of induction from the potential of those ponderomotive forces which, according to Andre-Marie Ampere's theory, acted between a closed circuit and a magnet. Neumann's work was both a generalization of Ampere's theory and a brilliant confirmation of the fecundity of the po­ tential method of Gauss and Green. Wilhelm Weber took a different approach to the induction law. In 1846 8 Cohen, op. cit. (note 3), underlines the deep relation between the theoretical physicist who wrote The Principles and the experimentalist who discovered the propagation of electromagnetic radiation, and he mentions the connection between Hertz's conception of the dielectric polarization of ether and his concept of hidden variables in mechanics. 9 This survey has been carried out along the lines presented by Edmund Hoppe, Histoire de la Physique (Paris, 1928), and Edmund Whittaker, A History of the Theories of Aether and Electricity, 2 vols. (London, 1951), 1.

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he published his elementary law of action between charged particles, which comprehended static, ponderomotive, and inductive phenomena. His program consisted in deriving Ampere's ponderomotive forces between currents from more fundamental hypotheses concerning the elementary forces exerted by positive and negative charge carriers constituting electric currents. To yield Ampere's ponderomotive forces between stationary cur­ rents, the elementary law of force had to depend on the components of the relative velocity of two charged particles along their radius vector. The law accounted for the induction of a current when a circuit moved rela­ tively to another circuit or magnet. Weber's conception of induction as an effect of an alteration through relative motion of the elementary forces between particles implied that the forces acting on electric particles pro­ ducing currents were of the same nature as the electrostatic forces between macroscopic charged bodies. Rudolf Kohlrausch announced the identity of electrostatic and electromotive forces for steady currents in 1849, which he considered an indication of the reality of the conception of current as a motion of an electric substance.10 Other Weber-type laws were developed, such as the one that Bernhard Riemann formulated in a course of lectures at Gottingen in 1861. Weber and his followers pursued the theory of elec­ tricity and magnetism in Ampere's spirit towards the goal of a central force physics. Their laws were considered a great advance at the time, awakening mathematical physicists to the possibilities latent in the theory of electricity.11 Another derivation of the law of electromagnetic induction was given by Hermann Helmholtz in 1847 in his memoir on the conservation of force. There he applied the conservation principle to the interaction of magnets and currents: "When a magnet is moving under the influence of a current, the Hving force that is gained by the magnet must be communi­ cated by the forces of the potential [Spannkraften] that are utilized by the current."12 This statement allowed him to express the current J in­ duced in a circuit of resistance W in the form:

where Vj is the initial potential of the magnet relative to the conductor when the latter carries unit current, I72 the potential at the end of the dis­ placement, a the mechanical equivalent of heat, and t the time. When 1 OHoppe,

11 Whittaker, p. 206. p. 553. ^Hermann von Helmholtz, "Ueber die Erhaltung der Kraft. Eine physikalische Abhandlung," in Helmholtz, WissenschaftUche Abhandlungen, 3 vols. (Leipzig, 1882) 1, 12-75, on p. 62.

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Helmholtz formulated his law he did not know of the potential energy ac­ cumulated in the magnetic field of a current, though this incompleteness does not qualify the validity of the law in this special case.13 At first Helmholtz considered forces depending on velocity and accelera­ tion to be in contradiction with the conservation of force or energy. He strongly insisted on the incompatibility of Weber's law with general prin­ ciples. Since the protracted debate between Helmholtz and Weber had con­ sequences for Hertz's approach to electrodynamics, I will give a short summary of it here.14 In 1870 Helmholtz criticized Weber's law on the grounds that it produced an unstable equilibrium in electricity in the in­ terior of a conductor. Weber answered that this instability would not ob­ tain if the relative velocity of the electric particles remained lower than the velocity of light, and that, in any case, the instability would obtain only for molecular distances. Helmholtz rejoined in 1873 that by Weber's law a partially charged particle endowed with mass would suffer a delay when moving in the direction of the force; Weber in 1875 rejected the validity of this conclusion. Eventually, in 1881, Helmholtz found a case in which the application of Weber's law yielded an imaginary velocity. Other German physicists were involved in this debate. Carl Neumann entered in 1875 on Weber's side, Rudolf Clausius in 1875 and 1876 on the other side. The strength of Weber's theory can be appreciated by noting that as late as 1884 E. Hoppe still considered it the only true explanation of the presence of an induced current. In light of Helmholtz' many theoretical efforts at dismantling Weber's theory, it is worth mentioning here that in 1872 Helmholtz commended Maxwell's theory on the grounds that it avoided the "anomalous kind of forces which depend not only on the posi­ tion of the masses but on their motion."15 When in 1876 Henry Augustus Rowland's experiment pointed to a velocity-dependent force (as an effect of a convection current), Helmholtz put forward the alternative view that the polarization current produced by motion at a point in the surrounding space was the only source of magnetic effects in the experiment.16 13 Whittaker,

p. 218. pp. 590-592; Whittaker, p. 203. 15 Hermann von Helmholtz, "Ueber die Theorie der Elektrodynamik," Monatsberichte der Berliner Akademie (18 April 1872), pp. 247-256; in Wtss. Abhandl., 1, 634-645, on p. 639. 16 "Die entstehenden und vergehenden Componenten dieser Polarisation wiirden den Strom constituiren, der durch das astatische Nadelpaar angezeigt wird" (Helm­ holtz, 1, p. 797). In an article published in the Phil. Mag., 11 (1881), 229, J. J. Thomson attributed the magnetic effect of moving electrostatic charges to the con­ tinuous alteration of the electric field in the surrounding medium, or, in the lan­ guage of Maxwell, to the displacement current. See Whittaker, pp. 306-307. 14 Hoppe,

266

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

Theoretieal and experimental investigations of a high level of refinement mutually supported one another and were made possible by improvements in instrumentation. In the 1870's in Germany, electric instrumentation in steady or slowly varying currents and static potentials had reached a re­ markable standard of precision, which was owing to rapid progress that took place in Germany—and in England, too—at the middle of the century in theoretical, metrological, and technical methods. In Germany Weber contributed by his invention in 1841 of the electrodynamometer—which he used in 1846 to test his induction law—and in 1846 of the mirror galva­ nometer. Kirchhoff advanced instrumentation techniques in his studies in 1845 of the distribution of currents in wires, as did Weber through his exact determination of electric units in 1852. Weber's determination had international repercussions: in 1861 the Royal Society appointed a com­ mission headed by William Thomson to fix the standard unit of resistance, the so-called "weber." Weber and Kohlrausch's application of the electro­ dynamometer in 1855 to determine the electrodynamic unit of current was inspired by the theoretical approach to electrodynamics deriving from Weber's elementary law of force. The unification of electrostatic, ponderomotive, and inductive forces through their incorporation within a single formula required the determination of a constant,

Cw,

proportional to the

conversion factor between the static and electrodynamic units of charge. German basic physics and physical instrumentation thus cooperated in furthering the advance of electrodynamics. Theory and instrumentation also cooperated in furthering the under­ standing of oscillations of currents in circuits. Helmholtz discussed theo­ retically in 1847 the oscillatory nature of a condenser discharge, and in 1851 and 1869 he detected oscillations in open circuits. 17 William Thom­ son treated condenser oscillations in 1853, presenting the well-known rela­ tion between period, capacity, and inductance; and W. Feddersen mea­ sured periods of oscillations by his mirror technique between 1858 and 1862. Theoretical problems such as those related to the inertia of charges developed an interest in oscillations of higher frequencies, and this interest carried over to propagation phenomena in wires. The propagation of currents in wires, an important experimental subject for Hertz, became amenable to scientific study. 18 According to Weber and 17 Hermann von Helmholtz, "Ueber die Dauer und den Verlauf der durch Stromschwingungen inducirten elektrischen Strome," Poggendorffs Annalert, 88 (1869), 505-540; m Abhandl., 1, 429-462, on p. 429. See also p. 531. 18 Rosenfeld, pp. 1636-1637.

267

SALVO D'AGOSTINO

Kohlrausch's determination, the value of

C

w

,

which has dimensions of

velocity, was close to the velocity of light in a vacuum, c; in fact, c w = c\j2.

However, because of the conceptual context in which Weber was

working, he failed to see in this near numerical coincidence a hint of a hidden relationship between electrical and optical phenomena. Nor did he see one in his conclusion in 1854 that his elementary law entailed periodic oscillations of electric currents with a propagation velocity equal to that of light in perfectly conducting circuits. Kirchhoff, too, in 1857 calculated the propagation of current for the case of short wires of small resistance, using expressions for local current and charge gradients. He noticed that the propagation velocity was equal to that of light, but the case of short wires of small resistance was one to which he attached little importance; he was primarily interested in the opposite case of long wires suitable for telegraphy, for which he found no propagation effect. The case of long wires had been treated a few years before, in 1854, in a correspondence between two British physicists, George Gabriel Stokes and William Thomson. From the idea that self-inductance L and capacitance C in the variable regime of currents produce electromotive transient forces, Thomson derived a telegraphic equation. However, the extreme cases that he treated were an aerial wire and a submarine cable, in which either L or C predominated and in which an ohmic resistance is present, too. In these conditions no definite velocity of transmission is to be expected for ordinary signals. In the general case, which Thomson did not treat, the velocity, for a small resistance, assumes the well-known value υ = 1/\JLC = c, the velocity of light in air. Prior to Hertz and Heaviside, neither Thomson nor the German physi­ cists related the propagation of current in wires to a conception of the propagation of waves in the space surrounding the wire or to any theory of the electromagnetic field. The propagation in wires was understood until 1885 as a propagation of waves of current within the wire. This understanding is illustrated by Wilhelm von Bezold's researches on oscilla­ tions in 1870.19 Bezold produced oscillations by a Ruhmkorff induction coil, whose spark-gap was connected to an aerial wire, which was the seat of propagation phenomena such as standing waves. To detect a propagation effect, Bezold used the technique of the so-called Lichtenberger dust-fig­ ures based on the appearance of a compound powder in the vicinity of either positive or negative charges. The presence of "positive" figures where 19 Wilhelm von Bezold, "Researches on the Electric Discharge—Preliminary Com­ munication," Poggendorffs Annalen, 140 (1870), 541.

268

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

he expected "negative" ones suggested to him characteristic oscillations of charge. He also initiated the method of balancing the difference of poten­ tial on a sparking micrometer by different lengths of the connecting wires, a method which Hertz would fully investigate and exploit. Bezold argued that "phenomena occurred in electrical disturbances similar to those which are observed in the motion of fluids under the name of aspiration phe­ nomena." 20 He spoke of "waves of electric discharge" or "electricity rushing along a shorter path," clearly showing that he saw oscillatory phe­ nomena as a manifestation of moving charges or displacement of currents, unlike Hertz's "waves of potential." His experiments on the propagation of currents show that Bezold belongs to the group of physicists working within the tradition of research on propagation in wires. As a consequence of their restricted view of current propagation, physi­ cists before Hertz and Heaviside did not bring together in clear mathemati­ cal form their conceptions concerning propagation and their conceptions of propagation of electric actions in free space. There is evidence that physicists who elaborated theories of propagation in wires, like Weber and Kirchhoff in Germany and William Thomson in England, were either not in the least concerned with free propagation or did not stress any connec­ tion between it and propagation in wires. Thomson not only concluded that there was no definite velocity of propagation in cables or lines, but that there was also none in air and ether. Maxwell, too, made a distinction in his Treatise on Electricity and Magnetism between cases of diffusion, as in heat flow, and cases of propagation with definite velocity. The former applied to the cable, the latter to free propagation of electromagnetic waves. 21 A major field of theoretical electrodynamic research in the 1870's was the construction of theories of retarded action. Two theories of retarded action were developed in Germany by Riemann and Carl Neumann. Riemann's remained almost ignored; he had immediately withdrawn his paper, having mistakenly attempted to prove that the retarded scalar potential of the charge elements in two conductors is equivalent to the electrody­ namic potential derived from Weber's law. 22 Carl Neumann, a follower of Weber, derived in 1868 a theory of delayed action at a distance inde20 Heinrich

Hertz, "From Herr Wilhelm von Bezold's Paper: Researches on the

Electric Discharge—Preliminary Communication," in Electric Waves, pp. 54-62, on p. 55. 21 J. C. Maxwell, A Treatise on Electricity and Magnetism, 2 vols., reprint of the original 3rd edition of 1891 (New York, 1954), 2, 448-449. 22 Rosenfeld, p. 1635.

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pendently of any conception of an etherial transmission of force. He ex­ pressed the potential energy between two electrical particles in motion in terms of a time lag, defined by the distance between the particles at the time when the action from the first particle reaches the second divided by the conversion factor c w . Neumann believed that the interaction between events separated in time was primary and not further explicable. He con­ sidered his concept of "retarded action" as a "transcendental concept," and electrodynamic action as basically different from the transmission of light or heat.23 The Danish physicist Ludwig Lorenz also published an im­ portant theory of retarded action, based on KircMi off's equations for con­ tinuous three-dimensional currents. Hertz's theory of 1884 led to results having a formal resemblance to those of Lorenz, as Hertz explicitly noted. Maxwell's theory of the electromagnetic field, which he developed be­ tween 1856 and 1873, grafted its conceptions of free propagation onto Faraday's dielectric conceptions, which wavered between the different views of dielectric action as polarization of space-filling matter and as inde­ pendently existing lines of force.24 A characteristic feature of Maxwell's theory was the attention it paid to the "medium," whether by attempting to imagine a "mechanism" of transmission of electric action or by simply stressing the "dielectric" property of ether and its capability of sustaining "electric displacement." Electromagnetic energy had its seat in the space surrounding the conductors, a feature that Thomson had started to de­ velop even before Maxwell's memoirs of 1862 and 1865. Maxwell under­ stood and rejected continental ideas of currents and charges, but his own ideas concerning currents and charges were anything but definitive and clearly expressed.25 Maxwell was thus unlikely to contribute to the theory of propagation in wires. Nor were the theoreticians of "retarded action" like Riemann and Carl Neumann in a better position to contribute to the theory. A possible exception is Lorenz, who derived an equation for current propagation from Kirchhoff's theory, but who soon identified the current density vector with the well-known free transverse light vector of the elastic theory of light; he also early introduced a retarded vector potential into his theory. Riemann, Carl Neumann, and Lorenz were not interested in 23 A. E. Woodruff, "Action at a Distance in Nineteenth Century Electrodynamics," Isis, S3 (1962), 439-459. 24P. M. Heimann, 'Maxwell and the Modes of Consistent Representation," Archive for History of Exact Sciences, 6 (1970), 171-213. 25 Joan Brornberg, "Maxwell's Displacement Current and His Theory of Light," ibid., 3 (1967),218-234.

270

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

theories of propagation in wires and made no significant contribution to them. The gap that existed between the conceptions and theories of the two modes of propagation was due, I believe, to their different historical de­ velopments. Circuital theories were mainly developed by experimentalists with mathematical and instrumental tools that were proper to stationary phenomena. Theories of retarded action, on the other hand, were mainly correlated to optics and elasticity, and they therefore required a more sophisticated mathematical approach. Moreover, the instrumentation suit­ able for detecting free propagation was in a primitive state. It was Heinrich Hertz who developed suitable instrumentation to show that waves of cur­ rent and waves in space mutually interfere and who elaborated theoreti­ cally the mutual relations of the two modes. Studying in Berlin, Hertz had the opportunity to attend Helmholtz' and Kirchhoff's lectures and semi­ nars and Helmholtz' laboratory. He was well acquainted with Helmholtz' theory and William Thomson's theoretical and experimental advances in understanding propagation in cables. In an 1884 paper he also mentions the theories of Riemann and Lorenz, and he had studied thoroughly the relation of Helmholtz' polarization theory to Maxwell's theory of free propagation in ether. Hertz was in an excellent position to unify experi­ mentally and theoretically the two research traditions. He reached a syn­ thesis first by an original theoretical approach in 1884 and then by his audacious experiments and theory in 1888. So far my main task in this section has been to outline the two research traditions leading to their unification by Hertz. Other points I wish to touch on in the following pages deal with the difficulties that had to be met and the price paid for the unification. The difficulties arose because the unification was achieved in the range of frequencies of what is now called the "electromagnetic band." In this range Maxwell's theory led no­ where and Maxwell's conceptions were peculiarly vulnerable. The price for unification was the need to abandon the concept of force in its NewtonianHelmholtzian interpretation. I will now examine Maxwell's theory from the point of view of its ex­ perimental confirmation, looking specifically to see if it suggested any experimental approach in the range of frequencies in the "electromagnetic band." The main experimental evidence that Maxwell presented in support of his theory was his formula for the speed of light, c = 1ly/ejl, where e and μ axe the "specific capacity for electrostatic induction" and the "mag­ netic permeability," respectively, and the Faraday effect concerning the

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rotation of the plane of polarization of light in a magnetic field.26 Max­ well's selection of evidence confirms the view that his strongest interest in testing the theory lay in the domain of the electromagnetic theory of light. As regards a possible test of his theory in the "electromagnetic band," the following remarks should be made. The whole first volume of Maxwell's Treatise deals with electrostatics and steady currents, and only a limited number of pages of the second volume deal with the theory of the electromagnetic field. In the second volume no trace can be found of a theory of electric oscillations, and in the first volume condenser discharges are treated as an aperiodic phenomenon.27 More important, perhaps, is the absence in Maxwell's writings of any theory connecting a propagating field and an oscillating current as its source; his well-known solution for plane waves28 corresponds to the case of a source at infinity and a vanishing d'Alembertian of the field. These remarks illustrate that experiments for testing the theory in the "electromagnetic band" were not immediately foreseeable. Indications of a possible detection of the displacement current were, however, given by Maxwell. In 1868 Maxwell pointed to the detection of the displacement current "within the dielectric itself by a galvanometer properly con­ structed" as a possible way of proving the theory. The displacement cur­ rent, which Maxwell considered "a natural consequence" of his theory, was "not yet verified by direct experiment. . . [which] would certainly be a very delicate and difficult one."29 Moreover, some passages in his Treatise30 imply that the displacement current should display magnetic effects on the same footing as the conduction current. Given Maxwell's presentations of his theory, it is not surprising that an experimental test of the "electromagnetic band" would have been possible only in a different theoretical context or in a wholly experimental one. In fact all experiments on free propagation prior to the 1880's were ex­ traneous to Maxwell's theory, indeed to any established theory.31 Thomas Edison in 1875 noticed sparks from metallic objects in the vicinity of a magnetic vibrator relay. In 1871 and after, Elihu Thomson noticed the 26 Thomas K. Simpson, "Maxwell and the Direct ExperimentalTest of His Electro­ magnetic Theory," Isis, 57 (1966), 411-431, on pp. 411-413, 416. 27 Maxwell, 1, 451-452 (par. 326); 1, 487-488 (par. 355). 28 Maxwell, 2, 438-440 (par. 790). 29 Maxwell, Scientific Papers, 2 vols. (New York, 1950), 2, 139. 30 Bromberg, p. 232. 31 C. Susskind, "Observations of Electromagnetic Wave Radiation before Hertz," his, 55 (1964), 32-42.

272

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

same in the vicinity of a Ruhmkorff coil; with proper adjustments he was able to detect sparks as far away as the sixth floor of an observatory. Amis E. Dolbear received signals in a telephone receiver in 1882, as did David E. Hughes in 1879. These effects were interpreted variously at the time as induction effects, or the manifestation of a new principle or a new "etheric" force "that was as distinct from electricity as was light or heat." Dolbear, Edison, and Hughes had a very limited scientific background, and none was likely to be familiar with partial differential equations. Later Thomson and Edison regretted that they had missed a practical invention in wireless communication, not an advancement of science. Hughes, who thought that he had discovered a new principle, was discouraged from further inquiries by the opinion of such a distinguished physicist as George Gabriel Stokes that he was observing ordinary induction effects.32 All of these experiments were qualitative, especially since what im­ pressed the experimenters was solely the distance over which the "induc­ tion" was detected. The distance effect was meaningless in absence of a theory of the source-field relation. Other experiments on the propagation of "induction" were performed in Germany in 1869 and 1871 in Helmholtz' Berlin laboratory, but this time in connection with a well-defined quantitative problem: to measure velocity of propagation of "induction" or, at least, a lower limit to it. Using a pendulum as a current-switch, Helmholtz measured, with the precision of 1/231,170 seconds, the time lag be­ tween the opening of a primary and a secondary coil. When the coils were 136 centimeters apart, a change in the delay of 1/231,170 seconds did not produce any change in the induced charge. Helmholtz interpreted this re­ sult as evidence that "if the induced action propagates with a finite veloc­ ity, this should be larger than 314,400 meters per second." 33 The experi­ ments were situated in a theoretical context of not very clearly defined contours, as they were inspired indiscriminately by theories of retarded action including Neumann's, Faraday's, and Maxwell's. Helmholtz saw in this experimental approach a possible refutation of Weber's action-at-adistance theory. Helmholtz appreciated the intrinsic limitations of a me­ chanical switch and the impossibility of sharply defining the initial and final values of current pulses for such a short interval of time. 34 He soon abandoned this method in his search for an experimental decision between the two main conceptions of electrodynamics; he turned instead to the indirect effects of finite propagation such as the polarization of dielectrics. In 1870 Helmholtz began publishing a series of articles that constituted 32 Whittaker,

p. 323.

33 Helmholtz,

1, 629.

34 ZbtiA,

p. 634.

273

SALVO D'AGOSTINO

a comprehensive study of electrodynamics. He approached the problem of action at a distance and contiguous action in an original way by com­ bining Poisson's theory of dielectrics with Franz Neumann's potential theory to yield a Maxwell-type theory of propagation through a "me­ dium." Helmholtz' first article of the series, "On the Equations of Motion of Electricity for Conducting Bodies at Rest," 35 to which Hertz often re­ ferred in the course of his work, was a vast "tour d'horizon" of the com­ peting theories of electrodynamics.36 It is significant that only sixteen out of the eighty-four pages of this large article were devoted to a theory of dielectric action; the remaining part was concerned with a form of poten­ tial theory and its consequences for induction and the motion of elec­ tricity in extended conductors. Helmholtz started with an electrodynamic potential of two elements of circuits daι , da2 at a distance r from one another and carrying currents of intensity U i , W2. In modern vector notation,37 the potential is: (1 + Κ) tIa1 • da 2 +(I--K)

r · άσχ τ · άσ 2 ^ r

where A is Weber's ratio or conversion coefficient from electromagnetic to electrostatic units. The different values of JC define the potential functions of Weber (JC = -1), of Franz Neumann (JC = 1), and of Maxwell (JC = 0). When Helmholtz' potential is integrated around a closed circuit, any de­ pendence on JC is lost, so that only experiments with open circuits seemed suitable for discriminating among the competing theories. Helmholtz ex­ tended his potential for linear currents at positions ρ and p' to volume currents: the potential per unit volume of a current of density u at the position ρ and time t is: 38 - A 2 U (p, t ) • u(p, t ) , where U(p, t )

1+ K u Ir

+

1 - JC r

r

2

r3

(r · u) d r , K

'

35 Hermann von Helmholtz, "Ueber die Theorie der Elektrodynamik. Erste Abhandlung. Uber die Bewegungsgleichungen der Elektricitat fur ruhende leitende Korper," Borchardt's Journal fur die reine und angewandte Mathematik, 72 (1870), 57-129; in Wiss. Abhandl., 1, 545-628. 36 SeeHirosige, op. cit. (note 4), and Woodruff, op. cit. (note 6). 37 Helmholtz, 1, 567. In this paper I use a modern vectorial notation throughout in place of the original coordinate notation. Here vectors are indicated by the !-com­ ponent in the original text. The meaning of the symbols I use I indicate in each sec­ tion separately. ^Ibid., p. 568.

274

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

and r = ρ - p'. From this potential, Helmholtz derived a theory for the motion of elec­ tricity in extended conductors, yielding the possibility of the propagation of longitudinal "electric waves" in a conductor. (This derivation was inde­ pendent of the introduction of dielectric action, so that on this point Helmholtz was on the same ground as Kirchhoff and Weber, who did not connect propagation in wires with free propagation.) The experimental de­ tection of longitudinal waves and the determination of K met with theo­ retical limitations; Helmholtz deemed experiments possible only for con­ ductors whose transverse dimensions were very large in comparison with the wavelength, a case which was then hardly testable. In Helmholtz' treatment of theories of dielectric action, he regards the polarization of dielectrics in Poisson's sense as resulting not only from static forces but also from electromagnetic ones; i.e., he recognizes an addi­ tional polarization produced by the time variation of an electric or mag­ netic field. His mathematical treatment of polarization begins with the definition of polarization in the static regime,39 P = e(x - grad ψ), where e is the dielectric constant, φ the electric potential function of the distrib­ uted electricity, and χ the electric force. The polarization in the dynamic regime is: P , , dU d ~ = - grad φ - A —— + A —rotL + X, e dt dt where L is the magnetic vector potential and X the external force. Here L = /λΙτάτ, where λ is the magnetic moment and is defined by λ = θ(£- grad χ), with θ the magnetic susceptibility, χ the magnetic scalar potential, and £ the external magnetic force. From the equation for the electric polarization and the corresponding equation for the magnetic mo­ ment, Helmholtz deduced an equation for the propagation of P when X = O: , d2 P VP = 4 i r e ( l + 4 π θ ) A — γ + dt

(1 + 4 π θ ) (1 + 4 n e ) K

grad div P.

He found solutions for the wave equation by considering P as composed of two vectors Pi and P2 such that rot P1 = O and div P2 = 0. Since the longi­ tudinal solution belongs to that component of P, say Pi, for which rot P1 = 3 9 Ibid.,

pp. 611-612.

275

SALVO D'AGOSTINO

0 and div P 1 = — 1/47T grad div-p, this component is an irrotational polariza­ tion dependent, according to Helmholtz, on the static force. I will call P 1 a static-type polarization indicating that this qualification refers to its spatial distribution and distance dependence, quite apart from its con­ stancy in time. The velocities of propagation for Pv and P2 are, respectively, 40 1

1

A y/4-ne(l + 4πθ)

4TreK

for transversal waves and

for longitudinal waves.

One of Helmholtz' subsequent researches is especially important to mention here: in 1874 he extended Franz Neumann's potential formula of 1848 to three-dimensional conductors and to the case of open currents, showing that from this extended potential ponderomotive as well as elec­ tromotive induction forces could be derived. The ponderomotive forces were different from those predicted by Ampere's formula, for they in­ cluded also ponderomotive and inductive forces due to the charges situ­ ated at the ends of open circuits. 41 Hertz later considered these forces emanating from the open ends of a circuit as an explanation for the failure of his early experiments on the electromagnetic effects of material dielectrics. I need now to assess the role of Helmholtz' theory in inspiring experi­ mental activity in his Berlin laboratory in the 1870's and, in particular, inspiring the experimental approach to dielectrics from which Hertz began his experimental study of electromagnetic radiation. I will begin with a brief description of the experimental problem and will follow that with a more detailed appraisal of the Helmholtz-Hertz relationship. Mechanical motion, in the form in which it had been exploited in induction-type ex­ periments, seemed at first to Helmholtz suitable for producing those varia­ tions of electric and magnetic forces to which the polarization of dielec­ trics was related in his formula. Accordingly, Helmholtz limited the major part of his experiments in the 1870's to testing polarization effects in the 4 Olbid.,

p. 628. von Helmholtz, "Ueber die Theorie der Elektrodynamik. Dritte Abhandlung. Die elektrodynamischen Krafte in bewegten Leitern," Borchardt's Journal fur die reine und angewandte Mathematik, 78 (1874), 273-324; in Wiss. Abhandl., 1, 702-762, on pp. 724-725. 41 Hermann

276

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

vicinity of charged conductors in motion. An experiment using a cylin­ drical condenser that turned around its axis in a uniform magnetic field was performed by N. Schiller in Helmholtz' laboratory and presented by Helmholtz in a memoir to the Berlin Academy in 1875. 42 Schiller con­ cluded that Franz Neumann's generalized law of induction derived from his potential theory was false, whereas the results of the experiment agreed with Neumann's potential theory when augmented by a dielectric ether, and they agreed with his electromagnetic induction law derived from Ampere's action-at-a-distance forces and Faraday's dielectric polarization. (Helmholtz regarded Neumann's potential theory augmented by a dielec­ tric ether as equivalent to Maxwell's theory.) An experiment that Helm­ holtz performed with Henry A. Rowland and that he reported to the Academy in 1876 confirmed that charges borne by moving material bodies exert, under certain conditions, magnetic actions. 43 But these magnetic actions could be interpreted as due either merely to the displacement of charges through the motion of their ponderable carriers, as in Weber's theory, or to the variation of the dielectric polarization of air, or ether, in a fixed volume of space resulting from the motion of the electric force. To discriminate between these two possibilities, experiments were required in which polarization effects could be produced without the motion, at least the macroscopic motion, of charges. Helmholtz proposed such experi­ ments as the theme for a research competition at the Academy in 1879, one that Hertz was to enter. Helmholtz' proposed experiments had the advantage, essential to experiments on electromagnetic waves, of requiring no mechanical motions to produce the expected effects; Hertz's new tech­ nique of detecting electromagnetic effects by purely electromagnetic means such as scintillations in a spark gap followed Helmholtz' line of thought.

2. THE HELMHOLTZ-HERTZ RELATIONSHIP Heinrich Hertz's decision to go to Helmholtz and to work in his labora­ tory in Berlin had great significance for his career in research. Helmholtz' 42 Hermann von Helmholtz, "Versuche liber die im ungeschlossenen Kreise durch Bewegung inducirten elektromotorischen Krafte," Poggendorff's Annalen, 158 (1875), 87-105; in Wiss. Abhandl., 1, 774-790, on p. 780. 43 Hermann von Helmholtz, "Bericht betreffend Versuche uber die elektromagnetische Wirkung elektrischer Convection, ausgefuhrt von Hrn. Henry A. Rowland," Poggendorffs Annalen, 158 (1875), 487-493; in Wiss. Abhandl. 1, 791-797, on p. 791.

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general outlook on science and physics had a major bearing on Hertz's own. Helmholtz' article of 1870, in which he placed the different electrodynamical theories on a basis that allowed for a decision between them, was consistent with his general ideas on scientific inquiry. He believed that the "impact of a new abstraction [such as the concept of electric displacement] can only be understood clearly when its application to the chief group of individual cases which it comprises has been thought out and found valid. It is very hard to define new abstractions in universal propositions, so as to avoid misunderstandings of all kinds." 44 His concrete interpretation of Maxwell's displacement current as the dielectric polarization of insulators is, perhaps, the best exemplification of this frame of mind. His mistrust of abstractions is not to be seen as an empiricist's fashion; rather, it expresses the ideal of a balance between theoretical and experimental capabilities, which Helmholtz' and Hertz's careers exemplified. Helmholtz was confi­ dent that the "conviction might gain ground that the only successful ex­ perimenter in physical science is the man who has a thorough theoretical knowledge," a combination that had been brilliantly demonstrated by Kirchhoff in the discovery of spectrum analysis. 45 That was exactly Hertz's attitude, as Helmholtz pointed out in his preface to Hertz's last work. 46 In Helmholtz' eyes, theoretical physics was also an empirical sci­ ence and he struggled "to break down the barrier between experimental and theoretical physics." His aversion towards a certain kind of abstractness stemmed, too, from his polemic against the late followers of German Naturphilosophie. 47 The basic tenet of Helmholtz' polarization theory of electrodynamics is the conceivability of a "bare" charge in a vacuum, or "empty space," as distinguished from a dielectric space or ether. He often qualified the word "ether" with the word "light." He considered the hypothesis of the polarizability of the light-ether as a tentative extrapolation from the dielectric polarizability of some material insulators and said that once the light-ether was considered magnetizable, the "moment is no longer far off when one can consider it also as a dielectric in Faraday's sense." 48 He related the "bare" charge of density E in a vacuum to the two potential functions ψ,

44 Leo Koenigsberger, Hermann von Helmholtz, transl. Frances A. Welby (New York, 1965), p. 293. 45 Koemgsberger, p. 284. 46 Helmholtz, preface to Hertz's Principles of Mechanics. 47 Koenigsberger, p. 284. 48 Helmholtz, 1, 556.

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HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

which gave rise to a force in a vacuum, and φ , which depended on the polarizability of the ether:49 1 4π

, V (Φ + φ ) = :

E

1 + 4ne0

where V is the Laplacian operator, e 0 the dielectric constant for etherfilled space or, equivalently, air. It is a property of the whole potential function that in a space where E exists, "ψ + ψ behaves as if only E/l + 47Γ€ο would be present in a non-dielectric space." As a consequence of this property any actual measure of charges by Coulomb forces would give El1 + 4ne 0 . The

bare charge E can only be measured together with a factor

1/1 + 4πβο, which is indeterminate owing to the unknown value e 0 (one cannot remove the ether and measure the force between bare charges). For Helmholtz the unit of the electrostatic charge, as experimentally de­ termined by Coulomb's law, is affected by the same indeterminateness of unknown multiplicative factors. Consequently, Weber's ratio A, defined as the ratio between bare electrostatic and electromagnetic units of charge, differs from the inverse of c, the velocity of light in air, by 1 / A = c ( l + 4π€ο)(1 + 4πθ 0 ), where θ 0 is the magnetic susceptibility of the ether.s0 Helmholtz developed an argument for θ 0 parallel to that for e 0 . The dis­ crepancy between the "true" velocity 1/A and the observed velocity c in air or ether entails a correction in the theoretical velocities of longitudinal and transversal waves of polarization P. The corrected values are:

V f-

. , / 1 +4πθ0

c(l + 4πε Eo)0)

4Tte 0 K

+ 4TT€ Q

for longitudinal waves,

for transversal waves.

4Tre 0

According to Helmholtz, the longitudinal waves of P 1 were dependent on the static-type force. It is my opinion that the presence of a static-type force in the variable regime must be correlated with deeper layers of con­ ceptualization. Helmholtz was inclined to consider "Kraft" in its substan­ tive relation to matter. In his 1847 memoir on the conservation of "Kraft," for example, he affirmed: "It is evident that in the application of the ideas

4 9 Ibid., so Ibid.,

p. 614. p. 627.

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of matter and 'Kraft' to nature, the two . . . should never be separated." 51 I think that for him the counterpart in electrical science was the substan­ tive relation between electric charge and electrostatic force. The relation was tied to the nature of electric charge and therefore could not be dis­ solved by accidents such as the motion of the charge. Although Helmholtz presented a wave equation for the polarization, his physical ideas were by no means identical with Maxwell's. Helmholtz was aware of the differences, pointing out that his and Maxwell's theories "are opposed to each other in a certain sense, since according to the theory of magnetic induction originating with Poisson, which can be carried through in a fully corresponding way for the theory of dielectric polarization of insulators, the action at a distance is diminished by the polarization, whereas according to Maxwell's theory the action at a distance is exactly replaced by the polarization." 52 Helmholtz' model of polarizability modi­ fied Maxwell's theory of the electromagnetic field in major ways: in HelmhoItz' modification not only were two distinct forces present, but the velocity of neither coincided with the velocity of light. Since this was a consequence of his model of polarizability, Helmholtz had to force his theory to yield the velocity of light. For a very large value of the dielectric constant the velocity of the transverse wave converges to c; the velocity of the longitudinal wave becomes infinite for K = 0, in which case the longi­ tudinal force acts at a distance. This condition also affects the intensity of the longitudinal force, as Helmholtz showed elsewhere: 53 in the case of very large values for the electric and magnetic susceptibilities, 6 0 and θ 0 , the longitudinal distance force vanishes together with the free electricity, E. The very large values of the susceptibilities do not effect the total charge, which remains finite. The idea that distance forces emanating from bare charges exist in a dynamic system in a vacuum was deeply engrained in Helmholtz' theory of polarizability. Two consequences were that longitudinal, static-type forces are present in dynamical phenomena over the entire band of frequencies, and that a correction must be applied to the velocity of propagation of 51 Yehuda Elkana, "Helmholtz' 'Kraft': An Illustration of Concepts in Flux," Historical Studies in the Physical Sciences, 2 (1970), 263-289, on p. 282, concerns, among other things, Helmholtz' conception of the relation between force and matter. 52 Helmholtz 1 1, 556-557. 53 Hermann von Helmholtz, "Ueber die auf das Innere magnetischer oder dielektrisch polarisirter Korper wirkenden Krafte," Wiedemann's Annahn, 13 (1881), 305-406; in Wiss. Abhandl. 1, 798-820, on pp. 819-820.

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HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

transverse and longitudinal forces as given by the d'Alembert equation of polarization. Thus, etherless vacuum and action at a distance had a con­ ceptual primacy in Helmholtz' theory. Helmholtz' theory was widely influential. Hertz took it as the starting point for his researches in 1887, as did H. A. Lorentz, who accepted action at a distance in the Helmholtzian formulation as the basis for his investiga­ tion of Maxwell's electromagnetic theory of light. 54 Henri Poincare de­ voted many pages of his Electricite et Optique ss of 1901 to an assessment of Helmholtz' theory and its relation to Maxwell's. Pierre Duhem, after a strong criticism of Maxwell's theory and Boltzmann's formulation of it, recommended Helmholtz' theory as "a natural continuation of the theories of Poisson, Ampere, Weber, Neumann," establishing a "continuity of tradi­ tion, without missing any of the recent conquests of electrical science." 56 Helmhgiltz' theory has received attention recently from historians of science. Le'on Rosenfeld, in his provocative essay, "The Velocity of Light and the Evolution of Electrodynamics," says that not only was Helmholtz' approach to Maxwell's theory "entirely alien to its spirit, but it tended to obscure its characteristic features and to make the theory appear as a somewhat singular limiting case of the scheme." 57 A. E. Woodruff says that the "conceptually completely different dielectric theory of Helmholtz . . . served to interpret Maxwell's equations for continental physi­ cists." 58 Tetu Hirosige, agreeing with Woodruff on the historical function of Helmholtz' electrodynamics, adds that "it was adapted to Maxwell's conceptions." 59 I accept Hirosige's and Woodruff's statements on the historical function of HeImholtz' electrodynamics and its relation to Max­ well's conceptions. At the same time I agree with Rosenfeld's judgment; for I believe that there is no contradiction in the assertions that Helmholtz was intelligible in the context of continental physics and that he did vio­ lence to Maxwell's ideas as they were understood by Maxwell and by some of his successors. I explain this seeming paradox by the differences be­ tween continental and British science; the former stressed the internal con­ sistency and phenomenological concreteness of theories, whereas the latter stressed models and modes of representation. Helmholtz' interpretation of Maxwell conformed to the continental objectives. 54 Hirosige,

pp. 174-175. Poincare, Electricite et Optique (Paris, 1901). See especially chapter 5. 56 Pierre Duhem, Les Theories electriques de J. C. Maxwell (Paris, 1902), p. 225. 57 Rosenfeld, p. 1665. 58 Woodruff, op. cit. (note 6), p. 301. 59 Hirosige p. 161. 1 55 Henri

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Helmholtz' polarization theory stimulated Hertz's interest in a concep­ tion of contiguous action in electromagnetic phenomena, although Hertz's early approach took its starting point in the Riemann and Carl Neumann tradition of retarded action. It is clear from Hertz's writings that he studied Helmholtz' theory with its peculiar combination of distance and contiguous action. 60 In contrast to Helmholtz' more phenomenological approach, however, Hertz's approach was more concerned with a physical representation of the modality of the action. Hertz called the condition under which the velocity of the Helmholtzian electromagnetic force con­ verges towards the velocity of light c and the velocity of the static, longi­ tudinal force diverges to infinity the "limiting condition or case of Helmholtz' theory." He wrote in 1891 that a closer examination [of Helmholtz' theory] shows that we can split up the resultant action (which alone can be observed) of material bodies upon one another into an influence due to direct action-at-a-distance, and an influence due to the intervening medium. We can increase that part of the total energy which has its seat in the electrified bodies at the expense of that part which we seek in the medium, and conversely. Now in the limiting case we seek the whole of the energy in the medium. Since no energy corresponds to the electricities which exist upon the conductors, the distance-forces must become infinitely small. 61 (Italics added.) An energy located in the medium did not fit well with Helmholtz' ideas; Hertz's interpretation was more oriented toward Maxwell's, especially toward the form it took in Maxwell's 1865 memoir. Concerning the rela­ tion between Helmholtz' limiting case and Maxwell's theory, Hertz's opin­ ion in 1891 was that the "mathematical treatment of this limiting case leads us to Maxwell's equations. . . . But in no sense must this be taken as meaning that the physical ideas on which it is based are Maxwell's ideas." 62 Hertz stressed the unsatisfactoriness of Helmholtz' theory from the point of view of logical consistency, for he found the same lack of consistency in Maxwell's theory. 63 For Hertz, force and free charge could not be primary concepts in a consistent representation of contiguous action because they 60 Hertz, 61 Ibid.,

Electric Waves, pp. 23-26. p. 24.

62 Ibid. 63 Heinrich Hertz, "On the Fundamental Equations of Electrodynamics for Bodies at Rest," Gottinger Nachr. (19 March 1890); in Wiedemann's Annalen, 40 (1890), 577; in Electric Waves, pp. 195-240, on p. 195.

282

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

could not be defined independently from the polarization of ether; in fact, "one cannot remove the ether from the space and yet allow the force to persist in it." 64 Hertz in 1891 spoke of Helmholtz' theory of 1870 as a modification of the "standpoint of the potential theory," 65 He said it was deduced "from the older views [potential theories]" and from three hypotheses: 1. Changes of dielectric polarisations in [ponderable] non-conductors produce the same electromagnetic [electrodynamic] forces as do the currents which are equivalent to them. 2. Electromagnetic [electrodynamic] forces as well as electrostatic are able to produce dielectric polarizations. 3. In all these respects air and empty space behave like all other dielectrics. 66 The third hypothesis played an important role in connection with Hertz's reactions to the research competition of the Berlin Academy in 1879. On Helmholtz' suggestion, the Academy offered a prize for the solu­ tion to the following problem: "To establish experimentally any relation between electromagnetic forces and dielectric polarization of insulators— that is to say, either in electromagnetic [electrodynamic] force exerted by polarizations in non-conductors, or the polarization of a non-conductor as an effect of electromagnetic [electrodynamic] induction." 67 Hertz did not think that the oscillations of Leyden jars or open induction coils would lead to observable effects. 68 He did not say why he thought the effects were unobservable, but his reason can be inferred from a note in his diary 69 and, especially, from the content of his 1887 paper, "On Very Rapid Electric Oscillations," his first response to the Academy problem. He felt that he needed more rapid oscillations than ordinarily obtainable, since any displacement or polarization effect was dependent on the time derivative. The Academy problem required, according to Hertz, 70 an experimental ft ^Ibid.,

p. 196. 9 ibid., p. 22. 66 Hertz, "Introduction, A Experimental," inElectric Waves, p. 6. 6 ^Ibid., p. 1. ^Ibid., p. 2. ®"Im Laboratorium die Arbeit begonnen iiber schnelle Schwingungen." Note for 7 September 1887, in Johanna Hertz, Heinrich Hertz. Erinnerungen, Briefe, Tagebucher (Leipzig, 1928), p. 175. 70 Hertz, "Introduction, A Experimental," in Electric Waves, p. 7. 65 Hertz,

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test of either one or the other of the first two hypotheses of Helmholtz' theory. The third one had been left aside, because to test all three seemed an unreasonable demand. Having successfully verified the first hypothesis in 1887, Hertz felt, however, that the third contained the center of interest of Maxwell's theory, and that the first two hypotheses "would be proved simultaneously if one could succeed in demonstrating in air a finite rate of propagation and waves." 71 For him, air ("Luftraum") and empty space ("leerer Raum") were synonymous. He saw that the essential point of Maxwell's theory was not polarization current in material dielectrics but ether polarization current—in our terms, vacuum displacement current. Whereas in Helmholtz' theory the third hypothesis was introduced as a tentative extrapolation from the material dielectrics to the ether, in Hertz's it assumed logical priority, as is clear from his theoretical paper of 1890. 72 From the experimental standpoint, too, the hypothesis was central to Hertz. The singularity of Hertz's contribution, both on the theoretical and the experimental side, to Helmholtz' electrodynamics was his recognition that the ρolarizability of material dielectrics was marginal to Maxwell's dis­ placement theory. This recognition was later developed by Lorentz, who separated the behavior of material dielectrics from that of the ether. 73 I have stated one aspect of the relation between Hertz and Helmholtz. Their relation, however, was many-sided. From the experimental point of view, it was decisive for Hertz's success that he should approach Maxwell through Helmholtz' interpretation. In fact, Helmholtz' program, which Hertz took up, of detecting the polarization of material dielectrics by in­ duction experiments implied circuital electricity; the dielectric body had to be inserted into the primary circuit to make its inductive effects ob­ servable. Helmholtz' circuital approach was an important factor in leading Hertz toward his understanding of the source-field relation. The stress on the electromagnetic forces of polarization currents brought to Hertz's attention the more general connection between conduction currents and fields in the vicinity of a linear oscillator. Hertz generalized this connection to that of a relation between sources and waves in the radiation field of the same oscillator. It will serve as an indication of the complexity of the historical situation to remark that Hertz's experiments, in their initial phase, turned out to be significant for Helmholtz' potential theory as well as for Maxwell's theory. 1 1 Ibid.,

p. 7. Electric Waves, p. 195. 73 Hirosige, p. 172.

72 Hertz,

284

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

The potential theories were concerned with the distribution of forces in the neighborhood of an unclosed current, and Hertz found a way to detect precisely that distribution. There are hints here and there that Hertz thought of using the new procedure to test these theories, especially the one which had received Helmholtz' imprint and sanction. 74 In a letter to Helmholtz, Hertz spoke of the possibility of measuring K in Helmholtz' potential formula and his dielectric constant of space. 75 However, he showed no protracted interest in potential theories; in the progress of his researches, in connection with Helmholtz' theme for the Academy prize, his references to Helmholtz' potential theory dropped out as his interest grew in the propagation of electric force and in the dielectric conception.

3. HERTZ'S FIRST APPROACH TO ELECTRODYNAMICS AND HIS 1884 THEORETICAL PAPER In the autumn of 1878 Hertz went from the University of Munich to the University of Berlin, where he spent his second year as a physics student. 76 In Berlin he followed Kirchhoff's and Helmholtz' lectures and attended Helmholtz' physics laboratory. He was soon drawn into Helmholtz' scien­ tific ambiance; when shortly he undertook original research on a subject proposed by Helmholtz, the latter provided him with research facilities in his institute and paid daily attention to Hertz's progress. Hertz pub­ lished his results under the title "Research to Establish an Upper Limit for the Kinetic Energy of Electric Current," 77 for which he was awarded a prize by the Berlin Philosophical Faculty. Since this research was repre­ sentative of the approach to electrodynamics common in Helmholtz'

74 Hertz,

Electric Waves, p. 123. to Helmholtz, 21 January 1888: "Bisher habe ich noch nicht versucht, eine bestimmte Theorie auf die Erscheinungen anzuwenden und etwa die Constante K oder die Dielektricitatsconstante des Raumes zu bestimmen. Nur glaube ich mich uberzeugt zu haben dass das Maxwellsche Gleichungssystem nicht genugt. Wenigstens vermochte ich aus demselben iiberhaupt keine bestimmte Geschwindigkeit in Drahten abzuleiten" (Hertz's Correspondence, Deutsches Museum, MS. 3120). I wish to express my gratitude to Dr. A. Opitz of the Bibliothek des Deutschen Museums for his help. 76 For details of Hertz's life, see Russell McCormmach, "Hertz, Heinrich Rudolf," Dictionary of Scientific Biography, 6 (New York, 1971), 340-349. 77 Heinrich Hertz, "Research on the Determination of an Upper Limit for the Kinetic Energy of the Electric Current," Wiedemann's Annalen, 10 (1880), 414-448; in Miscellaneous Papers, p. 1. 75 Hertz

285

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laboratory—an approach that Hertz was to abandon eventually—I shall comment briefly on it. Hertz set out to prove experimentally that only a limited fraction of the extra current in a self-inductive circuit was dependent on the inertia of the current; he also sought an upper limit for the density of mass per unit charge. The equation for an oscillating current in a circuit with inductance is: Aidt = i 2 wdt + d(Pi 2 ), where A is the electromotive force, i the intensity of the current, w the re­ sistance, and P the self-induction coefficient ("Potential des Leiters auf sich selbst"). Introducing the hypothesis of an inertial mass m of the cur­ rent, this equation reads: Aidt = i 2 wdt + d(Pi 2 + mi 2 ). In this case P should represent that part of the self-induction that is inde­ pendent of inertial effects. All inertial effects are included m m = pqVk, where λ is the unit of positive electricity contained in unit volume of wire, I the total length of wire, q the cross section of the wire, and ρ the density of mass per unit charge. Hertz sought to isolate the inertial element m by comparing the induc­ tive effects in a series of circuits with varying self-induction. 78 He mea­ sured the extra current with a galvanometer inserted into an arm of a Wheatstone bridge. The mechanical arrangement made it possible to estab­ lish contact with different circuits in quick succession. At first Hertz used, on Helmholtz' suggestion, double-wound or Knochenhauer spirals to re­ duce the self-induction. However, he soon found out that straight wires in circuits of a rectangular shape gave better results, since the calculation of the self-induction coefficient was then geometrically simpler. (Both rec­ tangular circuits and self-induction calculations would enter his later re­ searches on electric waves.) Assuming for the velocity of the current the values 1 mm/sec and 10 mm/sec, Hertz obtained from the experiment the corresponding inequalities: 79 ρ < 0.008 milligrams; ρ < 0.00008 milligrams. His conclusion was that the upper limit for the density of mass seemed to disprove Weber's electrodynamic law; for the small, if not vanishing, iner78

Zbici., p. 3.

lt3

Ibid., p. 33.

286

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

tial effects implied an instability in the charge distribution of a metallic sphere.80 This argument had been developed by Helmholtz in his 1870 essay, showing clearly that Hertz's first research belonged to the terms of the Weber-Helmholtz debate. Helmholtz confirmed this point in his 1894 reconstruction of Hertz's route to the discovery of electric waves. There Helmholtz stressed the importance for Hertz's future work of his early recognition of the quasi absence of inertial effects in the motion of elec­ tricity: "These experiments clearly impressed upon his [Hertz's] mind the exceeding mobility of electricity, and pointed out to him the way towards his most important discoveries."81 Hertz moved towards his decisive experiments on electric radiation by moving from a conception of electricity in which charges and currents in circuits were the sources of force to the different conception of electricity in which the electric force was the polarization of the ether. Hertz never returned in his mature work to the circuital approach to electric phenom­ ena that typified his initial research. The "exceeding mobility of elec­ tricity" was, perhaps, one of the first steps in his radical change in basic conceptions. In 1883 Hertz moved from the University of Berlin to the University of Kiel and from his position of assistant to Helmholtz to that of Privatdocent for mathematical physics. His outstanding theoretical work at Kiel was his 1884 paper, "On the Relations between Maxwell's Fundamental Electro­ magnetic [Electrodynamic] Equations and the Fundamental Equations of the Opposing Electromagnetics [Electrodynamics] ."82 In his paper Hertz developed a procedure for obtaining Maxwell's equations from Continental electrodynamics. He set out to show that the vector potentials for steady or slowly varying currents, on which the old electrodynamics had relied exclusively, are incomplete, and he calculated by an iterative process the missing parts. Once he had derived the complete potentials or, as they were later called, the "retarded potentials," Hertz proceeded to his main concern: Maxwell's theory. In his 1884 paper, Hertz claimed that Ampere had predicted the exis­ tence of ponderomotive forces between electric currents as a consequence of the identity of the ponderomotive forces exerted by a magnetic pole 80 Ibid.,

p. 34. preface to Hertz, The Principles of Mechanics, p. xxviii. 82 Heinrich Hertz, "On the Relations between Maxwell's Fundamental Electro­ magnetic Equations and the Fundamental Equations of the Opposing Electromag­ netics," Wiedemann's Annalen, 23 (1884), 84-103; in Miscellaneous Papers, pp. 273-290. 81 Helmholtz'

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with those exerted by an electric current. This identity was, in Hertz's opinion, an assertion of the "unity" of the magnetic force. He formulated an analogous principle for the electric force: "Those electric forces which have their origin in inductive actions are in every way equivalent to equal and equally directed forces from an electrostatic source."83 He regarded this "principle of unity of electric force" as "a necessary presupposition and conclusion of the chief notions which we have formed in general of electromagnetic phenomena."84 From the two principles of unity together with the accepted laws of electric and magnetic actions of closed currents, and from principles such as those of energy conservation, action and reaction, and the superposi­ tion of forces, Hertz deduced a new electrodynamics. His theory was valid only for closed circuits, unlike Helmholtz' which was also valid for open circuits. Hertz argued as follows. If there is a unity of electric force, a mag­ net of varying intensity should set in motion a charged body with the same force with which it induces a current. By the principle of action and re­ action the charged body should in turn set the magnet in motion. Further, two magnets of varying intensities should attract or repel each other with forces depending on the time rate of variation of the magnetic force. Such magnetic actions are not only omitted from but are also in contradiction with the laws governing the constant forces of the old electrodynamics. From energy conservation and the unity of magnetic force, the correction in the magnetic actions leads to a correction in the induced electric forces. This correction in turn requires a second correction in the magnetic forces because of the essential unity of forces between currents and forces be­ tween magnets. One obtains an infinite series of successive approximations in this way. Hertz begins by defining a magnetic current as the time rate of change of the magnetic polarization of a "ring-magnet" (toroidal magnet) of variable magnetic intensity. Due to the unity of electric force, the "po­ tential of the ring-magnet on an electric pole can, apart from its multi­ plicity, be represented by the potential of the double layer on the pole."85 Using an analogy with Ampere's theorem for magnetic double layers, he assimilates the ring-magnet to an electric double layer bounded by the magnetic current. Hertz's theory is symmetric in electric and magnetic forces and currents, since magnetic currents interact according to the same

83Ibid.,

p. 274. Mlbid., p. 274. 85 Ibid., p. 275.

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HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

laws as electric currents.86 As a consequence of this symmetry, he obtains a new, magneto-electric induction law: "Two ring-magnets which are placed close together and side by side will attract each other at the mo­ ment when they both lose their magnetism if they are magnetized in the same direction; they will repel each other if oppositely magnetized."87 The interaction of ring-magnets is a new type of action that is missing, according to Hertz, in the "ordinary electrodynamics" like Franz Neu­ mann's. Another "new" effect that he derives is the alternation of the mag­ netic polarization of a ring-magnetic when it is rotated around an axis perpendicular to an electrostatic force. Yet another new effect is the motion of electric charged bodies produced by a ring-magnet of diminish­ ing intensity. The new magnetic forces affect in their turn the electro­ motive forces and, therefore, the electric induction forces; this interaction of forces is evident from the Helmholtzian procedure of deriving induction forces from ponderomotive magnetic forces between circuits. But this, in turn, will entail a further modification in the force of magnetic interaction, and the argument will be repeated.88 Hertz develops a mathematical treatment of these qualitative ideas. He introduces an electric vector potential U in the usual way: 89 U=

J

"—dr,

div u = 0,

where r is the position vector, άτ the element of volume, and u the current density. The expression is valid also for the case of a current of variable density. Hertz defines the first order magnetic field L 1 : Lj = - A rot Ui,

(1)

where A is Weber's conversion factor and the reciprocal of the velocity of light in a vacuum. Due to the principle of conservation of energy, varia­ tions of U j produce a first order electric force X i : χ

Ibid., p. 281.

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HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

in equations (4) and (1). The correction is:

It is evident that the correction can be expressed in both forms (4) and (1) because of the possibility o f interchanging space and time operators. Let us call L 2 the corrected magnetic force in the form of equation (4):

The corrected equation (1) is:

Hence,

Through the same argument that derives U 2 from Uj and U*, the electric vector potentials of higher order U 3 , U 4 , . . . , can be found:

The reiterative process is mathematically equivalent to a series summation. The series converges, according to Hertz, towards the actual electric and magnetic vector potentials U, P. He demonstrates the convergence in a special case of sinusoidal variability.91 The potentials U and P in empty space appear to obey d'Alembert's equations and are propagated with a velocity equal to the reciprocal of Weber's conversion coefficient; i.e., the velocity of light in a vacuum:

d Although, as Hertz noted, Riemann in 1858 and Lorenz in 1867 had 9lIbid.,

p. 285.

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derived equations similar to the above, they had done so by different routes. Neither had regarded perturbative effects of higher order terms as consistent with general principles and as experimentally detectable. Hertz .92 defined the "completely corrected forces" X and L as:9 -A2

dU

, L = A rot U.

dt

He then eliminated the potential functions U and P: A

dL

= - rot X, div L = O,

at

(5) dX

A —— = rot L,

div X = O.

dt

Here for the first time the equations for the electric and magnetic forces are written in a symmetric form. Hertz comments at this stage: "The system of forces given by these equations is Maxwell's. Maxwell found them by considering the ether a dielectric, in which a changing polariza­ tion produces the same effects as an electric current. We have reached them by other premises, generally accepted even by the opponents of the Faraday-Maxwell view."93 Hertz deduced the equations by an alternative route to Maxwell's. He emphasized the great generality of his route, having avoided Maxwell's special assumption of a dielectric ether. He regarded Maxwell's system together with its deduction "as the most obvious from a certain point of view," but at the same time as not "necessary." Hertz's derivation of Maxwell's system from the old electrodynamics exposed the incon­ sistencies of the latter. He was then confronted with the dilemma of admitting that a necessary truth can be a necessary consequence of a false premise. He concluded that other systems besides Maxwell's were possible and that they could be as exact as Maxwell's. One was certainly Helmholtz'. Hertz regarded Maxwell's theory as more "complete" relative to "the usual system of electrodynamics" and the simplest in respect to other possible theories.94 Hertz does not claim that his derivation has the character of a logical demonstration, recognizing that Maxwell's equations 92Ibid., p. 284. V3Ibid., p. 288. ^4Ibid., pp. 288-289.

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are not the only possible modification of the classical ones. Hertz argues, however, that MaxweE's theory has the advantage that it does not contain within itself the proof of its own incompleteness. Furtherrtiore, it supplies a simpler way than other possible theories of representing electrodynamic phenomena. In any case, the fact that it provides a theory for such basic aspects as the attraction between variable magnetic shells makes it superior to others. The two principles of the unity of the electric and magnetic forces, which play a central role in the derivation of the equations (5) represent­ ing MaxwelPs forces, are presented by Hertz as being somehow related both to Faraday's views and, though less markedly, to Weber's elementary law. Since this dual indebtedness is relevant to the future development of Hertz's thought, I will quote at length his gloss on the principle of the unity of electric force in his 1884 essay. This principle is the necessary presupposition and conclusion of the chief notions which we have formed in general of electromagnetic phenomena. According to Faraday's idea, the electric field

exists in space inde­

pendently of and without reference to the methods of its production; whatever therefore be the cause which has produced an electric field, the actions which the field produces are always the same. On the other hand, by those physicists who favour Weber's and similar views, electrostatic and electromagnetic actions are represented as special cases of one and the same action-at-a-distance emanating from electric particles. The statement that these forces are special cases of a more general force would be without meaning if we admitted that they could differ other­ wise than in direction and magnitude, that is, in the nature and mode of action.95 In this passage Hertz first relates the principle of "'unity" ("Einheit") to Faraday's conception of an independent existence of fields in space. By independent

existence, Hertz clearly

means "independent of

their

sources." Static charges and currents have a different phenomenology, and the identity of the corresponding static and dynamic forces can only be understood if a strict causal correlation between force and source is broken and the independent existence of the force is affirmed. Faraday's conception is opposite to Helmholtz' conception of the connection between matter and force. 9 S J b i d „ p. 274.

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One of the theses of this article is that Hertz's conception in 1884 of the unity of electric forces is at the origin of his later conversion to the theory of a unique type of force in radiation. He thought that such a force was consistent only with Maxwell's theory, which he contrasted with Helmholtz' two-force theory. In 1888, when Hertz succeeded in demon­ strating the propagation of electric force in air and shortly before his interpretation of radiation in the Hertz-Maxwell context of a unique force, he stated the independent existence of the force in almost the same words as in 1884: "The most direct conclusion [from these experiments] is the confirmation of Faraday's view, according to which the electric forces are polarizations existing independently in space. For in the phenomena which we have investigated such forces persist in space even after the causes which have given rise to them have disappeared." 96 In 1884, Hertz also cites Weber's elementary law in support of the unity of force in the sense that this unique law includes forces of the two types. His citation is part of his strategy of presenting the unity principle as comprehensive, applying to the otherwise contrasting positions of Faraday and Weber. It is a sign of the importance he attributed to the principle at this stage. Hertz's 1884 article, which he published in the Annalen der Physik, found some reception in German scientific circles. It did not, however, in Helmholtz' entourage, as is shown by the debate on the article prompted by a series of articles in the Annalen by E. Aulinger and L. Lorberg. Aulinger in 1886, following a suggestion by Ludwig Boltzmann, finds an inconsistency in Hertz's formulation. Aulinger emphasizes that forces originating from currents are composed of electrostatic and electrodynamic forces, and prefers to formulate the principle of the unity of the electric force as follows: "Once the forces which act on a static or on a uniformly moving electric charge are determined, the whole of electric forces is determined." 97 He argues that from this unique principle all of Hertz's conclusions follow. Whereas Hertz invoked Weber's theory in defense of his principle, Aulinger proves that Weber's theory is con­ tradicted by the principle of the unity of force in Hertz's form. Aulinger affirms that it is not his intention to defend Weber's theory; rather, he

96 Heinrlch Hertz, "On the Finite Velocity of Propagation of Electromagnetic Ac­ tion," Sitzungsber. d. Berl. Akad. d. Wiss. (2 February 1888); in Wiedemann's Ann., 34 (1888), 551; in Electric Waves, pp. 107-123, on p. 122. 97 E. Aulinger, Wiedemann'sAnnalen, 31 (1887), 121.

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believes that Hertz's principle, in his own formulation, has a great deal of probability. Following an intervention by Lorberg in the Annalen in 1886, Boltzmann entered the debate in a conciliatory fashion. Boltzmann proposes not to discuss the "aprioristic" probability of the statements any further, but to discuss experiments. He points out that the action of a changing magnetic field on an unmoving static charge could be tested experi­ mentally, settling the question once and for all. This experiment would represent as well an "experimentum crucis" for Weber's electrodynamic theory.98 The same volume of the Annalen in 1887 that contains LOrberg's reply to Boltzmann contains Hertz's initial experiments dated from his Karlsruhe period, "On Very Rapid Electric Oscillations," followed in quick succes­ sion by two other articles on the same effect. Hertz's interest in the theoretical debate was superseded by his new challenging experimental approach to rapid oscillations, a matter which he felt was somehow connected to the same problem of deciding between the two contrasting electrodynamics. At this point I want to outline briefly the main conceptual features of Hertz's 1884 article: 1. Hertz sees the propagation of electric and magnetic forces as the result of the structure of electric and magnetic forces and potentials as expressed in the equations, a characteristic shared by the continental theories of retarded action of Riemann and Lorenz. He seeks confirmative evidence for the propagation of electric and magnetic forces in electro­ magnetic phenomena, not, as Maxwell did, in optical phenomena. 2. In 1884 Hertz pays no attention to physical hypotheses about a medium as the supporter of fields in the Faraday-Maxwell fashion; by contrast the conception of a polarizable ether is the main pillar of his 1888 experiments and 1890 theory. In 1884, Hertz's methodology is formalistic in that he proceeds by generalizing Franz Neumann's theory. 3. In 1884 Hertz deduces Maxwell's equations from fundamental principles, without regarding the deduction as a rigorous proof that Maxwell's system is the only possible one; by contrast, in 1890 he does not deduce Maxwell's equations from any prior principles, but postulates them and places them at the head of the theory. His exclusion in 1884 of 98 L.

Boltzmann, Wiedemann's Annalen, 31 (1887), 598.

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any claim of theoretical uniqueness is an aspect of Hertz's epistemology, which he fully developed later in his Principles of Mechanics. 4. The independence of fields from sources does not seem to have im­ portant consequences in Hertz's development of his theory in 1884, but a few years later it does; then it plays a central role in Hertz's rejection of Helmholtz' duality of electric forces. For an appraisal of the influence of Hertz's 1884 article on his later development, it is relevant to note that he never explicitly mentions it in his later articles. In particular, he never returns to his peculiar derivation of Maxwell's equations. In 1888 he revives only the conception of the independence of fields. This indifference seems at first surprising in light of the following detail: the symmetric form in which he writes the equa­ tions for Maxwell's electric and magnetic forces in 1884 is exactly the same as the one he writes in 1890 in his article, "On the Fundamental Equations of Electrodynamics for Bodies at Rest."99 Hertz, stressing their axiomatic foundation, seems to have forgotten in 1890 his prior symmetric rendering of the equations. In a passage there he acknowledges Oliver Heaviside's priority on this matter: "Mr. Oliver Heaviside has been working in the same direction ever since 1885. From Maxwell's equations he removes the same symbols [the vector potentials] as myself; and the simplest form which the equations thereby attain [in Heaviside's papers in 1885 and 1888] is essentially the same as that at which I arrive. In this respect, then, Mr. Heaviside has the priority."100 I think that one must understand Hertz's apparent amnesia as part of his general attitude towards his 1884 contribution. In 1887-1888 he began his researches from a completely different approach than he did in 1884. In his new approach, equations of the 1884 type were out of place; the 1884 Hertzian concep­ tion of the unity of force was in strident contrast with the Helmholtzian tenet, which Hertz supported in 1887, of the different nature of static and dynamic forces. Hertz could not graft the unity principle onto Helmholtz' theory without destroying it. In 1887 he guided his new experiments by the secure support of the more familiar and authoritative Helmholtzian theory. In 1888 he was led to a standpoint in which the unity of fields— both in its primary meaning as the "unity of electric fields in radiation" 99 Heinrich Hertz, "On the Fundamental Equations of Electrodynamics for Bodies at Rest," Gottinger Nachr. (19 March 1890); in Wiedemann's Annalen, 40 (1890), 577; in Electric Waves, pp. 195-240. 1 ^ 0 Hertz, "On the Fundamental Equations . . . ," inElectric Waves, pp. 196-197.

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and in its meaning as the independence of fields from sources—became central to his theory of radiation. In 1890 his conceptions of an axiomatic foundation and of the purpose of physical inquiry placed him in a differ­ ent context from that of his 1884 work, and he tended to ignore the latter. This remarkable difference in methodological context helps to explain why Hertz did not recognize or mention explicitly his prior introduction of the symmetric equations. 101

4. HERTZ'S EXPERIMENTS ON ELECTROMAGNETIC WAVES IN WIRES AND IN AIR In 1885 Hertz left the University of Kiel and accepted a position as professor of physics at the Karlsruhe Technische Hochschule, where he performed all of his experiments on electromagnetic waves. There in 1886 he experimented with the Riess or Knochenhauer spirals. These were double-wound wire spirals, a common electrical device for induction ex­ periments that he had already used in his experiments on the inertia of currents in Berlin. He used the spirals as induction coils of low selfinductance, obtaining a strong sparking in the secondary coil when dis­ charging the primary through a sparking gap. He attributed the strength of the sparking to the high frequency of oscillation in the spirals. Concerning the further development of his experiments, Hertz maintained that "in altering the conditions I came upon the phenomenon of side sparks [secondary sparks] which formed the starting point of the following research." 102 Hertz's transformation of the experimental setup from the Riess spirals to sparking in the secondary circuit ("Nebenkreis") indicates his con­ ceptual train of thought at the time. He was trying to give a first evalua­ tion of the frequency of the oscillations that produced the discharge in the primary circuit from the propagation of electrical effects in wires. This 101 Edmund Hoppe, who taught at Gottingen at the turn of the century, maintains that in 1884 "Hertz had already recognized the basic importance of his two equa­ tions, and one can explain the fact that he did not begin [his theory] with them, as Heaviside did, as the result of the situation at that time in Germany" (Hoppe, p. 612). Hoppe says that Hertz in 1884 had a "pedagogical" interest in establishing a connec­ tion between the old and the new electrodynamics. Hoppe seems to ignore the priority of Hertz's 1884 symmetric formulation of the equations, and, like Hertz himself, stresses Heaviside's priority in the axiomatic foundation of Maxwell's theory. Inasmuch as I accept that there was a difference in the situations in 1884 and 1890,1 agree with Hoppe's thesis. 102 Hertz "Introduction, A Experimental," in Electric Waves, p. 2. 1

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train of thought led him to modify the initial arrangement by connecting by wire the primary to a given point of the secondary circuit. He intended to verify his conjecture that sparking in the secondary gap "shows more clearly . . . that these disturbances run on so rapidly that even the time taken by electric waves in rushing through short metallic conductors [in the secondary] becomes of appreciable importance. For the experiment can only be interpreted in the sense that the change of potential proceed­ ing from the induction coil reaches the Knob 1 in an appreciably shorter time than the Knob 2." 103 It was an experiment on propagation in wires, but the conceptual context was now "the propagation of change of potential" in wires and in air, or waves of potential, not the propagation of currents or charges in wires as it had been in his former experiments on the inertia of currents. This circumstance might partially explain the little attention Hertz had paid until now to theories and experiments, such as Bezold's, on the propagation of "waves of current" in conducting wires. There is evidence that Hertz was acquainted with theories of propagation of current in wires, 104 though he did not explicitly mention them. He often assumed, for instance, that the velocity of propagation is inde­ pendent of the resistance of the wire in wires of small resistance, and this is one of the main tenets of wire propagation theories. What he thought was new in his experiment was the production of propagations of such short wavelength. He was surprised to learn after his article appeared that fifteen years before Bezold had produced effects equal to his own. Bezold had not attributed to them the same importance for electrodynamics as Hertz did, and his work had remained almost unnoticed in scientific circles. Hertz justified his oversight by pointing out that the external ap­ pearance of Bezold's paper had led him to think that it concerned only electric dust-figures. Hertz now viewed propagation phenomena as a manifestation of rapidity of oscillations, as is shown by the title of the paper, "On Very Rapid Electric Oscillations," in which he described the experiments. Accordingly, he viewed sparks as the manifestation of very strong potential gradients across the gap and, more generally, all over the secondary conductor. His view was also that a marked nonuniformity of potential distribution was a sign of propagation with very short wave­ lengths. It can be argued that he considered the above qualitative evalua­ tion of the frequency of oscillation through the wavelength as a way of 103 Heinrich Hertz, "On Very Rapid Electric Oscillations," Wiedemann's Annalen, 31 (1887), 421; inElectric Waves, pp. 29-54, on p. 29. w Ibid., p. 33.

Figure 1. Apparatus for demonstrating polarization currents in paraffin (Deutsches Museum, Munich)

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circumventing the impossibility of directly measuring the frequency by methods like Feddersen's for less rapid oscillations. The phenomenon of oscillations in both primary and secondary circuits also interested Hertz because the oscillator was a short metallic conductor with open ends, an "open circuit," and short open rectilinear circuits had an important position in Helmholtz theory. A letter from Hertz to Helmholtz in this period stressed precisely this point. 105 Previously, according to Hertz, oscillations had been obtained in open coils and Leyden jars, but never in short metallic conductors. Although all of these aspects of high frequency oscillations—propagation in the short wavelength region and open resonators—are of course connected in the modern theories, the connection between them was not so clear in the theories of that time, especially since the concepts of distributed capacity and induc­ tion had not been clearly formulated. The high-frequency aspects were responsible for the modifications that Hertz introduced step by step in the primary oscillator and the secondary circuit, as can be clearly seen in the sequence of figures in his paper, evolving eventually into the now familiar open radiator and receiver. But this was not precisely Hertz's object at the time; rather, he was interested in the rapidity of oscillations in the primary and in a procedure not only for detecting them but for evaluating their frequency through the secondary oscillations. At this stage Hertz studied the behavior of the secondary circuit as manifested by sparks in the spark gap, soon convincing himself that the secondary circuit was the basis of a resonance phenomenon and learning how to tune it with the primary to magnify the sparks. At the same time he realized that sparking was a more complicated effect than he had expected, and that causes other than potential gradients cooperated in producing it; some of the causes, such as electrostatic ones, could be eliminated by interposing a wet thread between the knobs of the micrometer. 106 Another cause of the complica­ tions was the "photoelectric" effect, then still unknown, which Hertz, with clear judgment, attributed to the presence of ultraviolet light from the primary discharge; to eliminate this cause, he undertook a special investigation of the phenomenon and published the result in a separate

105 "I have succeeded, unmistakably, in showing the inductive action of one open rectilinear current, and I venture to hope that this method will eventually yield the solution of one or other of the questions associated with this phenomenon" (letter from Hertz to Helmholtz, dated December 1886 [Koenigsberger, p. 268]). 106 HcrCz, "On Very Rapid Electric Oscillations," in Electric Waves, pp. 42-43.

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Figure 2. Hertz's original circular resonator (Deutsches Museum, Munich).

paper, "On an Effect of Ultra-Violet Light upon the Electric Dis­ charge." 107 In the theoretical section of "On Very Rapid Oscillations," Hertz com­ puted the half period T of the oscillation by Thomson's formula, T= π/c\/PC, where c is the velocity of light, C the capacity of either one of two large spheres of 15 cm radius attached to the ends of a straight metallic wire of the primary oscillator, and P the self-induction coefficient of the wire of length 150 cm. (Since he computed P and C in electro107 Heinrich Hertz, "On an Effect of Ultraviolet Light Upon the Electric Discharge," Sitzungsber. d. Berl Akad.. d. Wiss. (9 June 1887); in Wiedemann's Annalen, 31 (1887), 983; in Electric Waves, pp. 63-79.

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magnetic and electrostatic units, respectively, he introduced the conversion factor 1lc.) He found for T 1.77 X IO

8

sec. In computing C, he con­

sidered the relative capacity of the spheres instead of the absolute capacity of one of them, an error that Poincare remarked on in 1891 and that Hertz himself referred to. 108 To obtain the correct value, the half period T that Hertz first obtained should be multiplied by 1/λ/2", yielding 1.26 X IO -8 sec. The consequences of this error affected all of Hertz's subsequent calculations of T in his experiments on propagation both in wires and in air. 109 (In the free propagation experiments, however, the error in T had no practical consequences, since it was of the same order of magnitude as the imprecision in the measurement of λ in a system of stationary electromagnetic waves.) At this stage Hertz looked on the new rapid oscillations as a promising means for solving the problem of the Berlin Academy. He thought that it would be easy with the aid of these rapid oscillations to detect the electromagnetic effects of polarization current in a dielectric block of sulphur or paraffin. He was impressed by the presence of a position, or neutral point, of the gap in which sparks were either very feeble or absent. His first attempt at detecting the effects was to insert a dielectric block between the metallic plates of the condenser in the primary circuit and then to remove it quickly. He expected that the detector in the vicinity of the block would discriminate between the induction of the entire loop with the block present and the induction when the block was quickly removed. 110 Given Helmholtz' understanding of polarization, which was inspired by the static-type Poisson polarization of material dielectrics, it was reasonable that Helmholtz and Hertz should regard dense, usually solid, dielectrics with a high dielectric constant as suitable for experiments. That the dielectric was a solid favored its insertion into a circuit but prevented the detection of the effect in its interior, limiting its usefulness to its neighborhood. The experiment failed, since he noticed no change in the sparking in the secondary when the block was removed. He decided that he had attacked the problem too directly and that the various parts of the secondary in which neutral points were present had first to be studied. Modifying the rectangular form of the secondary circuit to that of a circle, he studied the primary oscillations in the absence of the 108 Heinrich Hertz, "Supplementary Notes, 1891," in Electric Waves, p. 270, n. 6. Henri Poincare, Comptes Rendus, 3 (1891), 322. 109 Hertz, "Supplementary Notes, 1891," vnElectric Waves, p. 272, n. 13. 110 Hertz, "Introduction, A Experimental," Electric Waves, pp. 4-5.

Figure 3. Large oscillator and circular and square resonators (Deutsches Museum, Munich).

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disturbing effect of the asymmetry of the secondary. He now introduced an optical device to observe in the dark very feeble sparks in the spark-gap, and he made the gap adjustable by means of a micrometer screw. The secondary circuit was mounted on a wooden base. By this arrangement, he discovered that other neutral points existed in different positions with respect to the primary circuit. Hertz consequently developed a theory of the secondary circular circuit. It was a phenomenological theory of the electric forces that affect the displacement of the "neutral point," in which he introduced concepts from electrostatics and the theory of electromagnetic induction at a semi-quantitative level. His theory assumes that stationary oscillations are induced in the secondary circuit and that the position of the spark-gap always corresponds to a node of the current. 111 He discusses theoretically the position and magnitude of the external exciting electric force when the spark-gap corresponds to the position of maximum sparking in the circular secondary detector. He assumes further that the oscillations in the secondary that are most effective in producing sparks are the fundamental ones and not the overtones. Accordingly, a maximum for sparking occurs when the position of the spark-gap is such that the plane of the circle is parallel to the primary inductor and the gap lies along the vertical to the plane, passing through the primary and the diameter of the circle. In this case, the theory predicts that the electric force is tangent to the circle at the spark-gap and to the position of the circle diametrically opposite. The direction of the external electric force can be theoretically determined by placing the plane of the circuit in a vertical position—the primary is horizontal—and by bringing the gap to the highest position and then turn­ ing the circle around a vertical axis until the sparks disappear. 112 The sparks that are sensible to this rotation are produced by the electrostatic force, whose direction can thus be determined. The electromagnetic force acts in every position along the tangent to the circle, and the sparks produced by it are not sensible to a rotation of the gap. Thus, the theory of the "circle" discriminates between electrostatic and electromagnetic forces. From the position of the "circle," Hertz was also able to determine either the direction of the electrostatic force or that of the electromagnetic force. 113 My discussion of Hertz's theory of the "circle" is to indicate the 111 Heinrich Hertz, "On the Action of a Rectilinear Electric Oscillation Upon a Neighbouring Circuit," Wiedemann's Annalen, 34 (1888), 155; in Electric Waves, pp. 80-94, on pp. 82-83. 112 Hertz, ibid., pp. 90 and 91. 113 Hertz, "On the Finite Velocity . . . ," in Electric Waves, pp. 110-111.

304

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES P i .

'

ν.

Figure 4. Oscillator with square capacitive plates and models of parabolic mirrors for the oscillator and the detector (Deutsches Museum, Munich).

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305

rather elaborate state of the theory. Some parts of the theory, such as the assertion that the gap always corresponded to a node of the current, were rough approximations or controversial. (Poincare disagreed with Hertz's interpretation of nodes; 114 A. Righi maintained that the gap corresponded to an antinode, 115 and modern theories would not accept either Hertz's or Righi's extreme positions.) From the point of view of an exact theory, Hertz's experiments were complicated by the following feature, which was remarked later on by Oliver Lodge who was working in 1888 on similar experiments. Hertz's radiators were strongly damped and consequently oscillated over a large band of frequencies, whereas the opposite was the case for the detectors, which were persistent vibrators oscillating with little damping over a very short band of frequencies. 116 From the practical side, this complication was a happy circumstance, because it made it easy for Hertz to tune his detectors to different wavelengths according to their size and shape. He had recognized this advantage very early in his work. On the other side, the damping was not so strong as to prevent any interference between primary and secondary reflected waves. Coming back to the main point, Hertz also infers from his theory of the detector that at positions beyond three meters from the primary circuit only the electromagnetic type of force seems active in producing sparks, and he diagrams approximate maps of the lines of force. 117 He is now ready to find a solution to the problem of the Berlin Academy, having discovered that the presence of an insulator modified the positions of the neutral point. He attributes this modification or, more precisely, angular displacement to the inductive effect of the polarization current in the dielectric block when the block was placed as close as possible to both primary and secondary circuits. In short, he uses the apparatus as a kind of "induction balance" 118 that displaces the neutral points by superposing induced currents from conduction or polarization currents. The experi­ ment is, however, mainly qualitative: the induction effect produced by 114 Letter from Poincare to Hertz, 11 September 1890 (Hertz's Correspondence, Deutsches Museum, MS. 3000). lls A. Righi, LOttica delle Oscillazioni Elettriche (Bologna, 1897), pp. 19-20. 116 Oliver Lodge, The Work of Hertz and Some of His Successors (London, 1894), pp. 8-9. 117 Hertz, "On the Action of a Rectilinear Electric . . . ," in Electric Waves, pp. 8691. 118 Heinrich Hertz, "On Electromagnetic Effects Produced by Electrical Distur­ bances in Insulators," Sitzungsber, d. Berl. Akad. d. Wiss. (10 November 1887); in Wiedemann's Annalen, 34 (1888), 273; in Electric Waves, pp. 95-106, on p. 96.

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electrical disturbances in insulators is manifested through the angular dis­ placement of the direction of the null point. Hertz shows that the induction effects produced by the presence of large blocks of insulators like paper, paraffin, and asphalt are of the same order of magnitude and sense as those produced by the approach of thin metallic plates. He does not give a quantitative evaluation of the electromagnetic effect of dielectrics and conductors, but only refers to a "very rough estimate" he made on the assumption that "the quantities of electricity displaced by dielectric polarization must be as great at least as those which are set in motion by conduction in thin metallic rods." 119 In this estimate, he probably uses Helmholtz' 1870 expression for the density of polarization current. Hertz considers the existence of the inductive effect of polarization currents in dielectrics as a confirmation of the views of Faraday and Maxwell. Hertz believes, too, that his experiment solves the first part of the prize problem of the Berlin Academy; namely, the problem of showing that "an electromagnetic force [is] exerted by polarizations in non­ conductors." He argues that he has shown an equal effect both with conductors, in which currents exert electromotive forces according to the accepted theory, and nonconductors. According to him, the second part remains untested. The research, for which he was awarded the prize, was communicated to the Academy on 10 November 1887. After successfully completing the first part of the research related to the theme of the Berlin Academy, Hertz considered the best method of attack­ ing the second part. It was to show "the polarization of non-conductors as an effect of electromagnetic induction" and "for this purpose [he] . . . cast closed rings of paraffin." 120 These remarks indicate that he possibly had in mind an experiment, like the experiments he described in his 1884 essay, in which ring currents mutually interact. However, he soon abandoned his initial attempts, having gained new insight into the problem of an experimental test of Maxwell's theory. Until the autumn of 1887, his experiments were mainly induction-type, following Helmholtz' approach to dielectric problems. Some of Hertz's ideas, however, had to be modified to take account of the behavior of the secondary circuit. Since this modification had some bearing on the decisive change of Hertz's researches a few months later, I will describe its salient features. The main modifica­ tion derived from Hertz's assessment of the relation between electrostatic 119 Ibid.,

p. 101. "Introduction, A Experimental," in Electric Waves, p. 7.

120 Hertz,

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and induction forces, a problem which he had faced in 1884 in his principle of the unity of electric force. In his early experiment on dielectric action, he explained the invariable and unexpected occurrence of sparks in the secondary circuit by arguing that both electrostatic charges at the open ends and currents in the wire cooperated in the process of induction when the dielectric block was being removed. Be­ cause, he explained, "on account of the rapidity of the motion even forces which possess a potential are able to induce sparks in the nearby closed conductor." 121 We are presented here with an instance of a partial modifi­ cation of a concept: Hertz conceded that when "electrostatic" forces are time-varying, they might even become irrotational, another step back towards his 1884 conception of the unity of force. To understand this modification better, I will quote a clearer statement by Hertz at the time on the same point: The reason of this behaviour of electrostatic forces is the rapidity with which the forces in these experiments alter their sign. A slowly alternat­ ing electrostatic force would excite no sparks in our secondary conductor, even if its intensity were very great, since the free electricity of the conductor could distribute itself, and would distribute itself, in such a way as to neutralize the effect of the external force; but in our experiments the direction of the force alters so rapidly that the electricity has no time to distribute itself in this way. 122 Note that Hertz still persists in distinguishing electrostatic from other dynamical forces even when the former is time varying, a distinction related to Helmholtz' characterization of two electric forces. Hertz will soon discover that this distinction is meaningless, but he retains it for the moment, believing that electromagnetic induction had to be supplemented by electrostatic forces to explain the sparking in the secondary circuit. The intensity of the electrostatic and electromagnetic forces is differ­ ently affected by distance: At distances beyond three meters the force is everywhere parallel to the primary oscillation. This is clearly the region in which the electrostatic force has become negligible, and the electromagnetic force alone is effective. ... It is worthy of notice that, in the direction of the oscillation, the action becomes weaker much more rapidly than in the 122 Hertz,

81.

p. 5. "On the Action of a Rectilinear Electric . . . ," in Electnc Waves, pp. 80-

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perpendicular direction. . . . Many of the elementary laws of induction which are accepted as possible will have to be abandoned if tested by their accordance with the results of these experiments. 123 However, though Hertz calls the first force "electromagnetic or induction force," he does not imply that the known laws apply to it. The elementary laws of induction to which Hertz refers are those derived from Ampere's law and the various potential laws of Franz Neumann and Helmholtz, which predict open-end effects in the direction of the current. His early suspicion that induction alone would not explain all the varieties of sparkings in the "circle" is now strengthened, exerting new pressures on the frame of the old established concepts: at first, he considered the secondary circuit as closed owing to the shortness of the gap, 124 but now he admits that "it is necessary to regard the secondary circuit also as being in every respect unclosed. Hence, it is not sufficient to pay attention to the integral force of induction; we must take into consideration the distribu­ tion of the electromagnetic force along the various parts of the circuit: nor must the electrostatic force which proceeds from the charged ends of the oscillator be neglected." 125 For a while, Hertz will proceed from this idea that sparks arise from the cooperation of the electrostatic and electro­ magnetic forces whose effects on the "circle" cannot be accounted for by the Faraday-Neumann induction law. Although Hertz's Berlin Academy experiment dealt with induction, hints of an electric propagation through air appeared here and there in various stages of the experiment. These hints would probably not have been clear and distinct to any experimenter other than Hertz. One gets the impression that Hertz never completely abandoned the context of free propagation of his 1884 essay. That context remained, so to speak, in a "recessive state," ready to make its appearance when the occasion was favorable. To give an example: in the fall of 1887, at the end of Hertz's research on the electromagnetic effect of a rectilinear oscillator, a prepa­ ratory stage of his work on the Berlin Academy problem, he first states the possible propagation of forces in air with a finite velocity. The occasion is his observation that the electric force is circularly polarized in certain regions of the space around the primary oscillator. He tentatively explains this observation by the superposition of an electrostatic on a normally 123 Ibid.,

pp. 91-92. "On Very Rapid Electric Oscillations . . . ," in Electric Waves, p. 40. 125 Hertz, "On the Action of a Rectilinear Electric . . . ," in Electric Waves, p. 80. 124 Hertz,

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directed electromagnetic force, with a phase shift between the two result­ ing from their different velocities of propagation. At least one of the two forces should therefore propagate with a finite velocity. Hertz writes: I have not succeeded in finding an explanation of this behaviour [i.e., circular polarization], either in the terms which have been neglected in our simplified theory [of the secondary circuit] or in the harmonics which are very possibly mingled with our fundamental vibrations. And it seems to me that none of the theories which are based upon the sup­ position of direct action-at-a-distance [unvermittelten Fernwirkungen] would lead us to expect anything of this kind. . . . A difference between the rates of propagation of the electrostatic and electromagnetic forces implies a finite rate of propagation for at least one of them. Thus it seems to me that we probably have before us here the first indication of a finite rate of propagation of electrical action. 126 1 should remark that circular polarization was a tenuous and indirect hint of a free, finite propagation, one which would have escaped another researcher less sympathetic to contiguous action. Another example of Hertz's early sensitivity to the possibility of finite propagation occurs at the end of his paper on the Berlin Academy problem: Hertz expects a change of phase in the secondary current and, hence, a variation in the null-point as a consequence of the increase in the distance between a metallic plate and the primary. Failing to observe the change, he cautions that the negative result should not be considered as cancelling the other positive results pointing to a finite propagation. 127 Hertz's paper on electromagnetic effects in insulators was dated 10 November 1887; his next paper was presented to the Berlin Academy on 2 February 1888. In this span of about three months, Hertz's conceptions underwent a remarkable change that was to affect all of his following work. In brief, the propagation of electricity in air and ether, the central theme of his 1884 investigation that he had subsequently abandoned in favor of Helmholtz' approach, again became central to his thought, this time in connection with ether polarization. At this point Hertz moved from a concern with polarization-current effects in the neighborhood of large blocks of material insulators to the consideration of free propagation itself. He never returned to the separate test of polarization effects of ™Ibid., pp. 92-93. 127 Hertz, "On Electromagnetic Effects Produced by Electrical Disturbances in Insulators," in Electric Waves, p. 106.

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material insulators, dismissing the phenomenon as marginal to Maxwell's theory. Hertz's conceptual change is evident from the new type of experiment he reported in his paper of February 1888. 128 In 1891 in the introduction to Electric Waves, the second volume of his Gesammelte Werke, Hertz reconstructed, about four years after the event, the process of his con­ ceptual change in the context of his experimental test of Maxwell's theory. His introduction contains a critical appraisal of the relation between Maxwell's theory and the experiment on dielectric induction effects that he had just performed. He states in the beginning of the introduction that Helmholtz had set the two parts of the Berlin Academy problem on the ground that the combination of certain assumptions with the electromagnetic laws, universally accepted in 1879, would yield Maxwell's equations. These assumptions are the three hypotheses that Hertz considers equivalent to those Helmholtz assumed in his 1870 paper. Hertz says that "the problem of proving all these hypotheses and thereby establishing the correctness of the whole of Maxwell's theory appeared to be an unreasonable demand; the Academy, therefore, contented itself with requiring a confirmation of one of the first two." 129 In the following few lines we are presented in quick succession with Hertz's reconstruction of the change of theoretical context that was momentous for the further development of his research: But while I was at work [preparing the closed rings of paraffin] it struck me that the center of interest [Hauptinteresse] in the new theory [i.e., Maxwell's theory] did not lie in the consequences of the two hypotheses. If it were shown that these were correct for any given insulator, it would follow that waves of the kind expected by Maxwell could be propagated in this insulator, with a finite velocity which might perhaps differ widely from that of light. These however could not be very surprising, not more than the circumstance, known long since then, that in wires electric perturbations propagate with a great but finite velocity. I felt that the third hypothesis contained the gist and special significance ["der Kernpunkt, der Sinn und die Besonderheit"] of Faraday's and therefore Maxwell's view, and that it would thus be a more worthy goal for me to aim at. I saw no way of testing separately the first and second hypotheses for air (the expression air ["Luftraum"] and empty space 128 Hertz, 129 Hertz,

"On the Finite Velocity . . . ," in Electric Waves, p. 107-123. "Introduction, A Experimental," in Electric Waves, pp. 6-7.

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311

["leerer Raum"] are here used as synonymous, as far as the influence of the air itself in these experiments is negligible) but both hypotheses would be proved simultaneously, if one could succeed in demonstrating in air a finite rate of propagation and waves."130 (The italics are mine; the expression in parenthesis is reported by Hertz in a note.) The English translator skipped the passage I put in italics. In this passage, Hertz juxtaposes the propagation of waves in material dielectrics and waves of current in wires, and considers the former like the latter as within the grasp of the accepted pre-Maxwellian electrodynamics. In both cases, the presence of a material support, in contrast to empty space, deprives the finite propagation in insulators of any special significance within the old theory. What Hertz considers new is the propagation and, hence, polarization in empty space. He gives priority to the third hypothesis, for it contains "the gist and special significance of Faraday's, and therefore of Maxwell's view"; this hypothesis is less significant in the Helmholtzian context. Hertz also states that if the Helmholtzian hy­ potheses are verified, the velocity "might perhaps differ widely from that of light" (my italics). This was the case with Helmholtz' theory in the limit when the dielectric constant was very small. Hertz's next research was the first that was planned to demonstrate propagation in air. It was reported to the Berlin Academy on 2 February 1888. "On the Finite Velocity of Propagation of Electromagnetic Actions" opens by stating that the problem of the existence of polarizations in air accompanying electric forces is "another question" than that of the polarization "within insulators whose dielectric constants differ appre­ ciably from unity." It concludes by stating that if air polarization exists, then "electromagnetic actions must be propagated with a finite ve­ locity."131 The shift is from the program of testing polarization effects in material dielectrics—i.e., of testing the first and second hypotheses—to that of testing waves of polarization in air, or empty space, the two being equivalent in this connection. The existence of waves in air would prove simultaneously the two first hypotheses for empty space. In the initial experiment on propagation, Hertz presents an interference between waves in air and waves in wires, the wire system being coupled to the primary by a capacitative coupling.132 Hertz had reasons for this hybrid combination,

Wlbid., p. 7. 131 Hertz, "On the Finite Velocity . . . ," in Electric Waves, p. 107. l ^Ibid., p. 108.

312

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

which caused him many difficulties: in case the velocity of electric waves in air was much greater than that of light, a result that would agree with Helmholtz' theory, it would be safer to measure it by comparison with the velocity in a wire. He rightly expected a lack of directionality in the dipole radiation that would hamper direct interference, and, most im­ portant, he was much better acquainted with propagation in wires than in air. Whatever Hertz's reasons for the comparison, what is significant fdf us is that to conceive of the likelihood of an interference between air and wire systems he had to regard propagation in air and in wire as essentially akin to one another. This comparative experiment was now congenial to his way of looking at wire phenomena and in its turn confirmed it. Hertz eventually conceived of wire propagation as a transfer of electro­ magnetic energy along the wire, an unusual viewpoint for one belonging to the continental school of electrodynamics. It was within this latter context that he spoke in the introduction to Electric Waves of the possibility that there would not be great difficulty "in producing interference between the action which travelled along the wire and that which had traveled along the air, and thus in comparing their phases." 133 This is exactly the experi­ mental setup of Hertz's first research on propagation in air, suggesting that at the time he was close to his later understanding of propagation in wires as a transfer of energy. In the introduction, he pointed to the context of a transfer of energy as that which inspired the research he carried out in the summer of 1888, when he "wished to test the correctness of the view according to which the seat and field of action of the waves is not in the interior of the conductor, but rather in the surrounding space." 134 He believed that his researches confirmed the correctness of this view. In the summer of 1888 he ascribed the understanding that "the electric force which determines the current is not propagated in the wire itself, but under all circumstances penetrates from without into the wire" to Oliver Heaviside and J. H. Poynting. He considered it as "the correct interpreta­ tion of Maxwell's equations as applied to this case." 135 Hertz had developed such a sophisticated technique with his circular detector that he was now able to determine from its response in two intermediate positions the relation of phases between forces from the 133 Hertz,

"Introduction, A Experimental," in Electric Waves, p. 7. p. 15. 135 Heinrich Hertz, "On the Propagation of Electric Waves by Means of Wires," Wiedemann's Annalen, 37 (1889), 395; in Electric Waves, pp. 160-171, on pp. 160a ^Ibid.,

161.

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313

primary and from the wire, and he was able to adjust this relation by dis­ placing one of the two capacitors and varying the coupling. This, however, was a final achievement. At the beginning, Hertz's results were so dis­ appointing that he gave up experimenting for some weeks. Only after he decided that it would be worthwhile to prove that Maxwell's theory was false did he resume experimenting. This, at least, is how he reconstructed the events in the introduction in 1891. In his first propagation experiment, Hertz succeeded in demonstrating propagation in air, though he had difficulty determining the velocity, and his doubts on the validity of Maxwell's theory were at their highest point. He remarked that "the resulting interference did not succeed each other at equal distances, but the changes were more rapid in the neighborhood of the oscillation than at greater distances." He explained this irregularity in the spatial distribution of the interferences along the wire by the supposition that the total force might be split up into two parts, of which the one, the electromagnetic, was propagated with the velocity of light, while the other, "the electrostatic force . . . is propagated with an infinite velocity." 136 Besides, the ratio of the velocity in wire to the velocity in air of the electromagnetic force was about two thirds. 137 This result was in­ consistent both with traditional theory and with Maxwell's theory; both predicted a velocity equal to the free velocity in air in a conducting wire of little resistance. The key to resolving this dilemma was to measure independently the velocity in air. Hertz accomplished this in the experiment he performed shortly after February 1888 and reported in "On Electromagnetic Waves in Air and Their Reflection." 138 The background of this experiment is the following: while experimenting with his generator, Hertz had noticed that the sparking hinted at a reflection of the waves from the walls of the room. He set about to exploit the phenomenon for measuring wavelengths in air in a stationary wave system. This plan presented the unique advantage of allowing the measurement of wavelength in air to be made independently of that of the wavelength in the wire, and, assuming in air a velocity equal to that of light, of allowing the period of oscillation to be calculated from the wavelength in air. Hertz found for the period 1.55 XlO 8 sec, which he showed compared favorably with that obtained 136 Hertz, "On the Finite Velocity . . . ," in Electric Waves, p. 121. See also ibid., p. 151. 137 Jbid., p. 121. 138 Hertz, Wiedemann's Annalen, 34 (1888), 610; in Electric Waves, pp. 124-136.

314

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

by Thomson's formula, or 1.4 X IO

8

sec. He attributed the small dis­

crepancy to the imprecision in the measurement of wavelength. I think that his error in the computation of the capacity affected the computed value for the period. He repeated the same experiment with a different geometry, obtaining results which were consistent with the former ones. 139 In his paper, "The Forces of Electric Oscillations, Treated According to Maxwell's Theory," 140 composed in the spring of 1888, Hertz firmly establishes the new theoretical context through a complete treatment of one of its main aspects, the source-field relation. This aspect is worth commenting on. In the paper, Hertz presents Maxwell's equations at the beginning in exactly the same form and with the same symbols as in his 1884 paper. He restricts their solution to the case of a rectilinear oscillator along the ζ axis. He derives the components Χ, Υ, Z of the electric and L, Μ, N of the magnetic force in terms of a quantity Π, known today as the polarization potential or Hertz's vector: 141 X=

d2 Π

,

Y=

dx dy L= A

d2 -

n—

dy dt

d2 Π

d2 Π d2 Π , ζ = -—τ + —τ; dy dz dx dy d2

π

M =Aτ ~ Γ >

dx dt

Ν

=

0

>

where A is, as usual, the reciprocal of the velocity of light. Π defines a function of the cylindrical coordinates ρ, ζ and time t which satisfies the d'Alembertian equation: λ

ν

=

ν

π

·

A suitable solution for Π, which is satisfied everywhere except at the origin, is: .. sin I m r - n t ) Π = El -, r where £ is a quantity of electricity, I a length, r the length of the position vector, m = π/λ and η = ιr/T; here λ and T are the wavelength and period, respectively, and are related by λ = Tl A, In the immediate neighborhood of the oscillator, where r is vanishingly small compared with λ, and mr is Ibid., p. 134. ^ 0 Hertz, Wiedemann's Annalen, 36 (1889), 1; in Electric Waves, pp. 137-159. 141 Ibid., p. 140. l39

1

315

SALVO D'AGOSTINO

negligible compared with nt, one has Π = -(El sin nt)\r. The electric force components are given in this case as the second derivatives of a doublepoint potential, which represents the statical potential of an oscillator of length I. By the use of the polarization potential Hertz succeeded in integrating Maxwell's equations for the particular situation of the dipole source. His method represents a special case of an approach of more general significance to the solution of the equations with source terms; the method was later to be known as that of retarded potentials. Hertz's introduction into the theory of the potential facilitates, among other things, the development of analytical expressions for the "dynamical lines of force" of the radiation field. Hertz plots neat diagrams of the lines for different values of time, which he reproduces as illustrations in the article. This is the first time that a radiation field is represented as a drawing. Hertz's theory of a source-field relation had an antecedent in a similar theory that G. Francis Fitzgerald communicated to the Royal Dublin Society in 1883. Fitzgerald solved the d'Alembertian equation for the vector potential of a small circular loop of current, and he computed the emitted energy as a function of frequency. In a short sequel com­ munication he remarked that by discharging a condenser through a small resistance, waves of ten meters or less could be produced. 142 Since his papers were unknown to Hertz at the time of his experiments, they have little significance here. Moreover, due to the persistence of vibrations and damping, I think it is doubtful that had Fitzgerald decided to pursue this path he could have detected the waves. Hertz's computation of the energy emitted in a half-period from his oscillator is reported as 2,400 ergs. 143 The dependence on the inverse cube of the wavelength in Hertz's formula for the emitted energy is the same as that given by Fitzgerald in 1883. Hertz's acceptance of Maxwell's theory entails a decisive rejection of the old concepts, among them the distinction between static and dynamic forces on which almost all of his previous thought was based. His intro­ duction of the potential allows him to write the ζ component of the electric force in the equatorial plane, lying on the axis of the oscillation and at a long distance from it, in the form: ^ Z

142 G.

3

El m

j ι

sin (mr - nt ) —

mr

cos (mr - nt ) 2 2 m r

i

sin (mr - nt) | 3 3 1 * m r

F. FitzGerald, The Scientific Writings (Dublin and London, 1902), p. 93. Electric Waves, p. 150.

143 Hertz,

316

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

Since the expression "can in no way be split up into two simple waves travelling with different velocities," Hertz argues that his earlier way of explaining the interference in wires by considering the total force as composed of an electromagnetic force propagating with the velocity of light and an electrostatic force propagating "with greater and perhaps infinite velocity . . . can only serve as an approximation to the truth."® 44 Hertz now regards the splitting of the force as meaningless in general and his new conception as a permanent achievement. In his subsequent paper in 1890, "Fundamental Equations of Electromagnetics for Bodies at Rest," one of the two theoretical papers with which he concluded his experiments on waves, he states that "the splitting of the electric force into an electrostatic and electromagnetic part does not in these general problems convey any physical meaning which can be clearly conceived, nor is it of any great mathematical use; so that, instead of following earlier methods of treatment, it will be expedient to avoid it." 145 Hertz's recognition of only one kind of force now raises the question whether or not Maxwell's theory leads to any irregularity in the special distribution of interferences. Hertz finds the accord with the theory satisfactory for interferences he attributed to the electromagnetic force, but not for those attributed to the static force. 146 He treats wire propaga­ tion in an original way, establishing an equation in which the direction of incidence of lines of force into the wire is correlated to their velocity of propagation. 147 He confirms that in a good conductor the wave should propagate with the velocity of light, not with the smaller velocity of his previous results; thus the situation really allows no escape. He also finds obscurities in the velocity of propagation along the axis of crooked wires and spirals, which he expects to be the same as the velocity along a straight wire. The fact that Hertz takes up wire propagation again after he has achieved air propagation confirms the importance he attributed to this aspect of electromagnetic theory. However, in view of his achievement of air propagation and his theoretical explanation of it, he does not regard the difficulties in wire propagation as an obstacle to the acceptance of Maxwell's theory. His conclusion at this time is: In our endeavour to explain the observations by means of Maxwell's theory, we have not succeeded in removing all difficulties. Nevertheless, 144 Zbid.,

p. 151. "On the Fundamental Equations . . in Electric Waves, p. 236. 1 4 6 Hertz, "The Forces of Electric Oscillations . . . ," inElectric Waves, p. 154. l ^Ibid., p. 156. 145 Hertz,

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317

the theory has been found to account most satisfactorily for the majority of the phenomena; and it will be acknowledged that this is no mean performance. But if we try to adopt any of the older theories to the phenomena, we meet with inconsistencies from the very start, unless we reconcile these theories with Maxwell's by introducing the ether as dielectric in the mahner indicated by v. Helmholtz." 148 To sum up, the research Hertz reports on in "The Forces of Electric Oscillations, Treated According to Maxwell's Theory" represents the achievement of propagation in air, the determination of its velocity, and the theoretical understanding of the source-field relation through Max­ well's symmetric equations. This achievement allows Hertz in turn to clarify the inconsistencies he left behind him, and he does it through a complete acceptance of the Maxwellian context. Here is the way Hertz elucidates this point in the same paper. He had measured the velocity in air independently of the velocity in wires and had found it to conform to Maxwell's theory or, equivalently, to the limiting case of Helmholtz' theory. However, some aspects of the phenomenon were still disconcert­ ing: the phase distribution in air seemed to point to an infinite velocity in the vicinity of the generator. 149 This inconsistency was similar to the one Hertz had already found in the case of wire propagation, and which he had explained by splitting the force. But now in the course of the experiment, Hertz advances tentatively a different explanation based on ether polarization: "In the sense of our theory we more correctly represent the phenomenon by saying that fundamentally the waves which are being developed do not owe their formation solely to processes at the origin, but arise out of the condition of the whole surrounding space, which latter, according to our theory, is the true seat of energy." 150 Hertz seeks to ex­ plain the instantaneous propagation, or propagation with a velocity higher than that of light, of force in the neighborhood of the oscillator on the ground that electromagnetic energy is localized and spreads out from the space surrounding the conductors. If one measures the velocity at the oscillator, one is deceived by a false result simulating an infinite velocity. Hertz affirms the new context more and more forcefully, and partly supports his judgment by referring to Heaviside's and Poynting's develop­ ments of Maxwell's theory. 148 Zfeici.,

p. 159. p. 146. 1 5 0 Ibid., p. 146.

1 4 9 Ibid.,

318

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

In the summer of 1888 he carried out the experiments described in his paper on the guided propagation of waves. 151 In the following months, after completing his final experiment on free radiation, he resumed the ex­ periments on wires, 152 an indication of the importance he attributed to them. In the 1891 introduction he pointed out that his research in the summer of 1888 was designed "to test the correctness of the view accord­ ing to which the seat and field of action of the waves is not in the interior of the conductor, but rather in the surrounding space." 153 The view he was testing and that he believed was confirmed by his researches was the one he ascribed to Heaviside and Poynting; namely, that "the electric force which determines the current is not propagated in the wire itself, but under all circumstances penetrates from without into the wire." Hertz considered it as "the correct interpretation of Maxwell's equations as applied to this case." 154 In his initial conception of guided waves, charges in the wire could still have the function of sources of external electric force, but in this last conception the force penetrates from without and determines the current. In supplementary notes to Electric Waves, written in 1891, Hertz elaborated on his new conception. There he maintained that he had ex­ perimentally proven that in the case of rapid variations of currents the change ["die Veranderung"] penetrates from without into the wire. It is thereby made probable that in the case of a steady current as well, the disturbance ["der Vorgang"] in the wire itself is not, as has hitherto been assumed, the cause ["die Ursache"] of the phenomena in its neighborhood; but that, on the contrary, the disturbances in the neighbourhood of the wire are the cause of the phenomena inside it. That the disturbances in the wire are connected with a regular circulation of material particles, or a fluid assumed ad hoc, is a hypothesis which is neither proved nor disproved by our experiments; they simply have nothing to do with it ["eine Hypothese . . . auf welche sich unsere Versuche gar nicht beziehen"] . We have neither any right to oppose this hypothesis, nor 151 Hertz, "On the Propagation of Electric Waves . . . ," in Electric Waves, pp. 160-171. 152 Heinrich Hertz, "On the Mechanical Action of Electric Waves in Wires," Wiede­ mann's Annalen, 42 (1891), 407; inElectric Waves, pp. 186-194. 153 Hertz, "Introduction, A Experimental," in Electric Waves, p. 15. 154 Hertz, "On the Propagation of Electric Waves . . . ," in Electric Waves, pp.

160-161.

SALVO D'AGOSTINO

319

have we any intention of doing so ["noch ist es unsere Absicht"], on the ground of the experiments here described.155 Hertz's statement presents impressive evidence for the conceptual change in the context within which Hertz was working; from a context of charges and currents he passed to the comprehensive context of the field. The concept of the field now challenged the earlier concepts that had been firmly established on the Continent for nearly a century. Hertz does not give a definite opinion on the locus of the disturbances in the case of a regime of steady currents. However, he also did not make a distinction between the variable and steady regimes in this connection; to have done so would have seemed inconsistent on his part after having had asserted the principle of the unity of electric force. At some stage in his researches of March 1888, Hertz discovers through his detector that his apparatus is capable of producing shorter wavelengths. His clear theory of the source-field relation now allows him confidently to shape his experiment to demonstrate the undulatory nature of the electric force. He concentrates electric waves by mirrors, refracts them by lenses and prisms, polarizes them by metal gratings, and reports on all this in "On Electric Radiation" ["Uber Strahlen elektrischer Kraft"] ,156 which he presents to the Berlin Academy on 13 December 1888. In place of the large Ruhmkorff coil of the previous experiments he uses a smaller induc­ tion coil. At times he substitutes for the circular detector the now wellknown dipole antenna; the antenna is 160 centimeters long and is not at this time synchronized with the radiator. He concentrates the radiation by means of a parabolic mirror, 2 meters high and with an aperture of 1.2 meters, made of sheet zinc. By reflecting the wave from a conducting sur­ face, he observes four distinct nodal points, and he finds the wavelength to be 66 centimeters. Hertz detects the sparking effect up to a distance of 16 meters, using a door aperture in the wall. He verifies the rectilinear propagation by means of the usual screening process; he demonstrates polarization with metal gratings; he detects reflected rays at forty-five degrees; and he observes refraction through a huge prism "made of socalled hard pitch." He comments at the end of his paper: "We have applied the term ray of electric force to the phenomena which we have in­ vestigated. We may perhaps further designate them as rays of light of very lss Hertz, "Supplementary Notes, 1891," in Electric Waves, pp. 269-278, on p. 175, n. 24. 156 Hertz, "On Electric Radiation," Sitzungsber. d. Berl. Akad. d. Wiss. (13 Decem­ ber 1888); in Wiedemann's Annalen, 36 (1889), 769; mElectric Waves, pp. 172-185.

320

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

Figure 5. Hertz's original polarization gratings and diffraction prism (Deutsches Museum, Munich).

321

SALVO D'AGOSTINO

great wave-length. The experiments described appear to me, at any rate, eminently adopted to remove any doubt as to the identity of light, radiant

heat,

tion." 157

and

electromagnetic ["elektrodynamischer"] wavemo-

Hertz views propagation here under its "optical" aspect, opening

up the new field of the optics of the electromagnetic spectrum which was rapidly developed by his successors. Hertz's December 1888 paper is commonly accepted as representing the climax of Hertz's experimental work. Followingits communication to the Berlin Academy and its publication in the Annalen der Physik, the fame of Hertz's work spread to international audiences. The modern reader of the paper is still struck by—in Hertz's words—the "demonstrative power" of the experiments. They have the force of simplicity, straightforwardness, and clarity. This demonstrative power was what Hertz had sought since he first began thinking about free propagation. In March 1888 he had at­ tempted to "exhibit the propagation of induction through the air by wavemotion in a visible and almost tangible form." In fact, he had then argued that in his previous experiment, the first on the propagation in wires and in air, "though the inferences upon which that proof rested appear to me perfectly valid . . . they are deduced in a complicated manner from com­ plicated facts, and perhaps for this reason will not quite carry conviction to anyone who is not already prepossessed in favour of the views therein adopted." 158 Aware of this defect in his first experiment, Hertz now, in March 1888, emphasized the phenomenological aspect and even stressed its quasi-independence from the theoretical interpretation. He maintained that "the demonstrative power of the experiment is independent of any particular theory. Nevertheless, it is clear that the experiments amount to so many reasons in favour of that theory of electromagnetic phenomena which was just developed by Maxwell from Faraday's views." 159 The rela­ tion between theory and experiment that Hertz hints at in the latter passage he develops and makes more precise in his two subsequent theoretical papers on electrodynamics in 1890 and especially in his introduction to the Principles of Mechanics. 5. CONCLUSIONS In this critical evaluation of Hertz's researches based on the historical evidence presented in his published work and in his correspondence, I have lsl Ibid.,

pp. 182-183. "On Electromagnetic Waves in Air . . , ," in Electric Waves, p. 124. 159 Ibid., p. 136.

158 Hertz,

322

HERTZ'S RESEARCHES ON ELECTROMAGNETIC WAVES

mainly stressed the importance of his 1884 theoretical paper, which is usually considered by Hertz scholars as parenthetical to his contribution to electrodynamics. To summarize: from 1884 Hertz developed a theory of the free propagation of electromagnetic forces which, unlike Maxwell's, was inspired by purely electromagnetic, not optical, phenomena. He showed that the propagation of the electric force was consistent with known electromagnetic laws provided that the conception of the unity of electric forces was accepted as a basic postulate. This conception of unity was an important contribution to the field concept and to the acceptance of Maxwell's type of equations. Hertz's 1884 contribution was, however, a rather formal and mathe­ matical theory, lacking a corresponding physical conception of propaga­ tion in the ether. The possibility for such a conception was presented to him when he started the experiments that were meant to confirm Helmholtz' theory of polarization of material dielectrics and ether. The experimental situation and reconsideration of his own and Maxwell's theories led Hertz to emphasize ether polarization. He then took the decisive steps toward his final experiments by developing Maxwell's theory in the electromagnetic band. The main pillar of his development was a theory of the source-field relation unknown to Maxwell. Hertz's develop­ ment entailed a profound modification of the relation of electrostatics to electrodynamics; it did so in the spirit of his 1884 analysis of the role and nature of the two electric forces. He also experimentally disproved in the variable regime of currents the conception of a current as a fluid motion or a motion of discrete charges under the action of electromotive forces. For the conception of charges in motion as sources of electrodynamic forces, he substituted the conception of electromagnetic energy localized in the dielectric ether surrounding the conductors. This conception helped him in finding an explanation for the inconsistencies he had observed in the nodal distribution in wire propagation and in the distribution of the radia­ tion in the near field. It helped him, too, to develop consistently the extreme consequences of the idea of the field. Its greatest help was in unifying free propagation and wire propagation, two aspects of electro­ dynamics that had not before come into a clear relation. Lorentz later rejected this unity and reintroduced discrete carriers of charge side by side with fields, and material polarization side by side with ether polarization. Although the spark-gap effect was known and had been used to detect electromagnetic effects, the method of using the effect for detecting fine details of the field amplitude and direction in a standing wave pattern was

SALVO D'AGOSTINO

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entirely Hertz's own. In arriving at this met]hod, he overcame the difficulties of finding optimum conditions for the emission and detection of radiation when all the conceptual tools of anten nas and vacuum and cable impedances were still unavailable. His exploratio η of the radiation field by his circular detector was an example of a rr asterly exploitation of a roughly approximated theory, using critical judgment and a sense of limits. I wish to close by making a general remark about Hertz's intellectual motivation. The basis of his strenuous electnodynamic researches was his conviction of the importance for science and philosophy of confirming contiguous action in electrodynamics.

ACKNOWLEDGMENTS The initial research for this paper was made possible by a scholarship from the Accademia Nazionale dei Lincei in 1970. I also gratefully acknowledge partial support for this work from the Consiglio Nazionale delle Ricerche, Rome. I am particularly grateful to Russell McCorm:mach, The Johns Hopkins University, for his accurate linguistic correctio ns, perceptive comments, and helpful editorial revision of the manuscript. I wish also to thank Mary Hesse, Cambridge University, for her encourage:ment in the initial stage of the work. This work would not have been possible with out the encouragement of Carlo Ballario, my colleague at the University of Rome.

God and Nature: Priestley's Way of Rational Dissent BY J. G. McEVOY* AND J. E. McGUIRE** Joseph Priestley was an eighteenth-century "rationalist" and Christian. This dual commitment gave substance to his conception of rational dissent and underlay his basic intellectual commitments. In a somewhat radical mood, he could say that no kind of knowledge "besides that of religion" is deserving of the name. Religious knowledge alone supplies an adequate grounding for "a virtuous and truly respectable conduct in life, or of good hope in death."1 Priestley believed at the same time that it is a duty for all men to behave rationally, and that it is only by proceeding "according to our nature" and "exercising that faculty [reason] which is peculiar to us" that "proper happiness" is attained.2 He harmonized these two commit­ ments by insisting on the attainment of religious knowledge through a rational analysis of nature and Scripture. He warned against the abandon­ ment of reason to dogma and mystery, claiming that "true Protestants will not part with it [reason] ." 3 Within the tradition of rational dissent, Priestley insisted that the "most obvious sense of the Scriptures is in favour of those doctrines which are most agreeable to reason."4 He saw it as his main mission to convince a "few thinking and intelligent believers" of the "reasonableness and truth of Christianity."5 Reason and religion formed a harmonious intellectual whole: "Christianity will be no obstruction to any­ thing that is truly rational, and becoming a man, with respect to either, ^Department of Philosophy, University of Cincinnati, Cincinnati, Ohio 45221. of History and Philosophy of Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15213. 1 Joseph Priestley, Institutes of Natural and Revealed Religion, 2 vols., 2nd ed. (Birmingham, 1782), in The Theological & Miscellaneous Works of Joseph Priestley, LL.D. F.R.S. etc., ed. J. T. Rutt, 25 vols. (London, 1817-1835), 2, xv. Subsequent references will be to "Institutes," Works. 2 "Institutes," Works, 2, xvi. 3 Priestley, An Appeal to the Serious and CandidProfessors of Christianity (Lon­ don, 1791), in Worfes, 2, 385. Subsequentreferencesto "Appeal," Works. 4 "Appeal," Works, 2, 385. 5 Priestley, Disquisitions relating to Matter and Spirit, 2nd ed. (London, 1782), in Works, J, 204. Subsequent references to "Disquisitions," Works. lfli Department

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and whatever is not rational ought to be abandoned on principles that are even not Christian."6 Although his work is not in the forefront of the intellectual achieve­ ments of the eighteenth century, Priestley is one of the great systematic thinkers of the century. Despite his diffuse and rambling writings, the categories of his thought reveal a mind with unusual synoptic power, dedi­ cated to articulating the interconnections and ramifications of the central doctrines in his philosophy of man and nature. As a consequence, a study of Priestley's thought must deal with the close conceptual ties between his doctrines and their manifestation in various spheres of thought. His moral and political thought, for example, cannot be fully understood apart from his natural philosophy. Ultimately, his entire intellectual system rests on theological foundations, the central concepts of which are determinism, necessity, causation, and materialism. Rational dissent shows how these concepts are compatible with Scripture, which contains nothing either paradoxical or "contrary to all natural appearances."7 Priestley's interpre­ tation of these concepts constitutes a distinctive philosophy of nature, which supports his attitude toward religious doctrines such as mortalism and anti-trinitarianism. These doctrines, in turn, are given full expression in his Socinianism with its denial of the "divinity of Christ" and the "preexistence of souls." His materialistic interpretation of man and nature in­ forms his views of mortality, the perfectibility of man, and the growth of natural knowledge. The key to Priestley's thought lies in his conception of theology. It is necessary to distinguish between his cosmological and his biblical Christi­ anity, although they are ultimately harmonious in a rational scheme of things. The core of Priestley's cosmological Christianity is his view of God's attributes and God's causal relation to the created world. We will argue that the substance of Priestley's rationalism, methodology, and sci­ ence arises from his theological principles. These principles are Calvinist in origin, although Priestley rejects the stern moral and political doctrines of the Geneva reformer.8 In contrast with the Calvinists, Priestley is opti6 Priestley, Letters to a Philosophical Unbeliever (Birmingham, 1787), in Works, 4, 446. Subsequent references to "Philosophical Unbeliever," Works. 7 Priestley, A Free Discussion of the Doctrines of Materialism and Philosophical Necessity in a Correspondence Between Dr. Price and Dr. Priestley (London, 1778), Works, 4, 143. Subsequent references to "Free Discussion," Works. See also "Dis­ quisitions," Works, 4, 204. 8 See Michael Walzer, The Revolution of the Saints (London, 1966), for an interest­ ing discussion of the political ideology of Calvinism.

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mistic, believing in the perfectibility of man. By studying physical reality and the principles of human nature, man can enlarge his knowledge andf his power over nature and thereby increase his stock of benevolence, happiness, and material well-being. Priestley's faith is faith in reason. Universal determinism forms the core of Priestley's rationalist approach to religion, science, morality, and politics. Although it is well known that Hartleyan associationism is an important influence on Priestley's views on determinism and materialism, the wider background of his intellectual in­ debtedness is largely unexplored. We will relate Priestley's thought to the origin of eighteenth-century controversies on causation and determinism, showing his intellectual affinities with Hobbes, Anthony Collins, Spinoza, Lord Kames, Jonathan Edwards, and Hume.9 Although we are not yet in a position to show the extent of Priestley's indebtedness to those thinkers, we know that he certainly read and admired the work of Hobbes, Collins, and Edwards.10 Furthermore, he was familiar with the writings of Hume and aware of the opinions of Spinoza. Moreover, a comparison of Priestley's characteristic ideas with Spinoza's throws Priestley's thought into a significant light. With respect to ancient systems of thought, Priestley's philosophy has Stoical connotations. It was Stoicism, moreover, that in various ways played a role in the philosophies of Hobbes, Collins, and Spinoza.11 Again, Priestley's examination and rejection of Scottish Common Sense philosophy is crucial for an understanding of his ideas on the external world, his theory of knowledge, and his doctrines of truth and hypothesis.12 Moreover, these aspects of his thought will be seen to merge significantly with his more basic doctrines of determinism and causation which are articulated by his associationist interpretation of the mind. Ac­ cordingly, he charges Common Sense philosophy with confounding the distinctions between truth and opinion, fact and hypothesis, resulting in an inadequate conception of science and, besides, encouraging religious dog­ matism and political authoritarianism. Priestley based his rational dissent on the natural harmony between his 9 See note 49. A measure of the extent to which Priestley was familiar with Spinoza's position is indicated by the way in which he has to distinguish his own pantheistic leanings from the latter. See "Disquisitions," Works, 3, 241. 10 Thus he regarded Hobbes "to have been no Aetheist, but a sincere Christian, and 1 a conscientious good man." ("Free Discussion," Works, 4, 12.) See also note 49. 11 Priestley says of Stoicism: "it is on several accounts the most respectable of all the Heathan systems, especially as it regards the being and providence of God, and the submission we owe to it, patience in adversity, and resignation to death." (Italics added.) ("Observations on the Increase of Infidelity," Works, 17, 473.) 12 This aspect of his thought is discussed in sections 3 and 4 below.

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philosophical doctrines and his biblical Christianity: "In short, it is my firm opinion, that the three doctrines of materialism, of that which is commonly called Socinianism and of philosophical necessity, are equally parts of one system, being equally founded on just observations of nature, and fair deductions from the scriptures, and whoever shall duely consider their connection, and dependence on one another, will find no sufficient consistency in any general scheme of principles, that does not comprehend them all. . . ." 13 Priestley is careful to stress the independent validity of each doctrine, for to establish rational religion at the expense of distorting the truth was unthinkable. He insists, therefore, not only on the rationality of "Revealed Truth," but also on the method by which it is acquired. For Priestley, "faith" is the outcome of consistent rationality; he admonishes natural philosophers to be consistent by applying their rational techniques both outside and inside the laboratory. Since a rational analysis of "Bibli­ cal history" demands the acceptance of the truth of Christianity, anyone who rejects Christianity must cease to be a philosopher. Priestley's ration­ ality demands "consistency" and not "conversion."14 Each of the three doctrines—materialism, socinianism, and necessity—is "capable of such separate demonstration, as subjects of a moral nature require or admit."15 Although he regards "mechanism" as "the undoubted consequence of materialism," he is careful to stress the independent status of determinism. Irrespective of the truth or falsity of materialism, there is sufficient proof to show that "every human volition is subject to certain fixed laws, and the pretended self-determining power is altogether imaginary and im­ possible."16 Although scriptural exegesis naturally leads to Socinianism, the "universally acknowledged rules of philosophizing"17 authorize mate­ rialism. The harmonious union of these three epistemologically indepen­ dent doctrines in a philosophical "monism" is the most significant feature of Priestley's theory of matter. We will show that there are connections be­ tween his theory of matter and causation that clarify the conceptual basis of his phlogiston theory.

13 "Disquisitions,"

Works, 3, 220. Priestley, Experiments and Observations relating to various branches of Natural Philosophy, 3 vols. (Birmingham, 1779-1786), 3, xvi-xvii. Subsequent refer­ ences to Natural Philosophy. 15 "Disquisitions," Works, 3, 220. 16 Ibid., p. 220. i ^Ibid., pp. 220 and 202. 14 See

J. G. McEVOY AND J. E. McGUIRE 1

A systematic account of the interrelated components in Priestley's thought must begin with his view of theism. In early life a Calvinist, Priestley, in his mature thought, held a rationalist conception of divine attributes. Prior to 1774, he very probably viewed God's causal relation to creation largely within a voluntarist framework which embodied the dualities of divine will and nature, mind and matter.18 Both biblical and cosmological Christianity afforded a rationale for Priestley's interpretation of nature, man, and society. The former lay at the heart of his thought; he made an exegesis of scripture the touchstone of rationality. With his Dis­ quisitions Relating to Matter and Spirit in mind, Priestley declared: "By the help of the system of materialism—the Christian removes the very foundation of many doctrines, which have exceedingly debased and corrupted Christianity; being in fact a heterogeneous mixture of Pagan notions, diametrically opposite to those on which the whole system of revelation is built."19 Whether in reference to his complete philosophy of nature or to particular doctrines like materialism, Priestley held that his thought was compatible with a rational view of scripture. In considering Priestley's conception of cosmological Christianity, it will be helpful first to outline the main orientation of Western thought regard­ ing God and divine causation. The idea that God created the world by an arbitrary fiat of his will originated in the theological thought of Paul and Augustine and was further developed in the medieyal thought of Scotus and Ockham. This voluntarist view of God's dominion as a sovereign action over all creation was reaffirmed in the reformed theology of Luther, Calvin, and Bucer.20 According to this tradition, thq sole attribute of God 18 The following provide useful accounts of voluntarism in relation to natural philosophy: Parry Miller, The New England Mind: the Seventeenth Century (Cam­ bridge, Mass., 1954), Bk. II, Ch. VIII; Edgar Zilsel, "The Genesis of the Concept of Physical Law," Philosophical Review, 51 (1942), 245-279; .fcharles S. Peirce, Values in a Universe of Chance, ed. Philip P. Wiener (Stanford, 195i8), pp. 289-303; Francis Oakley, "Christian Theology and the Newtonian Science: The Rise of the Concept of the Laws of Nature," Church History, 30 (1961), 433-457¾ J. E. McGuire, "Force, Active Principles and Newton's Invisible Realm," Ambix, 15, (1968), 187-208. Fora discussion of dualism and the ontological traditions whiclji Priestley opposed, see Η. M. Bracken, The Early Reception of Berkeley's Immaterialism., 1710-1733 (The Hague, 1959). 19 "Disquisitions," Works, 3, 257. 20 Francoise Wendel, Calvin (London, 1965); C. D. Cremeans, The Reception of Calvinistic Thought in England (Studies in the Social Sciences, Vol. 31, No. 1;

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that the human mind can comprehend is his omnipotence. Nature is the unconditional result of the sheer and arbitrary power of divine will. This traditional conception of God is characterized by two doctrines: God is immaterial and transcendental; his causal relation to the finite world is unique. The immateriality of God embodies unity, simplicity, and timelessness. God is thus categorically different from his finite creation. God is absolute and eternal; the world is conditional and temporal. The problem of divine causation arises: since God is categorically different from the world, he has nothing in common with it. How then is it possible that God's creative act gave rise to a world over which he continuously rules? It is clear that traditional difficulties regarding God's nature and divine causation arose historically from two basically irreconcilable theisms. The first is the neo-Platonic view of God as a pure immaterial being, who is unique, remote, transcendental, and simple; the second is the theism of the Old Testament in which God is a personal creator who, being immediately sovereign over creation, is the force that acts continuously in nature and history. Many problems in connection with divine causation result from these opposing theisms; e. g., the neo-Platonic idea of God's existence as a nunc stans is incompatible with the dynamic nunc movens of the biblical God. Both, however, have been ambiguously related in traditional views of divine presence and its causal action in nature. Among seventeenth-century philosophical ancestors of Priestley, two, Hobbes and Spinoza, were acutely aware of difficulties arising from the problem of divine causation. Although Hobbes never achieved a general solution to the problem, he was aware of a tension between the dynamic activity of a Judeo-Christian God, who commands and acts through nature, and the unchanging God demanded by his determinism. The Hobbesian solution merely recognized the difficulty: an inscrutable God of power and dominion in his present actions continuously carries out his timeless inten­ tions. To Spinoza, this solution would beg the question as to how God acts in the world. In arriving at his own conception of the relation between God and the world, Spinoza revealed many of the difficulties in the tradiUrbana, 1949); Edward A. Dowey, The Knowledge of God in Calvin's Theology (London, 1952); J. T. McNeill, The History and Character of Calvinism (Oxford, 1954); T. H. L. Parker, The Doctrine of the Knowledge of God: A Study in the Theology of John Calvin (London, 1952); V. Hepp, Calvinism and the Philosophy of Nature (Grand Rapids, 1940); A. M. Schmidt, Jean Calvin et la tradition calvinienne (Paris, 1957); Eugene Choisy, Calvin et la Science (Geneva, 1931); Auguste Lecerf, Le Calvinisme et Ies sciences de la Nature (Paris, 1935).

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tional conceptions of divine causation. Although Priestley and other eighteenth-century thinkers seemed only partially to appreciate the diffi­ culties, Spinoza's position provides an illuminating framework for dis­ cussing Priestley's thought. Moreover, there is evidence, direct and indirect, that Priestley knew his work. Spinoza adhered to philosophical monism. Arguing that an eternal, im­ material God cannot act causally in a temporal and material world, Spinoza denied the coherence of voluntarist theology. With this denial went a rejection of creatio ex nihilo and also the idea that the world originated by emanative causation. His main argument against emanation was that it does not obviate the traditional difficulties of divine causa­ tion.21 To account for the origin of matter by postulating the emanation of spiritual intermediaries existing between God and the world merely transfers the problem of how an immaterial God can create contingent existence to the intermediaries. Further, to understand how God acts in nature is as difficult on the emanationist view as on the voluntarist view of a direct and unconditional act of creation. According to Spinoza, the prob­ lem of the radical discontinuity between God and nature is solved only when matter is conceived as an intrinsic part of divine nature. This means that something contingent and imperfect arises necessarily from an in­ finitely perfect God, from which Spinoza concluded that a sense must be established in which matter can be conceived as an eternal mode of divine being. To this end, he gave the doctrine of unconditional creation ex nihilo short shrift. Since the voluntarist view of creation denies that either condi­ tions external to God or reasons inherent in the divine mind could have 21 For a discussion of Spinoza's critique of emanationism see H. A. Wolfson, The Philosophy of Spinoza (New York, 1969), 1, For a discussion of Spinoza's doctrine of timeless creation see E. M. Curiey, Spinoza's Metaphysics (Harvard, 1969), pp. 4482. Spinoza's thought was by no means unknown in the late seventeenth and early eighteenth century, although most of the pamphlet literature is sharply critical. The following are among the early eighteenth-century anti-Spinozistic tracts: Charles Gildon, The Deist's Manual: or, a Rational Enquiry into the Christian Religion, with some Considerations on Mr. Hobbs, Spinoza . . . (London, 1705); William Carroll,/! Dissertation upon Mr. Locke's Essay Concerning Humane Understanding: Wherein that Author's Endeavours To Establish Spinoza's Atheistical Hypothesis are Con­ futed . . . (London, 1706); Philippe Nande, Examen de deux Traittez . . . avec une addition, ou I'on prouve contre Spinoza que nous sommes libres, 2 vols. (Amsterdam, 1713). See Thomas McFarland, Coleridge and the PantheistTradition (Oxford, 1969), pp. 261-266, for a useful discussion of Spinoza's influence and rejection in the eighteenth century. McFarland cites considerable primary and secondary literature on the fortuna of Spinozism in the Enlightenment. Since Priestley knew the writings of the free-thinkers through his interest in Collins, it is reasonable to suppose that he knew some of the tract literature on Spinoza.

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decided God to create the world when he did, the creative act can be ac­ counted for solely in terms of God's will and design. Since God's will and design are held to be beyond finite comprehension, Spinoza regarded the voluntarist position as tantamount to conceiving of a world created by blind chance, and offering no explanation of how nature is related to God or why it was created. Ineluctably, Spinoza reached the conclusion that nature is inherent in God. The world is not, therefore, created in time, but flows necessarily from God's eternal presence. Limited neither in time nor space, God's po­ tential is expressed fully in the creative act. The finite mind can compre­ hend only two of the finite modes of God's infinite attributes, extension and motion. All of God's infinite attributes are realized, however, in the eternal act of creation. Consequently, Spinoza conceived of nature as a mode of divine substance. From God's infinite nature, infinite things fol­ low in infinite ways. Since God acts by necessity not by volition, there is nothing in the nature of the world that is not in the nature of God; the two are mutually implicative. Although Priestley denied that he completely accepted Spinoza's views, 22 his mature view of God and the world has intellectual affinities with that of Spinoza. These affinities extend to Priestley's views on divine causation, matter, theory of knowledge, and the doctrine of man's moral ascent, all of which are clarified by reference to the more systematic thought of Spinoza. Priestley's mature thought evinces a mixture of rationalist and volun­ tarist theism. Despite his emphasis on the inexhaustibility of nature in the History of Electricity in 1767, 23 he arrives at his final view of the relation of God to creation only after the publication of his Disquisitions Relating to Matter and Spirit in 1777.24 In the introduction to the Dis­ quisitions, however, Priestley argues adamantly against the medieval doctrine of creation by means of emanative causation, as he does later in 22 See

"Disquisitions," Works, 3, 241. note 43. 24 References to the "Disquisitions" are usually made to the second edition of 1782 which appears in Rutt's edition of the Works. When necessary for our argument we have checked these references with the first edition of 1777. This procedure is not only convenient but permissible in the light of Priestley's policy of preserving his original statements in subsequent editions of his works and supplying his new views in additional text. It is part of his general plan of publication, one of the objects of which is to familiarize the reader with the history of his "real views." It must be taken into consideration when any attempt is made to characterize the actual de­ velopment of Priestley's ideas over time. 23 See

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his History of the Corruptions of Christianity.25 Specifically, Priestley objects to the traditional distinction between matter and spirit "which made the Supreme Mind the author of all good, and matter the source of all evil." The same distinction holds "that all inferior intelligences are emanations from the Supreme Mind, or made out of its substance, and that matter was reduced to its present form not by the Supreme Mind itself, but by another intelligence, a peculiar emanation from it. . . ." For Priestley, this distinction was "the real source of the greatest corruptions of true religion in all ages."26 Not only does Priestley deny the validity of dualism, but he implies that dualism must have recourse to unhelpful and unnecessary agencies to bridge the ontological gap between God and nature. Moreover, he objects explicitly to the traditional categorical dis­ tinction between good and evil, and the attempt to explain the origin of evil in terms of a plentitude of degrees of existence. In neither case can a coherent account of the relation between good and evil be given in terms of emanative causation. if Priestley is against the doctrine of emanative causation, does he accept creation ex nihilo without causal intermediaries? He does, but in a diluted form as late as his Disquisitions in 1777. As do the voluntarist theologians, Priestley emphasizes the absolute power of God: "the Deity not only attends to everything, but must be capable of either producing or annihilating anything. For, since all that we know of bodies, are their powers, and the Divine being changes those powers at pleasure, it is evident, that he can take them all away, and consequently annihilate the very substance; for without power, substance is nothing. . . ." 27 Although this is not an overt statement of the voluntarist doctrine of creation ex nihilo, Priestley's position in the Disquisitions is compatible with it. More­ over, not only can we know little of God's attributes, but we cannot com­ prehend fully his intentions in creating the world: "God is, and ever must remain, the incomprehensible, the object of our most profound reverence, and awful adoration. Compared with him, all other beings are as nothing and less than nothing. He filleth all in all, and he is all in all. " 28 Despite the standard religious language, Priestley's view of the relation of God and the world is again compatible with voluntarism. Moreover, in the Disquisi­ tions, he stresses the transcendent perfection of God, who is "distinct 25 "Disquisitions," Works, 3, 218-221. Priestley, History of the Corruptions of Christianity, 2 vols. (London, 1782), in Works, 5. Subsequentreferencesto "Corrup­ tions," Works. 26 "Disquisitions," Works, 3, 219. 2 TIbid., pp. 297-298. ™IbitL, p. 299.

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from his productions. . . ." Again, in his Philosophical Necessity of 1778, he implies that since voluntary actions are more perfect than necessary actions, they were instrumental in the unconditional creation of nature. Will, power, and intelligence are identical in God, 29 though their identity is incomprehensible to the finite mind. Although man's ignorance prevents him from seeing, as the Deity sees, that "all seeming discord is real harmony, and all apparent evil, universal good," Priestley affirms: "So long as we can practically believe that there is but one will in the whole universe; that this one will, exclusive of all chance, or the interference of any other will, disposes of all things, even to their minutest circumstances, and always for the best of purposes, it is impossible but that we must re­ joice in, and be thankful for, all events, without distinction." 30 In this way, by stressing the priority of God's absolute will, Priestley sees creation ex nihilo as a possible but still incomprehensible act. In the Disquisitions, Priestley alleges that his materialism is not incom­ patible with the traditional doctrine of divine essence, and that his con­ ception of matter avoids immemorial difficulties in relating God and nature, mind and body. Arguing that we have no conception of God apart from his actions in nature and thus no warrant for forming a notion of an immaterial first cause, Priestley states that his materialism "is that philosophy which alone suits the doctrine of the Scriptures, though the writers of them were not philosophers, but had an instruction infinitely superior to that of any philosophical school. Every other system of philosophy is discordant with the Scriptures, and, as far as it lays any hold upon the mind, tends to counteract their influence." 31 Priestley's conten­ tion is unmistakable: his view of God and nature is compatible with the sense of scripture, and other philosophies manifestly are not. Not only is scriptural exegesis an essential source for Priestley's materialism; it is the paradigm of rationality. Although Priestley stresses the autonomy of God's will throughout his writings, in his Institutes of Natural and Revealed Religion, first published in 1782, he argues against creation conceived as a particular act in time: if we admit that there ever was a time when nothing existed, besides the Divine Being himself, we must suppose a whole eternity to have 29 Priestley,

The Doctrine of Philosophical Necessity Illustrated, being an Appendix to the Disquisitions relating to Matter and Spirit, 2nd ed. (London, 1782), in Works, 3, 507-515. Subsequent references to "Philosophical Necessity," Works. 30 "Philosophical Necessity," Works, 3, 451. 31 "Disquisitions," Works, 3, 302.

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proceeded any act of creation; an eternity in which the Divine Being was possessed of the power and disposition to create, and to make happy, without once exerting them: or that a reason for creating must have occurred to him after the lapse of a whole eternity, which had not occurred before; and these seem to be greater difficulties than the other. Upon the whole, it seems to be the most agreeable to reason, though it be altogether incomprehensible by our reason, that there never was a time when this great uncaused Being did not exert his perfection, in giv­ ing life and happiness to his offspring. We shall, also, find no difficulty in admitting, that the creation, as it had no beginning, so neither has it any bounds but that infinite space is replenished with worlds.32 if it is difficult for the finite mind to conceive "how creation should have been coeval with its Maker," that conception is nonetheless more agreeable to reason than the alternative that nature had a definite beginning in time. The principles of plenitude and sufficient reason as expressed in this passage make it reasonable "to consider that thinking and acting, or creat­ ing may be the same thing with God."33 Creation is thus an eternal act of God for Priestley. It does not occur in time, but flows necessarily from God's timeless presence. With Letters to a Philosophical Unbeliever in 1787, Priestley affirms that God's causation is necessary and not volitional or intentional as on the voluntarist hypothesis. By his nature, God "could not but have acted from all eternity."34 If God's will is eternal action, the world is the necessary effect; this action is incompatible with the arbitrary view of divine will that voluntarism ascribes to God. For Priestley, the affirmation of God's eternal and necessary creative act supports a rationalist interpre­ tation of determinism and materialism. Since all things necessarily arise from divine nature, they are necessarily linked in a deterministic chain. 32 "Institutes,"

Works, 2, 5. p. 5. Priestley reduces God's creative act to "thinking," i.e., "conjuring" something into existence. Priestley also thinks of God as a timeless being. But terms like "producing" or "making something happen" imply a beginning. Thinking as an activity does not seem to be tied to time, but it is absurd to claim that God can timelessly produce, even by thought, a temporal object. His omnipotence would be temporally coextensive with what he created. Nor does it help to reduce the doctrine of creation to that of divine preservation. Preservation, as a manifestation of divine activity, is also temporal, since the universe sustained by God is temporally extended. Priestley's doctrine of timeless, necessary creation is thus no more difficult than any other doctrine of creation. 34"philosophical Unbeliever," Works, 4, 343. See also pp. 341-342 for a discussion of the claim that the world has no beginning. 33 Ibid.,

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Determinism, for Priestley, embodies the principle that the mind can know how the world is causally related to God. If nature devolves from a necessary creative act, natural philosophy will give content to our concep­ tion of God. In Priestley's materialism, matter is conceived as a plenum of intensive powers extended in space, 35 and as such it becomes an expres­ sion of God's continuous activation of nature arising necessarily from the creative act. Contrary to the voluntarists, Priestley does not conceive of God as having greater perfection and power than his creation: God is fully actualized in the act of creating. Voluntarism cannot now provide Priestley with rational grounds for an account of divine creation. Ultimately, it provides only a partial basis for comprehending God through nature, and Priestley rejects it. Priestley will not, however, embrace Spinoza's view that nature is strictly contained in God. Speaking of matter as centers of action, Priestley re­ marks in the Disquisitions: "Nor, indeed, is making the Deity to be, as well as do everything in this sense, anything like the opinion of Spinoza." 36 Nevertheless, Priestley may have become more disposed by 1782 to the opinion that there is a universal substance of which everything existent is a mere mode. In any event, this ultimate conclusion of rationalism is con­ sistent with his materialism, his principles of plenitude and sufficient reason, and his doctrine of divine causation. Moreover, Priestley is adamant that his monistic interpretation of reality is more conducive to piety than the dualism of God and nature, of mind and matter: the common hypothesis [dualism] is much less favourable to piety, in that it supposes something to be independent of the Divine Power [i.e., matter]. Exclude the idea of Deity on my hypothesis and everything except space necessarily vanishes with it, so that the Divine Being, and his energy, are absolutely necessary to that of every other being. His power is the very life and soul of everything that exists; and strictly speaking, without him, we are, as well as can do, nothing. But exclude the idea of Deity on the common hypothesis, and the idea of solid matter is no more excluded than that of space. It remains a problem, therefore, whether matter be at all dependent upon God, whether it be in his power either to annihilate or to create it; a difficulty that has staggered many, and on which the doctrine of two original, independent principles was built. 37 35 See

pp. 384-391. Works, 3, 241. 37 Zbici, p. 241. 36 "Disquisitions,"

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For Priestley, the "common hypothesis" of dualism can lead to the con­ clusion that solid matter, like absolute space, is independent of God. Not only does this hypothesis mix the category of the contingent with that of the necessary, but it involves a nonrational and, thereby, non-Christian view of divine causation. It affords no grounds for comprehending how mind, body, and nature conceived as independent things are related to one another and to God. When Priestley's uncompromising attitude toward dualism is properly understood, his relation to the Boyle lecturers and the Newtonians be­ comes apparent. He read Bentley, Clarke, Cudsworth, Keill, Rowning, and Baxter only to reject them, 38 for their religious apologetics was predicated on the dualities of God and nature, mind and matter. Moreover, they were all voluntarists. With its rationalist cast, the work of Hobbes, Collins, Spinoza, Kames, and Hume has more instructive affinities with Priestley's mature thought on determinism and causation.

2 Determinism plays a central role in Priestley's philosophy of nature. It is related to his view both of God's causality and of the necessity of voli­ tional and physical events. Priestley links determinism with the harmony of nature and with the ascent to benevolence and happiness: We ourselves, complex as the structure of our minds and our principles of action are, are links in a great connected chain, parts of an immense whole, a very little of which only we are as yet permitted to see, but from which we collect evidence enough that the whole system (in which we are, at the same time, both instruments and objects) is under an unerring direction, and that the final result will be most glorious and happy. Whatever men may intend, or execute, all their designs, and all their actions, are subject to the secret influence and guidance of one who is necessarily the best judge of what will most promote his own excellent 39

purposes.

In this characteristic passage, man is seen as part of the deterministic structure of nature, embracing volitional and physical events. Although it 38 Priestley's reactions to Bentley, Clarke, Cudsworth, Keill, Rowning, and Baxter are scattered throughout his numerous philosophical and theological works. However, his negative attitude towards them is most evident in "Disquisitions," Works, 3. 39 "Philosophical Necessity," Works, 3, 450.

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is beyond our comprehension, all things are inextricably linked to the boundless fecundity of divine creation. Our knowledge of nature can never be complete, yet human understanding is moving toward a comprehension of more general truths. As this movement proceeds, the greater use of the rational faculties will, through the comprehension of this world as a "system of benevolence," elevate the mind and aid in the perfectibility of human nature. Since man is part of nature, Priestley maintains that the "laws of volition are as much as anything else in the system of nature the laws of God."40 Arguing that man is wholly material and can, therefore, be considered a mechanical being, Priestley concludes that "the doctrine of necessity is a direct inference from materialism."41 The laws, therefore, that govern material nature also apply to man. Accordingly, the necessary chain of cause and effect forms the basis for a rational understanding of the whole system of nature. It is important to emphasize once more that for Priestley a proper exegesis of scripture forms the touchstone of his doctrine of rationality. He repeatedly argues that the idea of an immaterial, separate soul is an embarrassment to the true Christian system, being the "foundation" of the "very grossest corruptions of Christianity."42 Holding that man's true nature is essentially a part of physical reality, Priestley concludes that this view is rational because it is compatible with a proper sense of Scripture. His scriptural claim will take on substance when it is seen that his theory of matter integrates into an intelligible whole the doctrines of materialism, philosophical necessity, cosmic optimism, psychological perfectionism, and Socinianism. The question of how Priestley's doctrine of physical determinism relates to his view of God's action in the world admits of no easy answer; never­ theless Priestley's view of the necessity of God's creative act implies the realization of every possible effect in nature. His view of the limitless extent and variety of creation is thus expressed in his History of Electricity in 1767, his Experiments and Observations on Air in 1774, and his Philosophical Unbeliever in 178 7.43 In the Institutes of 1782, Priestley 40"'PKiltisoplucal Unbeliever," Works, 4, 347. 41 "Philosophical Necessity," Works, 3, 453. 42ll Free Discussion," Works, 4, 10. 43 See Priestley, The History and Present State of Electricity (London, 1767), pp. iii-iv and xi; Priestley, Experiments and Observations on Different Kinds of Air, 3 vols. (London, 1774-1777), 1, vii-viii; "Philosophical Unbeliever," Works, 4, 341. Subsequent references to the first work will be to Electricity, to the second to Air.

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first explicitly relates it to the rationalist doctrine of an eternal world flowing continuously from eternal creation. Although the doctrine of natural plenitude is not incompatible with a voluntarist interpretation of divine causation, Priestley unambiguously links it with a nonvoluntarist conception of the world's relation to God. We can have rational knowledge of God through nature, as nature abundantly manifests the attributes of God and can thus be analyzed by the mind in its drive for simplicity. Unlike the voluntarist doctrine of divine causation, Priestley's doctrine recognizes no limitation to God's creative act. The eternal necessity of divine creation is therefore exemplified in the deterministic structure of nature which, in itself, is an expression of God's timeless and simple laws. The implications of this view, Priestley thinks, are significant. While commenting on the determinism of Hobbes and, by implication, Spinoza, he observes: What the ancients have said on the subject is altogether foreign to the purpose, their fate being quite a different thing from the Necessity of the moderns. For though they had an idea of the certainty of the final event of some things, they had no idea of the necessary connexion of all the preceding means to bring about the designed end; and least of all had they any just idea of the proper mechanism of the mind depending upon the certain influence of motives to determine the will, by means of which the whole series of events, from the beginning of the world to consummation of all things, makes one connected chain of cause and effect, originally established by the deity.44 There are a number of important points here. Again, Priestley relates matter and mind in terms of a deterministic chain of causes emanating from God's nature. Ultimately, he conceives the system of causes and effects in nature to exemplify a network of laws determined by God. With respect to God's nature, however, causal chains are instances of internal as opposed to external necessity. Like the Stoics and Spinoza, Priestley distinguishes between events coming "to pass by means of natural causes" and God interposing "to make sure of the event." The true sense in which the world, emanating from divine nature, is deterministic is expressed in the doctrine of philosophical necessity of Hobbes and Spinoza, not in the ancients' "Fate of the Heathens." Substantively, things come about by the internal necessity of divine nature, not by God's direct intervention. Internal necessity, therefore, manifests God's con44 "Philosophical

Necessity," Works, J, 455.

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tinuously effective power; omniscience and omnipotence are one. At the most general level of analysis, in which Priestley relates divine causation to his doctrine of determinism, he rejects the predestination of Luther, Calvin, and the Jansenists. Their doctrines suppose God to act by external necessity, which is a central doctrine of voluntarism; once nature is established in terms of immutable laws reflecting divine nature, causes and effects must come about as they do, unless God changes or suspends the laws. 45 Priestley holds two separate but compatible doctrines of determinism. In the first, events are necessarily determined once necessary and sufficient conditions are established within the framework of space and time. From the point of view of human knowledge, events could not have happened otherwise unless physical laws were different than they are. Second, as consequence of God's eternal action, power is manifested necessarily and continuously in nature. Like Spinoza, Priestley holds that the natural conatus of created things is not independent of divine action. From the necessity of divine nature, all material things are determined to exist and act. Divine power is as necessary to maintain them in existence as it was to begin their existence. The power whereby they operate is, thus, the internal power of God himself. For Priestley, this means that nothing can arise without an adequate and sufficient cause or motive; otherwise "the whole universe might likewise exist without a cause." Should it be other­ wise, "the foundation of the only proper argument for the being of a God" 46 would be overturned. Maintaining that all events are invariably and necessarily connected through a system of rules or laws, Priestley argues that "there is some fixed law of nature respecting the will," such that there is a "necessary connection between all things past, present, and to come, in the way of proper cause and effect, as much in the intellectual, as in the natural world." Even volition and choice are constantly regulated and determined by preceding motives, which Priestley calls the "necessary determination" of the mind "according to the established laws of nature." He is emphatic that man's nature is governed by physical laws. Since there is a constant and regular relation between human action, circumstances, and motives, that action is "as necessary as any mechanical motion whatsoever." Priestley concludes: "Though, therefore, a man's determination be his own, the causes of it existing and operating within himself, yet, if it be subject to any fixed laws, there cannot be any circumstances in which two different determinations might equally have taken place; for that would 4S

Ibid., pp. 455-456.

^!bid., p. 469.

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exclude the influence of all laws."47 For Priestley, man makes his own choice, "but in voluntarily making it, he follows the laws of his nature." These laws are an integral part of the wider system of things. Whether or not we distinguish a physical from a "moral mechanism," if there can be only one consequence from the preceding circumstances, "there will be a real necessity, enforcing an absolute certainty in the event." In this con­ text, Priestley is somewhat vague about what he means by necessity; he merely says it is that which "in a cause" produces "certainty in the effect." However, he wants to maintain that the characteristics of ante­ cedent causes and circumstances are such that there is absolute certainty that the effects will follow by internal necessity unless the laws of nature are suspended by God. For both motives and causes, then, there must be a sufficient reason why they occur. Here, Priestley's rationalistic presupposi­ tions lead him to oppose Clarke's and Newton's doctrine of selfdeterminacy. His view of divine determinism has affinities with the Leibnizian doctrine of sufficient reason.48 Consistently with his denial of the existence of a separate and immaterial soul, Priestley opposes the view that freedom of the will exists outside the nexus of universal determinism. His views on freedom are very much in the tradition of Hobbes, Collins, Edwards, Kames, Hume, and Hartley, whose writings he mentions often.49 Collins is perhaps the most important of the determinists whom Priestley read. Priestley published his own edition of Collins' Philosophical Inquiry Concerning Human Liberty, saying that: "It was in consequence of reading and studying this treatise that I was first convinced of the truth of the doctrine of necessity. . . ." 50 Collins was in­ fluenced by Hobbes, Locke, Bayle, Spinoza, and the Stoics, 51 an intel47 Ibici,

p. 465. ^ s Ibid., pp. 462-469. e.g., "Philosophical Necessity," Works, 3, 453-454. Here Priestley refers "those persons who have not yet entered upon the discussion of this great question" to "such writers as . . . Collins, Mr. Jonathan Edwards and Dr. Hartley" and to "some things very well written on it by Mr. Hume and Lord Kames, especially in his Sketches on Man." Besides his work on Collins (see note 50) and Hartley (see note 73), there are many references to all of these writers in Priestley's works. For a recent discussion of "polite determinism" in Scottish circles, especially in connection with Hume and the Select Club, see N. J. Phillipson, "Towards a Definition of the Scottish Enlightenment," in City and Society, McMaster Studies in the Eighteenth Century, Vol. 3, ed. P. Fritz and G. Williams (Toronto, 1973). 50 "Philosophical Necessity," Works, 3, 457. See A Philosophical Inquiry concern­ ing Human Liberty by Anthony Collins, Republished with a Preface by Joseph Priestley (London, 1790), in Works, 4. 51 See James O'Higgins, Anthony Collins: The Man and His Work (The Hague, 1970). This study is useful for the light it throws on eighteenth-century free thought, determinism, and free will. O'Higgins points to the Stoic writers whom Collins read. 49 See,

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lectual pedigree suited to Priestley's cast of mind. The basic position of the tradition Collins belonged to is that the existence of free and independent action outside the system of causes would deny God's prescience or omnipotence. This position is manifest in Priestley's view of evil; he says that the introduction of contingency into nature is tantamount to Mancheanism, or the "doctrine of an independent evil principle." 52 For Priestley, the consequences of contingency are worse than those of Mancheanism, since the latter can be controlled and the former by their very nature cannot. By contrast, Priestley's doctrine of philosophical necessity guarantees the absence of real evil in a world that is the best of all possible worlds. In any event, to deny divine prescience would be to "take away the whole foundation of Divine Providence and moral government, as well as all the foundations of revealed religion, in which prophecies are so much concerned." 53 Again, we see the extent to which Priestley uses biblical Christianity to give support to a philosophical position. Accordingly, an interpretation of determinism that holds the distinction between cause and motive to be merely verbal is not "anything that ought to alarm the philosopher or the Christian." 54 Believing that everything necessarily follows from God's nature, Priestley, like Leibniz, holds that just as evil is merely apparent, so too is contingency. Following the arguments of Hume and Kames, Priestley argues that if human character were independent of its actions, there could be no necessary connection between the two, and the morality of an action could not be related to character. Human beings would not be responsible for their actions and thus not subject to moral praise or blame. Actions must be determined by motives and therefore seen as part of the great chain of causes and effects. Human nature would otherwise be capricious, neither fitted for government nor capable of improvement by any relation of means to end: "For no creature can be the subject of rational or moral government whose actions, by the constitution of its nature are inde­ pendent of motives, whose will is capricious and arbitrary." 55 Since actions and events are necessary, human nature, in conformity with the laws of creation, fulfills ends that are compatible with God's design. One of the central doctrines of Priestley's determinism, and one that 52 Priestley, An Examination of Dr. Reid's Inquiry into the Human Mind on the Principles of Common Sense; Dr. Beattie's Essay on the Nature and Immutability of Truth; & Dr. Oswald's Appeal to Common Sense on Behalf of Religion (London, 1774), in Works, 3, 92. Subsequent references to "An Examination," Works. ^"Philosophical Necessity," Works, 3, 470. s i i Ibid., p. 485. 5 5 Ibid., pp. 499-509.

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expresses his affinity with the Stoics and Spinoza, is the interrelatedness of natural phenomena. Nature is a system of rules or laws for Priestley; without law, external reality would be unintelligible. Within the system of laws, all finite things have a place; they could not have been other than they are, short of having different laws." To understand finite things is to see how they fit into a system of causes and effects of which they are an integral part. Priestley's conception of nature has significant ramifications for his view of knowledge, explanation, and progress. In the first place, Priestley reasons that an interrelated system of laws is a necessary consequence of divine nature. "Upon this scheme we see God in everything and may be said to see everything in God, because we continually view everything as in connexion with him, the author of it."56 This most general consequence of Priestley's determinism places upon man a moral duty to use his rational faculties to understand nature. By so directing the mind to the study of nature, human beings can ascend to permanent happiness and perfection. In the tradition of Newton and David Hartley, Priestley holds that one of the chief roles of natural philosophy is spiritual enlightenment and moral edification. He states that "the greatest and noblest use of philosophical speculation is the discipline of the heart and the opportunity if affords of inculcating benevolent and pious sentiments upon the mind."57 The qualities of benevolence and piety are not only ends in themselves, but they also facilitate the comprehension of nature, Priestley affirms his posi­ tion in the following passage taken from Hartley: Since this world is a system of benevolence, and consequently its author the object of unbound love and adoration, benevolence and piety are our only true guides in our inquiries into it; the only keys which will unlock the mysteries of nature, and clues which lead through her labyrinths. Of this, all branches of natural history, and natural philosophy afford abundant instances. In all these inquiries, let the inquirer take it for granted previously that everything is right, and the best that can be ceteris manentibus: that is, let him, with a pious confidence, seek for s 6 Ibid.,

p. 507.

51 Electricity,

p. xxix. This viewpoint was a commonplace among eighteenthcentury natural philosophers. See, e.g., Isaac Newton, Opticks, 4th ed. (London, 1730; reprinted New York, 1952), p. 405; Colin MacLaurin, Account of Sir Isaac Newton's Philosophical Discoveries (London, 1758), p. 4; William Derham, PhysicoTheology (London, 1691); David Hartley, Observations on Man, his Frame, his Duty and his Expectations, 2 vols. (London, 1749), 2, 45. Subsequent references to Obser­ vations on Man.

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benevolent purposes, and he will be always directed to the right road; and after a due continuance in it, attain to some new and valuable truth: whereas every other principle and motive of examination, being foreign to the great plan on which the universe is constructed, must lead into endless maizes, errors and perplexities. 58 Natural philosophy, by revealing the wisdom and benevolence of God in creation, cultivates.piety in man. More important still, unless the natural philosopher develops requisite piety in his study of nature, he will not use fully that which is proper to him alone, his rational faculties, and his noble aim of understanding nature will be frustrated. Unmistakably, for Priestley the task of investigating nature has closely linked moral and intellectual dimensions. Without the balance and perspective of a pious, humble, Baconian approach to nature, Priestley claims that man will make natural philosophy an end in itself and will be consumed by such "ill passions" as "vain-glory, self-conceit, arrogance, emulation and envy, that are found in the eminent professors of the science." 59 By contrast with the common man, the natural philosopher has a more adequate knowledge of nature. In distinguishing between adequate and inadequate knowledge, Priestley expresses the cosmic optimism of the eighteenth century. 60 The seeming imperfection of things or evil of events result from the mind's ignorance of the necessary system of laws that connects all things and events. If we understood the necessary principles of individual things in Spinoza's fashion, we would understand the part that various things play in the system of nature as a whole. As we come to understand more of the ways in which things are interrelated, our knowl­ edge becomes increasingly adequate, if, however, we concentrate on things themselves, our knowledge will remain inadequate, and things will seem imperfect or evil. In the light of natural philosophy, or the systematic knowledge of nature's laws, nothing in itself can be said to be morally good or bad, morally perfect or imperfect; everything is what it is as the consequence of necessary laws. To say that a person is morally bad is, in popular usage, to imply that he could have been better, which reflects the speaker's inadequate knowledge. Concentrating on actions and things in themselves is, according to Priestley, the main source of error of the liber­ tarians: "Consequently, the associations which refer actions to themselves get so confirmed that they are never entirely obliterated, and, therefore, ss Electricity,

p. xxi. Hartley, Observations on Man, 2, 245-246. p. xxiii. Hartley, Observations on Man, 2, 255. ^^"Philosophical Unbeliever," Works, 4, 344-357. 59 Electricity,

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the common language, and the common feelings of mankind, will be adopted to the first, the limited and imperfect, or rather erroneous view of things." 61 Priestley the determinist does not deny that human beings can meaningfully speak of free choices between particular courses of action. What he does claim is that such "common language" reveals a partial or inadequate knowledge of the nature of things. To claim that we are free agents in the sense that our minds are not essentially connected with the system of nature's laws misrepresents rational thinking. We will necessarily abandon this notion of freedom as our knowledge and understanding of nature and of humanity as a part of nature increases. As our knowledge of human actions as a part of nature grows, it will become less reasonable to say that "he could have acted otherwise" in a totally nondeterministic sense. For Priestley, to say such a thing is a sign of the incompleteness of our scientific knowledge and an expression of our present state of ignorance. 62 Like Spinoza, Priestley regarded self-knowledge as the essence of freedom. The more man knows, the better he is able to act and decide; in this way, man can escape Ixion's wheel. Priestley's cosmic optimism and psychological perfectionism are inte­ grated into a psychological mechanism based on the principles of associationism. Given the mechanical genesis of man's personality, his perfect­ ibility is an inevitable consequence of his increasingly adequate knowledge of a benevolent natural world. Priestley bases his confidence in the perfectibility of the individual on Hartley's claim that "some Degree of Spirituality is the necessary Consequence of passing through life. The sensible Pleasures and Pains must be transferred by Association more and more every Day, upon things that afford neither sensible Pleasure nor sensible Pain in themselves, and so beget the intellectual Pleasures and Pains." 63 Priestley augments this associationist theme in his Essay on the First Principles of Government in 1768. There he traces the development of an individual from childhood to the state of perfection. Children are com­ pletely dependent on the present moment; their state of mind is deter­ mined by the pleasure or pain that naturally accompanies the objects with which they are momentarily concerned. However, with aging the memory and imagination develop so that the individual becomes less dependent on the present moment for his pleasure and pain. The pleasure or pain that 61 "Philosophical 62 IbicL,

Necessity," Works, 3, 516.

p. 516.

63 Hartley,

Observations on Man, 1, 82.

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accompanies "the remembrance of what is past, and the expectation of what is future" greatly influences the individual's reactions to given ob­ jects. When these "intellectual pleasures and pains" overpower "all temporary sensations," it happens that "some men, of great and superior minds, enjoy a state of permanent and equable felicity, in a great measure independent of the uncertain aspects of life. In such minds the ideas of things that are seen to be the cause and effect of one another presently coalesce into one, and present but one common-image. Thus, all the ideas of evil absolutely vanish in the idea of the greater good with which it is connected or of which it is productive." 64 Priestley's argument is similar to Hartley's whereby God, "who is the source of all Good," must even­ tually become "associated with all our Pleasures," so that the idea of ultimate goodness "must at last, take place of, and absorb other ideas, and He himself becomes according to the language of the Scriptures, All in All"65 In a passage reminiscent of Spinoza's "intellectual Love of God," Priestley says of the natural philosopher that it is "only in occasional seasons of retirement from the world, in the happy hours of devout contemplation, that I believe, the most perfect of our race can fully indulge the enlarged views, and lay himself open to the genuine feelings of the Necessarian principles; that is, that he can see everything in God, and in relation to him." 66 Although Priestley argues that nature must be con­ ceived as a completely intelligible, infinite, and self-contained causal system, he nonetheless recognizes that our finite knowledge of nature can never be complete. Nevertheless, as our knowledge increases so does our comprehension of the deterministic structure of nature. Whereas only the sage can approach divine knowledge of the world, all men can perfect their moral nature and happiness by progressively extending their understanding of nature: "And when our will and our wishes shall thus perfectly coincide with that of the Sovereign Disposer of all things, whose will is always done, in earth, as well as in heaven, we shall, in fact, attain the summit of perfection and happiness." 67 Although God is the author of sin, this "by no means implies that he is a sinful being; for it is the disposition of mind and the design that constitutes the sinfulness of an action." 68 God intends the general good. Man's moral and intellectual progress are inextricably 64 See Priestley, An Essay on the First Principles of Government and On the Virtue of Political, Civic, and Religious Liberty (London, 1768), pp. 2-3. - 65 Hartley, Observations on Man, 1, 114. 66 "Philosophical Necessity," Works, 3, 518. 6 IIbid., p. 451. 6 8 Ibid,, p. 510.

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linked, for he can only attain happiness and dignity by identifying him­ self, through his knowledge and understanding, with the whole order of nature and by submerging his individual interests in this understanding. Priestley denies the possibility of total explanation; nature is too in­ exhaustible in its fecundity for that. Divine plenitude as exemplified in creation is beyond finite comprehension. In his commitment to the consequences, if not the logic, of a "principle of plenitude," Priestley reveals a lasting and pervasive indebtedness to natural religion. The nature of God is reflected in his works which, like himself, are "infinite and inexhaustible";69 thus, the universe is an inexhaustible source of new in­ formation. Such ontological fecundity has epistemological consequences; enquiry into nature will always yield novelty and be forever incomplete. Therefore, the "necessary connection of all things in the system of nature ., . guarantees that every discovery reveals new domains of ignorance."70 As a result, "in completing one discovery we never fail to get the imperfect knowledge of others, of which we could have no idea before; so that we cannot solve one doubt without creating several new ones."71 In this way, every new discovery creates new problems. In fact, scientific progress is to be judged not only by an increase in knowledge but also by a proliferation of new problems. The image of knowledge as a circle of light in the vast darkness of ignorance means that the "greater the circle of light, the greater is the boundary of the darkness by which it is confined."11a This is not a lamentable state of affairs, but one that fills Priestley with religious exaltation. Taking a "romantic" view of man's destiny, Priestley sees man as involved in an endless process of progressive enlightenment: "In time the bounds of light will be still further extended;. . . and from the infinity of the divine nature and the divine works, we may promise ourselves an endless progress in our investigation of them: a prospect truly sublime and glorious."72 Although Priestley is conscious of the rich particularity of nature and is orientated toward the establishment of a factual basis for natural philosophy, his goal is to establish a single set of minimal laws. His search 69 Air, 1, vii. "ΌNatural Philosophy, 2, viii. Priestley was not aware of a difficulty in his necessi­ tarian position. If the vast proliferation of factual particulars arises by necessity from God's nature, there can be no ultimate contingency or factuality in nature, only necessities. His necessitarianism and determinism actually oppose his appeal to the brute and factual character of objective experience. 71a "Disquisitions," Works, 3, 26. " ll Air t 1, vii. ^Natural Philosophy, 2, ix.

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for single, unifying laws is one of the reasons for his great admiration of Hartley's psychology. In his introduction to Hartley's Theory of the Human Mind, Priestley asserts that "it does not appear impossible but that, ultimately, one great comprehensive law shall be found to govern both the material and the intellectual world." 73 This search for simplicity also gives epistemological and methodological content to the doctrine of progress from less to more adequate knowledge. It becomes increasingly evident how all finite things are measured by single, universal, and deterministic laws as the mind progresses towards more adequate knowl­ edge and generates new problems. Still, not even the sage can comprehend with the simplicity of divine knowledge. In the interest of benevolence and perfectibility, however, it is the duty of the human mind to struggle towards this end.

3 Priestley's epistemological writings reflect the influence of two clearly distinguishable traditions in eighteenth-century English philosophy. On the one hand, Newton's writings gave rise to the popular dictum hypothesis non fingo, according to which progress and success in natural philosophy and as well in all branches of intellectual endeavor lay in the abandonment and avoidance of hypotheses, conjectures, and speculations. The investi­ gator was to "induce" general laws from "particulars." 74 On the other hand, Lockean epistemology, which was in harmony with, though never directly related to, the Newtonian dictum, taught that the mind "comes naked into the world," having no innate ideas or principles. According to Locke all knowledge is derived from sense impressions and their associations and from ideas arising from them. 75 These two traditions tempered Priestley's strong rationalist view of knowledge by making him acutely aware of the brute fact of existence. 76 7 ^Priestley, Hartley's Theory of the Human Mind, on the principle of Association of Ideas With Essays Relating to the Subject of it, 2nd ed. (London, 1790), in Works, 3, 184-185. Subsequent references to "Priestley on Hartley," Works. 74 The sources of this tradition are to be found in L. L. Laudan, "Theories of Scientific Method from Plato to Mach: A Bibliographical Review," History of Sci­ ence, 7 (1968), 24-28. 75 For a discussion of the main features of Enlightenment epistemology see E. Cassirer, The Philosophy of the Enlightenment, trans. F.C.A. Hoeling and J. F. Pettigrove (Boston, 1962). 76 Although epistemological interests led him to be concerned with the systematic character of scientific knowledge, Priestley saw the central role of science as the pro­ duction of facts.

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Impressed by the achievements of their scientific contemporaries, eighteenth-century philosophers called for the application of the experi­ mental method to traditional philosophical problems. They sought general laws based on observation and experiment by which they could solve metaphysical, logical, epistemological, and psychological problems. 77 In this context, Priestley compared "moral philosophy" to "natural philoso­ phy": "By natural philosophy, we mean the knowledge of the external world, but by moral philosophy we mean the knowledge of the structure of our own minds, and its various affections and operations." 78 For Priestley, the observational basis for this "new science" lay in the realm of "introspective psychology." Because of his "psychologism," he tended to conflate logical and psychological relationships. This tendency is seen clearly in his distinction between "syllogisms" and "universal proposi­ tions," and in his attitude toward the roles of logic and language in the process of thinking. It is well known that natural philosophy also supplied the model of the mind for eighteenth-century philosophers. 79 According to this model, the mind is made up of simple ideas that correspond to atoms in the external world. The ideas continue in isolation or combine to form complexes analogous to natural bodies in the external world. This combination is achieved by a principle of union or cohesion analogous to a force of attrac­ tion. The use of this "principle of association" in considering mental phenomena is an important development in eighteenth-century English epistemology. The model, initiated by Locke and developed by Condillac and Hartley, is cfucial to an understanding of Priestley's theory of universal determinism and his conception of materialism. His "materialism of the mind" is important to his doctrine of the progress of knowledge from a less adequate to more adequate comprehension of the total unity of nature. 77 See, e.g., Priestley's "Introductory Observations" to "An Examination," Works, 3, 15-24. Here he applies the methods and concepts of his associationist psychology not only to the problem of the psychological development of the individual, but also to such diverse philosophical issues as the analytic/synthetic distinction, the relation between logic and thought, and the existence of an external world. 78 Priestley, Miscellaneous Observations Relating to Education more especially as it Respects the Conduct of the Mind (London, 1778), in Works, 25, 19. Subsequent references to "Education," Works. 79 See, e.g., John Locke, Aη Essay Concerning Human Understanding, ed. Alexander Campbell Fraser, 2 vols. (New York, 1959), 1, 145. Subsequent references are to Essay. David Hume, A Treatise of Human Nature, ed. L. A. Selby-Briggs, 1st ed. (London, 1955), pp. 12-13. Subsequent references are to this edition o{A Treatise. Gerd Buchdahl, The Image of Newton and Locke in the Age of Reason (London and New York, 1961), pp. 21-22.

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Priestley drew his philosophical inspiration mainly from the tradition of Lockean epistemology rather than from Newtonian methodology. He was conscious of his debt to Locke and Hartley; Locke's system, he said, suit­ ably modified by Hartley, "appears to me, and to others, to be the corner­ stone of all just and rational knowledge of ourselves." 80 Of all the philos­ ophers who had contributed to moral philosophy, Hartley was supreme; Hume and other moral philosophers lacked his insight into the working of the human mind. For Priestley, Hartley's "Doctrine of the Association of Ideas" supplied materials "for a satisfactory solution of Humean difficul­ ties." 81 Furthermore, where everyone else had seen diversity, Hartley had revealed an underlying unity, for it was his merit to have shown that "this single principle of association is the great law of the human mind." He thereby revealed as modifications of one principle what others regarded as the "independent faculties" of "memory, imagination, judgment, the will and the passions." Consequently, "we are what we are" by virtue of "this one property and the circumstances in which we are placed." 82 It was important for Priestley's admiration for Hartley that Hartley showed the qualities of "piety, benevolence, and rectitude of his heart," 83 placing him beyond the heights reached by other "Olympians" of the pe­ riod. So great was Priestley's admiration that he said of Hartley that he "has thrown more useful light upon the theory of the mind than Newton did upon the theory of the natural world." 84 The role of his writings in Priestley's intellectual development was second only to that of the Bible: "I think myself more indebted to this one treatise [Observations on Man] than to all the books I ever read beside, the scriptures excepted." 85 The source of eighteenth-century theories of the mind was Locke's Essay Concerning Human Understanding. 86 Of particular importance to Priestley was Locke's dismissal of the doctrine of innate ideas and his reduction of the contents of the mind to the combinations and permutations of simple ideas originating in experience. According to Priestley, "sensations" are the basic units of the mind; they are the mental outcome of the neural process which transmits the "impressions" that the "external world" makes 8 0 l l AnExamination," 8 1 "Philosophical

Mlbid.,

Works, 3 , 27. Unbeliever," Works, 4 , 368.

pp. 409-410.

8311 Disquisitions,"

Works, 3 , 92. Works, 3 , 26.

8 4 1 1 AnExamination," 85 Zfaid.,

p. 10. used the thirteenth edition which appeared in two volumes in 1748. Referenceshere are to the edition cited in note 79. 86 Priestley

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on our "sense organs" to the brain. "Recollected sensations" are "simple ideas," and observations on their interrelationships give rise to all other ideas in the mind.87 Locke's sensationalistic program was incomplete in two important re­ spects. First, he appealed to "reflection" as an introspective source, differ­ ent from "sensation," of ideas about the nature of mental processes. Furthermore, besides classifying the mind according to conceptual con­ tents, Locke classified it into faculties each of which characterized a spe­ cific kind of psychological activity. For Locke, these faculties were just as irreducibly simple as simple ideas themselves.88 The completion of Locke's sensationalistic program by Hartley and Priestley consisted in their rejec­ tion of "reflection" as a source of ideas different from "sensation" to­ gether with their reduction of the entire contents and activity of the mind to sensations and their "transformations."89 A concomitant of their sensationalistic program of reduction was a law governing the "transformation" of sensations. They derived their law from the "Doctrine of Association of Ideas," extending the mechanistic deter­ minism of the material world to the mental world. Locke used the "Doc­ trine of Association" to account for unreasonable behavior. He said that some ideas have "a natural correspondence and connection with one an­ other," and that natural connections are perceived by "our Reason" and are universally acknowledged. Sometimes, however, "ideas that are not at all a-kin" become united in some minds by mere "chance or custom"; they "are not ally'd by Nature," but are "associated" idiosyncratically in each mind according to differences in "inclinations, Educations, Interests, etc."90 It was the universalization of this 'principle of association' with its application

to

mental

operations

that

completed the program of

sensationalism. 87 Priestley's views on Lockean psychology are most fully discussed in "Introduc­ tory Observations" to "An Examination," Works, 3, 15-24, and in "Priestley on Hartley," Works, 3, 168-200. Locke, Essay, 1, Bk. II, Ch. VI, 159. Here Locke refers to the "faculties" of "understanding" and "will" as "simple ideas of reflection." 89 See E. Cassirer, The Philosophy of the Enlightenment (Boston, 1955), pp. 99100. Cassirer's discussion (pp. 100-108) shows that the reductionist program was completed in the works of Condillac, Hume, Voltaire, and Helvetius in a manner that contrasts sharply with Priestley's views. Whereas Priestley insists on reason as ex­ pressed in the mechanical association of ideas as the "dominating force in man," the former exhibit a "voluntaristic tendency" in their analysis of the cause and foun­ dation of knowledge in terms of the will and the passions. 90 Locke, Essay, 1, Bk. II, Ch. XXXIII, 527-535, especially p. 529.

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Hartley based his Observations on Man on the "Power of Association" together with the neurological "Doctrine of Vibrations." 91 This power is the general law according to which all our ideas and mental faculties are generated. Priestley defined the law: "the universal and simple law of as­ sociation being this, that two sensations, or ideas present to the mind at the same time, will afterwards recall each other. . . ." 92 Priestley en­ thusiastically and Hartley reluctantly perceived the deterministic con­ sequences of this law. It implied that "nothing is requisite to make any man whatever he is, but a sentient principle, with this single property [as­ sociation of ideas] (which, however, admits of great variety) and the in­ fluence of such circumstance as he has actually been exposed to." 93 Priestley's excursions into moral philosophy were based on the assump­ tion that personality was the outcome of the ordering and patterning of sensations according to the mechanical force of association. Together with his notion of the classificatory nature of natural philosophy, 94 this as­ sumption implied that moral philosophy classified the faculties of the mind according to "different modes or cases of the association of ideas" and analyzed all ideas into simple ideas or sensations. 95 Priestley was satis­ fied to give a short outline of the theory, referring readers to Hartley's Ob­ servations on Man for details. 96 It will suffice here to give a synopsis of Priestley's Hartleyian psychology without showing his full intellectual debt to his mentor. We will pay particular attention to Priestley's analysis of the understanding. Priestley and Hartley categorized the operations of the mind into the faculties of memory, imagination or fancy, understanding (Hartley) or judgment (Priestley), affections (Hartley) or passions (Priestley), and will, "to which may be added the power of muscular motion." 97 Their object was to show that the faculties were the diverse effects of the "law of as­ sociation" acting on a variety of "sensationalistic" raw materials. 91 See especially the first chapter of the first volume. A good account of Hartley's views is given in Basil Willey, The Eighteenth Century Background (London, 1940). 92 "Philosophical Unbeliever," Works, 4, 401-402. 93 "Priestley on Hartley," Works, 3, 184. Compare with Observations on Man, 1, vi, where Hartley speaks of the "reluctance" with which he belatedly recognized that the "doctrine of necessity" follows from that of association. 94 See pp. 395-397. 95 See "Priestley on Hartley," Works, 3, 183-196. 96 The main source of Priestley's views on Hartleyan moral philosophy is "Priestley on Hartley," Works, 3. There are also scattered fragments in "An Examination," Works, 3. 97 "Priestley on Hartley," Works, 3, 185. Observations on Man, 1, iii.

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Memory, according to Priestley and Hartley, involves the recollection of those ideas that are intimately associated with an idea present in the mind. In the process of remembering, the relations between the ideas are main­ tained "as they were once actually presented." 98 In imagination, no "new thoughts" are produced, only "new combinations of old simple ideas, or decompositions of complex ones." In neither memory nor imagination does an idea occur that does not have "a connection with some other im­ pression or idea previously existing in the mind. . .

The character of

the mind at one moment is, thus, completely determined by its content at a specifiable preceding moment. As Hartley put it, "every succeeding thought is the result either of some new impression or of an association with the preceding," 100 The affections, or passions, have "Pleasure and pains for their objects as the Understanding has the mere sensations and Ideas." 101 They excite us to pursue happiness and avoid misery. Priestley tells us that they are all modifications of fear and love and depend on the situation of the object of fear or love with respect to us. Fear and love are themselves not innate; they arise from the connection of disagreeable or agreeable feelings with a particular idea of a circumstance, the recurrence of which idea can recall the feelings by association. True to his deterministic program, Priestley looked upon volition as a modification of desire. Volition is generally fol­ lowed by those actions that have become associated with that state of mind arising from an awareness of the past success of such actions in the attainment of the desired object. Such voluntary muscular activity is mechanically evolved from the involuntary and random muscular activity of childhood by the effects of painful and pleasurable sensations on the nervous system. A painful sensation agitates the nervous system to produce muscular contraction resulting in a particular bodily movement; after a sufficient number of sensations of this sort, such movement will mechani­ cally follow the appearance of the source of pain. 102 Hartley broadly defines "understanding" as "that faculty by which we contemplate mere sensations and ideas, pursue truth, and assent, or dissent from propositions." 103 Priestley tends to employ the term "judgment" in­ stead of "understanding" and restricts its meaning to the recognition either 98 Observations on Man, 1, iii. See "Priestley on Hartley," Works, 3, 185. ""Priestley on Hartley," Works, 3, 185. l00 Observations on Man, 1, 383. 10 IObservations on Man, 1, iii. See also "Priestley on Hartley," Works, 3, 186-189. I02"p r i es tley on Hartley," Works, 3, 188. ^^Observations on Man, 1, iii.

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of a "syllogism" or a "universal proposition." Following his sensationalistic premises, he feels it necessary to isolate the origin of judgments in our "sensations." His approach is very sketchy and, in some cases, he is merely satisfied with claiming, without showing, the sensationalistic source of a given idea, presupposing his readers' familiarity with Hartley. Priestley considers the case of a baby existing in a kaleidoscopic reality of sights, sounds, tastes, smells, and touches. The baby experiences reality as a "whole," which "makes but one impression" on its "organs of sense, and consequently upon the mind." With time, order and pattern gradually emerge by the selective association of ideas to form the basic categories of experience. "Things" stand out by a process of abstraction from the vari­ able circumstances in which they occur. Although at first all parts of reality "are so intimately associated together, that the idea of any one of them introduces the idea of all the rest," eventually certain impressions are distinguished from others by their regular association: "these parts or properties that have never been observed asunder" are distinguished from their "variable adjuncts." Accordingly, the "idea of anything and its necessary inseparable properties. . . always occuring together is formed." 104 In this manner, all the complex ideas of the mind are constructed out of sensations. This process of "abstraction" gives rise to ideas of substance, mode, and relation. Ideas of moral right and wrong are similarly formed when the raw material of pleasure and pain are included in the domain of sensations. A consequence of Priestley's psychologism is his treatment of logic as a psychological theory which, together with language, he reduces to a useful, but not essential, role in the process of thinking. Following Hartley, Priestley describes propositions as verbalized judgments in which words de­ note ideas and arbitrary signs, or "copulas," are employed; words and signs acquire a use by virtue of the association of ideas. 105 Judgments are mental processes based on the "Association of Ideas" and are distinct from their verbal expressions: "Since propositions and reasoning are mental operations, and, in fact, nothing more than cases of the association of ideas, everything necessary to the process may take place in the mind of a child, of an idiot, or of a brute animal, and produce the proper affections and actions, in proportion to the extent of their intellectual powers." Priestley seems to regard judgments as nonreflective processes whereby ideas about the external world become related to each other according to 104"An Examination," Works, 3, 15. 1, 268-323.

105 ObservationsonMan,

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the association of ideas. For example, the experience of being burnt can give rise to the intimate association of the idea of fire with that of burning in the mind of any animal; a dog will spring back from a fire, indicating an apprehension based on such an association. His inability to verbalize his fear "in the form of regular syllogisms and conclusions" does not imply an inability to reason about the fire's effects. Although the dog lacks the words and the abstract idea necessary to assert the proposition that "fire has a power of burning," the "two ideas of fire and of burning are as intimately united in his mind as they can be in the mind of a philosopher, who has reflected upon his mental affections and is able to describe that union or association of ideas in proper terms."106 The union of ideas is the essence of reasoning, and it matters little for Priestley that men can express their judgments in verbal propositions. Philosophy facilitates the analysis and description of mental operations in the "doctrine of propositions and judgment," and is the "natural science" of the mind: "And as the doctrine of syllogism was deduced from observations on reasoning, just as other theories are deduced from facts previously known; so the doctrine of propositions and judgment was deduced from observations on the coincidence of ideas, which took place antecedent to any knowledge of that kind." Obviously, such knowledge is a very different thing from the operations themselves; it is "just as different as the knowledge of the nature of vision is different from vision itself." The relationship between the knowledge of mental operations and the operations themselves is that between a description and what it describes, between a scientific theory and its domain of enquiry. Obviously, such knowledge is irrelevant to the process of reasoning itself: "The philosopher only is acquainted with the structure of the eye, and the theory of vision, but the clown sees as well as he does, and makes as good use of his eyes." A consequence of Priestley's demand that philosophy become a mental science was, thus, the separation of logic and language from the process of reasoning. The latter is a natural phenomenon that exists independently of such human artifacts as logic and language. Propositions merely describe the various relationships between our ideas, and logic merely describes cer­ tain basic mental patterns that exist independently of our knowledge of them. "Words are of great use in the business of thinking, but are not necessary to it. In like manner, though the knowledge of logic is not with­ out its use, it is by no means necessary for the purpose of reasoning."107 l06"An Examination," Works, pp. 18-19.

107 Ibid.,

3, 18-19.

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A second consequence of Priestley's psychologistic approach to philoso­ phy was his classification of judgments by psychological rather than logical characteristics. Hume distinguished a priori and a posteriori truths by reference to their psychological origin rather than their logical status.108 Hartley and Priestley treated the problem in terms of empirical psychology, referring it to the discovery of "the natural ground of evidence or of the assent that we give to propositions of all kinds."109 In this way, they re­ duced the classification of judgments to a classification of the different psychological circumstances in which we are ready to affirm the truth of propositions. Priestley and Hartley considered all propositions as having the subject and predicate form whereby one term "is affirmed" of another. They dis­ tinguished between two kinds of "truth": "syllogism" and "universalprop­ ositions."110 In a "universal proposition" the subject refers to a thing, such as gold, and the predicate to one of its necessary, inseparable qualities, such as yellow. In the "syllogism" the "subject and predicate appear, upon comparison, to be in reality nothing more than different names for the same thing."111 He couched the distinction in psychological language: "the ground of our affirming one of these ideas of the other is either that when they appear to be in fact the same idea or perfectly to coincide, or else, that the one is constantly observed to accompany the other."112 Within his psychologistic framework, Priestley thus distinguished "truths of facts" from "truths of reason." Priestley's psychological classification of "judgments" harmonizes with his insistence on the "artificial" nature of "propositions and syllogisms." Thinking is the natural, mechanical process of the association of ideas, and propositions are man's artful summaries of such processes: "The idea of any thing, and of its necessary inseparable properties, always occurring together is the foundation of and supplies the materials for propositions, in which they are affirmed of one another and are said to be insepara­ ble."113 The ideas of "milk" and "whiteness," for example, which form the proposition "milk is white," are impressed on the mind at the same time to form a single complex idea without the help of such a proposition. 108 See

Hume, A Treatise, Pt. Ill, Sees. I and II. I09"philosophical Unbeliever," Works, 4, 328; Observations on Man, 1, 324-325. ""' 1 An Examination," Works, 3, 15-17; "Philosophical Unbeliever," Works, 4, 328-329; Observations on Man, 1, 325 and 329. 11111 AnExamination," Works, 3, 15. •^"Philosophical Unbeliever," Works, 4, 328. 11 ^ 11 An Examination," Works, 3, 15.

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To formulate a "universal proposition" is therefore to formulate a com­ plex idea as a proposition.114 It follows that a "universal proposition" re­ sults from the mechanistic process of the "association of ideas." Judgment is merely "inner perception," and as such it is "impossible but that we must judge of all things as they appear to us."115 By incorporating this "psychologistic" conception of "judgments" into his necessitarian frame­ work, Priestley attempted to distinguish "universal propositions" as "real knowledge" of nature and life from mere "opinions." It is apparent that Priestley advanced a prescriptive view of judgment in the guise of a descriptive classification of "judgments." As descriptive psychology, Priestley's account is plainly inadequate. The "psychological circumstances" of "assent" are various and varied, a fact that Priestley was painfully aware of when waging war on "prejudice." The above classifica­ tion should, therefore, be regarded as prescriptions by Priestley and Hartley about the nature of valid rational judgments in the light of their "sensa­ tionalism." For the moment, it suffices to point out that the psychologis­ tic approach led Priestley to present his epistemological prescriptions as a descriptive "natural science" of the mind.

4 Priestley was drawn into a public exposition of his epistemological and natural philosophical views in an attempt to offset the public impact of the Common Sense philosophy of Thomas Reid, James Beattie, and James Oswald,116 whose opinions were "the very reverse of those which I had learned from Mr. Locke and Dr. Hartley." Initially, Priestley failed to take them seriously and regarded their position as a piece of "amusing sophis­ try." Their growing public acclaim together with the consequences of their views for his religious publications led Priestley to give them serious con­ sideration and to attack "this new scheme of an immediate appeal to common-sense upon every important question in religion (and which superseded almost all reasoning on the subject)."117 Spurred on by a desire 114 Ibid.,

p. 18. 1 Letter to the Author of the Letters on Materialism and on Hartley's Theory of Mind (1777) in Works, 4, 128. 116 See Thomas Reid, An Inquiry into the Human Mind (Edinburgh, 1764). Subse­ quent references to An Inquiry. James Beattie, Essay on the Nature and Immutability of Truth, in Opposition to Sophistry and Scepticism (Edinburgh, 1771). Subsequent references to Essay. James Oswald, Appeal to Common Sense on Behalf of Religion, 2 vols. (Edinburgh, 1766). Subsequent references to 117 "An Examination," Works, 3, 4-5. 115 Priestley

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to defend the "rational basis" of religion, he published his Examination in 1774. This book was a collection of miscellaneous criticisms prefaced by a "preliminary essay" that formulated his basic epistemological position. Priestley referred the reader to his own "edition" of Hartley's Observations on Man, which appeared in 1775, and the "dissertations that I propose to prefix to it." 118 He hoped to "divert" the "more sensible part of the public" from the incoherencies of Reid and "to establish the true science of human nature" by facilitating the "study of Dr. Hartley's Theory." 119 After dismissing Reid, Priestley expected to draw attention to "what Dr. Hartley has done by following his steps," thus leaving the "dreams" of Reid far behind. 120 He found the path not "difficult and intricate" but simple and straightforward. Characteristically, Priestley disdained to delve into the "technicalities" of his philosophical position. He was not con­ cerned with the "amusements" of pure "metaphysics" but with their con­ sequences in "the regions of science, philosophy and life," using "philoso­ phy" in the broad sense of "morals" and "theology." Hence, he did not want to combat Common Sense philosophy as "a new method of explaining the manner in which we give our assent to self-evident propositions": in so far as they are "really self-evident," it "signified nothing in practice by what means we evince them to be so." But he was prepared to oppose the usurpation of "reasoning" by this "new power" in the "regions of science, philosophy and life." 121 The polemical context is valuable material for a detailed analysis of Priestley's "miscellaneous criticisms"; it also serves to highlight certain aspects and basic assumptions of Priestley's epistemolog­ ical and metaphysical outlook that must be understood for a full apprecia­ tion of his views on the nature and methods of natural philosophy. Common Sense philosophy was a reaction to Humean scepticism. Reid, the founder of the school, realized that the Humean "system of scepticism, which leaves no ground to believe any one thing rather than its con­ trary," 122 was the necessary result of a consistent development of the Lockean theory of ideas and knowledge. Hume's accurate reasoning left Reid with the "necessity to call in question the principles upon which it was founded, or to admit the conclusion." 123 He chose to replace the epistemological premises by new ones that would rescue "common sense" judgments from the abyss of scepticism. Reid attempted to dissolve scepticism with respect to such common i i s Ibid.,

p. 13. p. 27. 122 Reid, An Inquiry, p. V. l 2 0 Ibid.,

1 1 9 Ibid., 121 Ibid.,

p. 6.

p. 138. 12 ^Ibid., p. 5.

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sense beliefs as the existence of an external world, the uniformity of nature, and the existence of "real" causal relationships among phe­ nomena.124 Hume accepted "simple ideas" or "impressions" as the basis for knowledge. The mind "apprehends" these entities in their simplicity and perceives "agreements" and "disagreements" between them, which we call beliefs, judgments, or knowledge. Analysis of common sense proposi­ tions in Humean terms leads to the conclusion that they are not real knowledge since they lack rational justification. Although derived from experience, they merely express a belief or expectation that is habitual and nonrational.125 Reid argued that the problem would soon dissolve if knowledge and perception were viewed in different terms. Perception is not a simple matter of apprehension, nor do beliefs, judgments, or knowledge arise from apprehension. Judgment, not apprehension, is funda­ mental. Perception is not synonymous with sensation. Sensation is the oc­ casion of perception, which also involves belief and judgment. The mind is endowed with "original and natural judgments" which are involved in the very process of perception: "every operation in the very process of percep­ tion, implies judgment or belief, as well as simple apprehension. . . . When I perceive a tree before me, my faculty of seeing gives me not only a notion or simple apprehension of the tree, but a belief of its existence, and of its figure, distance, and magnitude; and this judgment or belief is not got by comparing ideas, it is included in the very nature of the perception."126 These "first principles" are the foundation of reasoning and science. To ask for proof is to misconceive their nature; they are constitutional, innate, instinctive. The term "common sense" is appropriate: although some ra­ tional beings may lack the ability to deduce conclusions from self-evident principles, all of them have the power to see self-evident "truths." In fact, this power defines a rational creature; it is "the inspiration of the Al­ mighty" and hence cannot be acquired by anyone who lacks it. "Deduc­ tive" ability, however, can be learned.127 The "first principles" contain necessary truths such as the axioms of logic, mathematics, morality, and metaphysics. They contain such contingent truths as "the existence of an external world" and "the uniformity of nature," both of which had been attacked by Hume.128 These views became the framework for the works of Reid, Beattie, and Oswald. 1J 4?ee, e.g., Thomas Reid, Essay on the Intellectual Powers of Man (Edinburgh, 1785), Chs. IV and VI. Subsequent references to Essay. 125 See, e.g., Hume, A Treatise, p. 170. 126 Reid, An Inquiry, p. 532. 127 Reid Essay, p. 556. Ibid, pp. 587-593 and 603. 1

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Reid's approach to the Humean problems of the existence of an external world and the uniformity of nature was a chief target of Priestley's Exami­ nation. Priestley's attack pointed to aspects of his epistemology, which he also emphasized in his more general remarks on the Scottish philosophers. In the process, he revealed his "universal rationality" and concomitant lack of "Humean scepticism." His remarks also revealed the general intel­ lectual outlook which led him to call Reid's appeal to "common sense" a distortion of the nature of truth, a threat to human liberty, and a possible encouragement to religious dogmatism and political authoritarianism. Priestley claimed that Common Sense philosophy distorts the essence of truth as formulated in Locke's theory of judgment. Locke based the truth of propositions upon the "perception of the agreement or disagreement of any ideas" and thus made "truth to depend upon the necessary nature of things, to be absolute, unchangeable and everlasting."129 By contrast the Common Sense philosophers referred the truth of a proposition to a dis­ position to believe or disbelieve it. 130 Priestley would not have objected if they had merely asserted "the existence of self-evident truths and the ne­ cessity of assuming them as the foundation of all reasoning." But they wished to make particular propositions into axioms because of "some un­ accountable, instinctive persuasion" to believe them. This persuasion is an instinctive matter "depending upon the arbitrary constitution of our na­ ture."131 Beattie argued that "a creature of a different nature from man" could ascribe different properties to the same object, as, for example, blackness, instead of whiteness to snow.132 In which case, all that can be said to such a creature is that what "in regard to your faculties be true" is "in respect of my faculties" false.133 Thus truth would come to depend on the faculties of the individual. Priestley injected overtones of complete relativism into this doctrine by concluding that "[to me] this doctrine ap­ pears to be entirely subversive of all truth; since speaking agreeably to it, all that we can ever say is, that certain maxims and propositions appear to be true with respect to ourselves but how they may appear to others we cannot tell; and as to what they are in themselves, which alone is, strictly speaking, the truth, we have no means of judging at all; for we can only see with our own eyes, and judge by our own faculties, or rather feelings." 1

A n E x a m i n a t i o n , " Works, 3, 70. is referring to Beattie in particular. See, e.g., Beattie j Biiay, p. 210. 131 "An Examination," Works, 3, 70-71. 132 Quoted by Priestley in "An Examination," Works, 3, 72. 133 See Beattie, Essay, p. 205. 130 Priestley

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Common Sense doctrine admits of no recourse to argument and discussion but encourages a man "to pronounce decisively upon every question ac­ cording to his present feeling, and persuasion; under the notion of its being something original, instinctive, ultimate, and uncontrovertible, though if strictly analysed, it might appear to be a mere prejudice, the offspring of mistake."134 Beyond doubt Priestley misunderstood the Common Sense views on the character and content of sensation. Common Sense philosophers argued that sensation did not support the traditional doctrine of primary and secondary qualities with its associated metaphysics.135 Priestley, missing their intentions, substituted his own view of sensation with its conceptions of progress from less to more adequate knowledge and of the equality of sensations. Priestley closely identified the content of the sensory with the concepts that are applicable to it, making judgment a form of perception. If the mind is passive, as Priestley assumed, and judgment is a form of per­ ception, then thought is a natural product of the laws of association. The resulting similarity of the contents and modes of conceptualization of the sensories of different individuals does not allow for the subjective relativism that Priestley perceived in the Common Sense position. Priestley's view of sensation has important epistemological consequences. Since the human sensory and its modes of conceptualization do not premediate the content of sensation, progress in knowledge is merely a matter of universalizing the scope of experience. As the mind comes to know more facts of nature, it may become possible for it to establish more general and, thus, more adequate laws. Sensation is essentially involved, therefore, in the progress from less to more adequate knowledge. In this way, Priestley linked his epistemology of sensation to his determinism by increasing the lawful con­ nections in nature. Priestley's dichotomy between truth based on the "necessary nature of things" and a "persuasion" that "might appear to be a mere prejudice, the offspring of mistake" was incorporated into a system of thought the key to which is the conception of "natural necessity." He thereby accused Reid of unnecessarily introducing scepticism when he had meant to com­ bat Humean scepticism. In his eagerness to find "independent arbitrary, instinctive, principles," Reid had overlooked "the most necessary connec134"An Examination," Works, 3, 71-72. 135 See P. M. Heimann and J. E. McGuire, "Newtonian Forces and Lockean Powers: Concepts of Matter in Eighteenth Century Thought," Historical Studies in the Physi­ cal Sciences, 3 (1971), 233-306.

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tions of things." Similarly, Priestley believed that in his criticism of the inductive principle as rationally unjustifiable but instinctively valid Reid had failed to see "the most closely connected chain of reasoning" and had been too eager to supply the supposed missing link, not with another link, but with "some invisible power."136 Overlooking the claims of natural necessity can only result in arbitrari­ ness, confusion and scepticism. In the same vein, Priestley went on to dis­ agree with Hume. As Hume wished to dissolve natural necessity in man's expectations, and Reid to replace it by instinctive principles, so Priestley wished to preserve it so as to save the autonomy of his conception of ra­ tionality. In Hume's thought, rationality led to scepticism and distrust of the adequacy of observation and experiment. Priestley argued that truth and certainty can be attained with the traditional tools of the rationalist. Truth, certainty, and goodness in life are guaranteed by the metaphysical, theological, psychological, and moral implications of his concept of "nat­ ural necessity." Having already related Priestley's theological and moral ideas to his Necessitarianism, it is now appropriate to consider the con­ sequences of this doctrine for his epistemology. Necessitarianism served Priestley as a justification of rationality. To clarify his position we need to examine the epistemological aspects of his conception of "judgment." Priestley accepted Locke's definition of judg­ ment as "the perception of the agreement or disagreement of any ideas present to the mind." He used Locke's definition to argue that judgment is a form of "inner perception." In perception, the mind is passive, the process is "mechanical," and the content is completely determined by ex­ ternal objects. In the process of judgment the mind is also passive. The mind is presented with the "agreement or disagreement of any ideas" in the same way as it is presented with external objects in perception. Any act of judgment is as "necessary and unavoidable" as the content of any perception. Consequently, it is "impossible but that we must judge of all things as they appear to us." Variations in judgments are due to variations in appearances from one individual to another and in the circumstances under which things appear to different individuals.137 Defining knowledge in terms of mechanical recognition, Priestley needed to distinguish be­ tween those relationships which may yield varying judgments because they are the outcome of individual education and environment and those which 136 "An

Examination," Works, 3, 58. Letter to the Author of the Letters on Materialism and on Hartley's Theory of Mind (1777) in Works, 4, 127-128. 137 Priestley,

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yield "real knowledge." The method Priestley devised to make such dis­ tinctions made use of his conceptions of rational judgment and natural necessity. It was a method of enquiry that distinguished between "prej­ udices" which "arise from what are commonly called false views of things, or improper associations of ideas" and "just knowledge" which results from "a just view of things."138 To pursue this method was to be rational. It also guaranteed absolute truth because its results arose from the "neces­ sary nature of things."139 In his "psychologist" analysis of the nature of judgment, Priestley had incorporated Hartley's views on the "Nature of Assent" in his discussion of rationality.140 Priestley also gave a definition of rationality shorn of these psychologistic overtones. In 1774, he said: "To prevent all mistake of my meaning, I shall here observe that a proposition may be said to be proved by reason when a third term is necessary to show the connection between the subject and predicate of it; and that a general proposition is proved by an induction of a sufficient number of particulars which are comprized in it."141 Again, the influence of Hartley is evident; Hartley had said: "Coincidence in mathematical Matters, and Inductive in others, where-ever they can be had, must be sought for as the only certain Tests of Truth."142 The first kind of proof is used in mathematics and syllogisms. Ignoring the philosophical difficulty of generalizing from "many" to "all," Priestley included judgments of substances, modes, and causal relationships among universal propositions. The "proper proof" of a universal proposition is a proof by "induction of particular facts, of precisely the same nature." Argument by "induction" involves the use of a "universal proposition" to predict the same result of some "future circumstances" which are the same as those delineated in the proposition. Argument by "analogy" as­ serts that the outcome of circumstances slightly different from those de­ tailed in the "universal proposition" will be the same as the outcome delineated in it.143 Naturally, Priestley recognized the analytic nature of syllogisms. In his own words, such propositions "if they be true at all, are universally or 1 38 "Phi)osoph i(;;il Unbeliever," Works, 4, 327; "An Examination," Works, 3. 139 "An Examination," Works, 3, 70. 140 See "Of Propositions and the Nature of Assent," Observations on Man, 1, 324367. 141 "An Examination," Works, 3, 125. 14 Zlbid., p. 343. 143 See, e.g., "An Examination," Works, 3, 15-17.

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necessarily so, and the evidence for them is called demonstration."144 However, mathematical truth was not Priestley's primary concern. Rather, his rationalist method was designed to avoid error and prejudice in estab­ lishing the truth of the material world. Given his notion of truth, the con­ clusions reached by judicious observation and generalization had to be necessary, universal, and permanent. If certain "properties" are always found together in an "object," Priestley concluded "that those circum­ stances are necessarily united, though by some unknown bond of union and that they will always be together." Similarly, if the same events always follow the same circumstances, the mind expects the same sequence of events in the future and "can have no more suspicion of a different event, than we can separate the idea of whiteness from that of the other proper­ ties of milk." "Universal propositions" express the "class of truths" in which "there is a universal, and, therefore, a supposed necessary connec­ tion between the subject and the predicate."145 Priestley's psychologist language tends to obscure the meaning of his claim about the meaning of universal propositions. It is difficult to decide whether he is referring to logical necessity, natural necessity, or an un­ avoidable psychological response to certain experiences. However, in de­ fending his position in the course of an attack on Hume, he distinguished between the three possibilities and clarified his position. In drawing out the full consequences of the sensationalist premises laid down by Locke and Berkeley, Hume's analysis of causality shook the foundations of eighteenth-century natural religion. Priestley, too, was moved to a concern about the possible atheistic and sceptical consequences.146 On a number of occasions, he gave a definition of causation that was based on the epistemological premises he shared with Hume and in which he applied the principle of association to mental atoms or ideas. In 1767, Priestley said, in the language of Hume's second definition: "One of the most intimate of all associations in the human mind is that of cause and effect."147 But he was troubled by Hume's view that there is "no absolute nor metaphysical relationship" between cause and effect. By equating rationality with de­ ductive inference, Hume had denied the rationality of causal and inductive arguments. Causal relationships are totally dependent on the "constant conjunction" of the autonomous objects involved and the mental habit or 144"phUosophical Unbeliever," Works, 4, 329. 145 "An Examination," Works, 3, 15-16. 146 See the preface to "Philosophical Unbeliever," Works, 4, 317-325. 1 4 7 Electricity, p. 441.

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"custom" which "determines the imagination to make a transition from the idea of one object to that of its usual attendant."148 Priestley sometimes gives the impression that he agrees with Hume: "In viewing the works of nature, we necessarily become first acquainted with appearances, or effects. We naturally attend to the circumstances in which such appearances always arise and cannot help considering them as the cause of these appearances."149 However, his psychologism is misleading. He denied that the subjectivist interpretation of causality fully accounts for the relationship. Elsewhere,150 where he was concerned more with meta­ physical than methodological issues, he vigorously opposed Hume's analysis of causality. He did so as a Christian and a rationalist: Hume's criticisms undermined rational religion and set unwarranted limitations to a rational knowledge of nature. In anti-Humean arguments scattered throughout a number of his theological treatises, Priestley set out to dispel the "apprehension" felt in religious circles as a consequence of Hume's philosophy.151 Hepresented Hume as the archsceptic and dealt with him accordingly. Hume's descrip­ tion of connections between ideas as "arbitrary" and of arguments from cause to effect as not "properly reasoning" but based on "the principle of habit or custom"152 had overtones for Priestley that the more philosoph­ ical Hume would not have intended.153 The significance for Priestley of such pronouncements as "arbitrary," "no proper reasoning," and "custom" can only be understood when these terms are studied in the context of Priestley's epistemological polarization of truth and prejudice. Priestley thought that Hume's "subjectivisation" of necessity in causal relationships equated them with human whim and prejudice and removed them from the realm of rational arguments and true reasoning that reflects connec­ tions of things in nature. He found untenable this reduction of causal argu­ ments to "an arbitrary and perhaps ill-founded, association of ideas." Fired 148 Hume,

A Treatise, pp. 170-172. p. 442. iso Ibid., p. 170. 151 "Philosophical Unbeliever," Works, 4, 398. ls2 Ibid., pp. 398 and 403. 153 Although Hume refers the ideas of causal necessity to "custom," he nevertheless insists that such mental habits are based on objective relations. Claiming that "con­ stant conjunction of objects determine their causation" he advocates "some general rules, by which we may know" when they really are causally related (Treatise, p. 173). Priestley, equating "custom" with "prejudice" or "whim," overlooks this aspect of Hume's thought and sees his reduction of causal necessity to "habit" as a reduction of causal relations to an "arbitrary . . . association of ideas." 14 ®Electricity,

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with a concern for truth and certainty, he set out to rescue the causal principle from the destructive grasp of the sceptic and to justify the asser­ tion that "in whatever manner we come by the idea of power or causation, it is an idea that all men have and corresponds to something real in the rela­ tion of the things that suggest it." In his first argument Priestley defined a necessary connection by refer­ ence to a theoretical framework: "When we say that two events, or ap­ pearances, are necessarily connected, all that we can mean is that some more general law of nature must be violated before those events can be separated." He rejected Hume's view of the necessary connection in causal relationships as a mental transition arising out of the accustomed union of the objects involved. It is true, Priestley admitted, that a causal relation­ ship is ascribed to two constantly correlated events: "For example, I find that the sounding of one musical string will make another string that is unison, etc. with it, to sound also, and finding this observation invariable, I call the sounding of the first string the cause, and that of the second the effect, and have no apprehension of being disappointed in my expectation of the consequence." However, the correlation does not entail the necessity of the conjunction. Necessity only enters when the natural law governing such a conjunction is discovered. Thus, in this case, the conjunction is made necessary when "I discover that sound consists of a vibratory mo­ tion of the air, and that the air being put into this vibratory motion by the first string, communicates the same to the second by its pulses, in the same manner as the first string itself was made to vibrate." In other instances of constant conjunction, such as the interaction between a magnet and iron filings or the phenomenon of falling bodies, we can only observe the corre­ lation without being able to give any "satisfactory reason" for it. How­ ever, the discovery of laws governing other similar correlations provides "an invariable experience in favour of some real and sufficient cause in all such conjunctions."154 Priestley's criticism shows that Hume's thesis of constant conjunction does not allow sufficient analysis of causal relationships. Something more is required before we can assert a necessary causal relationship between two events; for Priestley this is a theoretical context. Yet, Priestley also held that "natural necessity" could not be completely explained by a theoretical context. To his conception of psychological necessity, Priestley now added a deterministically conceived necessity in nature. Necessity is not attributed to any instances of constant conjunction until nature's 1

^"Philosophical Unbeliever," Works, 4, 399-404.

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mechanisms underlying such conjunctions are made intelligible. Ultimately, all comprehension of reality must follow from "adequate" knowledge of universal determinism. Nevertheless, Priestley is prepared to waive the re­ quirement of context and grant the sufficiency of constant conjunction alone for the ascription of necessity to nature: "Indeed, without having made any discovery at all, we could not but be sensible, that if two events always follow one another, there must be some sufficient reason for it."155 Priestley's psychologist approach to philosophical problems, apparent in his tendency to link psychological and logical arguments in the assertion of "natural necessity," becomes explicit in his discussion of the source of the idea of causation. Priestley saw the difficulties with Humean analysis arise from the opinion that "cause" or "necessary agency" is a simple idea, "or what could originally have been formed in the mind by the perception of any two other ideas." The illusion of a simple idea is soon dispelled when it is realized that the "necessary agency" is an abstract idea which "repre­ sents the impression left in the mind by observing what is in common to numberless cases in which there is a constant conjunction of appearances or events, in some of which we are able to see the proximate cause of the conjunction but with respect to the rest we only presume it from the similarity of the case."156 Although agreeing with Hume that all ideas are derived from impressions, Priestley set out to show that the impression of causal power is not created by a "determination of the mind" but by the properties of bodies pre­ sented to the mind. He argued as follows: volitional, bodily, and mental activity—the ability to change a situation at will—gives rise to a general feeling called power, "which is the result of a thousand different impres­ sions" in the mind of a child. Observations of others doing similar things lead the child to ascribe the same power to them. By noting the "invariable effects" of "inanimate things" in certain situations, the child obtains " the idea of power, universally and abstractedly considered."157 Thus, man ob­ tains the idea of power in the same way as that of any other property common to a number of bodies; namely, by abstraction. Priestley distinguished between the necessity of "universal propositions" and that of syllogistic arguments. In logically true propositions, necessity implies that their denial is self-contradictory. Priestley knew that this was not so for universal propositions; their necessity differed in modality from iss Ibid., 156 Ibid.,

p. 403. p. 404.

157"Priestley on Hartley," W o r k s , 3 , 191.

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logical necessity. Priestley rebuked Oswald, who, referring all modalities to the principle of Common Sense, said that it "is nonsense to expect that lead should swim in water." The "generality of philosophers," Priestley claimed, would find such language inappropriate. They would show by ob­ servation and experiment that "nothing of this kind has ever happened" and would hence claim to have proved that "the expectation of its happen­ ing was very unreasonable, but would think it a strange abuse of words to call it nonsensical." Only ideas "such as are inconsistent with one another" are attached to the term "nonsense" whereas "we can form as clear an idea of lead not sinking in water as of its sinking." Priestley summarized the contrast between the two modalities thus: "What is really nonsense can never become sense; but by miraculous powers the laws of nature can be suspended or reversed." 158 "Universal propositions" acquire their neces­ sity by expressing permanent relationships among ideas which are, in turn, the outcome of deterministic laws governing nature. Priestley's conception of "natural necessity" can only be fully illumi­ nated by an examination of his conception of natural "powers" or "general principles." Such an examination leads to a formulation of the metaphys­ ical foundations of his chemical concepts. Priestley used the term "general principles" in a way different from the sensationalist nominalism which he inherited from Berkeley and Hume. According to them, "nature exhibits nothing but particulars," and there exist in nature no "physical causes" or "active powers"; there are only the regularities observed among sensations. As Priestley pointed out, it follows from this that "all general propositions as well as general terms are artificial things." 159 Although the view that nature is comprised of particulars excludes the "signification" of general terms, Priestley was far from happy with this conclusion. But Priestley was not consistent in his use of the terms "general princi­ ples" and "principle." He sometimes uses "principle" as a linguistic en­ tity, 160 but he also uses it to refer to an unknown cause of a known effect, making it an expression for a scientific unknown. For example, inflam­ mability and gravity are well-known properties of bodies. The former may, according to Priestley, be "caused by the presence of a real substance called phlogiston," it may arise from the structure of the inflammable sub­ stance, or both properties may be caused by an ether. Until the physical nature of the cause is determined, the word "principle" is used to denote 158"An Examination," Works, 3, 127. 159 See Electricity, pp. 441-442. 160 See, e.g.,Air, 3, 323;Natural Philosophy, 3, 401.

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the unknown cause of a known effect: "Thus, whatever be the real cause of gravity, or of inflammability, we may speak of the principle of gravity, or of inflammability." 161 However, Priestley persisted in his use of the term "principle" even when he was satisfied of the physical nature of the cause of an effect. For example, though he was convinced of their status as substances, he continued to speak of the "acidifying principle," the "alka­ line principle," and the "principles of heat, light, and electricity." 162 Priestley's "principles" are "physical causes" or "powers" operating in nature. He made this clear when, contradicting his nominalistic premises, he defended the use of "abstract general concepts" in comprehending nature because "we actually see in nature a vast variety of effects proceed­ ing from the same general principles, operating in different circum­ stances." 163 He appears to have had in mind such "principles" as "associa­ tion," "gravity," and "electricity." 164 In one of his last publications, he calls the "adaptation to each other" of "powers" such as "those of elec­ tricity, and magnetism, etc." an indication of "design" in the universe. "Principle" and "power" are thus used synonymously by Priestley to refer to causal agents deterministically operative in nature. This ontology of "principles" or "powers" enabled Priestley to assert that "universal propositions" will be a source of necessary and permanent truth about the material world. The process of forming an appropriate "ab­ stract general idea" (which is expressed in a "universal proposition") leads to the abstraction of the common property in a given situation by virtue of its being an instantiation of a "generic principle." Thus, Priestley refers to the "single property" of association as if it were a quality possessed by each and every idea. 165 He held this to be the case for "universal proposi­ tions" concerning substances and their generic properties, as well as for those pertaining to causal relationships. 166 Priestley thus attempted to 161 Priestley, Heads of Lectures on a course of Experimental Philosophy, particu­ larly including Chemistry, delivered at the Neu> College in Hackney (London, 1794), pp. 4-5. Subsequent references to Heads of Lectures. l6 ^Ibid., pp. 8-9. 163 Electricity, p. 442. 164 See "Priestley on Hartley," Works, 3, 185. 165 See "Priestley on Hartley," Works, 3, 180. Here he says that the "single property [of association] comprehends all the other affections of our ideas, and thereby accounts for all the phenomena of the human mind, and what we usually call its different operations, with respect to sensations and ideas of every kind." Given Priestley's reductionist theory of the mind, "association" is not only a generic prop­ erty of ideas, but their only property. This is the sense to be attached to Priestley's use of the term "single property," as opposed to "general property," in this instance. 166 "An Examination," Works, 3, 16.

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make the idea of "active power" or "physical cause" in nature compatible with his sensationalism by claiming that the "abstract general idea" of "cause" or "power" represents a property common to all causal situations. To clarify Priestley's conception of generic principles, a further digression into his discussion of "causality" is imperative. Priestley's discussions of "causality" are beset by a conflation of the "substantive (generic) concept" with the "relational concept." 167 Use of the former implies that the causal agent is found by abstracting the common element from similar situations; use of the latter means establishing a causal relationship be­ tween "particulars" in a given situation by placing them in a definite rela­ tion to a "general law." In Priestley's thought, the former is a residual of Aristotelianism in the logic of the "phlogiston theory," and the latter de­ rives from Humean "causal terminology." The latter concept dominates Priestley's many discussions of the nature of causality, but it is essential to see the substantive overtones to fully understand his scientific conceptual­ ization and its metaphysical grounds. Indeed, Priestley's conception of "general principles," "powers," and the action of God in the universe can only be understood in terms of the substantive concept of causality. Moreover, Priestley's use of the substantive concept provides the only interpretation that does not conflict with his doctrines of materialism and determinism. If Priestley's version of the Humean definition of causality is to be fruit­ ful for an analysis of the universality and generality of scientific explana­ tion, it has to be expressed in terms of the relation of the "whole to the parts." 168 The parts receive their identity according to the identity of the whole. To conceive of an appearance "causally" is to subsume it "under 167 The distinction draws on the impressive analysis of the concept in E. Cassirer, Substance and Function (New York, 1953). The reader is referred to this text for an analysis of the way in which modern developments in mathematical and scientific knowledge demanded a complete revolution in the logic and psychology of concept formation. According to Cassirer, "the logic of the generic concept" (Aristotelian) had to be replaced by the "logic of the mathematical concept of function" (relational concept) in order to achieve an adequate explication of the foundations of scientific conceptualization. 168 We do not claim that Hume himself was aware of this requirement. He, as much as Priestley, appears to have conflated the substantive concept of causality with the relational concept. However, as pointed out by W. R. Grove in the nineteenth cen­ tury, the Humean reduction of (objective) causation to "constant conjunction" is in­ compatible with the "substantive concept." It has to be developed within the logic of the "relational concept" which reduces causality to "universal lawfulness" (see Cassirer, Substance and Function j p. 226n). See also note 175 below.

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general laws" that define the "complex" of events ("circumstances" and "appearances") to which it belongs. Such a viewpoint is at odds with Priestley's statement that the aim of science is to note "the whole effect of all the separate circumstances and situations of things" so as to "judge of their effect in all possible combinations." 169 The statement presupposes a one-to-one correspondence between a "circumstance" and an appearance such that the former is in relation of "contiguity and precedence" to the latter in all instances of its occurrence. Here Priestley has expressed the "substantive concept" in language that is only appropriate to the "rela­ tional concept." Since he considered a cause to be a physical "principle" rather than, a "circumstance," Priestley naturally considered it responsible for the same effect in diverse circumstances. 170 This is intelligible from the Aristotelian viewpoint in which the abstraction of the common element of things constitutes their real form, which is both their efficient and teleological cause. The logical relationship of genus to species indicates how the real "substance" unfolds itself in the special forms of being. The complete system of scientific definitions would give the substantive forces that con­ trol reality. 171 To establish a causal agent in terms of an Aristotelian conception of things is not to delineate the necessity of events in space and time, but to determine that element of a situation that characterizes and determines the "whole." Aristotelian logic underlies the phlogiston theory, which "conceives the element as a generic property belonging to all mem­ bers of a definite group and determining their perceptible type." 172 In spite of the Aristotelian logic of the phlogiston theory, Priestley still conflated the "substantive concept" with the "relational concept" of causality in his discussion of phlogiston as the cause of inflammability. In 1794, for example, he asserted that "the union of phlogiston to a particu­ lar kind of earth is the cause of its becoming a metal." 173 Phlogiston as the cause of inflammability is defined as a "relational concept"; i.e., it is de­ fined in terms of those "circumstances" in which a metal is produced from its "earth." Priestley went further: he tried to identify phlogiston with "inflammable air," but failed. 174 This is not surprising: since phlogiston is x6 ^Electricity,

p. 443. Cassirer, Substance and Function, pp. 204-205. 172 Ibid., p. 205. 173 Heacis of Lectures, p. 3. !" jl Ibid., pp. 4-9. 174 Priestley attempted to make the identification of phlogiston with inflammable air in "Experiments and Observations relating to Phlogiston and the seeming conver­ sion of Water into Air," Philosophical Transactions, 73 (1783), 398-434; reprinted in Natural Philosophy, 3, 1-169. However, he soon rejected this suggestion in "Experi­ ments and Observations relating to Air and Water." Philosophical Transactions, 75 (1785), 279-309; reprinted in Natural Philosophy, 3, 70-124. 170 See

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the "principle of inflammability," it has to be considered as "generally" the cause of inflammability. This is incompatible with the "relational con­ cept" of causation. For if "we regard causation as invariable sequence, we can find

no case in which a given antecedent is the only antecedent to a

given sequent," and thus there is no "abstract causation."175 In Priestley's statement about phlogiston, the "particular" earth can combine with a variety of substances to produce its metal. Hence, phlogiston cannot be identified with one of these inflammable substances and still be regarded as the "principle of inflammability." It is generic principle and as such is invariably present through varying circumstances. Priestley gave this in­ terpretation of phlogiston in 1786, when he claimed that "there is a prin­ ciple capable of being transferred to other substances, which, when united to the calces of metals, makes them to be metals and which, united to the oil of vitriol (deprived of its water) makes it to be sulphur."176 Phlogiston inheres in inflammable bodies and "makes" them manifest their peculiar properties. Priestley based most of his "chemical speculations" on the logic of the "substantive concept." In 1794, he suggested the possibility of an explanation of "all the appearances that have yet occurred to us" in terms of "dephlogisticated air, or the acidifying principle; phlogiston, or the alkaline principle," a variety of "earths," and the "principles" of heat, light, electricity, attraction, repulsion, and magnetism.177 He admitted that none of these "principles" was identifiable with known substances that could be isolated.178 Priestley's views on "principles" and "powers" in nature have significant theological dimensions which are clarified in his discussion of the regula­ tive principle of simplicity in natural philosophy. Simplicity of nature is to be expected because the diverse "effects" of nature are the product of the simplicity and immutability of God. Priestley held that in the study of nature we are "first acquainted with appearances, or effects," caused by "the circumstances in which such appearances always arise." These "causes" are themselves "effects," caused in turn by their conjoint "cir­ cumstances": "Thus, constantly ascending in this chain of cause and effects, we are led, at last, to the first cause of all; and then we consider all

175 W.

R. Grove, The Correlation of Physical Forces, 4th ed. (London, 1862), p. 12. Philosophy, 3, 425-426. l l l Heads of Lectures, pp. 8-9. 178 See, e.g., ibid., pp. 8-9; Priestley, "On Red Precipitate of Mercury as Favourable to the Doctrine of Phlogiston," New York Medical Repository, 2 (1799), 154-155; "Objections to the Antiphlogistic doctrine of Water," New York Medical Repository, 2 (1799), 156-157. l l 6 Natural

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secondary and inferior causes, as nothing more than the various methods in which the supreme cause acts, in order to bring about his great de­ sign." 179 It would be a mistake to interpret this statement in terms of Priestley's Humean conception of causality which served to emphasis the necessity of events in space and time. While Priestley was concerned with the necessity of events in space and time, the "ascension" of the causal ladder referred to here is essentially an ascension "from particulars to general." 180 It is an ascension from the "particularity" of the "effects" in nature, conceived in nominalist terms, through the generality of "generic principles" to the "universality" of God's simple and immutable action. It is important to realize that Priestley does not restrict God's action to that of a "First Cause" in the temporal sense. God maintains the universe. This view, as Priestley pointed out, harmonizes with the "Scriptures," according to which the "Divine nature" is "every where present, constantly supporting, and, at pleasure, controlling the laws of nature." 181 Every cause is a "proximate cause." 182 The real cause is God's action. Priestley borrowed Pope's words contrasting "human works" with God's: with human beings "a thousand movements scarce one purpose gain," in nature, "one single can its end produce." 183 Behind the "particularity" of appearances there operate "generic prin­ ciples." In a paper written towards the end of his life, Priestley made it clear that it is through their interrelatedness, i.e., through the interrelatedness of the "powers" in nature which have their source in God, that design manifests itself. He wrote: Dr. Darwin speaks of his organic particles as possessed of certain appertencies, or powers of attraction. But whence came these powers, or any others, such as those of electricity, magnetism, etc.? These powers discover as much wisdom by their adaptation to each other, and their use in the general system, as the organic bodies which he supposes them to form; so that the supposition of these powers, which must have been imparted ab extra, only removes the difficulty he wishes to get quite of one step further, and there is left in as much force as ever. There are still marks of design, and, therefore, the necessity of a designing ccm.se. 184 1 7 9 Electricity,

l s o Ibid., p. 442. pp. 441-442. Works, 3, 301. 182 See, e.g., "Philosophical Unbeliever," Works, 4, 404. 183"p r i es tley on Hartley," Works, 3, 184. 184 Priestley, "Observations and Experiments relating to equivocal, or spontaneous Generation," American Philosophical Transactions, 6 (1809), 129. 181 "Disquisitions,"

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A few years earlier, Ke had claimed that all known "appearances" can be explained by a few principles: As there will be frequent occasion to speak of the component and elementary parts of all substances, I shall here observe that according to the latest observation, the following appear to be the elements which compose all natural substances, viz. dephlogisticated air, or the acidifying principle; phlogiston, or the alkaline principle; the different earths, and the principles of heat, light, and electricity. Besides these, there are the following principles which have not been proved to be substances, viz. attraction, repulsion, and magnetism. By the help of these principles, we are able, according to the present state of natural knowledge, to explain all the appearances that have yet occured to us. 185 The ultimate source of these "powers" or "generic principles" then lies in God's action. 186 Following his "substantive logic," Priestley conceived of natural philosophy as a hierarchical system of natural laws culminating in "one great comprehensive law." Just as "all the varieties of languages" in the world are reducible to a "short alphabet," so contemporary scien­ tific progress indicates that the complexities and varieties of natural phenomena can be reduced to "simple and general laws." In fact, Priestley went on to assert that "it does not appear impossible, but that, ultimately, one great comprehensive law shall be found to govern both the material and the intellectual world." 187 His words justify the interpretation that he regarded such "a great comprehensive law" as elucidating the operation of the "first cause of all," and that he thought of the hierarchical system of "general laws" as the unfolding of God's simple and immutable action in the "special forms of being."

5 A comprehensive treatment of Priestley's rationality and, consequently, of his philosophy of science and the nature of his objectives and achieve­ ments in natural philosophy requires discussion of the issues that his rationalist program was meant to attack. Designed to discover the "truth," his program was to eliminate prejudice, dogma, and superstition, and to i ^ s Heads

of Lectures, pp. 8-9. "Institutes," Works, 2, 15, where he says that "all the powers of nature . . . can only be the effect of the Divine energy perpetually acting." I 8 7 t i Priestley on Hartley," Works, 3, 185. l i i 6 See

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oppose the forces of authoritarianism with the spirit of liberalism. The program took the form of opposition to the Common Sense philosophers. To Priestley, Associationism implied the political ideology of liberalism, which was favorable to the pursuit of truth, whereas Common Sense phi­ losophy accommodated prejudice, inequality, and authoritarianism. According to Priestley, the Lockean conception of "truth" implies freedom of enquiry and invalidates any appeal to tradition or authority. By the associationist criterion of knowledge all men are equally able to attain knowledge: "All just knowledge results from a just view of things, and that a habit of just thinking may be acquired by a course of observa­ tion and reflection duly persisted in; and, consequently that if he be in an error, it is in his own power to set himself right for that, naturally, he has as a good a power of distinguishing truth from falsity as his neigh­ bours. . . _" 188 Common Sense philosophy, however, which makes the power to distinguish true from false depend on common sense, a faculty men possess in different degrees, implies intellectual elitism. Differences in common sense are irrevocable. Beattie thought that no amount of "learn­ ing" could increase a man's allotment of common sense; "such diversities are, I think to be referred, for the most part, to the original constitution of the mind, which it is not in the power of education to alter." 189 Priestley was at pains to contrast the political and social consequences of the two epistemological positions. A Lockean empiricist or an associa­ tionist, assured of his epistemological equality, "is encouraged to indulge a freedom of enquiry, and to persist in his investigations, though they should prove very laborious." Furthermore, such freedom will aid him in the attainment of truth, which is accessible to all men in Priestley's mechanical view of thought. Priestley predicted a very different state of affairs should the Common Sense philosophy prevail. On that view, if a proposition is not accompanied by ". . . that instantaneous, instinctive, and irresistable . . ." assent which is the Common Sense hallmark of a true statement, one of two conclusions is appropriate. Either it is not the truth; or the percipient ". . . is not one of the great majority of mankind who are endued with the faculty that is necessary to the perception" of its truth. Either way, fur­ ther critical enquiry is discouraged by a view which sees the outcome as determined by "constitutional and irremediable" differences. Priestley also held that the position of Common Sense philosophers induces 110

188 "An

Examination," Works, 3, 74. Essay, p. 45.

189 Beattie,

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respect for freedom of enquiry and has "serious and alarming" social and political consequences. It makes humility, patience, and caution meaning­ less in the pursuit of truth and encourages conceit and arrogance toward critical opponents, who are regarded as "defective in their constitution" and hence not to be reasoned with but "treated as idiots or madmen." 190 Priestley seriously misrepresented the views of Reid and his followers. By extending the domain of application of the "principle of common sense" beyond the recognition of "first principles," he not only distorted their conception of the methodology of natural philosophy, but also gave an erroneous description of their political and social views. A correct interpretation of Common Sense philosophy is quite compatible with Reid's insistence on the patient investigation of man and nature according to Newton's dictum "hypothesis non fingo." 191 It is also consistent with Beattie's support of "liberty of speech and writing," his insistence on "rational enquiry," and his c'astigation of the use of "the civil power" or "the arm of flesh" to combat any opinion no matter how "whimsical or • •

pernicious.

>>192

It is a measure of Priestley's sensitivity on these subjects that he could easily distort them into doctrines of foreboding. His concern must be related to his religious interests. He claimed that the first principles of all knowledge, to which the action of common sense was to be restricted, are open to interpretation by the vagaries of religious prejudice. Priestley thought that the doctrines of Reid and his followers would encourage men to acquiesce in their religious prejudices, for they "act upon the mind as instantaneously and irresistibly as any of Dr. Beattie's first principles." 193 Furthermore, they leave men open to abuse by religious fanatics and political oppressors. If reason's limitations are laid bare by Common Sense philosophy, such disreputable men will "assert their favourite maxims with the greatest confidence." 194 Priestley feared that the subjective nature of the Common Sense criterion of truth will enable such men to claim as their 190 "An

Examination," Works, 3, 71-75. See L. L. Laudan, "Thomas Reid and the NewtonianTurn of British Methodo­ logical Thought," in The Methodological Heritage of Newton, eds. R. E. Butts and J. W. Davis (Toronto, 1970), pp. 103-131. 192 James Beattie, Essays on the Nature and Immutability of Truth, in Opposition to Sophistry and Scepticism, On Poetry and Music, as they affect the Mind. On Laughter, and Ludicrous Composition. On the Utility of Classical Learning (Edin­ burgh, 1776), p. 343. 193li An Examination," Works, 3, 76. Wlbid., p. 102.

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prerogative an interpretation of the "decrees" of common sense. 195 They will thus issue their mandates as decisions of "this new tribunal": "Papists may begin to avail themselves of them [Common Sense principles] for the support of all those doctrines and maxims for which the powers of reason had proved insufficient; and politicians also possessing themselves of this advantage, may venture once more to thunder out upon us their exploded doctrines of passive obedience and non-resistence. . . _" 196 Common Sense philosophy thus leads to consequences that are vastly different from those Priestley ascribed to his mechanical interpretation of associationism. Priestley's doctrine urges man to dispel prejudices and en­ courages him with the assurance that his ignorance is "naturally remedia­ ble." It rejects any form of intellectual and, hence, political or religious authority, for "it depends upon ourselves, so far as anything of practical importance is concerned, to be as wise, judicious and knowing, as any other person whatsoever." 197 Priestley encourages his students to draw all conclusions "from premises and data collected and considered by your­ selves." Teachers and educational institutions are not to be regarded as sources of information. The student must acquire knowledge by his "own industry," although it is incumbent upon teachers and educational in­ stitutions to supply a context and intellectual discipline that assure free­ dom of enquiry. 198 It is a moral duty to use free enquiry in all activities of life to improve the adequacy of knowledge. Priestley was convinced that all men could make significant contributions; in particular, he wished to emphasize the importance of such contributions to natural philosophy. This conviction was one of the many nonscientific factors that influenced the mode of Priestley's scientific output. Moreover, scientific knowledge of nature's determined structure was the very basis for the ascent of man to perfectibility. Priestley's hatred of religious prejudice and political authoritarianism had its source in the protestant tradition of rational dissent. His religious back-

1 VSIbid.: "every man will think himself authorised to assume the office of inter­ preting its decrees, as the new power holds in separate office its every man's own breast." 196 Ibid., pp. 101-102. See also p. 86, where the Common Sense viewpoint is re­ garded as alarming because it involves "setting aside all reasoning about the funda­ mental principles of religion and making way for all the extravagancies of credulity, enthusiasm and mysticism." 191 Ibid., p. 76. 19s Heads of Lectures, p. ix.

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ground made him a champion of rationality and liberalism. 199 His theory of rationality was an epistemological position, independent of rational dissent and widespread throughout the eighteenth century. His rationalist ardor, however, was the result of his religious background and subsequent position in society. Priestley asserted the essential rationality of the Christian revelation. Through the irrationalities of the established church, both in his time and in the past, the word of God, as preached by Christ and contained in the Scriptures, had been corrupted and distorted since the time of Christ. He regarded the doctrines of the trinity, the miraculous conception, original sin, predestination, the atonement, and the plenary inspiration of the Scriptures as departures "from the original scheme." 200 These "corrup­ tions" had been introduced into pure revelation by the prevailing philos­ ophies at different times and places which had come into contact with the Christian message. In his historical account of this process Priestley says: "It will also be seen, that I have generally been able to trace every such corruption to its proper source, and to show what circumstances in the state of things, and especially of other prevailing opinions and prejudices, made the alteration, in doctrine or practice, sufficiently natural, and the introduction and establishment of it easy." 201 It was necessary to rid religion of the errors due to prejudice and to return to the only proper authority, the Scriptures. As a Dissenter, Priestley regarded himself as part of a great tradition of struggle for religious truth and liberty. 202 He was painfully aware of the high price that his spiritual ancestors had paid for their bravery, of their social, political, and personal suffering at the hands of the established church. 203 "Religious rights," he said, "and religious liberty, are things of inestimable value. For these have many of our ancestory suffered and died." 204 Priestley fought prejudice not only for the sake of religious truth but also in the name of religious and civil liberty. For him, prejudice was synonymous with blind authoritarianism. He said that in "religion, we 199 In the later eighteenth and the early nineteenth century, Priestley was a culture hero and his writings were a leading legitimating force for dissenting opinion, dissent­ ing academies of education, and many provincial philosophical and literary societies. 200 See, e.g., "Free Discussion," Works, 4, 10; "Corruptions," Works, 5. 201 "Corruptions," Works, 5, 8. 202 See, e.g., "Institutes," Works, 2, xvii. 203a good account of Priestley's historical ancestry is found in H. Gow, The Origin of Non-Conformity (London, 1912). 204 "institutes," Works, 2, xvii.

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may, surely be allowed to think and act entirely for ourselves; in all cases obeying God and conscience rather than man."205 He urged the Prince of Wales to allow free operation of those "circumstances tending to expand the human mind, to show the inconvenience attending all establishments, civil or religious, formed in times of ignorance and to urge the reformation of them."206 At the time of Priestley's youth, some inroads had already been made into the blind prejudice and dogmatic authoritarianism of the political and religious establishment.207 Priestley experienced some freedom in the chapels and academies of the Dissenters. In 1772 he called upon the young congregation of Dissenters at Mill Hill, Leeds, to be grateful that "your minds are no longer bewildered with the gloom and darkness, in which our excellent religion was, for so many years, involved."208 Elsewhere, he ex­ pressed confidence that such enlightenment would "increase, and extend itself."209 However, the fight was not yet over; despite the comparative liberalism of his time, Priestley was acutely aware of the continuing resistance to the liberalism that Dissenters advocated. Some of his own experiences testified to the power of the political and religious establish­ ment to crush enlightened rationality and liberalism.210 He encountered 20s Heads

of Lectures, p. xxi. 1 Experiments and Observations on Different Kinds of Air and Other Branches of Natural Philosophy Connected with the Subject. In three volumes, being the former six volumes abridged and methodized, 3 vols. (Birmingham, 1790), 1, xi. Subsequent references to Air and Natural Philosophy. 207 The Act of Toleration of 1689 and Salters Hall rift of 1719 saw the rise of the Presbyterians with their demand for tolerance and liberty in religious matters. (See H. Gow, op. cit.) Their chapels and schools had an atmosphere of freedom demanding no credal adherence from anyone seeking admission. Priestley's childhood experi­ ences gave evidence of such pervasive "sentiments of piety without bigotry." His guardian aunt, though a Calvinist, befriended and sheltered the more heretical of her fellow Christians. Through her Priestley met and established a lasting relationship with George Walker, the most "rational of Christians" ("Memoirs of Dr. Priestley," Works, 1, 11). In his youth he profited from the intellectual freedom of the Daventry Academy ("Memoirs," Works, 1, 21-28). Later he returned to teach in the congenial atmosphere of the academies at Warrington and Hackney (ibid., pp. 58-59 and 118-123). 208 "Institutes," Works, 2, xvi. 209 "Corruptions," Works, 5, 4. 210 In his youth he was barred from communion in the local chapel on account of his heretical tendencies ("Memoirs," Works, 1, 14). His espousal of Arianism antago­ nized the faithful at Needham (ibid., p. 34). The proposal that Priestley accompany Cook on his second voyage was, after favorable reception, rejected by the Board of Longitude because of religious antipathy towards Priestley on the part of certain clerics employed by the Board (ibid., pp. 79-80). A few years later, in 1774, his "materialism" was misconstrued and firmly rejected by his religious contemporaries (ibid., pp. 202-204). 206 Priestley

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greatest opposition in the Birmingham riots of 1789, from which he barely escaped with his life. 211 Priestley agreed with his fellow Dissenters on the need for "that generous zeal for religion and liberty, which makes the memory of our forefathers so truly illustrious." 212 Even in the fight for religious and civil liberty no "other means than reason and argument" is to be used. Techniques of persuasion such as "riot and tumult" are to be left to others. Truth stands in no need of such support and will always triumph when assailed by such weapons. 213 Reaffirming his belief in the rationality of Christianity and reflecting the relative corruption of the established church in eighteenth-century En­ gland, he wrote in 1782: "Happy are they who contribute to diffuse the pure fight of this EVERLASTING GOSPEL. The time is coming when the detection of one error, or prejudice, relating to this most important sub­ ject, and the success we have in opening and enlarging the minds of men with respect to it, will be far more honourable than any discovery we can make in other branches of knowledge, or our success in propogating them." 214 Earlier, in 1774, he had made it plain that he expected the rise of scientific knowledge to play its part in this process of enlightenment: "This rapid progress of knowledge . . . will, I doubt not, be the means under God of extirpating all error and prejudice, and of putting an end to all undue and usurped authority in the business of religion as well as of science. . . ." 21s Thus, Priestley placed natural philosophy in the vanguard of his attack on prejudice, dogma, superstition, and authoritarianism.

6 Priestley's conception of the nature of matter can be shown to integrate his concept of man, his mechanical view of thought, and the doctrines of determinism and causation. He developed his views on the topic in two works: Disquisitions Relating to Matter and Spirit in 1777 and 1782, and A Free Discussion of the Doctrine of Materialism in 1778. He had two objectives which he set down in order of their priority. The principal goal was the establishment of the doctrine of materialism, which he claimed was supported by, though did not depend upon, his theory of the nature of matter. "The principal object, to prove the uniform composition of 211 See

"Memoirs," Works, 1, 16-23. Works, 2, xvii. 2 1 3 Heads of Lectures, p. xxii. 214 "Corruptions," Works, 2, 4. 2 1 s Air, 1, xiv. 212 "Institutes,"

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man, or that what we call mind, or the principle of perception and thought, is not a substance distinct from the body, but the result of corporeal organization; and what I have advanced preliminary to this, con­ cerning the nature of matter, though subservient to this argument is by no means essential to it; for whatever matter be, I think I have sufficiently proved, that the human mind is nothing more than a modification of it." 216 His "subservient" thesis stated the second objective: the establish­ ment of his philosophical monism. Priestley claimed that his reinterpretation of the relationship between man and nature accorded with the pristine sense of the Scriptures. To reject the traditional Christian view that "man has a soul distinct from his body" in favor of the complete materiality of man was to him an expression of rational Christianity; this in turn involved a return to the true system of "pure Revelation," the promotion of which was "the true object of this work." 217 By asserting that materialism is ra­ tional and truly Christian, he expected opposition from bigots, but he was confident that rationalists would approve. 218 Materialism, necessitarianism, and "that which is commonly called Socinianism" form one system of thought based on nature and the Scriptures. Priestley asserted that "who­ ever shall duly consider their connection and dependence on one another will find no sufficient consistency in any general scheme of principles, that does not comprehend them all." 219 Although it is the natural harmony of these three doctrines that forms the core of his rational Christianity, Priestley was careful to insist on the independent validity of each of them. His scriptural exegesis favored materialism, which could be brought into agreement with Hartleyan psy­ chology. As a young Calvinist, Priestley accepted the traditional dualism of "body and soul." He suppressed his philosophical qualms concerning the "intimate union of two substances so entirely heterogeneous as the soul and the body" until his dispute with the Common Sense philosophers led him to a reexamination of Hartley's work. In 1774-1775 he "first entertained a serious doubt of the truth of the vulgar hypothesis" 220 that matter and spirit lack "any one common property" in virtue of which they may interact with each other. He argued that on this view matter occupies space whereas spirit bears no "imaginable relation to space," and that, 2 1 6 "Disquisitions," Works, 3, 220. Priestley gave arguments other than those found in his theory of the nature of matter to support his position. W I b i d . , p. 219.

2 ^Ibid.,

pp. 203-204.

2 l 9 Ibid.,

p. 220. pp. 201-202.

2 2 0 Ibid.,

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"properly speaking, my mind is no more in my body than it is in the moon." 221 Hartley's doctrines of vibrations and association led Priestley to think that "man is of some uniform composition," his mental "powers" arising from "an organical structure as that of the brain." Accordingly, the "whole man" dies at death and any hope of "surviving the grave" is only "derived from the scheme of revelation." 222 When Priestley's tentative opinions were condemned by the public, he thought through his "casual conclusions" again and eventually published his views in the Disquisitions in 177 7. 223 There Priestley condemned the Common Sense philosophers' opposition to a theory of matter in which nature and man form a coherent unity. He met the sceptical challenge by pointing out that materialism eliminates the need to posit the existence of a soul beyond experience, to entertain such theological doctrines as the preexistence of souls, and to ex­ plain how the immaterial can act on the material. Priestley's views allow man not only to avoid the extravagances of vain imagining, but also to propound an interpretation of nature that is consistent with the primitive sense of the Scriptures. Priestley's use of Hartleyan psychology does not give the complete pic­ ture of his motivations in turning to materialism. Materialism was by no means an inevitable consequence of Hartley's doctrines. Hartley's view of the origin of an association of ideas in material vibrations in the brain was perfectly compatible with the traditional duality of body and soul. Hartley rejected the view that "matter can be endowed with the Power of Sensa­ tion" in favor of a parallelism between mind and body. 224 It would also have been uncharacteristic of the pious Priestley to make a religious con­ version hinge on a new solution to an old metaphysical problem. Although his advocacy of materialism was occasioned by his second encounter in 1774 with Hartleyan psychology and physiology and was given as a solu­ tion to the problem, Priestley eagerly embraced this doctrine primarily because it gave support to his particular interpretation of biblical Chris­ tianity. Priestley considered materialism the only rational view of man and nature. Priestley was brought up in the gloomy faith of Calvinism. 225 Never an

221 Zbid., 222 /i)id.,

p. 202. Priestley is quoting himself from "Hartley on Man," Works, 3, 18. pp. 202 and 182.

2 2 3Ibid.,

p. 202.

^^Observations on Man, 1, 33-34. 225 See Memoirs of Joseph Priestley to the year 1 795, written by himself (London, 1806), in Works, 1, 5-17.

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obedient disciple, he grew more radical in his religious views as he reached manhood. By the time he left the Academy at Daventry in 1755 to take up the ministry at Needham Market in Suffolk, he openly avowed the doc­ trines of Arianism.226 Scriptural exegesis and dialectics soon led him to abandon this compromise position for the more consistent Socinianism, and his conversion was completed soon after his move to Leeds in 1767 when he read "Dr. Lardner's letter on the Logos."227 As a Socinian, Priestley rejected as irrational the traditional dogmas and mysteries of Christianity in numerous discussions that centered on the nature of Christ. According to Priestley, the source of the sophistry and heresy found in traditional Christian dogmas and mysteries lay in "the very greatest cor­ ruptions of Christianity . . . that began to work in the apostles' times, and which extended itself so amazingly and dreadfully afterwards." The cor­ rupting influence came from "the oriental philosophy of the pre-existence of souls," which countenances belief in "the pre-existence and divinity of Christ, the worship of Christ and of dead men, and the doctrine of purga­ tory," and "all the popish doctrines and practices . . . accommodated by these beliefs." For example, if Christians had remained true to pure revela­ tion and regarded Christ as no "other than a mere man," the doctrines of atonement and transubstantiation would have lacked content since the sufferings of a "mere man" would never have been deemed sufficient to placate divine wrath; as a consequence, "the doctrine of the proper placa­ bility and free mercy of God would not have been impeached." Similarly, it would have been meaningless to claim "the transmutation of bread and wine into the real body and blood of Christ, if Christ had been a mere man." Priestley's Unitarian position was that "as a Christian, therefore, and a Protestant, I am an enemy to the doctrine of a separate soul. One who believes in a soul may not, but one who disbelieves that doctrine can­ not be, a papist. . . _"228 Thus, his materialism and opposition to the dualist doctrines of the Cambridge Platonists and the Newtonians were a natural corollary of his Unitarianism. Priestley developed his "subservient" thesis concerning the "nature of matter" in order to solve a particular philosophical objection to his doc­ trine of materialism. A common objection to the doctrine of a material 226 Ibid., 227 Ibid.,

pp. 17-26.

pp. 30-37, 57-61. Nathaniel Lardner, A Letter Writ in the Year 1730 Concerning the Question whether the Logos supplied the Place of a human soul in the Reason Jesus Christ (London, 1789). 228ll Free Discussion," Works, 4, 10.

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mind was that matter and its disposition to modify could not readily pro­ vide adequate grounds for perception or thought. The "essential nature" of matter or the properties that define it do not intrinsically embody ideas of thought or perception. Matter and motion are categorically different from thought or perception and could not, therefore, "become" or "af­ ford" a thought or perception. Hume, stating the objection clearly, said that since the ideas of matter and its various motions "never afford us any idea of thought or perception, it is concluded to be impossible that thought can ever be caused by matter." 229 Hume dissolved the problem of the connection between mind and matter by attributing causal relation­ ships to constant conjunctions. Priestley rejected the constant conjunction thesis as an exhaustive analysis of causal relationships; he saw a "real connection" between causes and their effects. Consequently, he tried to find an intelligible connection between motion and thought, body and mind, an attempt that led him to reject the traditional view of matter and endow it with a new "essential nature" to make it compatible with "sensa­ tion and thought." 230 We must now analyze Priestley's arguments for the materiality of mind in relation to his natural philosophy. The dualistic view that Priestley at­ tacked was a constituent of the orthodoxy of both Christian revelation and Newtonian cosmology; he denied that "there are two distinct kinds of substance . . . matter and spirit." 231 Matter, on the one hand, had "been said to be possessed of the property of extension . . . and also of solidity or impenetrability, but it is said to be naturally destitute of all power what­ ever," since the properties of attraction and repulsion are regarded as the effects of some "foreign power." 232 Spirit, on the other hand, is defined as "a substance entirely destitute of all extension, or relation to space, so as to have no property in common with matter and, therefore, to be properly immaterial, but to be possessed of the powers of perception, intelligence, and self-motion." Man's body consists of matter, to which is "intimately united" the "spirit or immaterial principle" in which the "principles of perception and thought reside." Priestleyreplied that neither matter nor spirit corresponds to these definitions. He argued that matter is endowed with "powers of attraction and repulsion," 233 which are not properties "imparted to matter" but "necessary to its being," such that without them "it would be nothing at all." 234 Matter is to be defined as "a 229A Treatise, pp. 346-347. 231 Ibid., p. 218. 233 Ibid.,

pp. 218-219.

230"Disquisitions," Works, 3, 230. 232 Ibid., pp. 218 and 224. ^Ibid., pp. 219 and 237.

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substance possessed of the property of extension, and of powers of attrac­ tion or repulsion." 23s As such and robbed of impenetrability, matter has a

nature approaching that of "spirit and immaterial beings." Thus regarded, it is "no more incompatible with sensation and thought, than that sub­ stance which, without knowing anything farther about it, we have been used to call immaterial." Furthermore, matter which has been deprived of the property of " solidity, inertness, or sluggishness" no longer merits the consequent ascription of "baseness and imperfection" leveled at tradi­ tional conceptions of matter. 236 The new conception of matter implies that "we have no reason to suppose that there are in man two substances so distinct from each other, as have been represented." 237 Having activated matter in this fashion, Priestley made no attempt to demonstrate the compatibility of the "power of perception" with the "powers of repulsion and attraction." In fact, he recognized the imperfec­ tion in his "idea of what the power of perceptions is," and compared the difficulty to that of the eye trying to see itself. However, although caution was required in considering "compatibility" with other properties, Priestley saw "no sort of reason to imagine" that the power of perception was "really inconsistent'''' with the powers of attraction and repulsion, whereas it was obviously incompatible with "that impenetrable, inert sub­ stance" that matter was usually thought to be. If it were possible that "one kind of substance" could support all the properties of man, its existence had to be established by observation and experiment. Since the "powers of sensation or perception, and thought, as belonging to man have never been found but in conjunction with a certain organized system of matter," Priestley concluded that "those powers necessarily exist in, and depend upon, such a system." To conclude otherwise is to "multiply causes without necessity," which is contrary to the "simple rules of philos ophizing." 238 According to his "rationalist" principles, the "necessary seat of thought" can be determined "by the circumstances that universally accompany it, which is our rule in all other cases." For Priestley, universal concomitance supplies the reason for believing "that any property is inherent in any sub­ stance whatever." The mutual dependence of states of mind and body also allows him "to conclude, that the powers of sensation and thought are the necessary result of a particular organization 'of the brain' just as sound is

23Slbid., 237Ibid,

p. 219. p. 219.

236 Ibid., 23sIbid.,

p. 230. pp. 242-243.

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a necessary result of a particular concussion of the air." Constant conjunc­ tion is the strongest evidence in nature ''for a necessary connection of any cause and any effect." To reject materialism in favor of another opinion "is to form an hypothesis without a single fact to support it," and to consider matter an "obstruction" rather than a "necessary pre-requisite" to thinking is to argue "not only without, but directly contrary to all ap­ pearances whatsoever." If matter were an obstruction to thinking, age and death, with the consequent "dissolution" of the body, should improve the faculty of thinking. "But this is the very reverse of what really happens." Priestley criticizes Locke for seeing that there was no real inconsistency between "the known properties of body, and those that have generally been referred to mind" and yet clinging to the traditional duality. 239 The argument that Priestley gives in the Disquisitions to justify his view of the nature of matter lacks philosophical precision and depth. His amorphous and frequently incomplete arguments derive their force from his unrelenting rationality. He sets out to show that his view of matter is the only one warranted by the facts. He ascribes the prevalent view of matter to a failure to apply "the universally received rules of philosophiz­ ing, such as are laid down by Sir Isaac Newton at the beginning of his third book of the Principia." Newton's rules have been employed in natural philosophy but were "entirely deserted" in enquiries that deal not with the "causes of particular appearances" but with "the most general and com­ prehensive principles of human knowledge." Newton's first two rules of reasoning distinguish between "mere fancy" and sure reasoning. Rational thought demands that "we are to admit no more causes of things than are sufficient to explain appearances" and that "to the same effects we must, as far as possible, assign the same causes." 240 Priestley accepts Newton's rules also as the principles that warrant a search for simplicity in nature as well as the universalization of induction and analogy in relation to ob­ served constant conjunctions. 241 His "transformation" of Newton's rules explains his omission of Newton's "third rule." Priestley explicitly denied it, since an invisible realm beyond the experience of the senses, though it may exist, is not a possible object of knowledge. Newtonian "plain rules" are to be used in consideration of the "fundamental properties" of matter.

242

239 Zfcid.,

pp. 244-247. p. 221. 241 For the meaning of these terms in Priestley's rationality, see p. 363. 242 "Disquisitions," Works, 3 , 222. 240 Zfcid.,

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It emerges from Priestley's discussion, however, that he is concerned with a misapplication rather than lack of application of the rules of reason­ ing. The facts, not the reasoning, are criticized. The "vulgar" notion of matter as a solid, impenetrable substance destitute of all powers is based on "common appearances," It is derived from observations of the resis­ tance objects offer to pressure and the inability of two or more objects to occupy the same place simultaneously. Similarly, observations on billiard balls give rise to the idea of inertia, and to the conclusion that in the absence of external obstacles a ball would continue for ever in its state of rest or motion because it has "no power within itself to make any change within either of these states." Priestley regarded the accepted views of matter as "superficial and false judgements" based on appearances. He claimed that recent scientific observations, guided by the "rules of philosophising laid down above," will throw "new light" on these "ap­ pearances" and lead to the "conclusion" that "resistance" is caused not by solid matter but by "a power of repulsion always acting at a real, and in general, an assignable distance from what we call the body itself." The "seeming contact" when a hand is pressed against or resisted by an external object is illusory; philosophers know that the two objects are not in con­ tact but kept "at a real distance from each other by powers of repulsion common to them both." From the point of view of epistemology, Priestley claims that a careful consideration of sensation does not warrant the con­ clusion that impenetrability is more basic than active resistance. In fact, "it generally requires a much greater power of pressure than I can exert to bring my fingers in actual contact with the table." Similarly, electrical phenomena show that a considerable force is required to bring bodies which are "kept asunder by a repulsive power" into contact. The expan­ sion and contraction of bodies on heating indicates that component parti­ cles of large bodies "do not actually touch one another"; they are kept apart by "internal forces of repulsion" which no one "can pretend to compute." The attractive force which is responsible for their cohesion may be estimated, but this supplies "no data" for determining the infinitely larger force necessary to bring them into actual contact. The "phenomena of light are most remarkably unfavourable to the hypothesis of the solidity or impenetrability of matter." 243 Thomas Melville showed that a drop of water can roll along a cabbage leaf without making contact with it. Doing away with "impact theory," Newton explained reflection and refraction of light at interfaces in terms of powers of attraction and repulsion. Transmibid., pp. 221-228.

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mission of light "without the least interruption . . . through a medium of uniform density indicates that bodies . . . have no solid parts or so very few, that the particles of light are never found to impinge upon them, or to be obstructed by them." Until light is shown to be reflected within a homogeneous transparent substance, there is no evidence from fact or appearance to conclude that such solid parts exist. On the contrary, there is "all the reason in the world" to reject their existence: "all the phenom­ ena can be explained without them and, indeed, cannot be explained with them." Priestley believed that the uniform transmission of light through matter can be explained if one accepts the ultimate penetrability of all matter. The "principles of the Newtonian philosophy" have rendered redundant the explanatory role of solid matter. The vast majority of natu­ ral phenomena are explained in terms of "powers which were only sup­ posed to accompany and surround the solid parts of matter." Furthermore, no one has disproved the assertion "that for any thing we know to the contrary, all the solid matter in the solar system might be contained within a nutshell, there is so great a proportion of void space within the substance of most solid bodies." Priestley expressed surprise that this theoretical insignificance of "solidity" did not lead philosophers to realize sooner that "there might be nothing for it to do at all, and that there might be no such a thing in nature." Hence, Priestley concluded from his observations that all known resistance to contact between bodies is caused "by powers of repulsion." In fact, there can only be one kind of resistance in nature; its variations are due to variations in the strength of the repulsive powers "but never to the supposition of a cause of resistance entirely different from such a power." 244 As a rationalist Priestley could not admit the existence of "anything absolutely impenetrable." "On the contrary, analogy obliges me to suppose that, since all the evidence of bodies being impenetrable, when rigorously examined, i.e., by actual experiments (as optical, elec­ trical, etc.) appear to be cases in which bodies are prevented from coming into actual contact by powers, acting at a distance from their surfaces, that all resistance is of this kind only." 245 It may be argued that the approach adopted by Priestley was inadequate to the task he had in mind. Attempting, in characteristic style, to give his position a rationalistic basis, he failed to see that the fundamental proper­ ties of matter cannot be established by observation alone. Also, an appeal to a particular scientific theory presupposes the problem at issue, which w Ibid.,

pp. 227-232.

245"Free Discussion," Works, 4 , 24 and 20.

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concerns the logical status of the terms employed. What was required of Priestley was not a scientific explanation of action by contact in terms of action at a distance, but a conceptual analysis which showed the logical dependence of such terms as solidity and impenetrability on the concept of repulsion. He overlooked this requirement in his eagerness to apply ra­ tionalist criteria to the problem. Priestley did make such a conceptual analysis when he tried to establish the power of attraction as a fundamental property of matter. He wanted to show that, far from being a "foreign property" of matter, the power of attraction is "essential to its very nature and being." If "we suppose bodies to be divested of it, they come to be nothing at all." Specifically, they would have no "particular form or shape," since "no such figured thing can exist, unless the parts of which it consists have a mutual attraction, so as either to keep contiguous to, or preserve a certain distance from, each other." Priestley's argument is applicable to the Newtonian solid and impenetrable atoms. They are "perfectly solid" with some "determinate form"; they are divisible and, therefore, have parts which must be depen­ dent on one another. If there were not "powers of mutual attraction in­ finitely strong. . . between the parts, the atom could not hold to­ gether . . . , that is, it could not exist as a solid atom." Without a power of attraction, therefore, all particles of matter, the "ultimate" and the "gross," would fall apart and be dispersed. The "whole substance must absolutely disappear, nothing at all being left for the imagination to fix upon." Powers are, therefore, necessary to the "solidity and essence" of matter. 246 Similarities between this view of the nature of matter and that promul­ gated by R.J. Boscovich must not be allowed to obscure the important differences that exist between them. Priestley's adherence to a Boscovichean tluory of matter was not as wholehearted and complete as has been supposed. 247 In particular, Priestley wished to avoid speculation on the 246"Disquisitions," Works, 3, 223-224. 247xhe work of R. E. Schofield is responsible for the prevalent historical view of Priestley as a wholehearted adherent of the Boscovichian version of "dynamic corpuscularity." See, in particular, his "Joseph Priestley, the theory of Oxidation and the Nature of Matter," Journal of the History of Ideas, 25 (1964), 285-294; "Joseph Priestley, Natural Philosopher," Ambix, 14 (1967), 1-15; "Boscovich and Priestley's Theory of Matter," in Roger Boscovich, ed. L. L. Whyte (London, 1961). This out­ look has been adopted by Jack Lindsay in his introduction to his edition of Auto­ biography of Joseph Priestley: Memoirs written by Himself (Bath, 1970). Schofield's views were criticized in J. G. McEvoy 1 "Joseph Priestley, Natural Philosopher: Some Comments on Professor Schofield's Views," Ambix, 15 (1968), 115-123. There it

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internal structure of matter and mentioned "physical indivisible points" only once in an account of the "hypothesis of Father Boscovich and Mr. MichelP' in his History of Vision. He insisted that "in what properly be­ longs to these Disquisitions, I have not, so far as I can recollect encum­ bered my doctrine with any of the difficulties attending the considera­ tions of the internal structure of matter; concerning which we know, indeed, very little, having few data to argue from." True to his rationalist principles, he was prepared to give full support only to those features that he thought "well-examined appearances proved." Beyond the "narrow bounds" of appearances, which were known and organized by the prin­ ciples of association grounded directly in sensation, the "metaphysician has no business to speculate any further, and the natural philosopher will find, I imagine, but few data for further speculation," 248 Again, Priestley rejected the invisible realm of the Newtonians, insisting that any theory of matter must be consonant with the content of sensation. 249 As he put it: "That it is possessed of powers of attraction and repulsion, and of several spheres of them, one within another, I know, because appearances cannot be explained without supposing them." 250 Priestley's use of generic prin­ ciples and causal relations in the articulation of his theory of phlogiston is not directly related to his general theory of matter as intensive powers. Still, it is apparent that his theory of matter functioned as a rationale for the sorts of causes he ascribed to chemical phenomena. The peculiarities of Priestley's materialism are brought out by further study of the theological objectives underlying his general approach. One consequence of his theologically oriented approach to the theory of matter is his failure to recognize all of the philosophical consequences of his new definition of matter. According to the traditional view, the concept of action at a distance was unintelligible because it could not be derived from the concept of "solid atoms." A "foreign power" of the "deity" was was shown that there is no evidence to support the claim that Priestley's chemical conceptualizations were determined by his views on the nature of matter as inherited from the tradition of "dynamic corpuscularity" in the Boscovichian variant of the Newtonian formulation. Our discussion in this paper should further undermine such a suggestion by indicating the way in which Priestley's basic epistemological commit­ ments excluded him from considerations involving an invisible realm that are integral to "dynamic corpuscularity." Unless this point is fully appreciated, Priestley's con­ tribution to an important revolutionary movement in eighteenth-century intellectual history will be overlooked. 2 4 8 "Disquisitions," Works, 3 , 237-238. 2 4 9 See also Heimann and McGuire, o p , cit. (note 135). 25 O it Disquisitions," Works, 3 , 229.

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necessary to explain it, and the system of the world constantly depended on its action. Priestley's definition of matter makes such a "foreign power" redundant. Action at a distance becomes the defining characteristic of matter, since a material body is conceived only in terms of its action. How­ ever, instead of insisting on this definition of matter, Priestley finds it difficult to ascribe action to bodies "at some distance from their real sur­ faces" and thinks it absurd that bodies should "act where they are not." He defends his position by claiming that it shares the absurdity with the Newtonian conception of matter, and that consequently, he can avail him­ self of the "same means" to overcome it. He rejects the attempt to reduce action at a distance to the impulsive action of an invisible ether which had yet to be shown to exist, and which, even if it did exist, could not "pro­ duce the effects that are ascribed to it"; the hypothesis of an ether involves an infinite regress requiring another ether to move the particles of the first ether. The alternative mechanism proposed by the Newtonians is the action of the Deity, and Priestley considers himself "at liberty to avail myself of the same assistance."251 Priestley's objective is to demonstrate the greater piety of his view vis a vis the common one. The powers essential to matter are not " self existent

in it"; they are communicated to matter by God. Should God withdraw his influence, "the substance itself necessarily ceases to exist, or is annihi­ lated."252 Here, too, Priestley's doctrine of determinism shapes his view of the nature and existence of matter. Since the world is deterministic ally structured and all existing things arise necessarily from divine nature, matter is a continuous manifestation of God's creative power. By compari­ son, the common view of matter is less pious "in that it supposes some­ thing to be independent of the divine power." If the idea of God is removed from Priestley's system, "everything except space necessarily vanishes with it"; if it is removed from the common view, "the idea of solid matter is no more excluded than that of space." Hence, the common

view limits the power of God, questions his ability to create or annihilate matter, and supports the doctrine of "two original independent principles." Priestley's hypothesis "leaves no foundation for this system of im­ piety." 253

That Priestley's theory of matter is central to his philosophical monism is obvious from his efforts to distinguish his system from Spinoza's panthe­ ism and from the "immaterialism" of Baxter and Berkeley. According to 25l Ibid.,

pp. 234-240. mibid., p. 224.

253ibid., pp. 241-242.

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Spinoza, the universe inheres in or is a modification of a simple, individual, omnipresent, and divine substance. According to Priestley, the universe is the divine power but not the Deity himself.254 As a consequence, H. Metzger claimed, Priestley's monistic view of reality may be as easily re­ garded as the "spiritualisation of matter" as the "materialisation of spirit."255 Priestley himself appears to lend support to such a conclusion when he registers his indifference to any suggestion that "on my hypothesis there is no such thing as matter, and that everything is spirit." So long as the common conceptions of "spirit" and "matter" appropriate to the old dualism are rejected in favor of his conceptions, such a dispute would be a matter of "mere names."256 Priestley is adamant in his rejection of the "true immaterial system" of Berkeley and Baxter, so that the characteriza­ tion of his position as the "spiritualisation of matter" misinterprets his monism by suggesting an intellectual kinship he was keen to deny. Accord­ ing to Priestley, Baxter reduces the essential properties of matter to the "immediate agency of the Deity himself," concluding "that there is not in nature any such thing as matter distinct from the Deity and his opera­ tions." Baxter's view, he claims, is very close to the "immaterialism" of Berkeley.257 Despite the reduction of nature to a manifestation of divine agency, Priestley rejects Baxter's position because it denies that spirit and matter have "common properties" and defines man's nature in terms of the traditional dualism of body and soul.2S8 The "spiritualisation of matter" as expressed by Berkeley and Baxter still harbors for Priestley a dualism he rejects. His own position is more accurately defined as the "materialisation of spirit." This expression, unlike its suggested alterna­ tive, reflects Priestley's monistic view of reality which reduces everything to a unitary whole intelligible through the rational analysis of immediate experience. Priestley achieves such an ontological reduction by redefining matter as a nexus of powers, by reducing man's nature to a comprehen­ sible "uniform composition" that is part of physical reality, and by identifying man and nature as one and the same manifestation of divine power. The reduction enabled Priestley to bring his materialism into closer harmony with his cosmic optimism and psychological perfectionism, 254 Zfcid,

p. 241. H. Metzger does not use these phrases, they accurately characterize her interpretation (Attraction Universelle et Religion Naturelle [Paris, 1938], pp. 178-189). 2S6 "Disquisitions," Works, 3, 236. 2s Ilbid., pp. 225-226. 25 SJbid., pp. 267 and 288-291. 255 Although

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since man develops according to the deterministic laws of nature. Thought becomes an analysis of these laws, determined by the principles of association. Although Priestley asserted man's ultimate ignorance of God's "nature" or "essence," he rejected the "immateriality" of the Deity. Immateriality implies that the Deity "has no property whatever in common with mat­ ter," "bears no relation to space," and "is necessarily cut off from all communication with, and all action and influence upon, his own crea­ tion." 259 To assert the materiality of the divine "essence" in accordance with Priestley's view of matter is not the same as imputing the divine essence on the "older view." Also, in Priestley's system, the problem of God's "interaction" with the material world vanishes: "As to the difficulty arising from the divine material essence penetrating other matter, it has no place at all in the hypothesis advanced from Father Boscovich and Mr. Michell, and certainly this idea is much more consonant to the idea which the sacred writers give us of his filling all in all, than that of a being who bears no relation to space, and thereof cannot properly be said to exist any where, which is the doctrine of the rigid immaterialists." 260 If the

divine material essence penetrates matter, it must penetrate the matter of man; body and spirit are equally manifestations of divine power. Divine energy is a necessary prerequisite for everything that exists; without it, "we ARE, as well as can do nothing." Man is the instrument of God's will. As matter is reduced to "spheres of attraction and repulsion" inhering in the divine power, so man, who is also matter, is reduced to "spheres" of "influence" inhering in the divine power. Rejoicing in the analogy, Priestley exclaimed: "My sphere, and degree of influence on other beings, and other things, is his influence." Priestley was happy in the belief that he was part of a purposeful design; as such he felt assured that "the opera­ tions in which I am concerned are of infinitely greater moment than I am capable of comprehending," and that with time "I shall see more of this great purpose and of the relation that myself and my sphere of influence bear to it." 261 In comprehending matter, manifested by varying degrees of intensity in relation to the content of immediate experience, man com­ prehends the wisdom of God as expressed in a reality that can be used for human ends. In comprehending reality, man comprehends all that is nec­ essary for an understanding of human nature. The interrelatedness of vari­ ous themes in his "philosophical system" was a source of continual joy to 259ibid., p. 298.

2 6 0 Ibid.,

p. 301.

261 Ibid.,

pp. 241-242.

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PRIESTLEY'S WAY OF RATIONAL DISSENT

Priestley; so, too, was the uniqueness of his system in its relation to God: I will take this opportunity of saying further, that, upon no system what­ ever, is the great author of Nature more distinct from his productions, or his presence with them, or agency upon them more necessary. In fact, the system now held forth to the public taken in its full extent, makes the Divine Being to be of such importance in the system, as the apostle makes him, when he says, In him we live, and move, and have our being. The contemplation of it impresses the mind with the sentiments of the deepest reverence and humility, and it inculcates a degree of benevolence to God, both active and passive, that no other philosophical system can inspire.

262

A full account of Priestley's system reveals that his theory of matter is the cornerstone of an edifice of philosophical monism which incorporates the doctrines of materialism, necessity, cosmic optimism, and psychological perfectionism and weds them to a pristine sense of the Scriptures.

7 Many scholars have agreed that a fundamental reevaluation of Priestley's scientific achievement is needed. Recent opinion claims that Priestley's seemingly stubborn adherence to the phlogiston theory and the "individual nature" of his work cannot be ascribed to "ignorance or lack of knowledge either of the history of chemistry or of work being done by his contem­ poraries." 263 Impoverished historiography accounts for the opinion that Priestley was a scientific amateur: that he stumbled into chemistry: that he consistently lacked a rationale for his scientific activities: that he per­ formed experiments by whim: and that he believed in the wrong chemical theory. 264 A contrary interpretation advanced by R. E. Schofield is 262 Ibid.,

p. 302. E. Schofield, "The Scientific Background of Joseph Priestley," Annals of Science, 13 (1957), 163. 264 This account is gleaned from the following sources: R. M. Caven, Joseph Priestley 1733-1804 (London, 1833); F. Jeffrey, "Review of Memoirs of Joseph Priestley," Edinburgh Review, 9 (1807), 137 ff.; S. Hartog, "Joseph Priestley," D. N. B., 46; A. N. Meldrum and H. Hartley, "The Bi-Centenary of Joseph Priestley," Joum. Chem. Soc. (1933), pp. 896-920; "Joseph Priestley and His Place in the History of Science," Proc. Roy. Inst. Great. Brit., 26 (1931), 395-430; A. Holt, A Life of Joseph Priestley (London, 1931); O. Lodge, "Joseph Priestley," Nine Famous Birmingham Men, ed. J. H. Muirhead (Birmingham, 1909); J. R. Partington, A History of Chemistry, 4 vols. (London, 1962), 3; Priestley's Writings on Philosophy, Science, 263 R.

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equally untenable.265 The evidence will not support the view that Priestley was a Newtonian theoretician following the dictum that "the whole bur­ den of philosophy seems to consist in this—from the phenomena of the motions to investigate the forces of nature."266 Nor is it tenable to argue that Priestley purposely concealed the thrust of his Newtonian program be­ hind a welter of experimental detail.267 It should be apparent from this study that Priestley's theory of matter is radically different from Newton's in both its nature and assumptions. So it is, too, in its conception of the nature of chemical explanation since it excludes any appeal to the invisible realm of particles and forces of either the Newtonian or the Boscovichean system. The key to Priestley's scientific personality lies elsewhere. The categories of his thought incorporate his natural philosophy into a new conceptual framework characterized by systematic unity and integrity. Moreover, this framework was formed in Priestley's thought by intellectual forces far wider in scope than the principles and problems of eighteenth-century natural philosophy and chemistry. So long as scholars neglect the nexus of theological, metaphysical, and epistemological categories, they will mis­ understand Priestley's views on the nature of scientific theories, the logic of scientific discovery, and the role in scientific enquiry of analogy and hypothesis. Although the problems cannot be dealt with completely in this study, a consideration of their more important aspects will provide a pro­ legomenon to any future examination of Priestley's scientific orienta­ tion.268 Priestley derives his conception of the aims of natural philosophy and the role of scientific theories from his sensationalism. As the principle of association shapes the primitive chaos of human experience, so does philos­ ophy systematically clarify the experimental data: "The great business of philosophy is to reduce into classes the various appearances which nature

and Politics, ed. John A. Passmore (New York, 1965);T. E. Thorpe, Joseph Priestley (London, 1906); F. W. Gibbs,/osep^ Priestley. Adventurer in Science and Champion of Truth (London, 1965). 265 For this account see sources cited in note 247 as well as A Scientific Auto­ biography of Joseph Priestley, 1733-1804: Selected Scientific Correspondence with Commentary, ed. R. E. Schofield (Cambridge, Massachusetts, 1966). 266 R. E. Schofield, "Joseph Priestley, Natural Philosopher," op. cit. (note 247). 267 Jbid., p. 7. 268 An attempt to apply the conceptual parameters considered here to an analysis of Priestley's scientific thought is given in J. G. McEvoy, Joseph Priestley: Philoso­ pher, Scientist and Divine (Ph.D. dissertation, University of Pittsburgh, forthcoming).

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presents to our view. For by this means, we acquire an easy and distinct knowledge of them, and gain a more perfect comprehension of their various natures, relations, and uses." In view of Priestley's thoroughgoing determinism, which bases a rational interpretation of reality on a necessary chain of cause and effect, it is not surprising that he reduces the classificatory procedure of natural philosophy to a search for causal relationships in nature. "Nature presents to our view particular effects, in connection with their separate causes, by which we are often puzzled, till philosophy steps in to our assistance, pointing out a similarity in these effects, and the probability of such similar effects arising from the same cause."269 It is the aim of science to determine "those circumstances in which any appearance in nature is certainly and invariably produced" and to study them with the aid of "analogy," for, Priestley claims, "all discoveries which are not made by mere accident have been made by the help of it." Priesdey holds that the scientist in his attempt to establish an invariable relationship of con­ tiguity and precedence between "appearance" and "circumstance" must pay attention to the common element in the variety of "circumstances" accompanying different instances of the "appearances"; "for on those common circumstances, all that is common in the appearances must de­ pend." This procedure, which is at the heart of Priestley's scientific work, traces differences in "appearances" to differences in their "circumstances." Ideally, the method is best employed in the comparison of those appear­ ances "where the difference consists in a single circumstance; the whole effect of which in different appearances is, thereby, perfectly known." The outcome of such an investigation is that having "noted the whole effect of all the separate circumstances and situations of things," we would be able to "judge of their effect in all possible combinations.270 When Priestley speaks of isolating the "whole effect" of each of "the separate circumstances" of things and thereby hopes to judge their "effect in all possible combinations," he is presupposing the substantive mode of causation. However, in Priestley's own terms, it is evident that the same circumstance can lead to a variety of appearances depending on the nature of the accompanying circumstances, or that a given appearance can be the outcome of a great variety of circumstances having no common character. Such a conception of causation is expressed in relational language. To define the complex of events to which an appearance belongs is to subsume it under a law. Despite the consequence of his analysis, Priestley 269 "An

Examination," Works, 3 , 25. pp. 443-444,

i l o Electricity,

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is attempting to mold Kis sensationalism to suit the substantive mode of causation. This commitment to substantive causality arises from his view of "principles" and "powers" acting in nature so as to produce deter­ mined effects. In this manner, he conceives that a particular circum­ stance, viewed as a substantive principle, can be responsible for the same appearance in diverse situations. This conception of the causal relation­ ship is implied in Priestley's definition of a "perfect theory" as "a system of propositions accurately defining all the circumstances of every appear­ ance, the separate effect of each circumstance, and the manner of its operation."271 This definition comes directly from his sensationalism: the substantive causality of principles expresses itself in the drive to define "the separate effect of each circumstance." Priestley described the state of natural philosophy at the end of the eighteenth century in terms of his conception of the aim of natural philos­ ophy as the elucidation of causes viewed as "principles" or "powers" in nature. It appeared to him that contemporary developments in chemistry led to the conclusion that natural substances are composed of a small num­ ber of "principles" causing "all the appearances that have yet occurred to us."272 As his many discussions of chemical problems indicate, the sub­ stantive view of causation formed the basis of his chemistry of phlogis­ ton273 and made it impossible for him to grasp the general significance of the oxygen theory. There is no evidence to support Schofield's claim that Priestley's ad­ herence to "general principles" expresses his frustration with Lavoisier's "jig-saw puzzle problems of the permutations and combinations of ele­ ments" and his conviction of the resulting need to reduce chemistry to Newtonian dynamism of the invisible realm.274 On the contrary, Priestley uses the term "principle" to refer to active agents in nature without com­ mitting himself to a specific conception of any physical nature such as substance, structure, or force. An examination of the debates between Priestley and the "anti-phlogistians" evinces a clash between the substan­ tive logic of the phlogiston theory and the relational logic endemic to the

271 Jfcid.,

pp. 445-446. of Lectures, pp. 8-9. 273 See, e.g., Air, 1, 258-286; Natural Philosophy, 3, 401-426; Air and Natural Philosophy, 3, 533-563; Priestley, The Doctrine of Phlogiston Established, and that of the Composition of Water Refuted, 2nd ed. (Pennsylvania, 1803). Subsequent references to The Doctrine of Phlogiston. 274 Schofield, "Joseph Priestley, Natural Philosopher," op. cit. (note 247), pp. 3-4. 272 Heods

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main thrust of the oxygen theory. 275 To understand Priestley's objections to the oxygen theory, his conception of the role of natural philosophy in the elucidation of causal agents in nature must be taken into account. So, too, must his view of hypotheses. The epistemological status that he ac­ corded them has an important bearing on his view that both the oxygen and the phlogiston theories are mere hypotheses. Both of these aspects of Priestley's thought throw considerable light on his role in the dispute. The search for causal relationships in nature affects the role Priestley assigns to hypotheses in natural philosophy. He treats the formulation of hypotheses as equivalent to the construction of analogies. His debt to Hartley regarding his views of the role of hypotheses in natural philosophy is important; 276 following Hartley, Priestley rejects the prevalent New­ tonian viewpoint expressed in the dictum hypothesis non fingo, insisting on the necessity and usefulness of hypotheses. 277 Priestley claims "every experiment in which there is any design, is made to ascertain some hy­ pothesis" in so far as it is designed to trace the "influence of any circum­ stance in an appearance." Such an experiment would never be attempted if there were not some preconceived idea of the outcome. Hypotheses about the results of experiments are drawn "from some other analogies in nature, more or less perfect"; for "an hypothesis is nothing more than a precon­ ceived idea of an event, as supposed to arise from certain circumstances, which must have been imagined to have produced the same or a similar effect, upon other occasions." 278 Priestley considers hypotheses in natural philosophy desirable as well as necessary because they facilitate the "boldest and most original experiments" and "the greatest and most capital discoveries" by allowing the hypothetical method to give free reign 275 This debate can be seen in terms of a conflict between the "chemistry of prin­ ciples," adhered to by Priestley, and the "chemistry of elements," initiated by Lavoisier. In the former, the units of analysis are active agents, which cannot be isolated, in the production of certain effects or properties; in the latter, analysis yields units of simplicity that are defined and characterized in terms of their opera­ tional relation to chemical substances, which can be isolated. Although Lavoisier's thought was deeply influenced by the tradition of "chemical principles" in which he was trained (see M. Daumas, Lavoisier, theoricien et experimentateur [Paris, 1955]), his "revolutionary" work in chemistry was based on the logic of "elements." Priest­ ley, however, remained firmly within the tradition of principles. Such an important difference has to be noted when Priestley's criticisms of the "antiphlogistic theory" are considered.

276pri e stley's methodological discoveries are greatly indebted to the section in Hartley's Observations on Man that deals with "propositions, and the Nature of Assent" (1, 324-367). 277 See

note 74.

278 Electricity,

p. 444.

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to the imagination in the association of ideas. The factual fecundity arising from this approach could not be matched by results obtained by the approach of "cautious, timid, sober and slow-thinking people."279 Priestley's view of the epistemological status of hypotheses is inconsis­ tent. He sometimes views natural philosophy as advancing towards the "perfect theory" by the hypothetical method of "conjecture and refuta­ tion"; he views hypotheses as approximations to the true theory which, under the corrective force of experimental refutation, are brought "still nearer to the truth."280 More often, however, Priestley views hypotheses as merely heuristic devices; their truth-generating aspect is unimportant when compared with their crucial role in the production of "facts." He reverses the respective roles of hypotheses and theories, restricting hy­ potheses to the generation of facts from which the theory is "induced." "An hypothesis absolutely verified ceases to be termed such, and is con­ sidered as fact; though when it has long been in an hypothetical state it may continue to be called, occasionally, by the same name."281 A "pre­ conceived idea" (hypothesis) about the causal relationship between an "appearance" and a given "circumstance" becomes a matter of "fact" when established by observations obtained through "analogy." Priestley's enthusiastic assertion of the importance and fruitfulness of hypotheses in natural philosophy does not imply that he was insensitive to the persistent possibility of their misuse, a fear which was an integral part of his rationality. He regards the premature "transition" from hy­ pothesis to fact as the "only danger in the use of hypotheses." As a result of such improper use of hypotheses, a philosopher not only "mistakes the cause of one particular appearance," but following up "its analogies, he mistakes the cause of other appearances, too, and is led into a whole sys­ tem of error."282 Priestley's rationality keeps him from such a "vain tran­ sition." Maintenance of a strict distinction between "fact" and "hy­ pothesis" and "truth" and "prejudice" is a basic weapon in Priestley's methodological armory. A full appreciation of the distinction and of the epistemological status of the terms "fact" and "hypothesis" can only be gained by an examination of Priestley's conception of the logical structure and epistemological status of a scientific theory. His conception of a scien­ tific theory can, in turn, only be completely understood if seen as a conse­ quence of his rationality, and his underlying ontological commitments. Priestley regards natural philosophy as an exhaustive causal analysis of 259. 2MIbid., p. 444.

V»Air, 1,

280Electricity, p. 445. 282ibid., p. 445.

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nature, establishing particular "circumstances" as universal causes of given "appearances." His view allows him to reveal fully the deterministic struc­ ture of reality through the concepts and statements arising from his cri­ terion of rationality; according to that criterion, sensations, determined by the principle of association, arise in the uniform composition of man. As man is totally integrated into the material system of reality, so judg­ ment is the natural outcome of sensations ordered deterministically. "Facts" are the consequences of a methodological framework based on such a conception of thought; they are "particular" propositions describing the state of affairs elucidated according to the observational procedure based on the methodology of "analogy." According to Priestley's defini­ tion of rationality, a sufficient number of instances allows the inductive generalization from such "particular" propositions to "general" or "uni­ versal" ones. In his opinion, a scientific theory consists of propositions arranged deductively so that the more general or abstract entail the more particular or concrete. In 1781 he said that "all that is properly meant by a theory exclusive of hypothesis is a number of general propositions, com­ prehending all the particular ones, deduced from single experiments." 283 Priestley's emphasis on the hierarchic, deductive arrangement between propositions is evident in his conception of the nature of scientific prog­ ress: "the greater progress we make in the analysis of nature, the nearer we come to first and simple principles, and in a fewer general propositions may the whole be comprised." 284 Priestley conceives of progress in the knowledge of nature as an ascension from the "particularity" of effects in an external world given initially in nominalist terms, through the generality of "principles," to the universality of God's simple and immutable action. Priestley's view of the nature of scientific theories explains why he insists on a distinction between "fact" and "hypothesis," between propositions that can be "proved" or reduced to a simple enumeration of "particular propositions" and propositions that either have not been or cannot be "proved." The former can be included in a scientific theory; the latter, "opinions," cannot. Priestley's methodology is the basis of his achieve­ ments in natural philosophy. We can here give only a few indications of the explicit methodology in Priestley's published work, which is evident very early in his scientific career. In his History of Electricity, he articulates "A SERIES OF PROPO283Natural Philosophy, 2, vii. 284priestley, Miscellaneous Observations relating to Education (Bath, 1778), in Works, 25, 11.

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SITIONS, comprising all the general properties of electricity," in which he carefully avoids "the principles of any theory, even the most probable" and deals only with "known facts. " 285 He attempts to reduce the knowl­ edge of all electrical phenomena to a list of "particular" and "general" propositions which shows their interrelationships. 286 Priestley praises Franklin for his "discovery of many new and important facts," which stand "independent of all hypotheses." 287 Throughout his chemical works, Priestley insists that emphasis be placed on the factual content of his scientific publications; these alone are to be regarded as real discoveries. Explanatory hypotheses that transcend the observational realm are to be given no "great stress": "Upon this, as upon other occasions, I can only repeat, that it is not my opinions on which I would be understood to lay any great stress. Let the new facts, from which I deduce them, be considered as discoveries, and let other persons draw better inferences from them if they can." 288 He is able to establish facts, but he readily admits his fallibility in framing hypotheses. He also insists that hypotheses must be changed in the light of new factual evidence. His claim that he has advanced knowledge only through his ability to discover facts 289 is well illustrated in 1781 in the long penultimate section of the fifth volume of his experimental researches, entitled "A Summary View of all the Most Remarkable Facts in this and the Four PrecedingVolumes." 290 Here he reduces his discoveries of more than a decade to a set of "particu­ lar" and "general" propositions relevant to the formation of a "general theory." 291 Priestley views hypotheses as subjective viewpoints with little objective validity, and shows the same sensitivity towards them as he does towards political and religious prejudices. 292 This sensitivity is seen clearly in his criticisms of the oxygen theory and his defense of the phlogiston theory. 285 Electricity,

2s6 Ibid., pp. 434-440. pp. 432-443. p. 467. ' 2ss Air, 3, xvii. 289 See, e.g., "Letter from Priestley to Wedgewood; Birmingham, 23 January, 1783," in Schofield, ed., A Scientific Autobiography of Joseph Priestley, op. cit. (note 265), p. 222. Similar sentiments are expressed by Priestley in letters to Joseph Banks, dated 23 June 1783, and to Henry Cavendish, dated 16 June 1784 (Schofield, op. cit., pp. 227 and 233, respectively). See also Schofield, op. cit., p. 192, for further comments by Priestley on this subject. 2 ^ 0 Natural Philosophy, 2, 325-366. 291 Ibid., p. vii. 292 Throughout Priestley's writings the terms "hypothesis," "opinion," "prejudice," and "speculation" are used interchangeably for similar purposes in his epistemology. See Natural Philosophy, 2, vii, and Λ ir, 3, xvii. 2s Vbid.,

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Neither satisfies his idea of a scientific theory since neither can be reduced to a set of "genera] propositions" related to the "particular" in a hierar­ chic, deductive structure. He regards both theories as hypotheses that are deficient in rational determination and thus akin to religious and political prejudice. 293 To Priestley, the growing entrenchment of the oxygen theory within the eighteenth-century scientific community is analogous to that of authoritarianism within political and religious establishments. He ad­ monishes the leading advocates of the theory, warning them of establishing a "reign to resemble that of Robespierre" and of silencing dissident voices like his own by "power," rather than converting them "by persuasion." 294 Priestley frequently rebukes his contemporaries for indulging in hypothe­ ses. Although it is important for the advance of knowledge to detect the causes of appearances, the search for causes can lead to "too much haste to understand." At the early stage of investigation the mind must remain content with "the bare knowledge of new facts" until it discovers "by their analogy more facts of a similar nature" and constructs a "general theory" according to the dictates of rational understanding. 295 The preva­ lent chaotic state of chemical knowledge cannot be improved by pre­ mature speculation but only by the proliferation of more facts: "For when a sufficient number of new facts shall be discovered (towards which ever imperfect hypotheses will contribute) a more general theory will soon present itself; and perhaps to the more incurious and least sagacious eye. Thus, when able navigators have with greater labour and judgement, steered towards an undiscovered country, a common sailor, placed at the mast head, may happen to get the first sight of land." 296 The analogy focuses on the discovery of new "facts"; it makes the con­ struction of theory a trivial matter by comparison. Only after conducting experiments to test hypotheses do we "generalise the conclusions we draw from them, and by this means . . . form a theory, or system of princi­ ples." 291 The emphasis on the collection of "facts" reflects Priestley's assertion 293 Thus,

contrary to prevalent historiography, Priestley was as conscious of the hypothetical nature of the phlogiston theory as he was of that of the oxygen theory. Although satisfied with the phlogiston theory he was always ready to reject it should it be shown to be incorrect. See, e.g., The Doctrine of Phlogiston Established, p. 104. Both theories fell short of his epistemological standards in positing substances that had not been isolated. 294 The Doctrine of Phlogiston Established, p. xiii. 295 See, e.g., Natural Philosophy, 1, x-xi. 296 Nijtwra/ Philosophy, 3, χ ii—xiii. 297 IbiW., p. 400.

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that according to his sensationalist epistemology all men have equal access to knowledge. Priestley identifies the content of the sensory with the con­ cepts applicable to it, so that judgment becomes another form of percep­ tion. His conception of a passive mind and the identification of judgment as perception form Priestley's theory that thought is a natural product of the mechanical law of association. In all human minds the conceptualizing power and content of the sensory are the same. Given a sensory basis for the accumulation of "facts," a general theory emerges as a product of nature shaped by the associationist powers of the mind. This is the heart of Priestley's conception of rationality. Discoveries in natural philosophy de­ pend on the ability to take infinite pains in gathering facts; they can there­ fore be achieved by any man. Even the most imperfect of hypotheses "may lead to the discovery of new facts." 298 The oxygen theory, too, is important in chemistry for Priestley because of "the many new experiments which it has occa­ sioned." 299 Priestley's belief in the equality of all men in intellectual ac­ tivity reinforces his regard for the "most imperfect hypotheses." Many people are inhibited from making discoveries by the "excessive admiration and wonder" inspired in them by some "first-rate philosophers." The philosophers do this by omitting in their published works "the intermedi­ ary steps" by which they reached their conclusions and by writing in a "synthetic style." Such philosophers give an exalted impression of their genius and discourage others from attempting a similar task. In Priestley's opinion, a good history of science would show that the works of genius depend on "faltering steps," "casual terms of thought," and qualities of "patience and industry," which can be "equaled by many persons." 300 He designed his History of Vision and History of Electricity not merely to in­ form the reader of the discoveries that had been made, but to show him "how they were made, and what the authors of them had in view when they made them." 301 Priestley did not except his own work from the rule: in all his writings he adopted the "analytic and historical method of pre­ sentation" and "made it a rule not to concede the real views with which I have made experiments." He hoped to "encourage other adventurers in experimental philosophy" by his example, 302 and his diffuse writings and rambling style are the result. 298 See,

e.g., Natural Philosophy, p. xxii. 300 Electricity, pp. 576-577. Doctrine of Phlogiston, p. 4. ^ ol Ibid., p. 577. The History and present state of discoveries in Vision, Light and Colours, 2 vols. (London, 1772). 302 SeeZlir, 1, x, and Natural Philosophy, 2, xi-xii. 299 The

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Priestley relates the fecundity of nature, of God's creation, to his con­ ception of progress in natural philosophy. Sometimes he emphasizes a thrust towards simplicity in the explanatory categories of thought. But it is also important to realize that Priestley's view of the fecundity of God's creation is a basis for his conception of the rich particularity of nature which reinforces the demand for the proliferation of "facts." Incomplete­ ness is an inevitable characteristic of all work in natural philosophy and, "paradoxical as it may seem, this will ever be the case in the progress of natural science, so long as the works of God are like himself, infinite and inexhaustible." 303 It must, therefore, be recognized that by reinforcing a methodological dictum derived from other sources, Priestley's view of progress in natural philosophy through the proliferation of knowledge of particulars holds heuristic sway over his view of progress as the establish­ ment of a single set of minimal laws for the comprehension of nature. Be­ cause of his rationality Priestley can argue that as the mind progresses towards more adequate knowledge and the generation of new problems, it will discover that all finite things are measured under single, universal, and deterministic laws; however, the search for simple laws is not as powerful methodologically as the search for particular facts. Our study will have achieved its purpose if it has rescued Priestley from the misrepresentations of history. He was neither an amateur stumbling through the world of natural philosophy nor a misguided theologian who misunderstood the religious traditions of his culture. Despite the chaotic appearance of his publications, it is apparent that they are the product of a mind concerned with the synoptic unity of thought. Priestley's intention to let natural philosophy play a crucial role in achieving a comprehensive philosophy is evident from a passage he chose from Bacon's works: So if there is any humility towards the Creator, any feeling of awe and praise for his works, any love for men, any concern to relieve human need and hardship, any love of truth and hatred of obscurity in the things of nature, any desire to make the mind pure; men should be asked over and over again, to dismiss trivial and absurd philosophies which have put thesis before hypothesis, and have led experience captive and triumphed over the works of God; and to approach with a certain rever­ ence to unroll the book of Creatures. They should not delay over this, but think deeply, and speak uprightly and honestly, free and untouched by prejudice. In searching the interpretation of Nature, let them spare no effort, but go with energy. Fix their minds on it, and never hang back. 304 303Air,

1, vii.

3 0 4 Title

page, Air, 1.

Laurent, Gerhardt, and the Philosophy of Chemistry BY JOHN HEDLEY BROOKE* INTRODUCTION: THE CHEMIST AND THE CHESSBOARD In a moment of insight Auguste Laurent once compared the chemist with a chess player. Those chemists, he declared, who rely exclusively on reac­ tions for the study of chemical constitution resemble a chess player who, wishing to know the disposition of the pieces on the board, begins by mixing the pieces up, then separates them into two groups, and then, by examining each of these groups in turn, tries to work out the original ar­ rangement. 1 Evidently Laurent could think of few more futile occupations than the attempt to infer the constitution of a compound from a knowl­ edge of its reactions, and he was not alone in this belief. His analogy with the chess board was merely a colorful gloss on the principle enunciated by his contemporary A. E. Baudrimont: A chemical reaction cannot take place without a movement of the atoms. Consequently a reaction . . . cannot and will never be able to in­ dicate the arrangement of the atoms in a combination. The same is true of the action of a battery. For a reaction, by establishing a molecular movement, destroys the preceding arrangements of the atoms. Therefore, being able to extract a compound substance from a combination does not mean that this compound already existed in this combination. 2 Plausible though it was, and eloquent a spokesman though it found in Laurent, the argument appears to have been disregarded by the main stream of organic chemists. Fifty years later when Ernst von Meyer wrote his massive history of chemistry, he included a section devoted to the de­ velopment of what he called "Important Methods for investigating the ""Department of History, University of Lancaster, Baiirigg, Lancaster, England. Laurent, "Sur Ie mode de combinaison des corps," Comptes Rendus de I'Academie des Sciences, 21 (1845), 852-860. 2 A. E. Baudrimont, Introduction a I'Etude de la Chimie par la theorie atomique (Paris, 1833), p. 50, as cited by S. C. Kapoor, "The Origins of Laurent's Organic Classification,"/•?!>, 60 (1969), 477-527, on 493. 1 A.

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Constitution of Organic Compounds." 3 We find among these "important methods" that which Laurent ridiculed: "a short sketch only can be given here," von Meyer wrote, "of a few of the more important methods which have been applied during these last decades, with the object of getting at the chemical constitution of organic compounds from their reactions, transformations and decompositions." 4 Closer inspection of von Meyer's account reveals his tacit admission that the method of inferring constitu­ tion from reactions would work only if one could make the prior assump­ tion that the carbon framework remained intact. 5 It curiously was Laurent more than anyone who had first emphasized the stability of carbon frameworks. Thus, when the organic chemists of the second half of the nineteenth century argued that constitution could be inferred from reactions, they were affirming a proposition that Laurent had denied, but they could only do so by accepting an assumption that Laurent had affirmed. In this paper I intend to examine the status of the presupposition that chemical constitution may be inferred from chemical reactions and the reasons why Laurent rejected it. It would be tempting to call this basic presupposition "empiricist," since the emphasis falls on the course rather than the cause of chemical reactions. But I hope to show that conventional labels are inadequate. It is precisely because attempts to label nineteenth-century chemists have pro­ duced too many sterile questions (Was Laurent a positivist? Was C. Gerhardt a positivist? Was J. B. Dumas a realist or a conventionalist?) that there is need for clarification. 6 I would like to suggest that it may be more profitable to ^nalyze the nineteenth-century chemist's response to this basic presupposition than to classify him by vague and usually anachronis­ tic philosophical labels. In other words the presupposition that chemical constitution can be inferred from reactions may be used as a kind of litmus paper: a chemist's reaction to it will bring out his true philosophical and methodological colors. It has been said, for example, that "like Dumas, 3 E. von Meyer, A History of Chemistry, transl. G. McGowan (London, 1898), p. 361. i i Ibid., p. 365. 5 "In many cases of transformation the chemist keeps his attention fixed upon particular elements or atomic groups united to carbon, the carbon framework itself

undergoing no change . . ." (ibid., p. 365). 6 Concerning the sterility of such questions, witness the conclusions of K. Boughey who, after examining "Positivism and Chemistry in 'the Age of Comte'," stated in an unpublished paper that "whether it is right to call Dumas, Laurent and Gerhardt positivists is all a question of definition." My own conviction is that the very attempt to subsume the three chemists under one definition is misconceived.

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Laurent was an anti-positivist who did not believe that the aim of science was the mere accumulation of facts." 7 Such a statement may obscure the fact that Mnlike Dumas, Laurent was an anti-empiricist who did not be­ lieve that constitution could be inferred from reactions. So different were their philosophical commitments that Laurent felt no compunction in deriding Dumas along with his other opponents. 8 If the philosophical positions of Laurent and Dumas have sometimes been mistaken for each other, those of Laurent and Gerhardt have almost always been. It is only during the last decade that historians of nineteenthcentury science have properly distinguished between Laurent's and Gerhardt's presuppositions at all; the pendulum of historical opinion has swung to the other extreme and now we have a picture of two correspon­ dents who did not correspond. 9 Without wishing to trespass on the pene­ trating and comprehensive studies of S. C. Kapoor 10 and N. W. Fisher, 11 I should like this paper to be construed as a contribution toward the reevaluation. Laurent and Gerhardt were united in their renunciation of the program of inferring constitution from reactions, but they were poles apart in their alternatives. To recognize this is, I believe, the first step to­ ward a balanced reinterpretation.

FROM REACTIONS TO CONSTITUTION It used to be argued that what characterized the campaign of Laurent and Gerhardt was their rejection of electrochemical dualism. 12 Their pro­ fessional alienation could then be conveniently explained in terms of the ostracism facing anyone who stepped outside the current dualistic para­ digm. But this interpretation will no longer do. In the first place, as Kapoor 7 Kapoor,

op. cit. (note 2), p. 501. Kapoor has to admit, ibid., note 92. 9 Cf. N. W. Fisher, The Taxonomic Background to the Structural Theory of Organic Chemistry, University of Wisconsin Ph.D thesis (Madison, 1970), p. 127, where Laurent and Gerhardt are portrayed as "two theoreticians talking at, rather than to, one another." 10 Kapoor, op. at. (note 2), See also the same author's "Dumas and Classification in Organic Chemistry," Ambix, 16 (1969), 1-65. 11 Fisher, op. cit. (note 9), together with his subsequent article: "Organic Classifica­ tion before Kekule," Ambix, 20 (1973), 106-131; "Organic Classification before Kekule. Part II," Ambix, 20 (1973), 209-233; and "Kekule and Organic Classifica­ tion,"Ambix, 21 (1974),29-52. l2 See C. de Milt, "Auguste Laurent. Guide and Inspiration of Gerhardt," ]. Chemi­ cal Education, 28 (1951), 198-199, where Laurent's doctoral thesis is construed as the first substantial attack on the electrochemical theory of Berzelius. 8 As

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has convincingly demonstrated, it is misleading to speak of paradigms and discontinuities in early organic chemistry: however radical the innovations of Laurent, they emerged from a constellation of ideas already current in the Uterature of the period, from the crystallography of R. J. Haiiy, the theoretical considerations of Baudrimont, and the chlorine substitutions of Dumas. 13 In the second place, Laurent's eclecticism contradicts any his­ torical interpretation that supposes that his intellectual horizons stopped— or even started—with his critique of dualistic doctrines. We have his own testimony that it was otherwise: in his doctorate thesis, which already contained the germ of his mature ideas, far from disclaiming the electro­ chemical theory, he conceded that it had made great strides when applied to organic chemistry. 14 Further, he explicitly stated that it was his inten­ tion to reconcile the constitutional goals of dualism with the theoretical considerations that frustrated them. 15 Laurent's ideas had developed 13 Kapoor,

op. cit. (note 2), pp. 490-501, 522-523. Jacques, "La These de Doctorat d'Auguste Laurent et la Theorie des combinaisons organiques (1836)," Bull. Soc. Chim. (May 1954), supplement, pp. D31D39. Laurent refers to the "avantages immenses" that the electrochemical theory "presente dans la nomenclature, dans l'etude de la chimie et maintenant dans ses applications a la chimie organique . . ." (italics mine). He even goes so far as to say that dualism has been so useful that he would still feel constrained to use it were it proved false. Subsequent events did not bear this out, but it remains that the dualistic approach to organic chemistry was far more fruitful than is commonly supposed. For a defense of this proposition see J. H. Brooke, "Chlorine Substitu­ tion and the Future of Organic Chemistry: Methodological Issues in the LaurentBerzelius Correspondence," Studies in the History and Philosophy of Science, 4 (1973), 47-94. 15 "Dans Ia theorie que je vais exposer j'ai cherche a concilier Ies deux precedentes, en conservant Ies avantages, que chacune d'elle presente" (Jacques, op. cit. [note 14], p. D35). The "deux precedentes" were the electrochemical theory and the unitary theory of Baudrimont. This concern for conciliation raises m another form the question whether it is appropriate to set up an antithesis between the dualism of the electrochemists and the unitary theories of Laurent and Gerhardt. Most commenta­ tors have taken this antithesis for granted, but it really requires careful scrutiny. The chemists of the 1830's were preoccupied with at least three different problems: those of constitution, classification, and the mechanism of combination. Once these distinc­ tions are recognized, the alleged antithesis can no longer be maintained. In its elec­ trostatic, mechanistic aspect the dualistic theory was genuinely dualistic, but in its constitutive aspect far less so. Similarly, in its classificatory aspect the unitary theory was genuinely unitary, but in its constitutive aspect, as Laurent's own models so clearly reveal, it was far less so. This means that when discussion focuses on the cen­ tral matter of chemical constitution, we find fewer differences between Berzelius and Gerhardt than we might expect—fewer indeed than either Laurent or Gerhardt cared to admit. By the time the French chemists began to caricature him, Berzelius no longer believed in a crude juxtaposition of two parts within his molecule. (Brooke, op. cit. [note 14].) 14 J.

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alongside and not in opposition to the prevailing chemical theories. 16 Eventually, of course, both Laurent and Gerhardt fought the dualists, but when they did so their primary concern was with something more funda­ mental. The ulterior principle to which they took exception was the pre­ supposition that constitution could be inferred from reactions, and al­ though that presupposition was frequently employed by the dualists, its negation was not inconsistent with electrochemical theory. What were the characteristics of this ulterior principle, and how was it applied by the organic chemists of the 1830's? Since the principle could not be applied in isolation, its exploitation cannot be used to illustrate a.purely empiricist program. Organic chemistry was in such a primitive state that supplementary principles were also re­ quired. None of these achieved greater success than that of J. J. Berzelius, who insisted that a sine qua non of progress was that in determining the constitution of organic compounds chemists should make use of analogies drawn from the inorganic domain. 17 With this supplementary principle the inference of constitution from reactions became a less daunting prospect. T. J. Pelouze and E. Fremy adopted both principles when they argued the superiority of (NH 3 + HCl) over (NH 4 + Cl) to represent ammonium chlo­ ride on the grounds that NH3 and HCl could be isolated whereas NH 4 was hypothetical. 18 In general terms, if a given compound X decomposed into parts Y and Z, then the reaction allowed that X could be represented as if it contained Y and Z as preformed units, providing that this conclusion was compatible with whichever supplementary principles were in opera­ tion. This was the prescription that dominated the organic chemistry of the 1830's. It was used at various times by Justus von Liebig, Friedrich Wohler, Dumas, and Berzelius, and it presupposed that chemical reactions could unveil the interior of a molecule. Not all its adherents were as con­ fident as Dumas who in his Leqons sur la Philosophie Chimique confessed that he had always believed in the preexistence of his radicals, 19 but few disputed that it was legitimate in many cases to infer a preformed group of elements. Collaborating with Wohler on establishing the derivatives of uric acid, Liebig had been troubled by problems of preformation, but not sufficiently so to be deterred from inferring the preexistence of urea in 16 J.

F. Persoz, Introduction a I'etude de la chimie moleculaire (Paris, 1839), p. 823. from J. J. Berzelius to Laurent, June 1844, in H. G. Soderbaum, ed., BerzeliusBref (Uppsala, 1920), Section VII (Miscellaneous Correspondence), p. 208. 18 T. J. Pelouze and E. Fremy, Cours de Chimie Generate (Paris, 1848), 2, 127 f. 19 "Leur preexistence me semble vraisemblable et . . . j'y ai toujours cru." (j. B. Dumas, Legons sur la Philosophie Chimique [Paris, 1837], p. 348.) 17 Letter

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the acid. 20 The most convincing evidence for his view was the decomposi­ tion of uric with nitric acid, a reaction in which urea was liberated. The preformation idea was also supported by Liebig's and Wohler's suggestion of a uril group present in uric acid, "alloxane," and "alloxantine." 21 More than mere convention was at stake, as entire research programs were defined in terms of reactions. As Liebig and Dumas declared in their mani­ festo of 1837: "Our object being to characterize each substance thoroughly, to establish what sort of radical it contains, we shall consecrate all our energy to the reactions peculiar to every substance we study." 22 If a compound X could both be prepared from and regenerate Y and Z, the diagnosis that X contains Y and Z as preformed ingredients was more secure than if only one of these reactions was familiar, especially if the missing reaction was that of preparation. It was supposed that agents of decomposition were more likely to scramble the elements than agents of regeneration. Thus, Berzelius in the first French edition of his Traite was not prepared to accept that certain oils could be constituted by acid plus glycerin until such time as they might be prepared from just those ingre­ dients. 23 Once the synthesis was achieved, Berzelius would have few scruples about the formulation. Furthermore, the diagnostic role of reac­ tions was not restricted to decomposition and composition. If a given compound were subjected to a series of transformations such that its derivatives could be written in the form R + E, where R was the highest common fraction and E was the residual proportion of elements in each case, then the series of derivatives could be assumed to contain the radical R. This was precisely the argument of Liebig and Wohler in their celebrated paper on the benzoyl radical, in which R became C 14 H 10 O 2 , the highest common unit in benzaldehyde (R + 2H), benzoyl chloride (R + 2C1), benzamide (R + N 2 H 4 ), benzoyl cyanide (R + C 2 N 2 ), and b enzoic acid (R + H 2 O 2 ). 24 The common radical was not always so readily discerned: Dumas 25 had to rewrite a series of camphor relatives, replacing various 2 0 J. Liebig and F. Wohler, "Recherches sur la Nature de I'Acide Urique," Annales de Chimie, 68 (1838), 225-337. 2 1 "In all these compounds only one single invariable can be followed, and it is the hypothetical body which we assume to be combined with urea in uric acid. This is the compound C 8 N 4 O 4 which we call uril. . ." (ibid.). 22 Liebig and Dumas, "Note sur Petat actuel de la chimie organique," Comptes Rendus, 5 (1837), 567-572. 23 Berzelius, Traite de Chimie (Paris, 1831), 5, 330 f. 24 Liebig and Wohler, "Researches concerning the Radical of Benzoic Acid,"Ann. derPharm., 3 (1832), 249-287. 25 Cf. R. Blanchet, "De la composition de quelques substances organiques," J. de Pharm., 20 (1834), 341-356.

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multiples of the radical C 2 H 3 with a common "camphogen" group C 10 H 16 . Nevertheless, the hunt for the common radical was an essential feature of the method; it was made more difficult by the desire to restrict the total number of radicals to a minimum. Liebig, for example, became more and more parsimonious, and would insist that his acetyl radical C 4 H 6 was inside almost everything. 26 Whether or not oxygen should be allowed in­ side a radical was another question, 27 but the prominent goal remained the inference of preformed groups from chemical reactions. With so much emphasis on the idea of preformation, it was inevitable that chemists would prefer organic compounds that had actually been isolated for radical status, since they would not appear hypothetical. The etherin theory 28 of Dumas, fox example, was admitted for so long because the hydrocarbon on which it was based was already well known, even though the hydrocarbon lacked the alkaline properties that Dumas' analogy required. Liebig saw in benzamide one of the elements of hippuric acid, 29 and so explicit a reference to organic compounds as elements serves as a reminder that the predecessors of Laurent and Gerhardt were interested in the relations between compounds only insofar as such rela­ tions pinpointed the constituent radical. A parallel between the dehydra­ tion reactions of ammonium oxalate, formate, and acetate was to suggest the preexistence of oxalic acid in both formic and acetic. 30 26 Liebig could defend his breaking down of the ethyl radical C 4 H 10 into C 4 H 6 and H 4 on the grounds that a common "acetyl" radical C 4 H 6 could then be pre­ sumed to exist within the derivatives of both acetaldehyde and ethyl alcohol (Traite de Chimie Organique, transl. C. Gerhardt [Paris, 1840-1844], 1, 375). Bunsen's cacodyl radical C 4 H 12 As 2 was broken down in similar fashion, Liebig transcribing the oxide into [(C 4 H 6 )O +As 2 H 6 ] by analogy with [(C 4 H 6 )O + N 2 H 6 + H 2 O], aldehyde ammonia (ibid., p. 470). 27 Berzelius' vacillation on this question is well known. Having hailed the work of Liebig and Wohler on the benzoyl radical as the dawn of a new day in vegetable chemistry, he subsequently declared that "Sauerstoff in einem Radikale ist ein Nonsens" (J. R. Partington, A History of Chemistry [London, 1964], 4, 329). It is less well known that Dumas, and Liebig himself, had similar reservations about the presence of electronegative oxygen within an ostensibly electropositive radical (Liebig,ibid., p. 280). 28 The essence of this theory was that alcohol and ether could be envisaged as hydrates of the same hydrocarbon', alcohol (4C 2 H 2 , 2HOH), ether (4C 2 H 2 , HOH) (Dumas and P. Boullay, "Sur Ies ethers composees," Annates de Chimie, 31 [1828], 15-53). It was possible to identify the common hydrocarbon with olefiant gas precisely because "il est dans la raison de partir de ce qui est connu pour etablir des theories." ("Quelques Reflexions de Chimie," Annates de Chimie, 68, [1838], 161204, on 170.) 29 Liebig, Traite de Chimie Organtque, op. cit. (note 26), 1, 86. 30 A. W. Hofmann, "A Course of Lectures on Organic Chemistry," Lecture 17, Medical Times and Gazette, 9 (1854), 561-564.

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The preoccupation with the search for radicals and preformed groups characterized the tradition that Laurent and Gerhardt were to malign. To understand their opposition to this tradition, we must examine the objec­ tions that could be leveled against the principle that constitution could be inferred from reactions. SOME AWKWARD OBJECTIONS By the end of the 1830's, there were weaknesses in the application of the principle that invited exploitation. One such weakness was the failure to isolate the vast majority of the conjectured radicals. A glance at any of the volumes devoted to organic chemistry during the ]830's shows that of the countless compounds analyzed many were acids of the vegetable king­ dom. Although there was no universal agreement 31 as to how these acids should be represented, the most popular formulation was based on a mate­ rial analogy with inorganic acids. Acetic acid would be written [(C 4 H 6 ) O 3 + H 2 O] by analogy with sulphuric [SO 3 +H 2 O] in conformity with its neutralization reactions. The problem concerned the status of the hy­ pothetical radical. The reactions of acetic acid implied the existence of the preformed radical, but its decomposition provided no proof. Since each acid ostensibly had its own radical, the failure to isolate a single one of them was viewed with dismay. By 1839 Gerhardt was already sensitive to the way in which organic chemistry was being enriched by a host of hy­ pothetical bodies, 32 and in that same year—still four years before they were to meet—Laurent expressed a similar objection: "When M. Berzelius shows me a single one of his radicals, when he combines a single hydro­ carbon with chlorine or oxygen, when he is able to make a single acid by uniting a hydrocarbon with oxygen . . . I shall abandon at that instant my bizarre ideas." 33 Laurent even took the trouble to count 111 hypothetical radicals in Liebig's Traite. 34 They were a considerable embarrassment to the chemists who failed to isolate them, even to those who, like Liebig, suspected that there were good reasons for their failure. 35 31 Cf. Dumas' discussion in Lesson 9 of his Leqons sur la Philosophic Chimique, op. cit. {note 19). 32 Gerhardt, "Sur la Constitution des Sels Organiques a Acides Complexes," Annates de Chimie, 72 (1839), 184-2 14. 33 "Who then has seen ethyl, formyl, the radicals of stearic, margaric, acetic, pyruvic, malic and a hundred other similar acids?" (Laurent, "Sur Ies Acides Pyromarique, Azomarique," Λ ΜΗ . Chim., 72 [1839], 383-415.) 34 J. Jacques, "La naissance de l'idee de structure chimique et Ies savants du XIX siecle," Conferences du Palais de la Decouverte, series D, No. 38 (Paris, 1956), p. 12. 35 Liebig, op. cit. (note 26), p. x.

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A commitment to [(C 4 H 6 )O 3 + H 2 O] for the rational formula for acetic acid implied not only the isolation of the preformed radical but also that of the acid anhydride. However, to postulate an anhydride within the acid on the basis of neutralization reactions and inorganic analogues be­ came meaningless if the anhydride could not be procured. Of the hundred or more organic acids then known, Gerhardt was soon to complain that only four or five actually lost the elements of water as required by the theory. 36 By a splendid irony it was he who first prepared the anhydrides of monobasic organic acids; but that, as he well knew, was by the conden­ sation of two acid molecules. 37 If the failure to isolate acid radicals and acid anhydrides was a short­ coming of the empiricist method, a more serious flaw was the equivocal nature of chemical reactions. In abstract terms the problem was this: if a compound X could be synthesized from either A and B or C and D, and if it could be decomposed into either E and F or G and H, then how should the preformed groups be selected? Why represent X by (A + B) rather than (G + H), by (C + D) rather than (E + F)? Because each chemist knew best, formulas for one and the same compound were multiplying at an alarming rate. The chemical reactions of an organic compound were too diverse to disclose its constitution and did not allow chemists to assume the preexistence of any product, as P. J.· Robiquet pointed out to Dumas. 38 Baudrimont elaborated on Robiquet's objection: chemical reactions were bound to be a capricious guide if two such isomorphous compounds as the nitrates of barium and lead relinquished disparate products when heated. 39 In organic chemistry the situation was rapidly becoming absurd: Liebig, Dumas, Berzelius, E. Mitscherlich, and F. J. M. Malaguti all had different formulas for a substance as mundane as alcohol, 40 and each could exhibit a characteristic reaction to justify his preference. 41 One could still defend 36 Gerhardt, "Sur la Classification chimique des substances organiques," Revue Scientifique et Industrielle, 12 (1843), 592-600. 37 L. E. Grimaux and C. Gerhardt, Charles Gerhardt. Sa Vie, Son Oeuvre, Sa Correspondance (Paris, 1900), p. 234. 38 P. J. Robiquet, "Reflexions sur un memoire de M. Dumas," J. de Pharm., 20 (1834), 489-497. 39 Baudrimont, Traite de Chtmie Generale et Experimentale (Paris, 1844-1846), 1, 281. 40 As Gerhardt assigned them: Dumas (C 4 H 8 + H 2 O 2 ); Liebig (C 4 H 10 O + H 2 O); Mitscherlich (C 4 H 10 O 2 + H 2 ); Malaguti (C 4 H 6 O + H 4 + H 2 O). (Gerhardt, Precis de Chimie Organique [Paris, 1844-1845], pp 12-13.) 41 Liebig's formula was constructed with an eye to the dehydration of alcohol, Malaguti's with an eye to the chlorination, and that of Mitscherlich to the reaction with sodium. Associated with this same equivocal nature of reactions was the con-

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the conventional principle, as Liebig did, by distinguishing between the decomposition of an organic compound under mild conditions and its various metamorphoses when the conditions were more violent. 42 Only a mild decomposition would then be privileged with a diagnostic role. How was the "empiricist" premise affected by the publicity given to chlorine substitution? This question was complex, since at first sight Laurent himself appears to have taken advantage of the diagnostic powers of chlorine substitution to corroborate his formulas for what he called "fundamental" radicals. It was by his experiments on the chlorination of naphthalene that he made the concept of persistent chemical "types" a viable one. 43 That the hydrocarbon naphthalene was susceptible of an enormous number of addition reactions (which greatly affected its proper­ ties) and an enormous number of substitution reactions (which did not) was consistent with the postulation of a hydrocarbon nucleus or funda­ mental radical, the structure of which remained intact during substitution. Yet, in the last analysis, as Berzelius so rigidly insisted, the types of the French chemists, of Dumas as well as Laurent, did transcend experience and were therefore at variance with a purely empiricist method. 44 Chem­ ical properties might be retained after chlorination, but this did not rigorverse problem that, when treated with identical reagents, two very different com­ pounds could still yield identical products. As Persoz observed, the action of strong alkali on acetic acid generated marsh gas and carbonate, but the same could be said of its action on acetone (Persoz, "Remarques a l'occasion de diverses communica­ tions de M. Dumas," Comptes Rendus, 10 [1840], 326-331). 42 See Liebig's own introduction to his Tratt'e, op. cit. (note 26). "En chimie organique, on observe des decompositions qui different des decompositions ordinaires de chimie mmerale; ce sont ce qu'on appelle des metamorphoses." 43 Laurent, "The'orie des Combinaisons Organiques," /1 nnah'S de Chimie, 61 (1836), 125-146; "Sur IaNitronaphtalase," Annates de Chimie, 59 (1835), 376-397; Methode de Chimie (Paris, 1854), pp. 224, 237; "Serie Naphtalique," Revue Scientifique et Industrielle, 14 (1843), 74-113. 44 Brooke, op. cit. (note 14), especially pp. 52-54. Dumas' theory of types may have been designed as a theory of classification, but, as he himself acknowledged, it was also designed to explain what his law of substitutions had merely summarized ("Memoire sur la Ioi des substitutions et la theorie des types," Comptes Rendus, 10 [1840], 149-178). Both Laurent and Dumas had to presuppose the principle of minimum structural change, and they both fell prey to circular reasoning. In one breath Laurent would argue that knowledge of the identical roles of hydrogen and chlorine already presupposed knowledge of exact replacement, while in another he could state that knowledge of exact replacement presupposed a knowledge of iden­ tical roles. Laurent's appeal to isomorphism as evidence of exact replacement did not improve his argument, since he had to redefine isomorphism for the argument to work (E. Millon and J. Reiset, "M. Laurent sur l'lsomorphisme," Annuaire de Chimie [1846], p. 367).

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ously prove that the chlorine occupied the precise place vacated by the hydrogen. An assumption of minimal structural change was being taken for granted. Once it was recognized that chlorine could replace the hy­ drogen within a radical, the very idea of a preformed, immutable radical lost its prestige. 45 This did not mean that the notion of radicals had to be sacrificed altogether—Dumas, 46 when trying to appease Bunsen, managed to h?rmonize the radical and type theories—but it did mean that when there could be as many as a hundred chlorine derivatives of one and the same compound (naphthalene), serious rethinking had to be done. The proliferation of radicals was perhaps the most serious problem of all. It was not occasioned by chlorine substitution alone; for if, as was often the case, a hypothetical radical was associated with a prominent member of a particular genus, then as the number of species increased so did the number of radicals. Referring to the rapid multiplication of alkaloids and their anilides, Laurent was soon to repudiate the amide and the imide radicals on the grounds that "we should necessarily have to imagine two or three new radicals for each amide, imide, etc. of aniline, methylamine, and the other alkaloids." 47 By 1843, organic chemistry was in a state of chaos, just as its masters like Liebig were retiring from the field.

LAURENT'S INITIATIVE In reacting against the traditional method Laurent spurned the advice of Dumas, who had told his students to base their formulas on nothing but "experience." 48 He had to ascertain constitution by other means, since it could not be inferred from experience. The phenomenon of isomerism was a sufficient rebuke to Baudrimont, who had retreated into empirical formulas. 49 At the same time Laurent had to concede the force of the 4s Conservatives, such as Bunsen, who had just isolated what he took to be the cacodyl radical, went so far as to suggest a "complete opposition" between the radical and type theories. (R. W. Bunsen, "Memoire sur I'acide cacodylique," Annales de Chimie, 8 [1843], 356-362.) 46 Dumas, "Note de M. Dumas au sujet du Memoire de M. Bunsen," Annates de Chimie, 8 (1843), 362-363. 47 Laurent, Chemical Method, transl. W. Odling (London, 1855), p. 226. 48 "Prenez pour Ies corps composes Ies formules qui, s'accordant avec l'analyse elementaire, representent Ie mieux 1'experience, et ne Ies basez jamais que sur elle . .." (Dumas, op. cit. [note 19], p. 357). 49 "Le systeme de M. Baudrimont est une negation." '"Il suffit d'observer que 1'acetate de methyle a la meme formule que Ie formiate d'ethyle, et que Ies sels d'ammonium sont isomorphes avec Ies sels de potassium pour prouver que Ies

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argument by which Baudrimont had dismissed the diagnostic role of reac­ tions. In this difficult position Laurent boldly asserted that if preformed groups could not be inferred from reactions, then preformed structures must be postulated to explain the reactions. Thrusting organic chemistry into three dimensions almost for the first time, he devised explanatory models based on the persistence of specific hydrocarbon structures. It is necessary to stress the methodological significance of this well-known solution to his problem. Precisely because they were three dimensional, Laurent's models so far transcended "experience" that they could not have been read out of chemical reactions. Since they had to be consistent with chemical reactions, Laurent introduced the idea of certain subtrac­ tion reactions that "laid bare" a central hydrocarbon nucleus common to each series of organic compounds. 50 Because he postulated his nuclei rather than inferred them, Laurent was free to represent them by hydro­ carbons that had actually been isolated, thereby minimizing their hypo­ thetical character. Given the current atomic weights or equivalents, one can see why his nuclei—his fundamental radicals—had empirical formulas 51 such as C 4 H 4 , C 16 H 16 , C 32 H 32 . Projected into three dimensions they would be represented by symmetrical prisms with carbon at the corners and hydrogen at the midpoints of the edges. Laurent's justification for his model was that with it one could readily explain the differences between addition, subtraction, and substitution reactions. Addition of chlorine to a hydrocarbon was merely the process whereby hydrogen equivalents of chlorine could adhere to the surface of a prism. Substitution of chlorine was the consequence of removing a hydrogen atom from the nucleus itself; i.e., of an action that would cause the whole structure to collapse if the atom were not replaced by another. It was then easy to understand why peripheral chlorine could be subtracted with KOH and why substituted chlorine could not: the latter had become part of a structure that resisted deformation. 52 chimistes qui cherchent a decouvrir Ie groupement des atomes dans Ies corps com­ poses ne poursuivent pas une chimere." (Laurent, "Serie Naphtalique," Revue Scientifique et Industrielle, 14 [1843),313-349.) 50 JfeW., 12 (1843), 179. 51 In order to transcribe Laurent's formulas into our own, the carbon should be divided by two. Laurent's C 4 H 4 was ethylene, C 8 H 8 butylene, etc. A primary nucleus as large as C 32 H 32 corresponded to a right prism with sixteen faces, each base of which would present sixteen solid angles and sixteen edges. (Laurent, "Reclama­ tion de priorite," Comptes Rendus, 10 [1840], 409-417.) 52 Although Laurent was not always consistent when advocating protective loca­ tions within a molecule, it was his belief in resilient frameworks that allowed him to

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Laurent's chemistry, as the author of one obituary perceived, was com­ pletely dominated by his vision of three-dimensional structures. 53 As he confided to Berzelius after contrasting the stability of substituted naph­ thalenes with the instability of their addition products, "I cannot help but see in all these compounds a nucleus of C 20 H 16 capable of undergoing a host of substitutions without changing its constitution." 54 Laurent's refer­ ence here to his naphthalene nucleus points to yet another sense in which his models took precedence over experience. When Dumas advised Laurent to construct his formulas on the basis of "experience" alone, he already presupposed that the empirical formula for a given compound was fixed and incontrovertible. But the methods of organic analysis were not so precise that the results of analysis could not be declared inaccurate if there were theoretical grounds for suspecting them. The facts—even such brute facts as parts by weight—were frequently theory-laden. The dispute be­ tween Laurent and Liebig concerning the empirical formula for naphtha­ lene illustrates the influence of theoretical assumptions. 55 There was no doubt in Laurent's mind that naphthalene could not contain fifteen atoms of hydrogen, for an odd number of atoms would destroy his nuclear hy­ pothesis. Liebig, who had no such prior commitment, thought otherwise. Laurent's quantitative analysis of course confirmed H 16 , Liebig's H 15 , and each chemist was incensed by the other. It happens that Laurent was right in this case if one makes the appropriate adjustment to his equivalents, but he did not gain his conviction solely from the data. In fact, much of the animosity generated by both Laurent and Gerhardt was the consequence not of paradigm collision but of their ostentatious practice of reanalysis. 56 repeat ad nauseam that the arrangement of atoms was as decisive a determinant as their electrical nature. (Laurent, "Theorie des Radicaux," Revue Scierttifique et Industrielle, 12 [1843], 175-183; Brooke, op. cit. [note 14], pp. 62-63.) 53 Laurent's researches "were not merely the inspiration of an active mind, but were conceived under the influence of a fundamental idea of which the substitution theory is one of the consequences." ("President's Address, Anniversary Meeting," J. Chem. Soc., 7 [1855], 144-159, on 154.) 54 Letter from Laurent to Berzelius, 12 May 1843, in Berzelius Bref, op. cit. (note 17), Section VII, p. 184. The italics are mine. 55 For Laurent's own account of this particular dispute, see his polemical reply, "M. Liebig et la Chimie," Revue Scientifique et Industrielle, 8 (1846), 300-320. 56 It was a consequence of Gerhardt's reform of chemical equivalents in 1842 that organic formulas then in use could not contain an odd number of carbon atoms, since these were the formulas that Gerhardt wished to halve. (Gerhardt, "Recherches sur la Classification Chimique des Substances Organiques," Revue Scientique et Industrielle, 10 [1842], 145-281; Grimaux and Gerhardt, op. cit. [note 37], pp. 64-65.) With this and similar laws, which included their "law of even numbers"

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To accuse a chemist of sloppy analysis was the gravest insult, especially if, as in this case, he happened to be Liebig: "M. Laurent is a mere beginner who would have deserved my every indulgence had he not had [such] pre­ sumption." 57 Just as Laurent's anticipation of the results of analysis indi­ cates the primacy of his model, so also does his prediction of new com­ pounds. He could predict the existence of many of his naphthalene derivatives before he had actually prepared them, 58 and he forecast a whole series of products to be obtained by successive and alternate treat­ ment of (what we call) ethylene dichloride with KOH and chlorine. Chem­ ical constitution could not be inferred from reactions, but it could be postulated to explain and predict them. The origin of Laurent's hypotheses and the source of his confidence in them are questions too involved to pursue here; in any case they have been examined by Kapoor in his study of the origins of Laurent's classification. The clue to Laurent's methodology is his background in mineralogy 59 and his particular debt to Haiiy's crystallography. He was at home thinking in three dimensions, and he employed his hydrocarbon nuclei in much the same way as Haiiy employed his crystal nuclei; they constituted the basic principle of a classification scheme. 60 The crystallographyc analogy did not stop there: the shapes of Laurent's structures were often replicas of Haiiy's primitive forms -tetrahedrons, hexahedrons, and parallelopipeds. 61 Al-

(Laurent, "Sur Ies combinaisons orgamques azotees," Comptes Rendus, 20 [1845], 850-855), the two innovators embarked upon a program of reanalysis. Offending formulas had to be extirpated. Gerhardt so eagerly "corrected" the analyses of other chemists that by 1850 he had completed the revision of no less than twentyfive formulas. ("Notice sur Ies travaux de M. Ch. Gerhardt," Comptes Rendus des travaux de Chimie, Sixieme Annee [1850], pp. 427-432.) Itwasa frustrating venture for them both, because no amount of reanalysis could compel their contemporaries to accept their reforms; and it was tiresome for their opponents who felt that they were being confronted with an a priority. "M. Gerhardt adopte une methode tres commode pour faire des theories dont Ie principal avantage consiste a declarer comme errones tous Ies faits connus qui ne s'accordent pas avec la theorie qu'il avance." This was Berzelius' response, and a typical one. See J. H. Brooke, The Role of Analogical Argument in the Development of Organic Chemistry, Cambridge University Ph.D. thesis (Cambridge, 1969), Ch. VI, pp. 194-204. 57 Cited by Laurent, op. cit. (note 55), p. 301. 58 Laurent, "Sur la Nitronaphtalase," Annates de Chimie, 59 (1835), 376-397. 59 Kapoor, op. cit. (note 2), pp. 494-498, 510-517. 60 Ibid., pp. 517-519; J. G. Burke, Origins of the Science of Crystals (California, 1966), Ch. IV. 61 Kapoor, ibid., p. 497.

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though tempted 62 to do so, Laurent did not allow himself to identify these nuclear shapes with the real constitution of the molecule. By his presup­ positions, he could never translate the model into reality through appeal to chemical reactions. As he conceded in his Chemical Method, "the argu­ ment deducible from chloro-substitutions does not prove that there are various groups existing in compound bodies." 63 This needs to be said be­ cause one of the most authoritative of Laurent's interpreters 64 has por­ trayed him as a naive realist who believed that the methods of the labora­ tory were sufficient to fix the real arrangement of the atoms. Laurent had his own reply to that interpretation: "We have not to occupy ourselves with the real arrangement of the atoms, but only to ascertain whether or not it is the same for such and such other body." 65 The chemist was still limited in what he could know: he could never fully comprehend the constitution of any one compound, but he could recognize that, whatever it was, it probably resembled that of analogous compounds. To acknowl­ edge this limitation Laurent eventually coined the phrase "synoptic formulas"; 66 they were formulas that made no pretence to express the real 6 2 As in Laurent's Chemical Method, when, after presenting his formulas for a whole series of halides, aldehydes, and acids, he could not refrain from saying that "observing the harmony, the elegance, and the extreme simplicity of their formulas, I cannot help considering the above, to be a representation of the real arrangement of the atoms" (Laurent, op. cit. [note 47], p. 331). 63 Ibid., p. 274. 6 4 J. Jacques, op. cit. (note 14), p. D33. See also the same author's "Essai bibliographique sur l'oeuvre et la correspondance d'Auguste Laurent," Institut GrandDucal de Luxembourg. Section des sciences naturelles. Extrait des Archives, 22 (1955), 14. 6 5 Laurent, op. cit. (note 47), p. 298. The italics are mine. 6 6 Letter from Laurent to Gerhardt, 19 April 1845, in Grimaux and Gerhardt, op. cit. (note 37), p. 482: "je veux bien abandonner avec vous Ies formules rationnelles, maisa condition que nous chercherons un systeme de formules synoptiques indiquant

des rapports de classe et de proprietes. . . ." This apparent volte-face of Laurent has sometimes been interpreted as the decisive step towards a positivist philosophy such as Gerhardt was already defending. It is tempting to contrast the early Laurent of his These (cf. note 14) with the Laurent who was now succumbing to the influence of Gerhardt. I believe, however, that this is a peremptory judgment. There are several considerations that show that Laurent was not drifting into a positivist position: i) Later that same year, 1845, despite his new commitment to synoptic formulas, Laurent was still convinced "qu'il existe dans Ies corps compose's divers groupes d'atomes. Si l'on veut apprendre quelque chose sur l'arrangement des atomes, ll est indispensable d'abandonner la route que l'on a suivie jusqu'a ce jour" (Laurent, "Sur Ie mode de combinaison des corps," Comptes Rendus, 21 [1845], 852-860). He may have been abandoning former routes, but he still wished to learn as much as possible about the arrangement of the atoms.

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constitution of the compound. Analogous formulas denoted analogous constitutions. As Gaston BacKelard rightly insisted, 67 Laurent's position is so delicate that it cuts straight through the categories of the philosopher. Clearly, Laurent was neither empiricist nor positivist, neither realist nor instrumentalist. He developed a sophisticated alternative position that was scarcely understood by Gerhardt, let alone by any of his less sympathetic critics. The chemist could still strive to know the constitution, but he could never know that he knew it. 68 This self-limitation was too much for those, like Liebig, who were still bound by the more traditional approach: "The entire theory of Dr. Laurent is an arbitrary play with ideas and formulas to which he attributes a significance they do not have; it has arisen out of a complete ignorance of the principles of true scientific re­ search," 69 Liebig of course knew what those true principles were, as did ii) Even when Laurent did appear to relinquish the quest for atomic constitution, it is clear from the context that he saw this as an expedient, provisional policy. He could refer to his synoptic formulas as his "cheval de bataille," and he addressed Gerhardt accordingly: u Nous ignorons quel est ce groupement. L'ignorerons-nous toujours? Qui Ie sait?" (Letter from Laurent to Gerhardt, 11 May 1845, in Grimaux and Gerhardt, op. cit, [note 37], pp. 485-487.) The point is that there is a great difference between being ignorant of chemical constitution at a given time and arguing that it is either meaningless to talk about it or impossible in principle to ascertain it. iii) Even when proclaiming the virtues of his synoptic formulas, Laurent still emphasized the need for the kind of hypotheses that Gerhardt deplored: "imaginer un systeme de formules tel qu'aux corps analogues correspondent des formules analogues, quand meme on devrait y faire entrer des corps hypothetiques" (letter from Laurent to Gerhardt, 11 May 1845, ibid.). The italics are Laurent's own, and they afford conclusive proof that his synoptic formulas were more than positivist constructs. iv) Laurent continued to assert that hypotheses must be tried (letter from Laurent to Gerhardt, 29 May 1845, ibid., p. 495) and, with due deference to Gerhardt's opinion, insisted that they must be hypotheses about the arrangement of atoms: "que ce mot ne vous effraie pas" (letter from Laurent to Gerhardt, 13 Sept. 1845, ibid., p. 505). 6 ?G.

Bachelard, Le pluralisme coherent de la chimie moderne (Paris, 1932), p. 61. particular reconstruction of Laurent's position does at least make sense of his enigmatic remark to Gerhardt: "Les autres chercheront des formules d'arrangement, et nous pourrons les attaquer a moins qu'ils ne trouvent la vraie formule, Mais ils n'y sont pas encore" (letter from Laurent to Gerhardt, 19 April 1845, in Grimaux and Gerhardt, op. cit [note 37], p. 482). This remark may be satirical, but one must not overlook the fact that Laurent still presupposed the possibility of stumbling across a "vraie formule." 69 See J. P. Phillips, "Liebig and Kolbe, Critical Editors," Chymia, 11 (1966), 8997, on 91. That Laurent was self-consciously departing from the generally accepted canons of "true scientific research" is evident from the cavalier manner in which he 68 This

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Dumas, who could never quite forgive his former assistant, Laurent, for having proclaimed the truth about chlorine substitution so far in advance of experiment. 70

GERHARDT AND THE SCOPE OF CHEMISTRY There are various reasons why the names of Laurent and Gerhardt have invariably been linked together. Their careers bear a superficial resem­ blance: both spent time in the provinces, Gerhardt at Montpellier and Laurent at Bordeaux; both were embroiled in priority disputes, Laurent over chlorine substitution, Gerhardt over homologous series; both were implacably jealous and sharp-spoken; both reformed organic classification; and both died young. Adolphe Wurtz, who perhaps did more than anyone to teach their innovations in France, linked them in his history of chem­ istry and in the compassionate eulogy it contained: what rare abnegation theirs had been, how sublime their poverty, how glorious their deaths! 71 The accessibility of the correspondence between Laurent and Gerhardt 72 is another reason why historians like to link them. There is evidence that they conspired against their peers, 73 and that Laurent encouraged Gerhardt to publish his new journal. 74 No one was more assiduous than

could classify Dumas' type theory along with the ideas of Berzelius on atomic ar­ rangement: "les types modernes ne sont que la reproduction de ce que l'on trouve dans tous les traites de chimie" (M. Tiffeneau, ed., Correspondance de C. Gerhardt (Paris, 19IB), 1, 285-287). So extravagant did Laurent's method appear to his con­ temporaries that Liebig could advise Gerhardt to reject it: "Rappelez-vous ce queje vous dis: vous brisez votre avenir et vous irritez tout Ie monde, comme Laurent et Persoz, si vous continuez a faire des theories" (letter from Liebig to Gerhardt, 1 March 1849, in Grimaux and Gerhardt, op. cit. [note 37], p. 42). 70 Dumas, "Memoire sur la Ioi des substitutions et la theorie des types," Comptes Rendus, 10 (1840), 149-178, on 165. 71C. A. Wurtz, A History of Chemical Theory, transl. H. Watts (London, 1869). 12 Grimaux and Gerhardt, op. cit. (note 37). Tiffeneau, op. cit. (note 69), pp. 96269. 7 ^No one reference could convey the sense of exasperation and persecution that pervades their correspondence, but this is how Laurent perceived their situation in May 1846: "personne n'est pour nous; tout ce que nous pouvons dire, c'est que Pelouze n'est pas contre nous. Quant au reste, les Dumas, Balard, Thenard, Regnault, Chevreul, ils desirent nous voir enterres en province afin qu'on n'entende plus parler de nous . . ." (letter from Laurent to Gerhardt, 7 May 1846, in Grimaux and Ger­ hardt, op. cit. [note 37], pp. 141-142). 74 Laurent was more than favorably disposed to the idea of a new journal (letter from Laurent to Gerhardt, 12 Feb. 1845, in Tiffeneau, op. cit. [note 69], pp. 1819), but he was soon disenchanted with the intrepid, belligerent, and self-centered

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Gerhardt himself in associating his and Laurent's names. When he wrote his own testimonial for the vacancy at the College de France in 1850, he insisted that his principles and inclinations were identical with those of Laurent. 75 He perpetually referred to "our system" 76 and perpetually misrepresented Laurent's position, indeed so much so that Laurent had to protest in his Chemical Method that his "residues" were on no account to be confused with Gerhardt's. 77 It was Gerhardt, not Laurent, who sug­ gested that they should publish a combined treatise, 78 and for all that they style of Gerhardt's Comptes Rendus des travaux de chimie. He had warned Gerhardt that "il faudra se battre avec courtoisie," and he was soon admonishing him again: "effacez de la couverture de votre recueil que vous donnerez Ies travaux des laboratoires de Montpellier et de Bordeaux. Cest connu, il n'est plus necessaire de Can­ noneer" (letter from Laurent to Gerhardt, 25 March 1845, ibid., pp. 29-30). But it was too late. The advice that Laurent received from Quesneville was not merely the outburst of a jealous editor: "Gerhardt se fait des ennemis sans nombre, qui deverseront sur vous Ieur colere plus tard. Vous etes tres aime personnellement des chimistes et ce petit journal va vous faire perdre cette estime . . ." (cited by Laurent in his letter to Gerhardt of 29 May 1845, ibid., p. 57). 7 5 Gerhardt, "Notice sur Ies travaux de M. Ch. Gerhardt," Comptes Rendus des travaux de chimie, Sixieme Annee (1850), pp. 427-441. At a time of counterrevolu­ tion, Gerhardt's socialism put him at a further disadvantage, and there is no doubt that Laurent was the more eligible. Despite Biot's warm recommendation, however, it was Balard, not Laurent 5 who was elected. (Grimaux and Gerhardt, op. cit. [note 37], pp. 204-206.) 7 6 Gerhardt, "Introduction a l'etude de la Chimie," J. de Pharmacie, 14 (1848), 63-67. Laurent, on the contrary, made a point of distinguishing "your (Gerhardt's) theories and mine." See, e.g., the letter from Laurent to Gerhardt, 25 March 1845, in Tiffeneau, op. cit. (note 69), pp. 29-30. 7 7 Laurent op. cit. (note 47), pp. 208, 294. For their failure to reach agreement on 5 the meaning of the term "residues," see the letters of Laurent to Gerhardt, and Gerhardt to Laurent, 17 May 1845, in Grimaux and Gerhardt, op. cit. (note 37), pp. 490 f. Gerhardt understood by "residues" those groups of elements that were trans­ ported during a double-decomposition reaction. The question for Laurent was whether or not Gerhardt could identify the correct groups without making some hypothesis about constitution. If Gerhardt summarized the nitration of naphthalene with this equation, C 1 0 H 8 + NHO 3 = C 1 0 H 7 (NO 2 ) + H 2 O, then Laurent would retaliate by enquiring why the residue should not be [NHO 2 ] corresponding to the formula C 1 0 H 6 (NHO 2 ) 1 with hydrogen from the acid appearing in the residue. "Make it clear to me," Laurent would plead, "whether by your residue formulas you are adopting a convention . . . or whether you are making a hypothesis about the arrangement." Laurent found no satisfaction in Gerhardt's reply, and the very nature of his challenge is a vindication of the argument that his preoccupation was with the limitations of chemical reactions. He could even impute to Gerhardt an un­ critical acceptance of the common premise, "for what proof have you that the origi­ nal arrangement has not been destroyed?" (Letter from Laurent to Gerhardt, 17 May 1845, ibid.) 7 8 See the letter of Laurent to Gerhardt, 15 Sept. 1845, ibid., in which Laurent deliberately contrasts their methods.

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learned from each other in their lively correspondence, Gerhardt's to Laurent was the greater debt. 79 The only real excuse for conflating Laurent and Gerhardt is that they were united by what they rejected, which was the prescription that chemical constitution should be inferred from reac­ tions. Liebig's reference to their "monstrous alliance" must be understood in the context of the dispute over that prescription. 80 Laurent's and Ger­ hardt's own remedies were hardly compatible. In his Traite de Chimie Organiquesi Gerhardt attacked the widespread "prejudice" that chemical formulas are capable of expressing molecular constitution. 82 According to Jean Jacques, the "prejudice" was propa­ gated by none other than Laurent. 83 I find this interpretation hard to accept. The presuppositions of Laurent were neither crude nor wide­ spread enough to constitute a common prejudice. Far from casting asper­ sions on Laurent's chemistry, Gerhardt was in fact endorsing Laurent's critique of an older "prejudice," that which allowed preformed groups to be inferred from chemical reactions. Following both Laurent and Baudrimont, Gerhardt 84 declared that if molecular constitution could be deduced from chemical reactions then barium sulphate must have at least three different formulas: (BaO + SO 3 ), (BaO 2 + SO 2 ), and (BaS + 20 2 ). The older "prejudice" was ridiculed by Gerhardt as it was by Laurent. 85 79 Gerhardt, who was never quick to acknowledge his debt to anyone, did make an exception in the case of Laurent. "Je suis tout fier qu'il ait voulu descendre jusqu'a moi, par consequent, avant ces derniers evenements, je n'ai jamais vu un homme qui eut une telle abondance d'idees; ses lettres sont pour moi quelque chose de precieux, je Ies etudie comme un evangile" (letter from Gerhardt to Cahours, 29 May 1845, in Grimaux and Gerhardt, op. cit [note 37], p. 147). One cannot but be impressed by Laurent's magnanimity in attempting to reprieve Gerhardt's reputation in Paris; there was the constant risk of guilt by association. See Laurent to Gerhardt, 7 May 1846: "Persoz est tres mecontent que j'aie pris votre defense . . ." (ibid., pp. 137 f.). 80 Liebig, "M. Gerhardt et la Chimie Organique," Revue Scientifique et Industrielle, 7, (1845), 422-439, especially 431. In the mid-1840's Liebig was far more hostile to­ ward Gerhardt, the "highwayman" (ibid., p. 438), than toward Laurent whom he regarded as one of the most talented chemists of the day (ibid., p. 430). My emphasis here is not intended to give the impression that there was no alliance at all. We know that Laurent and Gerhardt eventually worked together in Paris and even contemplated the foundation of a laboratory to be modelled on Liebig's Giessen laboratory or the Royal Institution of London (Grimaux and Gerhardt, op. cit. [note 37], p. 210). 81 Gerhardt, Traite de Chimie Organique, 4 vols. (Paris, 1853-1856). i2 Ibid., 4, 561. 83 This prejudice "que Gerhardt estime necessaire de la detruire, quel est vers 1850 Ie chimist" de renom qui pouvait Ie partager? . . . J'avoue pour ma part n'en connaitre qu'un, et c'est Laurent" (J. Jacques, op. cit. [note 64], p. 13). 84 Gerhardt, op. cit. (note 81), 4, 561. 85 Although it has little more than symbolic significance, the controversial passage that Gerhardt suppressed in his translation of Liebig's textbook was the one in which

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But whereas Laurent had argued that if we cannot infer constitution from reactions we must postulate plausible models, Gerhardt maintained that if we cannot infer constitution from reactions then all we can ever know are the reactions. It would be idle to pretend that their respective presuppositions were consistent enough to allow a definitive comparison. They were both capable of blatant inconsistencies. 86 There is little doubt that in his mature theory of types Gerhardt made more concessions to constitution than in his earlier career when he had advertised empirical formulas alone. 87 At the same time there are crucial points with respect to which Gerhardt and Laurent must be contrasted. Their presuppositions re­ mained essentially at odds: whereas Laurent continued to define a com­ pound with reference to a putative and characteristic constitution, Gerhardt could only do so with reference to a characteristic reaction. For the one, an amide might still contain a preformed radical N 2 H 4 ; for the other, it was a compound susceptible of hydrolysis into an ammonium salt. All compounds were, for Gerhardt, defined by their past and their future; i.e., by their reactions alone. On this matter he was explicit: "With the old method, one defines a compound such as it really is, one makes hypoth­ eses about its molecular constitution but in the method peculiar to my­ self, a compound is defined by its metamorphoses that is by its past and its future. . . ." 88 An equation summarized a reaction; it did not represent a process. Whereas Laurent's goal was the explanation of reactions, Ger­ hardt in his Precis was less ambitious: "The chemist must always compare the results of his experiments with those which precede them; for it is by this comparison alone that little by little we arrive at general laws, and consequently at the simplification of science." 89 Simplification not exLiebig approved the common principle and attributed it to Chevreul ("M. Gerhardt et la chimie orgamque," Revue Scientifique et Industrielle y 7 [1845], 431). Liebig complained that Gerhardt's omission had cost him the friendship and esteem of Chevreul, a supposition which Chevreul later denied (letter from Laurent to Gerhardt, 21 March 1846, in Grimaux and Gerhardt, op. cit. [note 37], p. 130). 86 Cf. Brooke, op. cit. (note 14), pp. 61-63. 87 Cf. Fisher, op. cit. (note 9), pp. 139-140. Gerhardt had been forced into the position of recognizing that in a compound such as bereophenone, the carbon was present "sous deux formes" (letter from Gerhardt to Chancel, 27 November 1848, in Grimaux and Gerhardt, op. ctt. [note 37], p. 549). 88 Gerhardt, "Notice sur Ies travaux de M. Ch. Gerhardt," Comptes Rendus des travaux de chimie, Sixieme Annee (1850), pp. 427-441, on p. 433. 89 Grimaux and Gerhardt, op. cit. (note 37), p. 109. He was as explicit, if not more so, in his Traite, when he avowed that "the particular objective of organic chemistry is the investigation of the laws according to which organic compounds are transformed" (Gerhardt, op. cit. [note 81], 1, 121). See also Fisher, op. cit. (note 9), pp. 140-141.

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planation remained his objective. Whereas a formula for Laurent could still be a candidate for the distribution of atoms, a formula for Gerhardt was logically equivalent to the reactions of the compound, since all it ever did was to summarize those reactions. As a consequence Gerhardt could quite happily ascribe more than one formula to one and the same compound; 90 since every reaction scrambled the elements he would waste no time in reconstructing unique solutions. He could give the formula for benzalde­ hyde susceptible of chlorination as C 7 H 5 O, H; and for benzaldehyde in its behavior toward ammonia as (θ {pj ^ J . Gerhardt's chemistry was a chemistry of disposition: of the disposition of a compound to react in a certain way, not of the predisposition of atoms within it. Restricting the scope of chemistry in this way, Gerhardt coined the term "residues" to refer simply to those groups of elements that were trans­ ported from one compound to another during a double decomposition. Since it was not known until after the reaction which elements had been transported, the formulas had no predictive potential. They merely re­ minded the chemist of what he already knew. Gerhardt admitted this when, in controversy with Wurtz about the formulation of amides, he said: "My residue formulas can only be written after experiment, to summarize a collection of relationships." 91 So that his formulas would not be completely sterile, Gerhardt devised an elaborate predictive machinery based on his concept of homologous series. 92 He predicted the properties of new compounds by means of formal analogies established between their empirical formulas. If physical properties varied uniformly along a series of homologues, 93 then any gap in the series could be documented in advance. 90 Gerhardt, op. cit. (note 81), 4, 577. The contrast with Laurent is particularly compelling at this juncture, since Gerhardt's principles of classification were based on "analogies of metamorphosis," whereas those of Laurent were ultimately grounded in his concept of the common nucleus. 91 Gerhardt, "Note sur la theorie des amides," Comptes Rendus, 37 (1853), 281284. 92 Dumas had shown that a series of acids—from formic to margaric—could be gen­ erated by the formula (C 4 H 4 ) n O 4 or, with Gerhardt's equivalents, (CH 2 ) n O 2 (Dumas, "Loi de composition des principaux acides gras," Comptes Rendus, 15 [1842], 935-936). Not only did Dumas predict the existence of five new acids to complete the series, but he also observed a regular variation in melting points along the series, recommending a similar comparison for alcohols, hydrocarbons, and esters. Although he had read Dumas' paper, Gerhardt denied him the priority when he generalized the idea. The four known alcohols were shown by Gerhardt to be homologous [(CH 2 ) n + H 2 O], and their respective oxidation, sulfonation, and halogenation products could all be denoted by formulas in which the characteristic (CH 2 ) unit recurred. 93 As Kopp had already demonstrated in his "On a Great Regularity in the Physical Properties of Analogous Organic Compounds," Philosophical Magazine, 20 (1842),

426

THE PHILOSOPHY OF CHEMISTRY

Gerhardt was always proud of the fact that he had predicted the boiling point of propionic acid (140°C). 9 4 His analogies were purely formal: they were based on numerical relationships alone, so that his formulas for benzaldehyde and cuminic aldehyde could both contain a negativp sign. 95 In order to stress their homology they were given the formulas 17 (CH 2 ) H 8 + O] and [10(CH 2 ) - H 8 + OJ, respectively. When reproached for dabbling in chemical algebra, Gerhardt accepted the accusation with special satisfaction. 96 Laurent, on the other hand, whose predictions were based squarely on the material analogues that had promoted his hydrocarbon structures, would not have accepted that criticism. He had no need of Gerhardt's purely formal relationships. The same contrast between formal and material analogy 97 leads us to the most fundamental difference between the two men. Laurent could foster his material analogies because he believed in the cross-fertilization of scientific disciplines. The chemist, as he frequently instructed Gerhardt, 98 had much to learn from crystallography. Ignoring the exhorta187-197. The principle underlying Gerhardt's predictive machinery was then quite simple: "on voit . . . qu'il suffirait de connaitre la composition, Ies propnetes et Ie mode de formation d'un seul produit obtenu soit avec l'esprit de vin [(CH 2 ) 2 + H 2 O], soit avec l'esprit de bois [(CH 2 ) + H 2 O], soit avec tout autre corps semblable, pour deviner la composition des propnetes et Ie mode de formation de tous Ies corps semblables a ce premier produit." (Gerhardt, "Sur la classification chimique," Revue Scientifique et Industrielle, 14 [1843J, 580-609, on 588.) 9 4 Gerhardt, op. cit. (note 81), 1, 123; Gerhardt, "Sur Ie Point d'Ebullition des Hydrogenes Carbones," Annales de Chimie, 14 (1845), 107-114; Gerhardt, "Recherches de Chimie Organique," Comptes Rendus des travaux de chimie, 1 (1845), 65-96. The empirical formula for propionic acid was C 3 H 6 O 2 m accordance with the generating formula [(CH 2 ) n + O 2 ] for the homologous acids. Drawing on Kopp's observations with the hydrocarbons, Gerhardt assumed that for each increment of the (CH 2 ) unit the boiling point would rise by roughly 20°C. Since formic and acetic acids boiled at 100°C and 120°C, respectively, Gerhardt could forecast 140° for propionic. There was just one difficulty. In the case of the corresponding alcohol, C 3 H 8 O, the boiling point could not be divined with certainty. Gerhardt predicted 98°C, which was very close to the true value for η-propyl alcohol (97°C); but before the last volume of Gerhardt's Traite appeared, Kolbe had foreseen the existence of another alcohol having this same empirical formula. Subsequently prepared by Freidel in 1862, iso-propyl alcohol was to boil at only 82°C. In the long run Ger­ hardt's scheme could not have coped with the multiplication of isomers. 9 5 Gerhardt, Introduction a I'etude de chimie par Ie systeme unitatre (Paris, 1848), p. 296. 9 6 "On nous a reproche avec une sorte de dedain de faire de 1'algebre chimique; nous acceptons Ie mot avec satisfaction . . ." (Grimaux and Gerhardt, op. cit. [note 37], p. 395 f.). 9 7 M. B. Hesse, Models and Analogies in Science (London, 1963). 9 8 Cf. Laurent to Gerhardt, 24 Feb. 1845, in Grimaux and Gerhardt, op. cit. (note 37), p. 476.

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tion, Gerhardt had to foster his formal analogies because he believed in the autonomy of his science. In this respect, at least, those who thought of themselves as evangelists for Comte's philosophy found a more promising ally in Gerhardt than in Laurent." It was of course impossible to develop a completely circumscribed chemistry, and there were grave problems con­ cerning where the line should be drawn. Reviewing the recent literature in 1840 Gerhardt was quite prepared to acknowledge that Regnault's work on the specific heat of carbon held extremely important implications for organic chemistry. 100 But his objections to the intrusion of physical data reasserted themselves when he suggested that too much importance was currently attached to optical activity. 101 History in the long run was not on Gerhardt's side in his argument that chemical species were to be dis­ tinguished by chemical methods alone. Optical activity was to be the touchstone for the tetrahedral carbon atom, and it was Laurent who in­ spired the respect for physical methods which were so constructive in the hands of Pasteur, Le Bel, van't Hoff, and others who followed him in working in three-dimensional chemistry. 102 In all these respects Laurent and Gerhardt must be contrasted. Their fundamental differences are thrown into relief by their divergent response to a premise which was so spent by 1840 that there were even German chemists, like Mitscherlich, who were beginning to speak of "predisposing affinities" rather than preformed radicals. 103 For good chemical reasons rather than bad philosophical ones, Laurent and Gerhardt had to innovate. 99 J.

F. H. Papillon, Introduction a I'etude de la philosophie chimique . . . conformement aux principes de la methode positive (Paris, 1865), p. 16. 100 Gerhardt, "Expose' Sommaire des Travaux de Chimie Parus en 1840," Revue Scientifique et Industrielle, 4 (1841), 145-219. On the basis of Dulong and Petit's law, Regnault argued that the current atomic weight of carbon should be quadrupled. The empirical formula of every organic compound would then be affected, much to Gerhardt's satisfaction. 101 "Pour differencier deux corps, il nous faut, a nous chimistes, des diffe'rences chimiques, et il nous semble par conse'quent que tous ceux qui attachent aujourd'hui une si grande importance au pouvoir rotatoire, s'abusent etrangement en y voyant l'avenir de la science." (Ibid., p. 209; see also p. 151.) 102 There was historical as well as philosophical continuity here since it was Laurent as well as Delafosse who whetted Pasteur's appetite for crystallographic studies. Dur­ ing the winter of 1846-1847 when they were both at the Ecole Normale, Laurent interested Pasteur in a new project and invited his collaboration. Shortly afterwards, Laurent left the Ecole to equip a laboratory of his own, and by April 1847, when Laurent was working at the Sorbonne, the joint project was abandoned. See the letters of Pasteur to Chappuis in R. Vallery-Radot, ed., Correspondance de Pasteur (Paris, 1940), 1, 148-149, 152-153. 103 E. Mitscherlich, "Uber die chemische Verwandtschaft," Annalen der Phystk und Chemie r 53 (1841), 95-117. J. R. Partington,/! History of Chemistry, 4, 417.

428

THE PHILOSOPHY OF CHEMISTRY

The crisis in the early 1840's was as great as it was because the constitution-from-reactions principle and the analogy principle of Berzelius were both in disgrace. 104 The paradox is that it was Laurent who appears to have provided the means of reinstatement of the former principle. Dis­ pensing with his premature models, the next generation of organic chem­ ists adopted his principle of stabilized structure and returned to the diag­ nostic role of reactions. Wurtz was typical of that generation in his insistence that "the study of reactions ought always to provide our guide in the construction of our rational formulas: the ideas on atomicity are a means of verification, a criterion, but the unique foundation: that will always be experience." 105 Confirming the prevalence of this attitude, Kekule had observed that "many chemists, strange to say, are yet of the opinion that from the study of chemical change the constitution of com­ pounds can be deduced with certainty." 106 Kekule was not of that opin­ ion, 107 nor was Butlerov, 108 for whom it was "quite natural that chemistry, which deals only with substances during the course of their transforma­ tion, is unable to make any statement about their mechanical structure, at least so long as there is no assistance from physical investigation." That the two most celebrated authors of structural chemistry should find it necessary to discard the once cherished principle as Laurent and Gerhardt had before them confirms that its rejection was a prerequisite for construc­ tive innovation. And just as the two French chemists had responded very differently to the failure of the traditional program, so did Kekule and Butlerov in their turn. Kekule returned to the elements themselves and applied himself to a mechanical concept of structure based on valency relationships; Butlerov strove for a more thoroughly chemical concept of 104 That the fundamental issue in the substitution debates was the inversion of Berzelius' analogy principle is one of the main theses of Brooke, op. cit. (note 14.) 105 G. V. Bykov and J. Jacques, "Deux Pionniers de la chimie moderne: Adolphe Wurtz et Alexandre M. Butlerov, d'apres une Correspondance Inedite," Revue d'Histoire des Sciences, 13 (1960), 115-134, on 122. Also cited by D. F. Larder, "A Dialectical Consideration of Butlerov's Theory of Chemical Structure," Ambix, 18 (1971), 26-48, on 30. 106 A. Kekule, Lehxbuch der Organischen Chemie (Erlangen, 1861), 1, 157-158. C. A. Russell, The History of Valency (Leicester, 1971), pp. 143-144. 107 In fact Kekule proceeded to articulate the very argument which had so im­ pressed Laurent: "through the study of metamorphoses one cannot ascertain the positions of the atoms . . . because the manner in which the atoms of the substance undergo change and destruction cannot possibly prove how they are arranged in an unreacting compound that remains unattacked" (ibid.). 108 A. M. Butlerov, Zeitschrift fur Chemie und Pharmacie, 4 (1861), 554. Cited by Larder, op. cit. (note 105), p. 31.

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structure that would incorporate all the atomic interactions during the course of a transformation. 109 It was left to van't Hoff 110 to enunciate the chemists' principle of inertia which stated that a stable carbon struc­ ture is rarely destroyed by chemical reactions. To many of his audience this principle would have seemed inconsequential, 111 but it concealed an issue in the philosophy of chemistry that forty years before had been inflammatory.

ACKNOWLEDGMENTS I am grateful to the British Society for the History of Science, the Society for the Study of Alchemy and Early Chemistry, and the Chemical Society under whose joint auspices the paper was first presented on 18 November 1972. 109 Larder,

110 J-

ibid., p. 47.

H. van't Hoff 5 Ansichten uber die organische Chemie (Brunswick, 1878-

1881). Partington, op. ext. (note 103), pp. 417, 658. l l l It appears so inconsequential today that chemists discussing the determination of structure by the traditional "wet" methods of chemical reactions completely overlook the basic presupposition behind all such methods: the principle of minimum structural change. For a typical example see W. J. Lehmann, Atomic and Molecular Structure (New York, 1972), pp. 381-385.

The Lewis-Langmuir Theory of Valence and the Chemical Community, 1920-1928 BY ROBERT E. KOHLER, JR.* 1. INTRODUCTION Perhaps the most important development in the history of twentiethcentury chemistry is the theoretical unification of physics and chemistry in the late 1920's and 1930's when wave mechanics was applied to the chemical bond. But even before the emergence of "quantum chemistry," many chemists had begun to use electronic ideas in a qualitative way to ex­ plain molecular structure and reaction mechanisms. The synthetic theory of the 1930's was the culmination of a trend that was established in the 1920's; to understand the history of quantum chemistry, one must look to the patterns that emerged in the crucial transition years 1920-1928. Without doubt the most significant event of this period was the accep­ tance by chemists of G. N. Lewis's theory of the shared electron pair bond. 1 In previous papers, I have discussed the background and origin of Lewis's theory in 1916, its initial neglect, and its rediscovery in 1919 by Irving Langmuir, whose vigorous promotion made the "Lewis-Langmuir" theory a sensational novelty. 2 In this paper I will analyze how this theory became within a decade an established and respectable doctrine within the chemical community. Such an analysis presents special problems. We know exactly when and how Langmuir "rediscovered" Lewis's theory. But can we say when precisely Lewis's theory was "accepted" by the chemical community? What indeed do we mean by "the community"? Iwould like to suggest some of the analytic dimensions that I have found useful in ap­ proaching these questions. * Department of History and Sociology of Science, University of Pennsylvania, Philadelphia, Penna. 19174. 1 H. B. Watson, Modern Theories of Organic Chemistry (London, 1937). Linus Pauling, The Nature of the Chemical Bond (Ithaca, N. Y., 1938). 2 R. E. Kohler, "The Origins of G. N. Lewis's Theory of the Shared Pair Bond," Hist. Stud. Phys. Sci., 3 (1971), 35-61. R. E. Kohler, "living Langmuir and the Octet Theory of Valence," ibid., 4 (1972), 39-87.

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LEWIS-LANGMUIR THEORY OF VALENCE

My fundamental assumption is that the proper level of analysis of the reception of new ideas is the level of groups, ranging from small informal "schools" with common background or interests to distinct disciplines or subdisciplines, such as organic chemistry, with more or less explicitly shared problems, methodologies, and theories. One can draw the boun­ daries between these partly overlapping groups in different ways, depen­ ding on the problem at hand. The most important dimension for my purpose is the physics-chemistry dimension. Atomic physicists, physical chemists, structural organic chemists, organic reaction chemists, and so on all reacted to the Lewis-Langmuir theory in characteristic ways, as a threat, as an opportunity, or as irrelevant nonsense. One group of organic chemists, the "electropolar" school, embraced J. J. Thomson's electron transfer bond, but rejected Lewis's bond. Other groups remained loyal to their traditional, nonelectronic chemical theories. An important nascent cluster adopted Lewis's shared pair bond and eventually defined some­ thing like a new discipline, "physical organic chemistry." Among physical chemists and physicsts one sees a different willingness to see problems of organic structure and reaction as legitimate problems. The historian's problem is to see the relation between group expectations and commit­ ments and the responses to the Lewis-Langmuir theory. A second dimension concerns national styles of chemistry. The geo­ graphical distribution of clusters and schools is not uniform. The electro­ polar school was mainly American; German and British physical chemists had distinctly different outlooks in the 1920's. In the long term theoreti­ cal chemistry did become uniform and international, but in the short term, local successes and failures and local socio-economic circumstances created and maintained diversity. In understanding the reception of the LewisLangmuir theory, this national dimension proves to be a natural and useful one. Some natural conceptual dimensions of analysis involve distinctions be­ tween static and dynamic theories, chemical and physical concerns with ideas, and theoretical and experimental concerns with ideas. Lewis's theory was both a theory of atomic structure (the cubic atom) and a theory of the chemical bond; it was thus relevant to both physics and chemistry. A good deal of the published papers on the Lewis-Langmuir theory in the early 1920's concerned the apparent paradox between Bohr's "dynamic" plane­ tary model of the atom and Lewis's "static" cubic atom; the former ap­ pealed to spectroscopists, the latter to structural chemists. The issue was perceived at the time as a clash between physics and chemistry.

ROBERT Ε. KOHLER, JR.

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Yet, both physicists and chemists had a common theoretical concern with the issue of static vs. dynamic atomic models. Their debate, though lively, was short-lived, owing to the rapid development of quantum physics that preempted the issue. Lasting consequences for chemistry arose when Lewis's theory became part of a program for experimental research by chemists. This meshing of theory and experiment did not occur in Lewis's group, or in Germany, but among certain British organic chemists; this differentiation of national styles deeply influenced the history of quantum chemistry in the 1930's. In the 1920's the intellectual dimension of theo­ retical vs. experimental concerns is useful for understanding why certain groups were able to incorporate Lewis's theory into an ongoing program of chemical research. In this paper I want to show how the reception of the Lewis-Langmuir theory was determined by the pattern of disciplinary groups, and to sug­ gest how its adoption influenced the subsequent history of these groups. The analysis works two ways; it illuminates an important conceptual episode and reveals the fine structure of the chemical community. When chemists are forced to take sides in response to a challenge to the estab­ lished aims and limits of their discipline, the historian is afforded a view of the underlying attitudes and loyalties that divide and unite the discipline. From the controversy over the Lewis-Langmuir theory we glimpse the shifting intellectual loyaltiesin the transition period between pre-electronic chemistry, with its competing schools, and the theoretically unified quantum chemistry of the 1930's. Foremost among the landmarks in the reception of the Lewis-Langmuir theory was Lewis's Valence and the Structure of Atoms and Molecules in 1923, the first survey of chemistry in terms of the new theory 3 and a lucid and popular guide for a generation of chemists. A second landmark was the symposium "The Electronic Theory of Valence" sponsored by the Farady Society on 13-14 July 1923 and arranged to coincide with a visit by Lewis, who gave the opening address. 4 It is clear from the roster of participants and from the discussions that a sizable avant-garde in Britain and America was using the theory to analyze molecular structure and reac­ tion mechanisms. Vigorous controversies among this avant-garde over the 3 G. N. Lewis, Valence and the Structure of Atoms and Molecules (New York, 1923). 4 Symposium on "The Electronic Theory of Valency," Trans. Faraday Soc., 19 (1923), 450-537. G. N. Lewis, "Valence and the Electron," ibid., 452-458. See letters from T. M. Lowry to G. N. Lewis, 3 and 20 January 1923, Lewis Archive, Uni­ versity of California, Berkeley.

434

LEWIS-LANGMUIR THEORY OF VALENCE TABLE 1 Distribution of published papers concerning the Lewis-Langmuir and related theories of the chemical bond, 1918-1927. Total

1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 Totals

4 7 17 12 20 37 16 6 4 2 125

British

American

—

5 4 7 8 2 5 4 1 1 37

9 3 10 29 10 1 — —

62

German 2 2 4 1 1 3 — —

2 —

15

Other 2 —

1 1 1 1 1 1 11

use of the theory characterized the mid-1920's. The end of this period of controversies was marked by the appearance of the first systematic text­ book from the new school, Nevil Sidgwick's The Electronic Theory of Valence in 1927. 5 Finally, with the development of quantum chemistry and resonance theory in the early 1930's, the shared pair bond acquired mathematical garb, and the Lewis-Langmuir theory, in its new form, be­ came the undisputed basis of theoretical chemistry. A survey of the Uterature concerning the Lewis-Langmuir theory con­ firms the qualitative impression drawn from the major landmarks. Between 1920 and 1928 about 120 articles were published specifically on this sub­ ject. The annual output of papers rose rapidly from almost none in 1918 to a peak in 1923, after which a steady decline set in. By 1926 only a few papers of a controversial sort were appearing, those almost exclusively of a cranky type. The decline does not indicate a decline of interest in the Lewis-Langmuir theory, but only an end of a self-conscious interest in it as an unfamiliar and controversial theory. The disappearance of contro­ versial articles signified the general acceptance of the new theory by the chemical community and was accompanied by more frequent papers in which Lewis's bond was routinely used. Not that every chemist had ac­ cepted it, but by 1928 it was too respectable a doctrine either to invite open criticism or to need self-conscious support. So much for the silhouette of the changing opinion profile; a closer anal5 Nevil

V. Sidgwick, The Electronic Theory of Valence (Oxford, 1927).

ROBERT Ε. KOHLER, JR.

435

ysis reveals a wealth of local diversity. Geographically, Britain, Germany, and the United States produced eighty percent of the papers on the theory, including virtually all the important ones. In France, Italy, and Russia interest in the theory lagged several years behind the trend. Old ideas held out longer and there was an unusually high proportion of eccentric or cranky contributions. 6 A second noteworthy pattern is the relatively small number of applications of the theory in America. With a few exceptions, all the early American papers came from Lewis's colleagues and students in Berkeley. They were mostly papers in physical chemistry, and all ap­ peared before 1923. The theory aroused little interest among American organic chemists, a group that potentially stood to profit most from it. This seems surprising in view of the great enthusiasm Langmuir aroused among American chemists in 1919. Even more striking is the lack of in­ terest in Germany, which for over fifty years had been the undisputed leader in all branches of chemistry. In the early 1920's German chemists ignored or deliberately rejected the Lewis-Langmuir theory, and in the next decade lost their lead in this progressive, developing area of chemical theory. It was in Britain that the new ideas were most enthusiastically received, both by physical chemists and by a group of organic chemists who culti­ vated the new field of physical organic chemistry. The British chemists' investigations of organic reaction mechanisms dominated the 1930's and 1940's, while German organic chemists continued their traditional focus on structural problems. It would be wrong to speak of a general decline of German chemistry in the 1920's. But in the highly visible and prestigious area of physical organic chemistry, the 1920's did see a shift of the center of chemical research from Germany to Britain and America. This trend is one of the most important in the history of modern chemistry. These changes in the social and conceptual structure of chemistry had roots deep in the past in the adaptation of German chemistry to British and American environments in the nineteenth century. In the early 1920's, however, the national tendencies became accentuated and fixed as a result in part of the different national responses to the opportunity opened up by the Lewis-Langmuir theory. The structure of the chemical community in the 1930's and 1940's was determined in part by the events of the 1920's. 6 An exception worth noting is the early and perceptive review by Giacomo Ciamician (1859-1922) and M. Padoa, "Considerations sur la nature de Paffinite chimique et de la valence des atomes,"/. Chim. Phys., 16 (1918), 97-106.

436

LEWIS-LANGMUIR THEORY OF VALENCE

2. THE AMERICAN SCENE: LEWIS AND THE ELECTROCHEMISTS It is axiomatic that for a new idea to be adopted by a scientific com­ munity it must either fit in with clearly recognized needs or else be pro­ moted by a nucleus of active and patient disciples. A priori one might have expected the most active interest in the Lewis-Langmuir theory to be found in America, given Lewis's personal influence and the attention Langmuir brought it in 1919-1920. But it must be remembered that the attention was short-lived, and that it reflected more an interest in Langmuir than in his theory: the theory was of interest because it was Langmuir's theory. 7 Moreover, Langmuir's interest in valence theory cooled abruptly in 1921, and not being in a university he had no opportunity to pass on his interest to student disciples. The General Electric Laboratory could not have become the center of a continuing school of research in this field. Lewis's influence was longer-lived; but like Langmuir, he was not primarily concerned with valence theory, and his active involvement ended with the publication of Valence. Moreover, both Lewis and Lang­ muir were primarily interested in theory per se, rather than any systematic experimental exploitation of the theory. Neither Lewis's 1916 paper nor Langmuir's papers of 1919-1921 described new experiments, and the papers from Lewis's group do not reveal the kind of practical interests that would lead to a sustained research program. Berkeley remained a progres­ sive and influential center of general chemical education; but no distinctive school of research took root from Lewis's theory. The first paper on the theory, and one of the best, by Lewis's former students appeared in 1923. Its authors, Wendell Latimore (1893-1955) and Worth Rodebush (1887-1959), had taken their Ph.D.'s with Lewis in 1919 and 1917, respectively. Their subject was a familiar phenomenon to organic chemists: the ability of an electropolar atom to change the proper­ ties of a nearby reactive group in a molecule. For example, the proton in chloroacetic acid, Cl-CHj-COO-H, dissociates more easily than in acetic acid. The explanation of this effect, known later as "induction," followed from Lewis's idea that polar bonds were electron pairs that were closer to one atom than the other. 8 Following Lewis's brief suggestion in his 1916 paper, Latimer and Rodebush interpreted induction as a small displace-

7 See

Kohler 1 "Irving Langmuir," op. cit. (note 2). N. Lewis, "The Atom and the Molecule," J. Am. Chem. Soc., 38 (1916), 762-785. See p. 782. 8 G.

ROBERT Ε. KOHLER, JR.

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ment of the electron pairs of the bonds adjacent to a polar atom. 9 They explained heightened acidity of chloroacetic acid as a shift of electron pairs toward the electron-attracting chlorine atom and away from the dis­ sociable hydrogen atom. Lewis's concise and flexible double dot formulas soon became a standard part of organic chemical notation. Equally impor­ tant was Latimer's and Rodebush's explanation of the property of asso­ ciation in water as the simultaneous attachment of a hydrogen atom to the free electron pairs of oxygen atoms in two H 2 O molecules. Theirs was the first proposal of what came to be called the "hydrogen bond," which Lewis himself singled out as "the most important addition to my theory of valence." 10 The idea of the hydrogen bond was also conceived about the same time by Maurice Huggins (b. 1897), who received his degree under Lewis in 1922. It is perhaps not surprising that the hydrogen bond was in the air at Berkeley around 1921, since it drew on Lewis's insight that free pairs of electrons were not inert, even those in saturated molecules. The tone of Huggins' papers clearly reflects Lewis's taste for sophisti­ cated theory. From Lewis's rather overly optimistic non-Coulombic force model of atomic structure, 11 Huggins derived an elaborate Aufbau theory of the higher elements, 12 asserting that his work on the X-ray crystallo­ graphy of diamond was "incontrovertable proof" that his theory was cor­ rect. Equally ambitious was his long paper on the structure of benzene, for which he proposed a variant of Korner's six tetrahedra, having a free sextet of electrons in the center of the ring. 13 Dismissing sixty years of conflicting evidence, Huggins asserted that his diamond work "proves this structure to be the correct one." He also interpreted the four traditional types of organic reaction mechanisms in terms of shared pair bonds, a procedure that changed little more than the symbols, and proposed that tautomerism was due to the formation of a special stable group of four 9 W. Latimer and W. H. Rodebush, "Polarity and Ionization from the Standpoint of the Lewis Theory of Valence," ibid., 42 (1923), 1419-1433. See also J. H. Hildebrand, "Wendell Latimer," Biog. Mem. Nat. Acad. Sci., 32 (1958), 221-237. C. S. Marvel and F. T. Wall, "Worth H. Rodebush," ibid., 36 (1962), 277-288. 10 Lewis, Valence, op. cit. (note 3), p. 109. 11 G. N. Lewis, "The Static Atom," Science, 46 (1917), 297-302. 12 M. Huggins, "Atomic Structure," ibid., 55 (1922), 459-460. 13 M. Huggins, "Conjugation and the Structure of Benzene,"/. Am. Chem. Soc., 44 (1922), 1607-1617. The four traditional kinds of reaction were addition, substitu­ tion, exchange, and cycloaddition. Tautomerism involved the rearrangement of a three carbon system containing a double bond and a mobile atom; e.g., Br-CH 2 -CH=CH-R^ CH 2 =CH-CHBr-R.

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electrons. Ermon D. Eastman (b. 1891), who received his Ph.D. in Lewis's department in 1917, wrote a similar paper on the problem of the reactivity of double and triple bonds. He proposed that unsaturated bonds consisted of one shared pair of electrons and an "extended octet" made up of the free outer pairs of valence electrons and one or both of the inner doublets of the helium shell. 14 He argued that bonds formed by means of this ex­ tended octet would be reactive; and he gave them special new symbols and provided elaborately detailed explanations of such chronic problems of organic chemistry as tautomerism and aromaticity. Huggins and Eastman were bright, ambitious, and self-confident young men; both had acquired Lewis's taste for theory building, and both imitated Lewis's studied brilliance and iconoclastic style. Their papers re­ flected the lively and open intellectual atmosphere of Lewis's department and, in particular, the excitement generated by Lewis's theory of valence. But they were uninterested in developing a program of experimentation. The factors that made Berkeley the source of the valence theory prevented it from also being the place where it was best put to use. More modest papers on the theory were published by two other graduate students in Lewis's department, Dwight Bardwell (Ph.D. 1921) and Eustace Cuy (Ph.D. 1922). Cuy's concerned the shape of the H 2 O molecule, which long had been thought to be linear, but which recently had been shown to be bent. He pointed out that the noted German physical chemists Walther Kossel and Peter Debye had failed to explain this fact by traditional theory, but that according to Lewis's theory of the tetrahedral atom, the successor to his cubic atom, the two hydrogen atoms and the two free electron pairs of the H 2 O molecule would occupy the four vertices of the oxygen tetrahedron. The predicted bend was close to that observed. 15 Bardwell's brief paper was an elegant experimental demonstration that hydrogen in lithium hydride was electronegative, 16 which confirmed Lewis's 1916 prediction that this was so. The stability of the electron pair had suggested to Lewis that the hydride ion, (:H ), should be stable, and that hydrogen was thus the "halogen of the helium family." Bardwell showed that in fact hydrogen was released at the anode during electrolysis of lithium hydride. His experimental paper is an exception among the 14 E. D. Eastman, "Double and Triple Bonds, and Electron Structures in Unsatu­ rated Molecules," ibid., 43 (1921), 438-451. 15 E. J. Cuy, "Die Valenztheorie von G. Lewis und die Asymmetrie des Wassermolekiils," Z. Elektrochem., 27 (1921), 371-373. 16 D. C. Bardwell, "Hydrogen as a Halogen in Metallic Hydrides," J. Am. Chem. Soc., 44 (1922), 2499-2504.

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theoretical papers of Lewis's other students. Experiments with hydrides had been done as early as 1916, 17 but had been delayed by technical diffi­ culties and, one can assume, by flagging interest on Lewis's part. Success in this "critical experiment" in 1916 would likely have attracted a great deal of attention to Lewis's theory. In retrospect it is surprising that so little was done at Berkeley to pursue the opportunities that Lewis had opened up in bond theory. A major difficulty was that the best opportunities were in organic chemistry, a field Lewis was not comfortable in and which he did little to encourage at Berkeley. In his letters to Langmuir, Lewis mentioned other experimental applications of his theory that were under way. One concerned the struc­ ture of the amine oxides, for which his theory predicted an unexpected dipolar structure; 18 but this work was never published. Lewis simply did not care for problems of organic structure, and did not give his students work in this field. Nor did he care for chemical kinetics. Even Latimer's work on induction was not pursued, though it opened up rich possibilities for further work. Activities in the organic field remained occasional at Berkeley and did not develop into a lasting school of research. Although American organic chemists were generally not receptive to the Lewis-Langmuir theory, there were a few notable exceptions. In 1921 the young Harvard chemist James Bryant Conant (b. 1893) was puzzled by the formation of reversible addition complexes of carbonyl compounds and phosphorus chlorides. Lewis's notion of a free electron pair, which Conant ascribed to the phosphorus atom, and its attraction to the "positive" carbon atom of the carbonyl group resolved the difficulty. 19 This inter­ pretation of addition reactions became widely used by physical organic chemists in the 1920's. Conant's application of the double dot bond was one of the few that did not stem from Lewis's inner circle, but he noted that the usefulness of Lewis's theory was suggested to him in 1917 by Eliot Q. Adams (1888-1971), who was then an active member of the Lewis group, taking his degree in 1919. 20 In 1928, however, Conant revealed an agnostic attitude toward electronic theories of valence, partly in response to the collapse of the Bohr atom model and the introduction of wave 17 Lewis,

op. cit. (note 3), p. 774. Kohler, "Irving Langmuir," op. cit. (note 2), appendix. 19 J. B. Conant, "Addition Reactions of the Carbonyl Group,"/. Am. Chem. Soc., 43 (1921), 1705-1714. 20 Ibid., p. 1712. About 1920, Adams composed an extensive manuscript on valence theory, which was never published and which is now lost. (E. Q. Adams, personal communication, 1969.) 18 See

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mechanics. He recommended that the safest course for organic chemists was to think of valence electrons as "merely the number of negative charges which the atom can gain or lose in making up the mystic number of eight," and to leave atomic structure to atomic physicists. 21 Several other American organic chemists took up the Lewis-Langmuir theory in the mid-1920's. In 1924 Wallace Carrothers (1896-1937) pro­ posed a theoretical explanation for addition reactions of double bonds based on Lewis's 1916 paper. 22 He adopted Lewis's cubic atom, and Lewis's mechanical picture of the double bond that swings open upon one shared pair of electrons like a door on its hinges. Carrothers combined Lewis's taste for high theory and an organic chemist's feeling for organic reactions. But his paper remained an isolated harbinger of the 1930's. A brilliant chemist, Carrothers left the University of Illinois to do polymer chemistry at Dupont, where he won fame as the discoverer of neoprene and nylon. In 1924 Howard J. Lucas (1885-1963) published the first of a series of four papers on Lewis's idea of induction, or, as he called it. "electron displacement." 23 Lucas had published only five occasional papers since 1909, and it appears that Lewis's theory was a crucial influence on his career in providing him with a significant research program. His main in­ terest at first was the choice between the electropolar bond and the shared pair bond. He argued that Lewis's bond was preferable because it ex­ pressed degrees of polarity, which the electron transfer model could not. In 1926 he stated that "the development of a rational procedure by which the properties of carbon compounds can be related to [Lewis's] theory is one of the pressing problems of organic chemistry," and he ambitiously tried to use Sommerfeld's idea of electron screening as a qualitative physi­ cal explanation of electron displacement. 24 Despite Lucas' apparent sense of the Lewis-Langmuir theory as a general program, his work in the 1920's was overshadowed by the British school. In the mid-1930's, however,

21 J. B. Conant, "Atoms, Molecules, and Ions ,"J. Chem. Educ., 5 (1928), 25-35. Quote from p. 33. 22 W. H. Carrothers, "The Double Bond," J. Am. Chem. Soc., 46 (1924), 22262236. See also Roger Adams, "Wallace H. Carrothers," Biog. Mem. Nat. Acad. Sci., 20 (1939), 293-309. 23 H. J. Lucas et al., "Electron Displacement in Organic Compounds," I, II, III, and IV, J. Am. Chem. Soe., 46 (1924), 2475-2482; 47 (1925), 1459-1461 and 14621469: 48 (1926), 1827-1838. See also W. G. Young and S. Winstein, "Howard J. Lucas," Biog. Mem. Nat. Acad. Sci., 43 (1973), 163-176. 24 H. J. Lucas,/. Am. Chem. Soc., 48 (1926), 1827.

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Lucas and his group of outstanding students, including notably Saul Winstein (1912-1969), formed an active and distinctively American school of physical organic chemistry at the California Institute of Technology. One final paper that deserves mention is a brief lecture by Morris Kharasch (1895-1957) to a group of chemical educators in 1925. 25 Trained in organic chemistry at the University of Chicago, Kharasch was particularly attracted to Lewis's idea of the "partial polarity" of bonds, which he called "the Lewis extension of the Stark idea." By "partial polarity" Kharasch meant roughly the same as Lucas's "electron displace­ ment," and though he took Lewis to task for misapplying it to organic chemistry, he preached it as the salvation of a science perpetually on the brink of becoming a jumble of facts and disunited theories: "Personally, I like to think of the discarding of all our old pet theories of organic chemistry, 'the old foundations of the science,' and the adoption of the theory of partial polarity as a real victory for the organic chemist. . . . In adopting this course and the really revolutionary theory of partial polarity, we shall gain . . . in prestige, for we shall live to see our beloved subject really become a science." 26 Kharasch's two longer papers in 1928 and 1931 on the electron in organic chemistry extended his ideas of partial polarity, and in the 1930's he had a brilliant career in the physical chemis­ try of free radical reactions. Yet, in the 1920's, these papers by Conant, Lucas, Carrothers, and Kharasch remained somewhat isolated. All four men became preeminent chemists; none initiated a research school apply­ ing the Lewis-Langmuir theory to organic chemistry before the mid-1930's. From Kharasch's remarks, one gets the feeling that "the pet theories" of most American organic chemists still had a wide appeal. A special feature of American organic chemistry that probably hindered the adoption of the new theory was the long-standing commitment of leading organic chemists to the electropolar theory of valence. As early as 1901 William A. Noyes (1857-1941) and Julius Stieglitz (1867-1937) had suggested that even the inert bonds of organic molecules were formed by the transfer of one electron between two atoms. Both were sympathetic to the rather self-consciously theoretical electropolar school that formed 25 M. S. Kharasch, "Polar and Non-Polar Valences as Applied to Organic Chemistry," J. Chem. Educ., 2 (1925), 652-654. See also his "The Electronic Conception of Valence and Heats of Combustion,"/. Phys. Chem., 29 (1925), 625-658; "The Elec­ tron in Organic Chemistry," I and II, J. Chem. Educ., 5 (1928), 404-418, and 8 (1931), 1703-1748. For information on his career, see F. H. Westheimer, "Morris S. Kharasch," Biog. Mem. Nat. Acad. Sci., 34 (1960), 123-152. 26 M. S. Kharasch, "Polar and Non-Polar Valences . . . ," ibid., p. 654.

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in America about 1910, centering around the work of George Falk (18801953), Harry S. Fry (1878-1949), and others. It was the rise of this vocal school that provoked Lewis's proposal of a special nonpolar bond in 1913, and the electropolar school in turn vigorously criticized Lewis's idea of a nonpolar bond. They were already committed to the rejection of the shared pair bond when it began to draw public notice in 1920. Within the electropolar school, however, there was a remarkable variety of reactions to the Lewis-Langmuir theory. Noyes, the most progressive of the group, had a taste for novel ideas like Lewis's own. In 1915 he had arranged for the publication of Alfred Parson's magneton theory of nonpolar bonds, an idea close to Lewis's shared pair, and in 1917 he proposed the advanced idea that the chemical bond consisted of a single electron orbiting around two nuclei. 27 Unlike most organic chemists, Noyes was not afraid of "atomistics," though he was not really adept in the use of recent theories of atomic structure, as shown by his 1917 model in which each carbon atom had four nuclei. Noyes was always most comfortable with the electropolar theory. In a lecture to the American Chemical Society in 1919, he allowed that Lewis's nonpolar bond might exist in special cases, but asserted that the real key to the chemical bond was the electropolar idea of positive and negative atoms. 28 For Noyes the main difficulty of Lewis's theory was his belief that Lewis's "rule of eight" de­ nied the existence of the Cl + ion, which has only six electrons in the outer octet. The chemistry of electropositive halogen had been Noyes's main concern for twenty years. But he also believed that a reconciliation of the nonpolar and electropolar views was possible and desirable, and in a serious and self-conscious way he took that task upon himself. In 1923 he hit upon a workable compromise: Cl + ions did not exist as such in (¾ or HOCl, but only at the instant of chemical reaction. 29 He continued to pro­ mote this "reconciliation" in numerous lectures and papers during the following years. 30 27 W. A. Noyes, "A Kinetic Hypothesis to Explain the Function of Electrons in the Chemical Combination of Atoms," J. Am. Chem. Soc., 39 (1917), 879-882. On Noyes see Roger Adams, "William A. Noyes," Biog. Mem. Nat. Acad. Sci., 27 (1952), 179-208. 28 W. A. Noyes, "Valence," Science, 49 (1919), 175-182. 29 W. A. Noyes, "A Possible Reconciliation of the Octet and the Positive-Negative Theories of Chemical Combination," J. Am. Chem. Soc., 45 (1923), 2959-2961. 30 W. A. Noyes, "Valences positives et ne'gatives," Bull. Soc. Chim. France, 35 (1924), 425-446; "Ueber die Polaritat der Valenzen," Ber. deut. chem. Ges. } 57 (1924), 1253-1242; "The Relation of Shared Electrons to Potential and Absolute Polar Valences," Chem. Reviews, 5 (1928), 549-556.

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Noyes's feelings about Lewis's theory were always ambivalent, and he never really understood how it worked. In 1922 he used Lewis's double dot symbols, at an editor's request, although he preferred the plus and minus symbols of the electropolar school. 31 He interpreted the hydrolysis of amides in terms of shared pair bonds, but the result reveals how little Noyes understood the idea. 32 in 1925 he published a paper on the struc­ ture of the amine oxides, using double dot bonds, 33 and he corresponded at some length with Lewis on the subject. 34 But the persistent errors in his formulas, which Lewis generously interpreted as typographical, make it clear that Noyes was not at ease with Lewis's theory. As late as 1928 he was still fretting about the need for a transition from the old to the new. Since this transition was already an established fact, it is clear that despite goodwill, Noyes was never able to make the transition himself. Julius Stieglitz's response was cooler and more critical. In 1922 he pub­ lished a paper comparing the usefulness of the electropolar and the LewisLangmuir theories in a specific test case; namely, the rearrangement of a triphenylmethyl hydrazine. 35 He drew the structural formula of this com­ pound in both the double dot and the plus and minus symbols, pointing out that Lewis's formula gave no indication why rearrangement should occur. By contrast, the electropolar formula revealed that the molecule was not electrically symmetrical, one nitrogen atom being one charge short of its saturated condition; i.e., N +

rather than N

. This "flaw" in the

molecule was the reason why a reaction occurred, Stieglitz asserted. He had been using the idea of an electronic flaw for twenty years, and he saw no advantage in switching to the Lewis-Langmuir view. He was careful to point out, however, that in his view the bonds in organic molecules symbolized by + and - signs were not the completely ionized bonds of Na + Cl . But the question of what the bond consisted of he set aside as "a problem of atomistics," one that belonged to physics and not chemis­ try. 36 Many organic chemists at the time resented the intrusion of un31 W. A. Noyes and T. A. Wilson, "The Ionization Constant of Hypochlorus Acid," J. Am. Chem. Soc., 44 (1922), 1630-1637. 32 W. A. Noyes and W. F. Goebel, "Catalysis of the Formation and Hydrolysis of Acetamide," ibid., pp. 2286-2296. 33 W. A. Noyes, "Ionization of Trimethylethoxyammonium Hydroxide," ibid., 47 (1925), 3025-3030. 34 Correspondence, Lewis Archive, Berkeley. 35 J. Stieglitz, "The Electron Theory of Valence as Applied to Organic Com­ pounds," J. Am. Chem. Soc., 43 (1921), 1293-1313. On Stieglitz see W. A. Noyes, "Julius Stieglitz," Biog. Mem. Nat. Acad. Sci., 21 (1939), 275-314. 3 ^Ibid., pp. 1311-1312.

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familiar physical models into their specialty, and felt threatened by the Lewis-Langmuir theory. Stieglitz's attitude was typical of this school. Unlike Noyes, Stieglitz took no further part in the discussion of valence theory. He did not reply to Lewis's criticism of his adherence to the electropolar orthodoxy, 37 but in a letter to Fry in 1928 he complained that Lewis had unfairly ignored his distinction between "doublet polarity" and "ionic polarity," asserting that "our views on polarity work, Lewis notwithstanding." 38 By then Stieglitz himself had drifted away from ac­ tive research, but in his students' theses through the early 1930's double dot formulas appeared uneasily in discussions of molecular "faults." 39 One senses a persistent loyalty among the Chicago chemists to Stieglitz and the old electropolar cause, even though Stieglitz' "doublet polarity" had long since, by other names, been incorporated into the modern theory. Similar overtones of attachment to a lost cause can be felt in a letter from Falk in 1928, though Falk had switched to biochemistry many years earlier. Falk allowed that the octet theory was "interesting to study, fascinating to work with and permits of ready popular presentation," but he doubted that it "contributes any essential relation to the simple elec­ tron transfer valence view." 40 The electropolar chemists could and did re­ gard themselves as progressives as late as 1920, when suddenly they found themselves cast in the role of reactionaries. One suspects this professional dislocation was the source of Falk's and Stieglitz's nostalgia for their lost cause. The emotional strains that accompanied this shift in the locus of pres­ tige and influence are most clearly seen in the response of Harry Fry of the University of Cincinnati. In 1928 Fry published an extraordinary diatribe against the new theory. 41 He refused to jump on the "LewisLangmuir bandwagon," despite the well-intentioned advice of friends; he scorned the new fad and rejected the false distinction between polar and nonpolar bonds. (In fact, Lewis insisted on the unity of polar and nonpolar bonds and did his best to disavow his earlier dualism.) Fry pro­ nounced Lewis's double dot formulas cumbersome and confusing, and he ridiculed Lewis's cubic atom: "the structural formula of the organic chemist is not the canvas on which the cubist artist should impose his 37 Lewis,

Valence, op. cit. (note 3), p. 151. S. Fry, "A Pragmatic System of Notation for Electronic Valence Conceptions in Chemical Formulas," Chem. Reviews, 5 (1928), 557-569. 39 See, for example, the unpublished theses of R. B. Cooper (1930) and P. V. Brower (1933) in the Chemistry Department Library, University of Chicago. 40 Fry, op. cit. (note 38), pp. 565-566. ^ 1 Ibid. 38 H.

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drawings which he alone can interpret." 42 (Lewis had not used the cubic atom since 1916, and after 1923 it had been quietly forgotten.) Assuming the mantle of the "pragmatic chemist," Fry rejected all "metaphysical" theories of atomic structure with their "hypothetical electron shells or elusive orbits." Unlike Noyesand Stieglitz, Fry was not a first-rank chemist, and he had not enjoyed the high prestige his colleagues had. His leadership in the electropolar bandwagon of 1910-1914 obviously had been central to his hopes for his career, and up to 1920 there had been little to dampen them. His magnum opus, a lengthy survey of the electropolar theory, appeared in 1921, 43 just as the Lewis-Langmuir theory achieved its greatest popularity. One understands Fry's desperate refusal to abandon the past.

3. THE GERMAN RESPONSE: RETREAT TO THE PAST In postwar America the Lewis-Langmuir theory had to contend with chemists' established ideas, but at least there was no impediment to awareness of the new ideas. This was not the case in Germany, where the five years of war and the postwar political and social turmoil had isolated Germanscientists from scientific developments in the West. The difficulties of travel and exchange of information were greatly increased after 1920 by the inflation which ravaged the German economy. As early as 1919 the mark had depreciated to one half its prewar value in dollars, and by 1922 to one fiftieth. Even before the rampant inflation of 1922-1923 Germany had become an economic island. 44 German scientists were unable to travel outside Germany, and German universities were unable to subscribe to foreign scientific journals. In December 1921, for example, Fritz Haber wrote to Langmuir requesting him to send reprints of his latest papers: "our literary communication with the United States is in such a terrible condition that I have been unable to find this journal anywhere in Berlin." 45 It is possible that the Lewis-Langmuir theory was not widely available in Germany at the critical time when it was having its first real impact on British and American chemists. The purely economic impediments to the influx of new ideas would probably not have had more than a passing effect had there been real *Vbid„ p. 539. 43 H. S. Fry, The Electronic Conception of Valence and the Constitution of Ben­ zene (London, 1921). 44 F. Ringer, The Decline of the German Mandarins (Cambridge, 1969), pp. 62-66. 45 Letter, F. Haber to I. Langmuir, 23 December 1921. Langmuir papers, Library of Congress.

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interest among German chemists. But there was in postwar Germany a selfimposed emotional and intellectual isolation from Anglo-American influ­ ence. This nationalistic response to military defeat was very much a part of the postwar political mood, and it extended to science as well. In early 1920 Jacques Loeb noted in a letter: "From all I hear the Germans are still on the whole in a very hostile attitude towards scientific work done in this country." 46 There are indications in the chemical literature that chemists, too, shared in this deliberate turning inward. It is hardly surpris­ ing that the enthusiastic interest in new ideas that Langmuir found in the United States did not exist in Germany, given the very different mood there. This temporary mood might not have had a lasting effect, except that a particular feature of German chemistry made the rejection of the new bond theory seem not only patriotic but scientifically progressive. In pre­ war Germany there had been considerable speculation about the nature of nonpolar chemical bonds of a distinctively different kind from that of Thomson, Parson, Lewis, and Langmuir. This tradition was associated with respected names and had been well publicized before the war, and it ap­ peared to be capable of much further extension in the early 1920's. Post­ war German chemists had an established and promising native alternative to the Anglo-American view. That alternative enabled the relatively brief emotional isolation of the years 1919-1923 to deflect German chemists for some years from what was more and more clearly the main line of chemical theory. The two principal figures in the German school of valence theory were Johannes Stark (1874-1957) and Walther Kossel (1888-1956). Both were physicists, and both derived their speculations on the nonpolar bond from physics, especially from electrostatic theory. Stark set forth his views in a massive three-volume work during the years 1909-1913. 47 His principal argument was that all chemical bonding depended on electrostatic attrac­ tion, but that not all bonds involved complete electron transfer. Nonpolar bonds, Stark asserted, consisted of electrons, connected by lines of force, located between two atoms, which he visualized as Thomsonian positive spheres and electrons. Stark's final volume was filled

with pictures of

amoeboid positive atoms connected by one, two, or more electrons, bear­ ing a striking resemblance to Lewis's electron pair bonds. But the resem46 Letter, J. Loeb to T. H. Morgan, 17 February 1920. Loeb papers, Library of Congress. 4 7 J. Stark, Prinzipien der Atomdynamik 1 3 vols. (Leipzig, 1910, 1911, and 1915).

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blance is superficial: Stark's atom was the pre-Rutherford model, which Thomson had given up by 1912, and his reliance on electrostatics was totally different from Lewis's reliance on electron sharing, Parson's mag­ netic bond, and Bohr's quantum groups. Even in comparison with Thom­ son's dipolar bond of 1914, Stark's view of bonding was years out of date. Kossel's more sophisticated version of the electrostatic bond was pro­ posed shortly before Lewis's paper appeared in 1916. 48 This coincidence has traditionally, but incorrectly, been regarded as a case of simultaneous discovery. As far as electropolar bonding was concerned, Kossel and Lewis saw eye to eye; both emphasized the "rule of eight" and pointed out how the transfer of electrons completed the group of eight and explained the familiar series of valence numbers in each row of elements. But this was the least novel part of Lewis's paper; it was just a more sophisticated version of Abegg's theory of 1904, which did not include a nonpolar bond. Kossel believed in the existence of a special nonpolar bond, which did not involve electron transfer, and he depicted such bonds as rings of two to five electrons in orbits perpendicular to the bond axis, an idea undoubtedly adopted from Bohr. But there the resemblance to Lewis's theory ends. Kossel had no conception of the special stability of electron pairs, and no notion that electrons might be shared by two atoms. For him the mechanism of chemical bonding was electron transfer; nonpolar bonds were those in which transfer was incomplete. He remained firmly within the electrostatic tradition, which Lewis had left behind in 1916. As Langmuir pointed out: "the theories of Kossel, Lacomble, Trendt and others which have recently been proposed in Germany, have not advanced beyond this point and are therefore very unsatisfactory as a general theory of valence." 49 In the early postwar years the German electrostatic tradition received considerable publicity. W. Jacobs reviewed Stark's work in 1918; 50 in 1919 the physicist A. E. Lacomble extended Stark's and Kossel's theory of valence; 51 in 1920 Kossel spoke on bond theory to the Bunsen Society. 52 48 W.

Kossel, "Ueber Molekiilbildung als Frage des Atombaues," Ann. d. Physik, 49 (1916), 229-362. 49 I. Langmuir, "The Structure of Atoms and Its Bearing on Chemical Valence," J. Ind. Eng. Chem., 12 (1920), 388. 50 W. Jacobs, "De Valentie-Hypothese van J. Stark," Chemisch Weekblad, IS (1918), 1476-1483, 1566-1571. 51 A. E. Lacomble, "Grundlinien einer Valenztheorie," Z. physik. Chem., 93 (1919), 257-274. 52 W. Kossel, "Die Valenzkrafte im Lichte der neueren physikalischen Forschung," Z. Elektrochem., 26 (1920), 314-323.

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The central question for Kossel was whether or not "homopolar" (nonpolar) bonds were essentially different from "heteropolar" (polar) bonds. Although the nature of the homopolar bond was becoming "increasingly more mysterious," 53 he stated that it was "extremely unlikely" that nonelectrostatic or magnetic forces were involved. In his opinion the homo­ polar bond was due to stray electrostatic fields that caused electrons to shift slightly from their normal positions in the atom. He did not mention Lewis's and Langmuir's names and he asserted that the homopolar bond was "a purely physical problem," and that it was "up to us physicists to interest chemists in this conception." 54 The distinctive bias and insularity of the German tradition is equally well illustrated in Fritz Arndt's (b. 1885) historical introduction to Kossel's talk. 55 He mentioned Alfred Werner, Richard Abegg, J. J. Thom­ son, Stark, and Kossel, but not Bohr, Lewis, and Langmuir. The same German version of the history of valence theory appeared in a lecture by Wilhelm Biltz (1877-1943) to the Verein deutscher Chemiker in 1920. 56 He briefly mentioned a German abstract of Langmuir's paper, but said nothing of Lewis's papers. He adopted Kossel's homo- and heteropolar terminology and his electrostatic point of view. In 1921 Heinrich Remy (b. 1890) explicitly rejected Langmuir's theory, which he said was arbi­ trary and incapable of explaining from first principles why one, two, or three electron pairs were shared in various cases. 57 (Langmuir had made exactly the same criticism of Lewis's theory before he understood it.) Remy preferred Kossel's idea of partially transferred electrons, and he adopted the idea of Elektronenverein or electron group bonds undoubt­ edly also from Kossel's pictures of two to five electron bonds. All this suggests that the Lewis-Langmuir theory was not widely familiar in postwar Germany, at least among physical chemists, and that to the ex­ tent that it was known it was rejected in favor of the more familiar and much more conservative German theory. Not all German chemists were antagonistic to the Anglo-American va­ lence school. A hybrid theory of the nonpolar bond was proposed in 1923 by Kasimir Fajans (b. 1887), an instructor in physical chemistry at s3 Ibid.,

s ^Ibid., p. 322. p. 319. Arndt, "Die Valenzkrafte im Lichte der neueren chemischen Forschung," ibid., pp. 305-313. 56 W. Biltz, "Ergebnisse und Aufgaben neurer chemischer Valenzforschung," Z. angewandete Chem., 33 (1920), 313-317. 57 H. Remy, "Ableitung der Saureformeln auf Grund eines Gesetzes fiber die homopolare Atombindung," Z. anorgan. Chem., 116 (1921), 255-266. 55 F.

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Munich. 58 Fajans suggested that electrostatic deformation of the outer electrons in a negative ion by the attractive force of a nearby positive ion could tear electrons loose and propel them into an orbit around both atoms, thus forming a nonpolar bond. 59 He mentioned both Lewis and Langmuir, as well as Kossel, and noted with approval the concurrence of his basically electrostatic view with the Lewis-Langmuir theory. Fajans also noted with approval a recent paper by Carl A. Knorr (18941960), a young student of his at Munich. 60 Although Knorr was primarily a physical chemist, he also had a strong interest in organic chemistry. His paper was an extremely sophisticated application of the Lewis-Langmuir theory to the structures of complex organic molecules. 61 In it he gave a thorough review of the various theories of the nonpolar bond and opted for the shared pair, which he visualized in Bohr's manner as electrons in elliptical orbits around two atoms. Fajans stated that Knorr developed his ideas quite independently of his own, and noted that "this conception has the great virtue that it links my new results with Langmuir's point of view." 62 Knorr did not adopt Lewis's double dots, but rather a double line symbol of his own devising. Although he added nothing really new to what Lewis had said in Valence, his paper revealed a grasp of the new ideas equal to Lewis's own. Knorr's paper was with one exception totally ignored by German organic chemists, a neglect that was striking enough for H. Fischer to discuss it at length in his obituary of Knorr. The exception was a paper published in 1925 by Erich Miiller (1870-1948), a professor of organic and physical chemistry at Dresden. 63 Miiller's paper was an explicit extension of Knorr's, which he regarded as the most comprehensive to date, totally ignoring Lewis, Langmuir, and the British school. 64 Nevertheless, Miiller's treatment of the mechanism of a variety of often extremely complex organic reactions was sophisticated for the time. His use of curved arrows to represent shifting electron pairs—one of the earliest uses of this devicegives his paper a remarkably modern look. But besides the papers of 58 E. Lange, "Kasimir Fajans zum 70 Geburtstag," Z. Elektrochem., 61 (1957), 773-774. 59K. Fajans, "Struktur und Deformation der Elektronenhiillen . . . ," Naturwiss., 11 (1923), 165-172. 60 C. A. Knorr, "Eigenschaften chemischer Verbindungen und die Anordnung der Elektronenbahnen in ihren Molekiilen," Z. anorgan. Chem., 129 (1923), 109-140. 61 H. Fischer, "Carl Angelo Knorr," Z. Elehtrochem., 64 (1960), 453-455. 62 Fajans op. cit. (note 59), p. 171. 1 "G. Grube, "Erich Miiller," Z. Elektrochem., S3 (1949), 337-338. 64 E. Miiller, "Zum Valenzproblem," ibid., 31 (1925), 143-157.

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Knorr and Miiller, there are no signs that German organic chemists were at all interested in the Lewis-Langmuir theory, or in the activities of the British physical-organic chemists. If we ask what was special about Fajans, Knorr, and Miiller that made them see the value of the Lewis-Langmuir theory, a pattern emerges that suggests indirectly why the larger community of German organic chemists was indifferent to the theory. All three chemists had unusually broad backgrounds. Fajans was best known for his radiochemical work, but he was also interested in the physical chemistry of organic reactions. Knorr was at home in both physical and organic chemistry, and Miiller had held chairs in both organic and electrochemistry. Their particular combination of interests, which also characterized Lewis and Langmuir and the founders of the British school, were in striking contrast both to the narrow physicalist outlook of Kossel et al. and to the traditional organic chemists' distaste for "atomistics." The essential novelty of the Lewis-Langmuir theory was that it combined physical ideas of atomic structure with ideas of chemical structure and reactivity, and it seems that this hybrid combination was crucial to those who responded to the theory. It is also suggestive that Fajans, Knorr, and Miiller all studied abroad: Fajans with Rutherford at Manchester in 1910-1911, Knorr at Oxford, and Miiller in France and the United States. This was a remarkable turnabout at that time, when a post­ doctoral year in Germany was still obligatory for young British and Amer­ ican chemists. There is a striking contrast between the openness of Fajans, Knorr, and Miiller to Anglo-American chemistry and the narrow views of most German physical chemists. All this suggests that most German organic chemists operated within rigid, traditional discipline boundaries that limited the influence of ideas from physical chemistry. One suspects that the long preeminence of Ger­ man chemistry had encouraged conservative attitudes, whereas British and American chemists, with a smaller stake in past successes, responded more easily to cross-disciplinary influences. Moreover, German structural organic chemists tended to oppose theorizing of any sort, not just "atomis­ tics." One recalls the famous story of Fritz Arndt's failure to get his paper on resonance theory published in 1925 because it was too theoretical and contained no new experiments. 65 By these criteria, neither Lewis's nor Langmuir's papers could have been published in Germany. For all these reasons German chemists failed to respond to the Lewis-Langmuir theory. 65 E. Campaigne, "The Contributions of Fritz Arndt to Resonance Theory," /. Chem. Educ., 36 (1959), 336-339.

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Unquestionably one of the major developments of modern chemistry was the shift of its research center from Germany to Britain and the United States. The question is how important the failure of German chemists to receive the Lewis-Langmuir theory in 1920-1925 was for this shift. It seems clear that one cannot speak of a general "decline" of Ger­ man chemistry in the 1920's. German biochemistry remained preeminent until Hitler drove the biochemists out, and structural organic chemistry remained strong, notably in natural products. What happened was that German chemists failed to participate in certain crucial developments, notably in physical organic chemistry, which in the 1920's and 1930's was the most active and prestigious new chemical specialty. Here the German response to the Lewis-Langmuir theory was of crucial importance. The new theory of valence, which in time transformed the basic ideas under­ lying all branches of chemistry, arrived at a time when German chemistry had turned inward to its own heroes and past triumphs. The resistance of German chemists to the new ideas was temporary and certainly did not outlast the 1920's. Ordinarily this delay might not have been crucial, but the rapid development of the hybrid discipline in Britain, where local con­ ditions were particularly favorable for it, gave British chemists a lead that Germany did not challange before Hitler's policies initiated a true decline in all of German science.

4. THE BRITISH RESPONSE: THE LEGACY OF THOMSON The first manifestation of interest by British chemists in the LewisLangmuir theory was a spate of notes in Nature in early 1920. The first was in February. William E. Garner (1889-1960), reader in physical chemistry at University College London, 66 was interested in an ap­ parent case of isomerism in an organic molecule without structural asym­ metry. He suggested that an ordinary bond could be asymmetric if, as Bohr had proposed, it consisted of electrons in clockwise or counterclock­ wise orbits around the bond axis. 67 In March, Herbert S. Allen (18731945), lecturer in physics at the University of Edinburgh, suggested that Alfred Parson's "magneton" or ring electron was preferable to an orbiting point electron, and provided a model of the bond as a pair of stacked rings 66 Dict. Nat. Biog., Seventh Supplement (1951-1960) (London, 1971), pp. 391392. 67 W. E. Garner, "An Electronic Theory of Isomerism," Nature, 104 (1920), 661-

662.

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rotating in the same or in opposite directions. 68 He mentioned both Lewis and Langmuir, and the "remarkable success that has attended Langmuir's development of the octet theory." Allen was intrigued by the possibility that the two-magneton bond might explain optical activity. In October 1920 he published a long paper on this subject, 69 and sought out Lang­ muir's opinion as to whether two ring electrons were stacked face to face or side by side. 70 Garner, too, was intrigued by this idea, acknowledging the advantages of "Langmuir's atom" over Bohr's planetary one. 71 In March 1920 Samuel C. Bradford (1878-1948), chemist and librarian at the Kensington Science Museum, pointed out the discrepancy between the fixed electrons of "Langmuir's theory," and the planetary orbits of Bohr's atom. 72 He suggested that the four electrons of one face of the cubic atom might rotate as a group. Bradford's doubts about the cubic atom were assailed by A. E. Oxley, a student of J. J. Thomson and then lecturer in physics at University College, London. Oxley pointed out that Langmuir's theory did not require fixed electrons, and suggested that each electron might describe a small circle around its corner of the cubic atom. 73 Bradford accepted Oxley's suggestion, protesting that he had not meant to criticize Langmuir. 74 InJuly 1920 Bradford published a long and enthusiastic review of Langmuir's papers in Science Progress: "the theory propounded by Langmuir . . . explains so wonderfully the properties of elements and compounds and brings to Hght such remarkable relationships, formerly unsuspected, that it necessarily contains a large element of truth . . . and must have the widest application." 75 He was still uneasy, however, 68 H.

S. Allen, "An Electronic Theory of Isomerism," ibid., 105 (1920), 71-72. S. Allen, "Optical Rotation, Optical Isomerism and the Ring Electron," Phil. Mag., 40 (1920), 426-439. 70 Langmuir papers, in correspondence for 1920. 71 W. E. Garner, "An Electronic Theory of Isomerism," Nature, 105 (1920), 171. 72 S. C. Bradford, "On Langmuir's Theory of Atoms," ibid.., p. 41. Bradford was a science bibliographer, but he had been trained as a chemist, and he combined librarianship with work on the physical chemistry of colloids. See Η. T. Pledge, "S. C. Brad­ ford," Nature, 162 (1948), 917-918. 73 A, E. Oxley, "On Langmuir's Theory of Atoms," ibid., 105 (1920), 105. See also A. E. Oxley, "Magnetism and Atomic Structure," Proc. Roy. Soc., 98A (1920), 264-274. 74 S. C. Bradford, "Langmuir's Theory of the Arrangement of Electrons in Atoms and Molecules," Science Progress, 15 (1920), 50-59. 15 Ibid., p. 50. Langmuir also agreed with Allen that there was no necessity of postulating immobile electrons. He also pointed to the neglect of Lewis's work by British chemists: "it is scarcely fair to Lewis to refer to the theory as 'Langmuir's theory.' " (I. Langmuir, "Theories of Atomic Structure," ibid., p. 261.) 69 H.

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as to precisely how Langmuir's static atom and Bohr's dynamic atom were to be reconciled. In November 1920 a reconciliation from the physicist's point of view was proposed by Norman R. Campbell (1880-1949). Since the BohrSommerfeld theory was "beyond doubt" and the Lewis-Langmuir theory "extremely plausible," a real inconsistency would be intolerable.76 He pointed out that according to Bohr's correspondence principle, even the dynamic constants of atomic spectra did not require electrons to be really moving. Likewise, there was no problem with the fixed bonds of chemical compounds: "if intensity and polarization can be predicted from orbits that are wholly fictitious, why not energy?" Perhaps the most important consequence of Campbell's note was that it stimulated Bohr himself to reply in early 1921.77 Bohr objected to Campbell's talk of "fictitious orbits," which he interpreted as an attack on the correspondence principle. He also took the opportunity to withdraw his planetary atom model, out­ lining for the first time in print his new model of interpenetrating electron orbits oriented in space with polyhedral symmetries. His revised theory of atomic structure—which he elaborated in his Cambridge lecture of 18 October 192178—provided a satisfactory resolution of the static-dynamic paradox. Despite the resolution, the Lewis-Langmuir theory continued to be dis­ cussed in widening circles, stimulated perhaps by Langmuir's presentation of his ideas to the British Association meeting at Edinburgh in September 1921.79 His talk had wide publicity among both chemists and physicists, and he made the most of the controversial static-dynamic issue. The dis­ cussion following his talk centered on the question of atomic structure, as he explained in a letter to Willis Whitney: I opened the discussion by speaking for about an hour along the lines covered by the paper that I published recently in Science on Type" of Valence. To stimulate discussion I emphacized [sic] the question in re­ gard to the electrons being stationary or moving altho I pointed out that this is quite immaterial from the chemical point of view. The discussion 76 N.

R. Campbell, "Atomic Structure," Nature, 106 (1920), 408-409. Bohr, "Atomic Structure," ibid., 107 (1920), 104. 78 N. Bohr, "The Structure of the Atom and the Physical and Chemical Properties of the Elements," in Bohr, The Theory of Spectra and Atomic Constitution (Cam­ bridge, 1922). 79 "Discussion on the Structure of Molecules," Rep. Brit. Assoc. Adv. Sci. (1921), pp. 468-472. 77 N.

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was continued by Prof. A. Smithells, who had excellent models of atoms and molecules, Prof. W. L. Bragg, J. R. Partington, S. H. C. Briggs, Svante Arrhenius, and Sir Oliver Lodge. Bragg mentioned briefly data that he has recently obtained on the distribution of electrons about the nucleus that most of the electrons are very close to the nucleus. I expect to see Bragg again and will get more details in regard to this point.80 The static-dynamic issue continued to attract attention. In 1922 James Walker (1863-1935), professor of chemistry at Edinburgh, said in his presidential address to the Chemical Society in 1922 that the static and dynamic atoms were "irreconcilable." He hoped that a third theory would emerge that would satisfy the requirements of both chemists and physi­ cists.81 Walker was an organic chemist who was also the author of a text­ book of physical chemistry, and whose special interest was the electropolar properties of organic molecules. In 1922 the physicist Oliver Lodge (18511940) suggested that the magneto-chemical binding force, which had been brought up occasionally, might profitably be revived.82 Garner, too, favored an electromagnetic rather than a purely electrostatic bond. A mag­ netic bond force seemed to resolve the paradox that moving electrons pro­ vided rigid, directional bonds between atoms. The claims of spectroscopists and chemists were both satisfied.83 A more ingenious way out of the static-dynamic paradox was proposed by W. Hughes, who pointed out that if the nucleus rotated inside the shells of fixed electrons, the principle of relativity required that the electrons be regarded as rotating. But since the electrons remained fixed in position with respect to each other, they could form directed bonds.84 The rotating nucleus theory was developed at great length by Ronald Fraser and James Humphreys, chemists at the University of Aberdeen,85 and by Herbert 80 Letter to W. Whitney from I. Langmuir, 18 September 1921, Langmuir papers. Samuel H. C. Briggs (1880-1935). a student of J. B. Cohen, gave up a career in or­ ganic chemistry to run his family's textile business, but also pursued as an amateur his interest in valence theory and coordination chemistry. See H. S. Raper, "S. C. H. Briggs,"/. Chem. Soc., 139 (1936), 169-170. 81 J. Walker, "The Role of the Physicist in the Development of Chemical Theory," J. Chem. Soc., 121 (1922), 735-745. 82 O. Lodge, "Bohr and Langmuir Atoms," Nature, 110 (1922), 341. 83 W. E. Garner, "Polar and Nonpolar Valency in Organic Compounds," ibid., pp. 543-544. 84 W. Hughes, "A Possible Reconciliation of the Atomic Models of Bohr and of Lewis and Langmuir," ibid., pp. 37-38. 85 R. Fraser and J. E. Humphries, "The Problem of Substitution in the Benzene Nucleus and the Thomson-Lewis-Langmuir Theory of Covalence," Chem. News, 126 (1923), 161-168.

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Henstock of the Chemical Research Laboratory in Shrewsbury.86 In 1923 the various attempts to reconcile the chemical and physical atoms were noncommittally reviewed by F. H. Loring, the editor of Chemical News. 87 By 1923, however, the static-dynamic issue was dead, at least among ad­ vanced chemists. In April 1923 Campbell noted that recent discussions of the alleged paradox had failed to recognize that "any inconsistency there may have been between [the two views] has vanished completely with the publication of Bohr's later views on atomic orbits."88 I know of no chemist who took issue with Campbell's view after 1923. Further debate centered on the exact shape of the electron orbits.89 The comparison of British and American responses to the Lewis-Langmuir theory suggests that the British chemical community was unusually open to new ideas. The large literature and the participation of organic chemists, physical chemists, and physicists point to an elasticity of disci­ pline boundaries in Britain. The intense concern of British chemists with the static-dynamic issue suggests that they had a more genuine interest in "atomistics" than American chemists, who had been more fascinated by Langmuir than by the cubic atom. In part their interest can be attributed to the strong British tradition in atomic structure, led by Thomson, Rutherford, and Bohr (the latter published in English and apparently had a large following among British chemists). Thomson had long exercised a profound influence on chemists, perhaps more than on physicists after 1910. It is not surprising that the Lewis-Langmuir theory of the static atom found special favor in Britain. The body of literature on the static atom remained controversial and as ephemeral as the static-dynamic issue itself. The literature was important in giving the new ideas wide familiarity, but it did not result in a lasting school of research. The future of atomic structure theory was in the hands of Bohr and the physicists, not the physical chemists, whose speculations on atomic structure remained somewhat amateurish until the advent of quantum chemistry in the early 1930's. A lasting practical application of the Lewis-Langmuir atom was made by a small group of organic chemists, who formed a thriving school of chemical research.

86 H. Henstock, "The Influence of the Atomic Nucleus upon Valence . . . ," ibid., pp. 129-135. 87 F. H. Loring, "Valency and Radiation," ibid., pp. 273-274. 88 N. R. Campbell, "A Static or Dynamic Atom?"Nature, 111 (1923), 569. 89 See, e.g., G. T. Morgan, "A Dynamic Hypothesis of Chemical Combination," Chem. & Ind., 43 (1924), 1071-1073.

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5. THE BRITISH PHYSICAL ORGANIC CHEMISTS What was special about the British organic chemical community that enabled it to form a new school of research around the Lewis-Langmuir theory in 1922-1923? The new ideas were readily available in Britain, but this was hardly a sufficient reason, as the American case shows. British organic chemists were not impeded by an emotional attachment to the electropolar theory. But more important were two local circumstances that especially favored adoption of the new ideas. First, there was already a tradition of theoretical speculation in organic chemistry in Britain, which was immediately translatable into terms of the new theory. And second, there was a long-standing local tradition of practical research in exactly those problems that were central to physical organic chemistry; namely, reaction mechanisms. The Lewis-Langmuir theory was the unify­ ing doctrine that allowed these separate traditions to become an organized movement. The key figures in the rise of this movement were Arthur Lapworth (1872-1941), Nevil Sidgwick (1873-1952), and Thomas Martin Lowry (1874-1936), all men of Lewis's generation, and Lapworth's protege, Robert Robinson (1886-1975). Lapworth was a student of Henry Arm­ strong (1848-1937) and shared his teacher's active interests in both physi­ cal and organic chemistry.90 Lapworth was professor of organic chemistry at Manchester from 1913 to 1922, when he received a chair of physical chemistry there. As early as 1898 he had published a theory of the mecha­ nism of rearrangements in tautomeric molecules, based on van't Hoff's mechanical stereochemistry.91 In the next fifteen years he was deeply in­ fluenced by Arrhenius' ionic theory, which he applied to organic reaction mechanisms. Robinson later recalled: When in the early Manchester days, one discussed synthetical projects with Lapworth, it was quite clear that he had some unusual private way of deciding whether they would "go" or not. It turned out to be a scheme of alternating polarity in a chain of atoms, and the theory was published in 1920. Although somewhat hidden away in the Memoirs of the Manchester Literary and Philosophical Society, the paper evoked much interest and not a little criticism.92 90 R.

Robinson, "Arthur Lapworth," Obit. Notices F. R. S., 5 (1947), 555-572. Lapworth, "A Possible Basis of Generalisation of Intramolecular Changes in Organic Compounds," J. Chem. Soc., 73 (18 9 8), 445-459. 92 R. Robinson, op. cit. (note 90), p. 563. 91 A.

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Lapworth's basic idea was that an electropolar atom, such as nitrogen or oxygen, induced an opposite polarity in an adjacent carbon atom, which had a like effect on the next atom, and so on. In this way one "key atom" induced a chain of alternating polarities in a carbon chain, and these polarities determined where, for example, addition could occur in an un­ saturated molecule. 93 Lapworth used + and - symbols to represent polarities, but he explicitly stated that they did not signify the completely ionized bonds of the electropolar school. His inspiration was not Thom­ son's pre-1914 theory of electron transfer bonds, but the earlier dissocia­ tion theory of Arrhenius, which involved no speculation as to the electrical structure of the atom. 94 With this conception Lapworth ambitiously tackled the classic problems of tautomerism, conjugation, and aromaticity. Equally novel and ambitious was a paper published simultaneously by Lapworth's colleague Robert Robinson, 95 one of the most active young British organic chemists. Robinson shared Lapworth's taste for theorizing. Unlike Lapworth, however, Robinson had been deeply influenced by the German theories of partial valence associated with Johannes Thiele (1865-1918). Thiele postulated that the unit valence bonds of Kekule's structure theory could be split into separate "partial valences." He repre­ sented these by special dotted, dashed, and broken lines, using them to explain the anomalous reactions of unsaturated and tautomeric molecules. He also invoked other kinds of special "latent" and "residual" valences. By 1920 Thiele's family of special valences formed the basic tenets for a school of organic chemists, and, as new problems arose, the theory became more and more highly refined. 96 Robinson's was yet another variation on this theme. He proposed that valences could be divided into three inde­ pendent partial valences, and depicted reactions taking place by way of a cyclic complex of reactants in which a continuous cyclical shift of partial valences resulted in the rearrangement of bonds and the formation of products. 97 The point of his elaborate scheme was to avoid postulating the formation of free ionic charges. Lapworth's and Robinson's schemes were basically conservative offshoots of organic chemical traditions; in neither was an electron even mentioned. 93 A. Lapworth, "Latent Polarities of Atoms and Mechanism of Reaction," Mem. Manch. Phil. Soc., 64 (1920), 1-16.

9 ^Ibid., 95 R.

pp. 15-16.

Robinson, "The Conjugation of Partial Valencies," ibid., pp. 1-14. 96 For a useful summary, see F. Henrich, Theories of Organic Chemistry (New York, 1922). 97 R. Robinson, op. cit. (note 95), p. 4.

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In 1922 Lapworth and Robinson were both converted, independently, to the Lewis-Langmuir theory. Lapworth's paper of 1922 catches him in the act of changing his mind. The first half of this paper is an elaboration of his earlier theory, in which he adopts Robinson's idea that valences can be divided three ways, and postulates yet another variety of "virtual valence," a sort of deficit affinity. In the second half of this paper, clearly added late in the game, Lapworth translates this complex and obscure sys­ tem into the language of electron octets and shared pair bonds. 98 His conversion, he noted, was stimulated by a letter from Julius B. Cohen (1859-1935) in October 1921. Cohen had written: "why do you split up your bond into three partial valencies rather than two? If you took two it would fit in with the Lewis-Langmuir atom, and your partial valency might represent one electron." As Lapworth observed, "the transformations re­ quired are so simple as to be almost self-evident to any who are familiar with these modern views." A saturated valence became a shared pair of electrons, a latent valence a free pair, and a virtual valence a missing pair in an incomplete octet: "it at once becomes apparent on applying Prof. Cohen's suggestion . . . that a remarkably consistant application of modern electronic theory to carbon compounds . . . has already been developed and was only awaiting such a suggestion before taking definite form." 99 The source of Cohen's inspiration is not known. Cohen, professor of organic chemistry at Leeds, was mainly known as an author of excellent textbooks, 100 and as such he may have made a point of being up to date on the latest theories. It may also be significant that his letter to Lapworth followed Langmuir's address to the British Association by only three weeks. Langmuir's lecture may also have been the stimulus for Robinson's con­ version. In December 1921 Robinson wrote to Lapworth from St. Andrews, where he was professor of organic chemistry, that he had been able to translate their earlier theory into Lewis-Langmuir terms; Lapworth at once sent him a copy of his manuscript, and they agreed to publish their papers together. 101 Robinson's main insight was that the principle of alter­ nating polarities could be derived from the Lewis-Langmuir octet by as98 A. Lapworth, "A Theoretical Derivation of the Principle of Induced. Alternate Polarities,"/. Chem. Soc., 121 (1922), 416-427. Quote from p. 423. 99Ibid., p. 423. 100H. S. Raper, "Julius B. Cohen," ibid., 138 (1935), 1331-1337. 101W. O. Kermack and R. Robinson, "An Explanation of the Property of Induced Polarity of Atoms and an Interpretation of the Theory of Partial Valencies on an Electronic Basis," J. Chem. Soc., 121 (1922), 427-440. J. N. Davidson states that

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suming that the stable octet of an electronegative atom tended to draw electrons to it at the expense of neighboring octets. This "unstable" octet in turn permitted its neighbor to gain electrons at its expense, and so on. The alternating stable and unstable octets corresponded to the plus and minus polarities of Lapworth's theory.102 Robinson identified partial valences and conjugated bonds with one and three shared electrons, and he recognized latent valences, though not very clearly, as free electron pairs.103 He adopted Lewis's double dot symbol, demonstrating that he could use it correctly. Like Lapworth, Robinson was keenly aware of the enormous simplification that the Lewis-Langmuir theory brought to the various theories of partial valence and the various dotted and dashed lines used to represent them. He wrote: "Whilst all these theories and . . . de­ vices of symbolisation have proved servicable as working hypotheses, the connecting link in the form of a common physical basis is lacking;. . . such may be found in the Thomson and Lewis-Langmuir theory of the atom and valency, . . . as expounded by Langmuir at the Edinburgh meeting (1921) of the British Association."104 In short, the old theories were doing the same thing as Lewis's octet and electron pairs, only in a confused and arbitrary way; the Lewis-Langmuir theory clarified and legitimized physi­ cally what the organic chemists had done by chemical intuition alone. Thomas Martin Lowry was converted to the Lewis-Langmuir theory in 1923. Like Lapworth, Lowry was a student of Η. E. Armstrong and had the same combination of interests in organic and physical chemistry.105 His early work on the complex rearrangements of the camphor terpenes involved him in the problems of tautomerism and reaction mechanisms. In 1920 he became the first occupant of the new chair of physical chemistry at Cambridge. Perhaps owing to his interest in the physical properties of organic molecules, Lowry was more deeply influenced than Lapworth or Robinson by the electropolar school, and especially by J. J. Thomson. His idea of the "semipolar bond" reflected Thomson's radical distinction be­ tween polar and nonpolar bonds.106 Lowry's basic idea was that unsatu-

this theory originated before Kermack and Robinson left Oxford in 1921. J. N. Davidson, "William O. Kermack (1898-1970)," Biog. Mem. F. R. S., 17 (1971), 399-429. 102 Ibid., pp. 431-432. 1 03 Zbid., pp. 433-435. IO 4 Ibid., pp. 428-429. 10S C . B. Allsop and W. A. Waters, "Thomas Martin Lowry," in A. Findlay and W. H. Mills, eds., British Chemists (London, 1947), pp. 402-418. 106 J- J· Thomson, "The Forces Between Atoms and Chemical Affinity," Phil. Mag., 27 (1914), 757-789.

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rated bonds, as in acetaldehyde or ethylene, really consisted of one covaIent

and one electrovalent, or

ionic, bond: CHj-CH+-O

HjC + -CHj . 107 Although he did not at first

and

adopt Lewis's double dot

symbol, he visualized the positively and negatively charged atoms in the semipolar bond as having an octet and sextet of electrons, and realized that these groups of electrons replaced the old partial valences of the Thiele school. Two letters from Lowry to J. J. Thomson in January 1923 reveal that the inspiration for Lowry's semipolar bond was a lecture given by Thom­ son at Cambridge. The text of this lecture has not survived, but Thomson set forth his ideas on the new developments in bond theory in a curious paper published in 1921.108 In this paper Thomson adapted the LewisLangmuir theory to his own uses in an eccentric and arbitrary way, clearly without really understanding how it worked. He adopted the cubic atom, for example, but objected to the stable electron octet. To explain the reactivity of the unsaturated bond, Thomson adopted the naively mechanical view that it was easier to open one "hinge" between two cubic atoms with a shared face (i.e., a double bond) than the one shared edge of a single bond. On this point Lowry objected, as he explained in a letter to Thomson.109 Cambridge, 6 January 1923 Dear Sir Joseph, I was interested to hear your references to conjugated compounds in your lecture on Thursday morning. There are two possibilities as regards the opening of the hinge between two doubly bound carbon atoms. I think your scheme involved the formation of two steptets; but I have been following up the alternative hypothesis that one carbon atom takes both electrons, giving rise to an octet and a sextet. This makes the alternate atoms positively and negatively charged, so that the formula for butadiene becomes CHj-CH-CH-CH 2 . Thisview was foreshadowed by Thiele himself, long before octets were thought of, and there is a good deal of evidence to show that these conjugated systems are polar, although this aspect was not developed by Thiele and is usually neglected by organic chemists. The view that the double bonds in a conjugated !07T. μ. Lowry, "Studies of Electrovalency I. The Polarity of Double Bonds," J. Chem. Soc., 123 (1923), 822-831. 108 J- J· Thomson, "On the Structure of the Molecule and Chemical Combination," Phil. Mag., 41 (1921), 510-544. 109 Letters in the J. J. Thomson papers, Cambridge University Library.

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system include one covalency and one electrovalency is, however, quite a fascinating one and appears to fit in with almost all the known evidence. I think I should differ from your interpretation of active nitrogen on the ground that this must be a form possessing much more energy than the ordinary gas. Chemists have usually assumed that active nitrogen consists of free atoms, but there is not very much evidence to prove this. Yours sincerely, Thomson's reply has not been preserved, but he apparently approved of Lowry's suggestion. Lowry wrote again. Cambridge, 9 January 1923 Dear Sir Joseph, Many thanks for your letter. I am glad to know that you regard the alternative method of breaking open the double bond as a possible one, for I have been building up quite a big structure on this foundation. It leads to all sorts of queer conclusions in organic chemistry and even gives rise to a new formula for graphite, in which all the bonds in a sheet of atoms are covalencies, whilst the sheets themselves are held together by electrovalencies. I am concocting a scheme for organising sometime during the summer, when G. N. Lewis will be in Cambridge, some sort of a conference on the application of the electronic theory to organic compounds. If anything comes of the scheme, I shall look forward to securing your assistance in making it successful. I remain, Yours sincerely, Thomson had suggested a symmetrical opening of a double bond to give a nonpolar intermediate, but Lowry saw that a dipolar intermediate ex­ plained the peculiar reactions of conjugated molecules such as butadiene. Although he did not mention it, he may also have appreciated the re­ semblance of this dipolar intermediate to Lapworth and Robinson's scheme of alternating polarities.110 In any case, he recognized the short­ comings of Thomson's mechanical explanation, and the advantages of the "very suggestive system of formulae" obtained from the Lewis-Langmuir theory.111 110 T. M. Lowry, "Intramolecular Ionization in Organic Compounds," op. cit. (note 4), pp. 488-496. Reprinted as "Electron Theory of Valency II," Phil. Mag., 46 (1923),964-976. l l i Ibid., p. 966.

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Lowry became one of the most active promoters of the new theory of valence and published numerous papers on the semipolar bond in 1923 and 1924. He found semipolar bonds in oxyacids and amine oxides, for which Langmuir had drawn simple double bonds. 112 He adopted Lewis's double dots and derived from the shared pair bond a novel, but short­ lived, theory of acidity. 113 In his teaching and in his widely used text­ books, Lowry was an ardent disciple of the theory: His books supplemented his constant attempts to drive home in lectures the importance of fundamental concepts, such as the electronic theory of Langmuir and G. N. Lewis. . . . Lowry contributed a great deal to achieving the preeminence of English-speaking chemists in studies of electronic structures and of the mechanisms of reactions of simple or­ ganic molecules. Lowry's personal contribution to the electronic theory was but slight, but as a writer he has undoubtedly influenced most chemists of the present generation. 114 The son of a Methodist minister and an ardent Methodist himself, Lowry preached the Lewis-Langmuir theory with almost evangelical fervor. Lowry's semipolar bond attracted a great deal of criticism, and he soon withdrew to the position that real positive and negative charges in un­ saturated molecules developed only at the instant of reaction. By 1925 he ceased to publish on the theory of valence and the semipolar bond, and settled down to the more mundane task of measuring the physical proper­ ties of organic compounds. 115 The excesses of his brief enthusiasm proved an embarrassment even for his admirers, 116 but on the whole his instincts were sound. Like Lapworth and Robinson, he recognized the great simpli­ fication that the new theory brought to organic chemistry: Hitherto it has been the rule to introduce a new nomenclature and a new symbolism to express each anomaly as it has been encountered, e.g., centric bonds, carbonium bonds, mobile hydrogen atoms, residual 1 1 2 T. M. Lowry, "The Electronic Theory of Valency I. Intramolecular Ionization," ibid., 45 (1923), 1105-1118. 1 1 3 Ibid. See also T. M. Lowry, "The Electronic Theory of Valency IV. The Origin of Acidity," ibid., 47 (1924), 1021-1024. n 4 Allsop and Waters, op. cit, (note 105), pp. 406-407. l l s Lowry's other contributions are "Studies in Electrovalency II. Coordinated Hydrogen,"/. Chem. Soc., 123 (1923), 2111-2124, and "Transmission of Chemical

Affinity by Single Bonds," op. cit. (note 4), pp. 488-496, reprinted as "The Elec­ tronic Theory of Valency III," Phil. Mag., 46 (1923), 1013-1024. 1 1 6 W. J. Pope, "T. M. Lowry,"/. Chem. Soc., 140 (1937), 701-705.

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affinities, partial valencies, etc. Most of these anomalies can now be recognized as being due to the development of electrovalencies, and a single symbolism may be used to express them all. The time is indeed ripe for chemists to state definitely how many types of valency they re­ quire the physicists to provide. 117 Lowry was certain that two types of valence—covalence and electrovalence—would serve, and his sense that chemical theory had acquired a unity was shared by other fledgling physical organic chemists. Like Lowry, Nevil Sidgwick had early interests in both physical and organic chemistry. 118 He studied with Hans Pechmann, an Organiker of the old school, and was assistant for many years to William Perkin, Jr., who once remarked that "physical chemistry is all very well, but it does not apply to organic compounds." 119 Sidgwick disagreed; he had also studied with the pioneer kineticist Vernon Harcourt (1834-1919), and had him­ self studied the kinetics of tautomeric isomerization and other organic re­ actions. Before 1923, however, Sidgwick's work was somewhat desultory. He published little, and he was not appointed reader at Oxford until 1924, when he was forty-nine, though he was highly respected by his col­ leagues. 120 It is clear that until his conversion to the theories of Bohr, Lewis, and Langmuir, Sidgwick had no real cause to which he could fully apply his intellect and energy. Sidgwick's first

application of the new theories was in coordination

chemistry, a wholly new field for him. He later told his biographer that his interest had been aroused by wartime contacts with Rutherford, by Bohr's 1921 note in Nature and his book on atomic theory in 1922, 121 and by Lewis's Valence. 122 The immediate cause of his active interest in valence theory is not precisely known. Sidgwick recognized that Bohr's Aufbau theory explained why the lower elements with a quantum group of four electrons formed a maximum of four shared pair bonds, whereas the higher elements with a quantum group of six could form extra "coordinate bonds" by attaching neutral molecules possessing free electron pairs. 123 117 Lowry,

op. cit. (note 110), p. 967. E. Sutton, "Nevil V. Sidgwick," Proc. Chem. Soc. (1958), pp. 310-319. H. Tizard, "Nevil Sidgwick," Obit. Not. F.R.S., 10 (1954), 237-258. 119 Sutton, ibid., p. 313. •20ibid. 121 See notes 77 and 78. 122 Sutton, op. cit. (note 118), p. 313. 123 N. V. Sidgwick, "Co-ordination Compounds and the Bohr Atom," J. Chem. Soc., 123 (1923), 725-730. 118 L.

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According to the prevailing theory of Alfred Werner, coordination bonds were fundamentally different kinds of bonds; Sidgwick realized that both consisted of shared electron pairs. He was deeply impressed by the sim­ plicity and economy of the new theory, in which both inorganic and or­ ganic chemistry rested on the same theoretical foundation.124 Like Lowry, Sidgwick quickly became an energetic advocate of the new theory. He took an active part in the Faraday Society Symposium in July 1923,125 and in September he presented his theory to the British Association meet­ ings.126 His Electronic Theory of Valence (1927) had an enormous in­ fluence: "the new correlations in it gave a fresh unity to the whole of chemistry; the division between inorganic and organic chemistry was finally broken down. By its comprehensiveness it convinced; by its lucidity it delighted. It became a classic."127 In the 1930's, through his review articles and books, Sidgwick remained a leading spokesman for the new chemistry.128 Many organic chemists, however, were deeply committed to traditional theories. Perkin was one. Another was Jocelyn Thorpe (1872-1940), who asserted at the Faraday Symposium that "the polarity theory explains everything and predicts nothing."129 Bernard Fliirscheim (1874-1955), who before the war had proposed a scheme of "alternating affinities" (a kind of alternating polarity without electric charges or electrons), re­ mained sceptical that electrons were involved in chemical bonding at all.130 Samuel Sugden (1892-1950) objected to any theory that involved the "interchange, rearrangement, or sharing of electrons."131 Two years later Sugden became a convert to the new chemistry,132 and his work on the "parachor" (an empirical function of the dielectric constant, density, etc.) was for a few years regarded as the most compelling evidence for the semi1 24 Ibid., p. 735. 125 N. Sidgwick, "The Nature of the Non-Polar Link," op. cit. (note 4), pp. 468475. 126 N. V. Sidgwick, "The Bohr Atom and the Periodic Law," Chem. & Ind., 42 (1923), 901-903. 127 Sutton, op. cit. (note 118), p. 314. 12«see Ν. V. Sidgwick, Some Physical Properties of the Covalent Link in Chemis­ try (Ithaca, 1933). 129 Discussion, Trans, Faraday Soc., 19 (1923), 527-528. 130 Ibid,, pp. 531-535. 131 S. Sugden, "Electron Valency Theories and Stereochemistry,"/. Chem. Soc., 123 (1923), 1861-1865. 132 S. Sugden, J. B. Reed, and H. Wilkins, "The Parachor and Chemical Constitu­ tion I," ibid., 127 (1925), 1525-1540. See also L. E. Sutton, "Samuel Sugden," ibid., 155 (1952), 1987-1992.

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polar bond. An even later convert was Christopher K. Ingold (1893-1971), a traditional Organiker, whose first published use of the double dot bond in 1927 did not suggest that he understood the theory very well even then. 133 Later he became an outstanding leader of the British physical organic school. The conservatism of established coordination chemists is represented by J. D. Main Smith's attack on Sidgwick in 1923: "No at­ tempt may be made to alter the basis of [Werner's] theory or to graft on to it any theory of atomic electrical polarity or electron structure of atoms. . . . Werner is dead and his coordination theory should remain as he propounded it." 134 The study of the nature of valency, he asserted, was "the province not of chemistry but of physics," and therefore the elec­ tronic theory was not applicable to "pure chemistry." Werner was vigor­ ously opposed to electronic, even electrical, theories of valence, which he regarded as "metaphysics." Smith had fought a long, solitary, and success­ ful battle for Werner's cause only a decade earlier, and his reluctance to embrace the Lewis-Langmuir theory is understandable. Even among the avant-garde there was a striking lack of agreement on fundamentals. Robinson became uneasy about concrete atom models, such as Lewis's cubic atom, and noted in 1923 that his use of the octet was "more or less symbolic." 135 Lewis was annoyed by the British tendency to make a sharp distinction between polar, nonpolar, and semipolar bonds. 136 Robinson and Lapworth were sharply critical of Lowry's semipolar bond and doubted that the normal molecule was actually polarized. 137 Such doubts were widely felt. 138 Lowry found Lapworth and Robinson's ideas difficult to understand "in the sense of being able to use [them] inde­ pendently to solve my own problems." 139 He held the view that a string of conjugated semipolar double bonds would indeed have alternating polarities, but objected to Lapworth's and Robinson's "promiscuous scattering" of plus and minus signs over a chain of saturated carbon 133c. K. Ingold and E. H. Ingold, "The Nature of the Alternating Effect in Carbon Chains, Part V," ibid., 129 (1926), 1315. 134 J. D. Main Smith, "Chelate Co-ordination," Chem. & Ind., 42 (1923), 847-850. See p. 847. See also Main Smith, "The Bohr Atom," ibid., pp. 1073-1078, and N. Sidgwick, "The Bohr Atom and Covalency," ibid., pp. 1203-1206. 135 R. Robinson, "Octet Stability in Relation to Orientation and Reactivity," op. cit. (note 4), pp. 506-507. 13 6See, for example, a letter from Lewis to Linus Pauling, 1 May 1925, Lewis Archive. 13 ^A. Lapworth and R. Robinson, "Remarks on Some Recent Contributions to the Theory of Induced Alternate Polarities," op. cit. (note 4), pp. 503-504. 13s Ibid., pp. 536-537 (discussion). 139 Ibid.

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LEWIS-LANGMUIR THEORY OF VALENCE

atoms.140 Sidgwick supported Lapworth's alternating polarities, but ob­ jected to Lowry's mixed bonds,141 while James Kenner (b. 1885) sup­ ported alternating polarities but objected to Lapworth's derivation of them from the Lewis-Langmuir atom.142 Vigorous debates over these problems continued throughout the 1920's. The ferment was regarded by conservatives as a sign of failure; Fliirscheim, for example, remarked that since there was no agreement over the new theories none was of any use.143 Robinson acknowledged that "the application of present day physical conceptions to the mecha­ nism of chemical reactions is clearly in a transition stage, and no scheme to which the term theory may properly be applied has yet been evolved."144 But he read the absence of agreement as a sign of vigorous health, and compared it to the similar excitement of the 1840's and 1850's, when the structure theories of Gerhardt, Laurent, Williamson, and others were vying for attention. He thought that "the chemists of two or three generations hence will look back upon the present confusion with the same feelings as we regard that time."145 Lowry, too, sensed the historical significance of the present events: "It may be that the electronic formulae will be merely a translation of the traditional formulae of inor­ ganic and organic chemistry, adding nothing but a new nomenclature. . . . All the precedents, however, are against this."146 As precedents, Lowry cited Dalton's atomic theory and van't Hoff's theory of the tetrahedral carbon atom. These remarks point to the keen awareness of this small group of British chemists of their historical mission as the vanguard of a new kind of chemistry.

6. CONCLUSIONS It is clear that local circumstances in Britain around 1923 were particu­ larly favorable for the crystallization of the discipline of physical organic chemistry. Sidgwick, Lowry, and Lapworth all combined an interest in 140 T.

M. Lowry, op. cit. (note 107), p. 824. op. cit. (note 125), p. 471. 142 J. Kenner, "The Significance of Induced Polarity," Rep. Brit. Assoc. Adv. Sci. 141 N. Sidgwick,

(1922), pp. 358-359. 143 B. Fliirscheim, "The Electronic Theory of Valency," Phil. Mag., 47 (1924), 569-576. 144 R. Robinson, "Remarks," op. cit. (note 4), pp. 483-484. I 4 S Ibid. 146 T. M. Lowry, "Introductory Remarks," ibid., pp. 485-487.

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physical and organic chemistry, and they were among the most respected and influential chemists in Britain. Although this crucial combination of interests could be found in Germany, it was more prevalent in Britain. Here the pervasive influence of Η. E. Armstrong may be central to the specific orientation of British organic chemistry. Moreover, the concerns of many British chemists before the war hap­ pened to be those which in the early 1920's emerged as the key concerns of physical organic chemistry. British physical chemists were unusually interested in ideas of atomic structure, probably owing to the influence of Thomson, Rutherford, and Bohr. British organic chemists were unusually interested in reaction mechanisms, especially those like tautomeric re­ arrangements that raise questions as to the nature of the chemical bond. Even in the details of specific theories there was a remarkable continuity between the older ideas on valence and the Lewis-Langmuir theory. Lapworth and Robinson's theories of partial valence were almost tailor-made for direct translation into terms of shared electron pairs and octets. Only the slightest change in symbols was required. Lapworth, Robinson, and Lowry all remarked on the ease with which the transition was made, once the possibility had been suggested. There was no crisis, no revolution, and this easy transition was certainly a major reason for the initial success of the new discipline. It is interesting in this regard that the majority of the avant-garde were not young men: Lapworth, Lowry, and Sidgwick were all about fifty; Robinson, the youngest, was thirty-six. Equally as striking as the theoretical continuities were the experimental ones. The experimental investigation of electropolar effects in organic re­ actions was an established enterprise in British laboratories long before the Lewis-Langmuir theory came on the scene. What organic chemists did in their laboratories changed little after 1923, and this is a second major reason for the success of the new movement. To last, a discipline must pro­ vide for the steady flow of experimental research papers. The lack of obvious experimental leads was one reason why the theoretical specula­ tions of Lewis's group failed to lead to a permanent research program. The volume of experimental work put out by the fledgling British school in­ sured that it would not be ignored or stagnate. In one sense physical organic chemistry was a going concern well before 1923. It had set forth its characteristic set of problems and experimental techniques, but it still lacked unity and a sense of group mission. For the emergence of physical organic chemistry as a movement, and ultimately as a discipline, the Lewis-Langmuir theory was crucial. Before 1923, Lap-

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worth, Robinson, and Lowry were on parallel but separate tracks; after 1923 they clearly had a sense of being part of a single enterprise. More­ over, one need only try to imagine organic chemists proceeding on the basis of Lapworth's cumbersome and obscure theory of 1920 to realize the conceptual importance of the shared pair bond. Robinson, Lowry, and Sidgwick all spoke eloquently of the unity that the Lewis-Langmuir the­ ory conferred on chemistry. It is this unity and sense of historical mission that made the chemistry of the 1920's more than a collection of com­ peting factions. Without this unity a real crisis would surely have arisen in which the plethora of competing theories inherited from the period 19001920 would have become less and less able to cope with the facts. The Lewis-Langmuir theory arrived at precisely the right time to have maxi­ mum effect on British chemists. It was the impetus behind the eventual formation of an organized and lasting new professional and intellectual configuration in chemistry in the 1930's. The subsequent history of the nascent physical organic school and its relation to theoretical quantum chemistry is a separate story; but the emergence of quantum chemistry in the 1930's was profoundly influenced by the manner in which the LewisLangmuir theory was taken up by the chemical community in the 1920's.

G. Ν. Lewis on Detailed Balancing, the Symmetry of Time, and the Nature of Light BY ROGER H. STUEWER* 1. INTRODUCTION The years immediately following the discovery of the Compton effect in late 1922 were ones of intense activity in radiation theory. As Ε. B. Wilson remarked in 1927, "To cover all the recent speculations on the nature of light would be fairly well to cover the interesting and disputed parts of modern physics."1

At last physicists were forced to take Einstein's

neglected 1905 light quantum hypothesis seriously, and to squarely con­ front the wave-particle dilemma. Interference and diffraction phenomena on the one hand and the photoelectric and Compton effects on the other exemplified two apparently conflicting models of radiation.2 Physicists everywhere realized, as C. D. Ellis put it in 1926, that the "wave-theory itself cannot be correct, but except for its greater age it has no greater claims than the light-quantum view."3 To Niels Bohr, the resolution of this crisis in radiation theory lay in recognizing that wave and particle are complementary but mutually ex­ clusive manifestations of light. Bohr enunciated his principle of comple­ mentarity for the first time in the fall of 1927,4 after years of struggling with the problems and paradoxes associated with the creation and interpre*School of Physics and Astronomy and Minnesota Center for Philosophy of Sci­ ence, University of Minnesota, Minneapolis, Minnesota 55455. 1 E. B. Wilson, "Some Recent Speculations on the Nature of Light," Science, 65 (1927), 271. 2 It should be noted that historically Millikan's 1915 photoelectric effect experi­ ments were not taken as proof of quanta—Millikan himself did not accept his own experiments as such. For a full discussion see Roger H. Stuewer, "Non-Einsteinian Interpretations of the Photoelectric Effect," in Roger H. Stuewer, ed., Historical and Philosophical Perspectives of Science (Minneapolis, 1970), pp. 246-263. 3 C. D. Ellis, "The Light-Quantum Theory," Nature, 117 (1926),895. 4 N. Bohr, "The Quantum Postulate and the Recent Development of Atomic Theory," Suppl. Nature, 121 (1928), 580-590.

470 tation of quantum

LEWIS ON DETAILED BALANCING

mechanics.5

Any number of Bohr's contemporaries,

however, were unprepared to embrace Bohr's principle of complemen­ tarity as the final resolution of the wave-particle dilemma.6 At least one major reason was that in the mid-1920's a persistent and pervasive trend of thought, originating much earlier with Einstein,7 was moving in precisely the contrary direction. It centered on the conviction, as H. A. Lorentz ex­ pressed it in mid-1923, that "it must after all be possible to reconcile the different ideas. Here is an important problem for the physics of the imme­ diate future. We cannot help thinking that the solution will be found in some happy combination of extended waves and concentrated quanta. . . ." 8 The search for this "happy combination"—for some type of constructive theory of radiation that would unite rather than separate wave and particle—was a major theme in Einstein's thought throughout his life. But Einstein was not alone in this quest, at least not in the mid-1920's. Louis de Broglie, Harry Bateman, E. C. Stoner, J. J. Thomson, E. T. Whittaker, J. C. Slater, and W. F. G. Swann were among those who also offered quantitative theories, or qualitative suggestions, designed to reconcile wave and particle.9 Another was Gilbert Newton Lewis, who since 1912 had been dean of the College of Chemistry and chairman of the Department of Chemistry at Berkeley.10 In several respects, Lewis's work on the nature of radiation 5 For discussions of Bohr's work, see Max Jammer, The Conceptual Development of Quantum Mechanics (New York, 1966), pp. 323-345; Martin J. Klein, "The First Phase of the Bohr-Einstein Dialogue," Historical Studies in the Physical Sciences, 2 (1970), 1-39; and Roger H. Stuewer, The Compton Effect: TurningPointinPhysics (New York, 1975), Chapter 7. 6 For a contemporary statement that no claim of ultimate validity for Bohr's principle should be made, see E. C. Kemble, "The General Principles of Quantum Mechanics. Part I," Reviews of Modern Physics, 1 (1929), 158-160. 7 Einstein's attempts to find a quantitative constructive theory of radiation began shortly after he introduced his light quantum hypothesis into physics in 1905. For a discussion of his work, see Martin J. Klein, "Einstein and the Wave-Particle Duality," The Natural Philosopher, 3 (1964), 1-49. See also Russell McCormmach, "Einstein, Lorentz, and the Electron Theory," Historical Studies in the Physical Sciences, 2 (1970), 41-87. 8 H. A. Lorentz, "The Radiation of Light," Nature, 113 (1924), 611. 9 For discussions of and complete references to all of these theories, see Roger H. Stuewer, Compton Effect (reference 5), Chapter 7. 10 Lewis (1875-1946) was educated primarily at Harvard University, where he received his Ph.D. degree under T. W. Richards in 1899 at the age of twenty four. He subsequently taught at Harvard for a total of four years, studied for one year in Europe m Wilhelm Ostwald's and Walther Nernst's laboratories, and spent one year in

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was the most original and distinctive of the pre-complementarity period. First, his initial ideas derived from what he argued was a very general principle of nature, the symmetry of time, and from its implications for detailed balancing in radiative processes. Second, he soon proposed an extremely discerning direct particle interaction theory that was based upon both Einstein's light quantum hypothesis and his special theory of rela­ tivity. Third, Lewis's ideas in general were often as controversial as they were original. Nevertheless, he advocated them single-mindedly, in spite of strong opposition, as he did for example when he concluded that Einstein's concept of stimulated emission was invalid, and when he realized that his theory of radiation violated common sense notions of causality. Fourth, he was eventually led to introduce a new term, "photon," into physics and chemistry, whose meaning, however, changed very rapidly. Finally, all of his work bears the unmistakable mark of a chemist who attacked some of the most profound questions in physics and chemistry, but at the same time thought and worked in relative isolation from those physicists and chemists who could have contributed most to his understanding. All of these points suggest the significance of an examination of the origin and evolution of Lewis's ideas on the nature of light.

2. DETAILED BALANCING, THE SYMMETRY OF TIME, AND STIMULATED EMISSION The history of what we now commonly call the principle of detailed balancing dates at least to 1911 when P. Kohnstamm and F. E. C. Scheffer concluded that in oppositely directed chemical reactions the same inter-

a government position in Manilla before A. A. Noyes attracted him in 1905 to the Massachusetts Institute of Technology, where he rapidly advanced through all of the professional ranks and established an international reputation for himself. In 1912 he was called to the University of California at Berkeley, and apart from wartime and other interruptions, he remained at Berkeley for the rest of his life, building there an eminent school of research and teaching. For accounts of Lewis's life and work, see Arthur Lachman, Borderland of the Unknown: The Life Story of Gilbert Newton Lewis (New York, 1955), and Joel H. Hildebrand, "Gilbert Newton Lewis," Obit­ uary Notices of Fellows of the Royal Society, 5 (1945-1948), 491-506; reprinted with minor additions in Biographical Memoirs of the National Academy of Sciences, 31 (1958), 210-235. Hildebrand's biography includes a bibliography of Lewis's writings. Also see Robert E. Kohler, Jr., "The Origin of G. N. Lewis's Theory of the Shared Pair Bond," Historical Studies in the Physical Sciences, 3 (1971), 343-376, and his article for th e Dictionary of Scientific Biography.

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mediate states are occupied.11 Subsequently, this principle, or aversion of it, was used either implicitly or explicitly by any number of other chemists and physicists, including M. R. Marcelin (1915), I. Langmuir (1916), Einstein (1917), O. Klein and S. Rosseland (1921), J. Franck (19221924), R. H. Fowler (1924), E. A. Milne (1924), P. A. M. Dirac (1924), and R. C. Tolman (1924). Tolman referred to it as the "principle of micro­ scopic reversibility," and formulated it for a system in thermodynamic equilibrium as follows: "the total number of molecules leaving a given quantum state in unit time shall equal the number arriving in that state in unit time, . . . [and] the number leaving by any one particular path, shall be equal to the number arriving by the reverse of that particular path."12 In January 1925 Lewis introduced his own formulation, calling it the "law of entire equilibrium": "Corresponding to every individual process there is a reverse process, and in a state of equilibrium the average rate of every process is equal to the average rate of its reverse process."13 To illustrate his law, Lewis presented the following "crude analogy": Suppose that during a period in which there are no births or deaths the population of the several cities of the United States remains constant, the number leaving each city being balanced by the number entering it. This stationary condition would not correspond to our case of thermal equilibrium. We would require further, to complete the analogy, that as many people go from New York to Philadelphia as from Philadelphia to New York. If there were three railroad lines between these two cities we should require that the number of passengers going by each line be equal in both directions.14 Lewis's analogy also illustrates Tolman's definition, and hence one might infer that Lewis was familiar with Tolman's work at this time. This, how­ ever, does not seem to have been the case, since Lewis felt that his was a very original definition.15 What was in fact highly original about it was the 11 Richard C. Tolman, "The Principle of Microscopic Reversibility," Proceedings of the National Academy of Sciences, 11 (1925), 436-439, provides references to the work of the scientists I cite. 12 Richard C. Tolman, "Duration of Molecules in Upper Quantum States," Physical Review, 23 (1924), 699, n. 8. 13 Gilbert N. Lewis, "A New Principle of Equilibrium," Proc. Nat. Acad. Sci., 11 (1925), 181. Lewis's italics have been removed. 14 Ibid., p. 182. 15 Lewis did not cite Tolman's paper although he may have been aware of it and others, as he hints in the final paragraph of a letter he wrote Tolman on 25 June 1925. The only predecessor Lewis actually cited was Einstein, "but he has not proposed this law of equilibrium." Ibid., p. 183.

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way in which he deduced it from what he took to be a very general prin­ ciple of nature, the symmetry of time: The law of entire equilibrium might have been called the law of reversi­ bility to the last detail. If we should consider any one of the elementary processes which are occurring in a system at equilibrium, and could, let us say, obtain a moving-picture film for such a process, then this film reeled backward would present an equally accurate picture of a reverse process which is also occurring in the system and with equal frequency. Therefore in any system at equilibrium, time must lose the unidirectional character which plays so important a part in the development of the time concept. In a state of equilibrium there is no essential difference between backward and forward direction in time, or, in other words, there is complete symmetry with respect to past and future.16 This contention ran completely counter to the traditional and common sense view of time as the unidirectional flow envisioned by Newton.11 Nevertheless, Lewis repeatedly stressed the importance of the principle of symmetry of time in physics and chemistry. He came to regard it as a heuristic principle of great generality with consequences not only for the theory of thermodynamic equilibria but also for the theory of radiation. Indeed, Lewis's preference for his terminology—the "law of entire equilib­ rium"—stemmed from his insistence, which he regarded as an original con­ tribution, that this law must encompass both radiative and nonradiative processes.18 It also had to be applicable, as he remarked with tongue in

i 6 Ibid., pp. 182-183. It may not be quite clear from this quotation that Lewis was actually led to his law of entire equilibrium from his belief in the symmetry of time, but he removed all ambiguity on this point five years later when he stated this fact explicitly in his paper "The Symmetry of Time in Physics," Science, 71 (1930), 576. 17 See Newton's Scholium to his Definitions in hisPrincipia, translated by Andrew Motte and reprinted in the Great Books of the Western World (Chicago, 1952), 34, 8. I cannot go into the history and philosophy of the concept of time in physics here, but those who are interested in this subject could begin by consulting Richard Schlegel's Time and the Physical World (East Lansing, 1961), and T. Gold, ed., The Nature of Time (Ithaca, 1967). 1 8 In his same 1930 paper (reference 16, p. 575), Lewis stated explicitly: "I believe I was the first to set up this principle as a universal law in all physics and chemistry, applicable not only to chemical and physical processes involving material substances, but also to processes involving light." The sense in which Lewis inter­ preted the symmetry of time was always in the sense of motion reversibility, or as we would now say, in the sense that the laws of motion are invariant under a time rever­ sal transformation (replace t with ~t everywhere). Today, of course, theory and experiment in particle physics treat more directly the question of time reversal invariance.

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cheek, to that "entering wedge of scientific bolshevism, which we call quantum theory. . . ." 19 The full application of the law of entire equilibrium to radiant energy seems to me a crucial test of its validity, and since by this application we are going to be led to conclusions of a quite unorthodox character, many will doubtless prefer to deny the law of entire equilibrium rather than abandon many of the accepted laws of radiant energy. But I believe that the law of entire equilibrium will ultimately be recognized as one of the most fundamental of natural laws, and that whatever consequences may be drawn from it must be accepted, even though they contradict well established beliefs.20 To Lewis in May 1925 the major "well established belief" demanding scrutiny was Einstein's concept of stimulated or induced emission, which Einstein had introduced in the course of his famous 1917 derivation of Planck's law.21 Einstein had emphasized that his stimulated emission term was absolutely essential to his derivation, since omitting it and including only the spontaneous absorption and spontaneous emission terms would lead to Wien's, not Planck's, law. After 1917, Bohr had enhanced the im­ portance of Einstein's work by taking a step Einstein himself had been re­ luctant to take; Bohr had emphasized the probabilistic implications of Einstein's three coefficients.22 Lewis fully recognized, therefore, that any challenge to Einstein's concept of stimulated emission would be greeted with skepticism and probably with serious criticism. Nevertheless, Lewis was convinced that such a challenge was necessary, because he was con­ vinced that Einstein's concept of stimulated emission was incompatible with his own law of entire equilibrium. Consider, he argued,23 the problem attacked by Einstein himself, namely, the emission and absorption of 19 Gilbert N. Lewis, Valence and the Structure of Atoms and Molecules (New York, 1923), p. 163. 20 Gilbert N. Lewis, "The Distribution of Energy in Thermal Radiation and the Law ofEntire Equilibrium," Proc. Nat. Acad. Sci., 11 (1925), 423. 21 A. Einstein, "Quantentheorie der Strahlung," Physikalische Zeitschrift, 18 (1917), 121-128; translated and reprinted in B. L. Van der Waerden, ed., Sources of Quantum Mechanics (New York, 1968), pp. 63-77. Although an earlier version ap­ peared in 1916, this is the paper that is usually cited. 22 N. Bohr, "On the Quantum Theory of Line-Spectra," Det kongelige Danske Videnskabernes Selskabs Skrifter t Naturvidenskabelig og Mathematisk Afdeling, Series 8, 4 (1918), 1-118; Part I reprinted in Van der Waerden, ed., Sources, pp. 95-137. For a discussion of this paper, see Max Jammer, The Conceptual Develop­ ment of Quantum Mechanics (New York, 1966), pp. 113-114. 23 Lewis, "Distribution" (reference 20), pp. 423-426.

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radiation by an atom in equilibrium with radiation of frequency v, energy hv, and energy density u v . The spontaneous absorption of radiation is accompanied by an atomic transition from a lower energy state Z n

to an upper energy

state Z m , which Lewis represented

symbolically as Z n +hv—*Z m . He then represented the spontaneous emission of radiation, which he took to be the inverse of spontaneous absorption, as Z m —> Z n + hv. Lewis argued that these two inverse pro­ cesses are completely distinct from the stimulated emission of radiation, since here the atom in its upper state Z m acquires radiant energy hv, a process which must be represented symbolically as Z m + hv —• Z n + 2hv. This transition, Lewis asserted, has no corresponding inverse transition, and hence it "absolutely contradicts the law of entire equilibrium"—and with it the symmetry of time. Einstein's concept of stimulated emission therefore had to be discarded. Lewis knew, however, that it was only by including the stimulated emis­ sion term that Einstein had been able to derive Planck's law. "At first, therefore," Lewis noted, "it would seem that this crucial test of the law of entire equilibrium demonstrates its invalidity." We should, however, "not make this judgment too hastily."24 Instead, we should recall that except for ideal cases chemical thermodynamics teaches us that "equilibrium be­ tween substances is determined not by their concentration but by a thermodynamically corrected concentration which I have called the activity."25 One should not assume with Einstein that the rate of spon­ taneous absorption of radiation is proportional to its energy density u v . Instead, one should assume that it is proportional to its "activity" a v , which, when represented by a m and an for the upper and lower atomic energy states, should be identified with the Boltzmann probabilities of those states. Thus, taking account of two new temperature-independent coefficients K nm and K mn , Lewis asserted that his law of entire equilib­ rium required that K nm a n a v = K mn a m . But this expression is formally identical to Einstein's equilibrium expression without the stimulated emis­ sion term. Thus, Lewis concluded that his law of entire equilibrium in general implied that the activity av of the radiation is given by Wien's law: ίο Λ \ {l.\)

2 ^ — u 0 -hvlkT a 3 V e , v c

where the symbols have their usual meanings. Hbid., p. 425. Ibid. Lewis argued that the activity a v approaches the ratio trations of both the matter and the radiation approach zero. 2

25

Uv I h v

as the concen­

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LEWIS ON DETAILED BALANCING

This result could be interpreted, Lewis argued, by recalling the wellknown formal similarity between Wien's law and the Maxwell-Boltzmann distribution in kinetic theory. In the first place, this formal similarity im­ plied that just as the Maxwell-Boltzmann distribution holds only for ideal gases, so equation (2.1) holds only for "ideal radiation." Andjust as any departure from the Maxwell-Boltzmann distribution corresponds to a de­ parture from the ideal gas pressure-volume relationship, so any departure from equation (2.1) corresponds to a departure from the ideal radiation pressure-energy density relationship. Furthermore, just as the MaxwellBoltzmann distribution is based on the assumption that gas molecules interact with each other, so equation (2.1) is based on the assumption that light quanta interact with each other. Lewis supported this conclusion by pointing out that light quanta must interact with each other, at least gravitationally, as a consequence of Einstein's mass-energy relationship. Finally, just as the Maxwell-Boltzmann distribution is strictly valid only for small collision times, so equation (2.1) is strictly valid only for small interactions or for large frequencies

V,

since, as Lewis had concluded

earlier in the year, the "cross section" of a light quantum is inversely pro­ portional to the square of its frequency.26 Taken together, all of the above meant that "we can speak of ideal radia­ tion in the same sense that we speak of an ideal gas, and that the exact distribution equation for ideal radiation is the Wien equation." "As a corollary it may be pointed out that any equation like Planck's which con­ forms to Stefan's law and Wien's displacement law, cannot represent actual [ideal] radiation." "Lest, however, it seem that the results of this investi­ gation are too largely destructive in character, I shall restate, in a different form, the one positive result of the discussion, namely, that in a system of radiation in thermal equilibrium the activity of the radiation follows exactly the Wien distribution formula."27 Not surprisingly, Lewis's "one positive result" struck many other physicists and chemists as a bewildering, if not iconoclastic, negative result. The first to respond was R. C. Tolman, who wrote to Lewis on 26 Gilbert N. Lewis and David F. Smith, "The Theory of Reaction Rate," Journal of the Chemical Society of America, 47 (1925), 1515-1517 ["The Size of a Light Quantum"]. Their conclusion was that the light quantum's cross section σ = λ 2 /8π = c 2 /87rf 2 , which was exactly Rayleigh's classical value; it prompted Lewis to remark that: "If this surmise proves to be correct it will not be the first time that a result ob­ tained from classical theory has retained its value even after the premises upon which it is based have been abandoned" (pp. 1516-1517). 27 Lewis, "Distribution" (reference 20), pp. 427-428.

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14 May 1925, opening his discussion by commenting on Lewis's law of entire equilibrium: "I talked about the principle during the war with Langmuir at the Cosmos Club, and had a good deal of conversation with Ehrenfest about it last year." But, he added, "I feel some doubt as to the universal applicability of the principle and considerable doubt as to its best formulation. This may be, however, because I haven't thought about it as much as you have."28 Tolman restated his doubts one month later in a second letter to Lewis: "Although I believe that the principle of micro­ scopic reversibility is a very useful one, I feel that we have got to do some pretty close thinking before we can state it in an acceptable form. I have found a number of cases where the principle certainly does not hold and where statistical equilibrium is certainly maintained by cyclical processes. I am not sure, however, whether they are more than trivial in nature. I also feel uncertain as to the propriety of considering the effect of catalysts on microscopic processes. ...>>29 It is not entirely clear what cases Tolman had in mind here, but one possibility is the thought experiment he discussed in his 1927 book on statistical mechanics in which he considered a collision between a sphere and a wedge of equal mass, initially at rest. Assuming that the wedge takes up all of the energy of the sphere, Tolman concluded that the inverse of this admittedly "somewhat artificial" collision does not exist, because it "is immediately evident that no single collision is possible which will re­ turn the sphere and the wedge to states congruent with their original motions."30 Caution therefore had to be exercised in defining and apply­ ing the principle. Up to this point, Tolman had not yet seen Lewis's criticism of Einstein's concept of stimulated emission. He first became aware of it toward the end of June 1925, when Lewis sent him a copy of his paper along with a copy of a letter Lewis had just received from R. H. Fowler in Cambridge. Tolman expressed his opinion on Lewis's ideas in a final letter to Lewis on 29 June 1925: I am much interested in Fowler's letter and your article. I have not yet had time to go over the article carefully. At first sight, however, I feel 28 Tolman to Lewis, 14 May 1925, Lewis Correspondence, College of Chemistry, University of California, Berkeley. 29 Tolman to Lewis, 13 June 1925, Lewis Correspondence, Berkeley. 30 Richard C. Tolman, Statistical Mechanics With Applications to Physics and Chemistry (New York, 1927), p. 165. Tolman also discussed the whole problem of detailed balancing in his enlarged version, The Principles of Statistical Mechanics (Oxford, 1938), especially pp. 166-170.

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that there are a number of points with which I don't agree. This doubt­ less will be very pleasing to you. And it certainly is one criterion of progress that the new shall be different enough from the old so as to offend conservatives such as myself. In particular it seems to me that you do not give sufficient weight to the fact that the Planck radiation law can be derived by applying the Wilson-Sommerfeld rules of quantiza­ tion to the modes of vibration of a holraum [sic], combined with ordi­ nary statistical mechanical treatment. Since I myself lay great stress on this simple derivation of the radiation law, which does not go into the mechanism of light emission and absorption, I feel that we must be very friendly to Einstein's attempts to find a mechanism of absorption and emission which will give exactly the same law. 31 The extent to which Tolman agreed with Fowler on this point may be seen from Fowler's letter to Lewis: Trinity College, Cambridge June 6 Dear Lewis, Many thanks for your nice letter, & the copy of your next paper to the Academy on this subject. Yes I do agree that you are taking the principle more strictly at its face value & carrying it to its logical consequences further than anyone has done before. And there certainly are points of difficulty in Einstein's stimulated emissions. They don't appear in con­ nection with the ordinary switches between definite levels, but in the photoelectric effect & its converse treated by Milne. When you try & calculate the mean absorption coefficient of hot material in ionizative equilibrium & include the stimulated captures you get into difficulties. Milne himself hasn't got clear on the point, which I only knew of from discussions with him, so I can't make myself more explicit. All the same my impression is that the Einstein coefficients are essentially correct & give the right picture of what the atoms are doing & that insofar as you regard this as denying the law of entire eqm then I would take the view of denying that law for radiative processes. I am inclined to think that it may be necessary to distinguish between two types of process [es], one in which (like ordinary slow collisions) there is conservation of energy & momentum in detail & reversibility to the last detail & the other type where there is no conservation & no reversibility—(except statistically). ^ 1 Tolman to Lewis, 29 June 1925, Lewis Correspondence, Berkeley.

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ROGER Η. STUEWER

Radiative processes are a case in point for I don't regard light quanta as a possible alternate basis for the wave theory of light (which any theory has got to reproduce) & then as you point out E's coefficients cant tell the whole story & the process cant be reversed in detail without con­ verging spherical waves. [These ideas are derived from Bohr. I dont know if they are right or not, & I believe he would hedge himself.] The reason why I believe that the stimulated emissions ought to come in in Einstein's way, is that only so does the quantum description of line-emission & absorption fit in with the classical picture. Thereis a very good paper by Van Vleck in the Physical Review 1924 I think which does a great deal to make this correspondence clear. Apart from this I would really be rather tempted to follow your new application & stick to the reversibility law at all costs, but as it is I be­ lieve the picture so drawn would be wrong. Yours v. sincerely RH Fowler 32 Fowler's reference to the 1924 paper of J. H. Van Vleck 33 at the Uni­ versity of Minnesota requires immediate comment. Defining the differen­ tial absorption of an atom to be the excess of stimulated absorption over stimulated emission for corresponding upward and downward transitions, Van Vleck proved that the quantum expression for the ratio of differential absorption to spontaneous emission asymptotically approaches, at large quantum numbers, the classical value of the ratio of absorption to emis­ sion. There is, therefore, a close correspondence between the quantum and classical theories of emission and absorption of radiation. Hence, Van Vleck's paper should have prompted Lewis to reexamine thoroughly his rejection of Einstein's concept of stimulated emission, since Van Vleck proved in effect that Einstein's concept was absolutely essential to main­ tain reversibility and hence to maintain Lewis's law of entire equilibrium in quantum radiative processes. Lewis did not read Van Vleck's paper and therefore did not understand 3 2 Fowler to Lewis, 6 June [1925], Lewis Correspondence, Berkeley. Fowler, of course, was an expert on these questions; his 1923-1924 Adams Prize Essay at the University of Cambridge was enlarged into his Statistical Mechanics (Cambridge, 1929). On p. 436, he cites Lewis's work and claims that detailed balancing is now (1929) regarded as generally valid. In the 2nd edition (1936), p. 660, he makes an even stronger statement. 3 3 J. H. Van Vleck, "The Absorption of Radiation by Multiply Periodic Orbits, and its Relation to the Correspondence Principle and the Rayleigh-Jeans law," Phys. Rev., 24 (1924), 330-346 and 347-365 (Parts I and II).

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LEWIS ON DETAILED BALANCING

this point. For the time being he was most concerned with the other main point that Fowler had raised; namely, that his law of entire equilibrium may be valid only for nonradiative, nonstatistical processes since the con­ servation laws may not hold in microscopic interactions, a suggestion that Bohr had recently brought to the forefront of physics in the BohrKramers-Slater paper of 1924.34 Lewis expressed his views on this point when he answered Fowler's letter on 25 June 1925: "I believe," he wrote, "that in spite of the interference of light which presents difficulties of a most serious character, that eventually we are going to establish the prin­ ciple of entire equilibrium and maintain the conservation laws, although perhaps the wish is father to the thought."35 Two months passed before Fowler replied to Lewis. By that time new facts had come into Fowler's possession which, in his opinion, placed Lewis's work in an entirely new light: Trinity College Cambridge Aug 30 Dear Prof Lewis, I read your second note on reversible processes & the 'activity' of radiation with a good deal of interest & some scepticism (I admit), but my scepticism has recently been considerably weakened by a new line of attack which seems to be going ahead. Its nothing to do with me, & very likely you have already noted it (with pleasure I am sure) but in case you have not I thought I would point out some of the main papers for your notice. The original idea is a statistical one & reinterprets the Einstein coeffi­ cients in a way which must be extremely like your point of view. This is in a paper by a Hindoo—Bose Zeit fiir Phys 27 ρ 384. published about a year ago. I am not yet prepared to say I fully appreciate the full implica­ tions as I have only just come across it. It involves radical changes in the proper [ ? ] way of making the calculations of statistical mechanics which will certainly be interesting to follow up. But the same idea has already been taken up & developed in gas theory by Einstein, Sitzungsberichte 34 N. Bohr, H. A. Kramers, and J. C. Slater, "The Quantum Theory of Radiation," Philosophical Magazine, 47 (1924), 785-802. For full discussions of this paper in its historical context, see Martin J. Klein, "First Phase" (reference 5), Max Jammer, Conceptual Development (reference 5), pp. 181-188; and Chapter 7 of my book (reference 5). 35 Lewis to Fowler, 25 June 1925, Lewis Correspondence, Berkeley.

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ROGER Η. STUEWER

Berlin 1924 & 1925 (3 papers) & shown to lead to a perfectly natural theory of gas degeneration at low temperatures—I have never seriously thought such a theory necessary but it is necessary I believe now in view of experimental specific heats—I expect I ought to have realized this before—& certainly there was no such theory before which was not hopelessly artificial. The thing is being taken up & rediscussed in recent Zeitschrifts, which I have not yet absorbed. Of course there will now be a severe break of the correspondence be­ tween classical & quantum descriptions of the emission & absorbtion [sic] of radiations, which may after all have to be accepted. With best wishes Yours v. sincerely R.H. Fowler 36 Thus, Fowler's initial reaction to the discovery of Bose-Einstein statis­ tics 37 was that the discovery weakened the link between the quantum and classical theories that Van Vleck had greatly strengthened only a short time earlier. Einstein himself would have thoroughly disputed Fowler's contention had he been aware of it. Lewis once again did not take Fowler's advice to familiarize himself with Bose's and Einstein's papers, since he was extremely pressured for time in the summer and fall of 1925. He wrote Fowler on 29 October 1925 that "I have been obliged to give practically all my thought to the Silliman Lectures which I am going to give at Yale University next month." 38 In spite of his general reluctance to deliver public lectures, 39 Lewis looked forward with a great deal of pleasure to delivering the Silliman Lectures at Yale. He relished the thought, as J. L. Hildebrand has observed, of doing "his best to shock scientific prejudices in several fields." 40 For Lewis the most important of these fields now was radiation theory, and he was determined, as he wrote Fowler, to go well beyond his past work and "resolve the serious paradox between quantum theory and wave theory." He added: "I do not expect many people to accept my views immediately, 36 Fowler

to Lewis, 30 August [1925], Lewis Correspondence, Berkeley. N.] Bose, "Plancks Gesetz und Lichtquantenhypothese," transl. into German by A. Einstein, Zeitschrift fur Physik, 26 (1924), 178-181. For a discussion of Bose's discovery and Einstein's extensions of it to gas theory, see Martin J. Klein, "Wave-Particle Duality" (reference 7), pp. 26-38. 38 Lewis to Fowler, 29 October 1925, Lewis Correspondence, Berkeley. 3 ^Hildebrand, Biographical Memoirs (reference 10), p. 222. 40 Ibid., p. 223. 37 [S.

482

LEWIS ON DETAILED BALANCING

but if they, or something like them are eventually accepted it will remove the obstacles that you mention to the acceptance of my application of the law of entire equilibrium." 41 By implication, they would also remove any obstacles to the acceptance of his belief in the symmetry of time.

3. DIRECT PARTICLE INTERACTION AND SPECIAL RELATIVITY "Sir, to leave things out of a book, merely because people tell you they will not be believed, is meanness." So said Johnson to Boswell, and so said Lewis to the readers of his Silliman Lecture on "Light and the Quantum" when he published it in 1926. 42 Although he recognized that his ideas were radical, Lewis nevertheless considered them to be of the utmost im­ portance; he published them in three different places: in his book The Anatomy of Science, which constituted his Silliman Lectures, 43 in Nature, 44 and in the Proceedings of the National Academy of Sciences. 45 He stated that some might regard his ideas as "extremely repugnant to common sense." He also freely admitted that since they had not yet "run the gauntlet of scientific criticism," they might turn out to be "thoroughly erroneous." "Often," he remarked, "a 'watcher of the skies' beholds some brilliant nova which later proves to be only a candle on a neighboring hillside." 46 The general state of affairs in radiation theory in 1925-1926 invited speculation, however, since its very foundation had been challenged. "Re­ cent experiments, especially those of A. H. Compton," Lewis observed, "have fully corroborated Einstein's brilliant surmise that the energy of radiation consists of quanta." 47 The knowledge that Einstein's twentyyear-old "heuristic viewpoint" finally had to be taken seriously prompted repeated attempts to resolve the wave-particle dilemma, the most famous and fruitful of which no doubt was J. C. Slater's 1924 virtual radiation

41 Lewis

to Fowler, 29 October 1925, Lewis Correspondence, Berkeley. N. Lewis, The Anatomy of Science (New Haven, 1926), p. 113. Johnson's words were used by Lewis to introduce his chapter. 43 Ibid., pp. 113-134. 44 Gilbert N. Lewis, "Light Waves and Light Corpuscles," Nature, 117 (1926), 236-238. 45 Gilbert N. Lewis, "The Nature of Light," Proc. Nat. Acad. Sci., 12 (1926), 22-29. 46 Lewis, Anatomy (reference 42), p. 124. 47 Lewis, "Light Waves" (reference 44), p. 236. 42 Gilbert

ROGER Η. STUEWER

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field concept 48 which soon led to the Bohr-Kramers-Slater paper. 49 It was in this generally speculative atmosphere that Lewis advanced his own ideas. Lewis felt that approaches like Slater's and Swann's that considered the possibility of assigning a virtual, classical-like Poynting vector field as a guide for light quanta had one major drawback: since light quanta were assumed to propagate rectilinearly, they could not follow the "tortuous path of the Poynting vector" in an interference field. 50 Even if the Poynting vector field were to determine only the points at which quanta strike a receiving screen, "we are met by contradiction." Thus, Lewis considered a typical two-slit arrangement, and supposed that a given quantum can strike a certain point on the screen only when the upper slit is open, but cannot strike that point when both slits are open. He suggested that one start the experiment with only the upper slit open, and then suddenly open the lower slit also. The Poynting field that was thereby suddenly ad­ mitted through the lower slit could not "tell" a quantum passing through the upper slit not to go to the forbidden point. For to do so, the field would have to intercept the quantum at some point between the upper slit and the forbidden point on the screen; but by then the quantum's tra­ jectory had already been determined, and hence it was necessarily on its way to the forbidden point. The more we think about this contradiction, Lewis wrote, the more "the hardly credible thought" occurs to us "that in some manner the atom in the source . . . can foretell before it emits its quantum of light whether one or both of the slits . . . are going to be open." 51 Although it sounded "absurd," this was the basic idea that Lewis would attempt to develop into a consistent theory of light. And since his theory would clearly involve fundamental challenges to our common sense notions of temporal order and hence of causality, it was imperative for Lewis at the very outset to present a clear picture of the concept of time in physics. "There is," Lewis observed, "some discrepancy between the equations of mathematical physics and the less formal physical explanations with which we are accustomed to annotate them. The equations themselves recognise no distinction between positive and negative extension in time; they are symmetrical. But, in the language of physics, a great distinction is made between past and future." 52 Mechanical systems run backward in 48 J.

C. Slater, "Radiation and A corns," Nature, 113 (1924), 307-308. reference 34. 50 Lewis, "Nature" (reference 45), p. 23. 5 1 Ibid., p. 24. 52 Lewis, "LightWaves" (reference 44), p. 237.

49 See

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LEWIS ON DETAILED BALANCING

time as easily as forward, and Gibbs and Boltzmann have taught us that even the "so-called irreversible processes" may be regarded "merely as an enormous number of elementary processes, each of which obeys simple mechanical laws." Only radiative processes have in the past seemed to be temporally asymmetric, but "we now know that this is not the case, and in advancing the theorem of 'entire equilibrium,' I have recently shown how we may consider all these elementary processes as completely re­ versible and symmetrical with respect to past and future."53 The key to understanding radiative processes, therefore, lay in recogniz­ ing that time is symmetric. Lewis required two further assumptions, how­ ever: first, that an emitting atom loses energy only in the form of a particle of energy hv, momentum hv/c, and mass hv/c2 , which travels rectilinearly to an absorbing atom unless deflected, in which case the conservation laws of energy, momentum, and mass are obeyed; and second, that a single light particle emitted from a single atom is subject to the laws of interference.54 Compton's experiments lent plausibility to the first of these assumptions, Taylor's experiments to the second. The crux of the matter was to couple these two assumptions with that of the symmetry of time. To do so, Lewis denied that an atom simply radiates "into space," but rather that an atom never emits light except to another atom, and . . . that it is as absurd to think of light emitted by one atom regardless of the exis­ tence of a receiving atom as it would be to think of an atom absorbing light without the existence of light to be absorbed. I propose to eliminate the idea of mere emission of light and substitute the idea of transmission, or a process of exchange of energy between two definite atoms or mole­ cules. Now, if the process be regarded as a mere exchange, the law of entire equilibrium . . . requires us to consider the process as a perfectly symmetrical one, so that we can no longer regard one atom as an active agent and the other as an accidental and passive recipient, but both atoms must play coordinate and symmetrical parts in the process of exchange.55

"Ibid. s4 Lewis,

"Nature" (reference 45), p. 22. pp. 24-25. R. C. ToIman and Sinclair Smith, "On the Nature of Light," Proc. Nat. Acad. Sci., 12 (1926), 344, note that Schottky (1921-1922), Smekal (1922), Wentzel (1924), and Herzfeld (1924) earlier discussed views on radiative processes "in some ways similar" to Lewis's. For references to these works, see Tolman and Smith's article. They missed at least Tetrode's 1922 paper, which Wheeler and Feynman (reference 117) discuss. 55 Ibid.,

ROGER Η. STUEWER

485

This perfect symmetry between emitter and absorber, between past and future, led directly to a causal paradox. Lewis considered the following illustration: "The light from a distant star is absorbed, let us say, by a molecule of chlorophyl which has recently been produced in a living plant. We say that the light from the star was on its way toward us a thousand years ago. What rapport can there be between the emitting source and this newly made molecule of chlorophyl?"56 If we suppose for the sake of argument that the star served as the source of light in the two-slit experi­ ment above, and that the absorbing molecule of chlorophyl was placed precisely at the forbidden point on the screen, then, if both slits were suddenly opened to the starlight, could we thereby have prevented the light from being originally emitted? "If so it would mean that we could, perhaps in a trivial way, but nevertheless in principle, alter the course of past events."57 Perhaps the most striking feature of Lewis's ideas, including the above causal paradox, was that they could be regarded as a "natural" and "in­ deed inevitable" extension of Einstein's special theory of relativity. Lewis, who was proud to recall that it was he who in 1909 had presented the first paper on relativity before the American Physical Society,58 was thoroughly familiar with Einstein's theory. He now considered a Minkowski diagram representing the four-dimensional manifold of special relativity (Figure 1). As usual, in the diagram the time axis OT, one spatial axis OX, and the light cone OL, for which the four-dimensional distance ds 2 = dx 2 + dy 2 + dz2 - c2 dt2 = 0, are shown on a two-dimensional plot. Any line drawn from the origin O to a point inside the light cone TOL is called a time-like line and represents the locus of a material particle, since in this region ds2 < 0, and the slope dx/dt of any such line is always less than c, the velocity of light. Any line drawn from the origin O to a point outside the 56 Lewis,

"Nature" (reference 45), p. 25.

51 Ibid. 58 Lewis, Anatomy (reference 42), p. 85. Lewis was here referring either to his paper "A Revision of the Fundamental Laws of Matter and Energy," Phil. Mag., 16 (1908), 705-717, which apparently formed the basis for his talk "Non-Newtonian Mechanics" at the 24 October 1908, New York meeting of the American Physical Society, or to his paper (written with R. C. Tolman) "The Principle of Relativity and Non-Newtonian Mechanics," Proceedings of the American Academy of Arts and Sciences, 44 (1909), 711-724. The latter paper evidently formed the basis for his talk "Non-Newtonian Mechanics and the Principle of Relativity" (with R. C. Tolman) at the 28-31 December 1908, Baltimore meeting of the AmericanPhysical Society. For the abstract of the former talk seePhys. Rev., 21 (1908), 525-526, and for that of the latter seePhys. Rev., 28 (1909), 150.

486

LEWIS ON DETAILED BALANCING

T

' •

/

/

/

/

/

/

/

/

/

/

/

L

0

Figure 1. Minkowskidiagram for special relativity.

light cone TOL is called a space-like line, since in this region ds 2 > O and the slope dxldt of any such line is always greater than c, and "does not even suggest a velocity." The line OL is unique. It is the line for which ds 2 = 0, and for which the slope dxldt = c. "Now," Lewis wrote, "in spite of the symmetry demanded by the geometry we affiliate the line OL with the time-like lines and say that it represents the velocity of light. As a con­ cession to traditional thought we do violence to our geometry when we call the light process a form of motion at all; and while we shall continue to make this concession, it will be with a realization of the unique charac­ ter of radiation." 59 To represent both the emission and absorption of radiation, two Min­ kowski diagrams are required, one for the emitting atom, and one for the absorbing atom. Suppose that the lines OT and QL represent the spacetime loci of these two atoms (Figure 2). Suppose further that the inter­ cepts O and L, and O and Q, are on the light cones, and hence are joined by lines OL and OQ of zero four-dimensional length (ds 2 = 0). This is an idea, Lewis observed, "of which much use has been made in the mathe5 9 Lewis,

"Nature" (reference 45), p. 26.

487

ROGER Η. STUEWER

/o\

\

\

Figure 2. Minkowski diagrams for two atoms.

matics but none in the physics of relativity. The proposals which I am making . . . are tantamount to assuming that such a distance is also zero in a physical sense, and that two atoms whose loci are OT and QL may be said to be in virtual contact at any two points such as O and L or O and Q, which are connected by singular lines." 60 For example, "I may say that my eye touches a star, not in the same sense as when I say that my hand touches a pen, but in an equally physical sense." 61 In other words, when "two atoms are in ordinary physical contact we do not inquire how one atom ascertains that the other is in a position to receive energy, nor need we so inquire in the case of virtual contact, even though the time of emis­ sion and the time of absorption are said to be separated by thousands of years. Such a statement depends upon an arbitrary choice of a time axis. If in our figure we should take, not OT, but time axes lying nearer and nearer 60 Ibid. 6 1 Lewis,

"LightWaves," (reference 44), p. 237.

488

LEWIS ON DETAILED BALANCING

to OL, not only the time elapsing between O and L but also their spatial distance would approach zero." 62 The symmetry of the transmission process, which was also embedded in the so-called retarded and advanced potentials, and which owed its origin to the symmetry of time, was therefore beautifully reflected in the sym­ metry of special relativity. It was only through "our notion of causality" that a "dissymmetry alien to the pure geometry of relativity" had been introduced into physics. But if relativity had taught us anything, it had taught us to be wary of common sense notions of space and time. And indeed, Lewis felt that relinquishing these common sense notions was a small price to pay for a theory that was capable of yielding quantitative predictions of radiative transmission processes. These predictions potentially included quantitative predictions of the probability of transmission of radiation from one atom to another. For, Lewis argued, if one were to draw the world-lines of two atoms, A and B, in virtual contact with each other and capable of emitting and absorbing energy hu, respectively, these world-lines would assume the form of two helices of equal radius with axes parallel to each other (Figure 363). One could then connect a point A' on the axis of one helix to a point B' on the axis of the other with a singular line and associate the relative difference in the positions of these points with a relative difference in phase between the two atoms. One could also mentally project each helix onto a plane, where the projected figure would ordinarily be an ellipse but would turn into a circle for one particular characteristic orientation of the plane, and associate the relative angular orientations of these two characteristic planes with the relative polarizations of the atoms. "Thus we speak not of the phase and polarization of light but of the relative phase and relative polar­ ization of the atoms themselves; and we shall assume that the chance that the atom B accepts radiation from A depends upon these two quantities, and upon the distance between A and B."64 The analysis could also be extended to encompass the reflection of light from a mirror C; in fact, it could be extended to encompass all of the "quantitative laws of optics." However, Lewis would reserve the extensions of his theory for "another communication.'' Meanwhile, the question arose whether or not it was possible to test Lewis's theory experimentally. This question was particularly important vis-a-vis theories like Slater's or Swann's in which a Poynting vector field 62 Lewis,

6 ^Ibid.,

"Nature" (reference 45), p. 26. p. 27.

M Ibid„

pp. 27-28.

ROGER Η. STUEWER

489

Figure 3. Lewis's diagram illustrating two atoms in virtual contact with each other.

seemed to play a role. Fortunately, Lewis wrote, "there is a crucial experi­ ment [between such theories and mine] which does not seem absolutely beyond the reach of our present experimental technique." 65 Consider a bi-mirror experiment (Figure 4) in which the mirrors AA' and BB' have been adjusted to produce a bright fringe at D and a dark fringe at C. Sup­ pose now that the mirror AA' is suspended by a torsion wire, and that its 6s Ibid.,

p. 28.

490

LEWIS ON DETAILED BALANCING

Figure 4. Lewis's bi-mirror experiment.

width is only one half the screen distance CD. Then, Lewis asserted, on the one hand, the Poynting vector field (and hence the radiation pressure) would be uniform across the mirror AA'. On the other hand, according to Lewis's theory light quanta should strike point A (en route to the bright fringe) but should not strike point A' (en route to the dark fringe). Given these experimental conditions, Lewis's theory, in contrast to Slater's or Swann's, predicted that the mirror AA' would experience a torque. Lewisrecognized that his theory was very bold and speculative. He wrote Paul Ehrenfest on 4 February 1926: "As you know, I do not follow the fashion much in physics and chemistry, but take a path of my own, which I do not doubt often leads nowhere. But I have a feeling that in this paper on radiation I have hit upon something pretty fundamental, and I should like very much to have your opinion. I think you are one of the few men who will not condemn them instantly and without a hearing."66 Lewis provided a more sober statement of the importance he attached to his 66 Lewis to Ehrenfest, 4 February 1926. This letter is actually dated 4 February 1925, but it is clear from its contents that this was a typographical error.

ROGER Η. STUEWER

491

theory when he summarized it for publication. It "goes a long way," he wrote, "toward bringing closer correlation between our physical and our geometrical concepts; it emphasizes the unique character of the singular lines (motion of light), it makes physical use of the theorem of zero dis­ tance along singular lines, and it does away with that distinction between past and future which, however useful it may be in other cases, seems to have no significance in a purely reversible process." 67

4. REACTIONS TO LEWIS'S THEORY The response to Lewis's theory was immediate and varied. Some com­ ments and criticisms, of course, were too general to be illuminating. For example, one "outer layman," who identified himself only by the initials F. P., could not fathom how Lewis's theory helped to understand ques­ tions such as "how does polarization separate the whole light into two parts vibrating at right angles?" 68 William Band, a physicist at the Uni­ versity of Liverpool, supported Lewis's ideas in general but thought that it would be "more intelligible and more in accordance with the historical development of physics" if instead of concentrating only on the end points of the causal chain—the emitting and absorbing atoms—Lewis also took into account other intervening elements like lenses or diffracting obsta­ cles. 69 C. D. Ellis termed Lewis's theory "an original view on the whole, problem," 10 and Ε. B. Wilson, sharing Ellis's enthusiasm, considered it to be "a reasonable interpretation of the mathematics fundamental to rela­ tivity."" 71 Only three days after Lewis's paper had appeared in Nature (13 February 1926), Niels Bohr had also studied it and reported his impressions of Lewis's theory in a letter to O. W. Richardson: "Every day seems the 67 Lewis,

"Nature" (reference 45), pp. 26-27. P., "What is a Beam of Light?" Nature, 117 (1926), 344. 69 William Band, "Prof. Lewis's 'Light Corpuscles'," Nature, 120 (1927), 405-406. 70 C. D. Ellis, "The Light-Quantum Theory," Nature, 117 (1926), 897. 71 Wilson, "Some Speculations" (reference 1), p. 266. Wilson saw a connection between Lewis's theory and J. J. Thomson's 1903 suggestion of a positive and nega­ tive charge being connected by a Faraday tube which transmits electromagnetic pulses between them. At the same time, he was skeptical of Thomson's current views: "All we need now," he asserted, "is to have some physicist who has read up the new psychology as a minor tell us that the Faraday tube that draws the negative and positive electricity together is but a gross materialization of the real funda­ mental force of nature, the sex instinct, and our molecules have become as in­ humanly lewd as we are alleged to be!" (p. 268). 68 F.

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LEWIS ON DETAILED BALANCING

solution of the radiation riddle more distant. I am just reading a paper of Lewis which suggests ideas which we have often touched upon in our discussions here [in Copenhagen], but considered too wild to follow up more closely. Still I wonder what progress may be obtained in that way, and it shall be very interesting to see Lewis' more detailed publications."72 Richardson replied: "I think there is a good deal of nonsense in Lewis's ideas if I have understood them properly." 13 The first physicist to offer detailed criticisms of Lewis's ideas was, once again, R. C. Tolman. Tolman wrote to Lewis on 9 March 1926 that al­ though he felt "sympathetic" to Lewis's "point of view," he could not agree with the conclusiveness of Lewis's "proposed crucial experiment." 74 Tolman specified his reasons nine days later in an article written jointly with Sinclair Smith. 75 Tolman and Smith suggested that a dark fringe on one edge of the receiving screen in Lewis's setup and a bright fringe on the other did not necessarily mean that no light quanta were traveling to the dark edge, but only that they produced no observable effects there. As in the Lippmann process of color photography, standing wave patterns ex­ tending into the screen could be present at both edges, with an antinode at the surface of the screen at the bright edge and a node at the surface of the screen at the dark edge. Hence, equal numbers of quanta could actually strike both edges of the screen as well as both edges of the suspended mirror, which would mean that even on Lewis's theory the mirror would experience "the same or nearly the same forces . . . as would be predicted from the wave theory." 76 Lewis reacted almost immediately to Tolman's and Smith's suggestion,77 calling it "untenable" for the following reason. Consider a thought experi­ ment in which the receiving screen was replaced by a thin calorimeter of equal width after the interference pattern had been established. Accord72 Bohr to Richardson, 16 February 1926, Bohr Correspondence, Archive for History of Quantum Physics (Copenhagen, Philadelphia, Berkeley), and Center for History of Physics (New York). 73 Richardson to Bohr, 20 February 1926, Bohr Correspondence, AHQP, CHP. 74 Tolman to Lewis, 9 March 1926, Lewis Correspondence, Berkeley. 75 Richard C. Tolman and Sinclair Smith, "Nature of Light" (reference 55), pp. 343-347. Tolman and Smith suggested (p. 347) that perhaps one "heuristically adequate" way of reconciling quanta with the wave theory would be to assume that the waves "carry no appreciable energy but provide the signaling system by which in accordance with the laws of interference the atoms can 'know' whether or not they are allowed to interact with an oncoming [energy carrying] quantum." 16 Ibid., p. 346. 77 Gilbert N. Lewis, "The Path of Light Quanta in an Interference Field," Proc. Nat. Acad. Sci., 12 (1926), 439-440. The passage quoted is on p. 439.

ROGER Η. STUEWER

493

ing to the usual wave theory, the bright edge of the calorimeter would heat up, while the dark edge would not. According to Tolman's and Smith's suggestion, however, since quanta, and hence energy, would ac­ tually strike the dark as well as the bright edge of the calorimeter, both edges would heat up. Conservation of energy would be violated therefore, since "the total amount of energy arriving at the plate . . . [would be] largely increased merely by the interposition of the optical apparatus which produces interference." Lewis concluded that Tolman's and Smith's objections were invalid and that his crucial experiment would indeed yield a "positive result." Lewis submitted his refutation of Tolman's and Smith's argument for publication on 31 May 1926. He evidently also sent a preprint to Tolman, because on 3 June Tolman replied to Lewis by letter as follows: "Dr. Smith and I do not agree that our suggestions involve any contradiction to the principle of the conservation of energy. In case the screen is highly opaque, we believe that quanta falling at the center of a dark band would be deflected on passage through the surface of the screen to regions where absorption is permitted by the wave theory." 78 Tolman went on to cite a passage in his and Smith's paper which permitted this interpretation of their views. "Our position then is," Tolman concluded, "that the theory which you have adopted, the failure of your proposed crucial experiment, and the conservation of energy, are all three compatible propositions." 79 Tolman's rejoinder, which he soon published, 80 might have precipitated yet a further response from Lewis, but it did not. Nor was the issue settled experimentally, as it might have been. Rather, it was settled—along with the fate of Lewis's entire theory—through correspondence with Al­ bert Einstein. Nothing, of course, could have been more natural than for Lewis to seek Einstein's opinion on his theory of radiation. The theory itself was solidly based upon both Einstein's special theory of relativity and his light quan­ tum hypothesis. Moreover, Lewis had had the highest possible respect and admiration for Einstein ever since Lewis had experienced the "thrill of excitement" when first studying the "strange but alluring doctrine" of relativity. 81 Early in his career, evidently between 1909-1911 or 191278 Tolman to Lewis, 3 Tune 1926, Lewis Correspondence, Berkeley. "Ibid. 80 Richard C. Tolman and Sinclair Smith, "Remarks on Professor Lewis's Note on the Path of Light Quanta in an Interference Field," Proc. Nat. Acad. Sci., 12 (1926), 508-509. 8 1 Lewis, Anatomy (reference 42), p. 84.

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1913, 82 Lewis had even made a special trip to Zurich to talk personally with Einstein about relativity, a visit Einstein could not remember in later life. 83 On 27 July 1926, Lewis decided to seek Einstein's opinion of his ideas, iritiating a correspondence with Einstein, who was then in Berlin, and sending him copies of his papers on his law of entire equilibrium and on his theory of light. Lewis wrote Einstein that his law of entire equilibrium and its applica­ tion to black body radiation were "based essentially upon your own ideas" and "probably owe their origin to a conversation that I had with you in Zurich many years ago. . . ." He was now trying to carry them "a little far­ ther than anyone has ventured to do hitherto," and as a result had been led to a conclusion which "is not in accord with . . . your derivation of the Planck distribution law." Finally, Lewis told Einstein: "The paper on The Nature of Light I should like very much to get your views upon. Although I state that it is an extension of your principle of relativity, it may be a step that you would be quite unwilling to take. I hesitated a good deal be­ fore accepting it, but am now thoroughly convinced that it is correct, and that although it is not the whole truth it does make a fair beginning to­ ward eliminating the paradox of the quantum." 84 Few subjects were as close to Einstein's heart, and less than one month later, on 22 August, he replied to Lewis. Einstein's letter provides detailed insight not only into Lewis's ideas, but also into the evolution of Einstein's own thought: 22. VIII. 26. Dear Mr. Gilbert Lewis: Many thanks for your letter and your papers, which I read with great pleasure. The ideas you suggest in "The Nature of Light" are the same as I have agonizingly turned over in my own mind without coming to a conclusion. Also, the idea of a direct action with respect to the fourdimensional distance 0 appears extremely tempting; what is sad, how­ ever, is that if A - B = 0 and B-C = O (more precisely, if -Syis = 0; s BC

=

then A - C (s AC ) is nevertheless not [necessarily] 0. And yet,

the action from A to C via a mirror B is just as intense as if A and C 8 2 Lewis seems never to have specified an exact date for his visit, although he men­ tions the visit itself explicitly in his letter of 27 July 1926 to Einstein. The dates given are the post-1905 dates of Einstein's residence in Zurich. ^ 3 Einstein to Lachman, 24 August 1951, quoted in Lachman, Borderland, pp. 24-25. 8 4 Lewis to Einstein, 27 July 1926, Lewis Correspondence, Berkeley.

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would have a four-dimensional distance of zero. One should really carry out your mirror experiment . . .; unfortunately, it is as good as certain— in spite of all of the difficulties in understanding it—that the time average of all radiation pressures behaves according to Maxwell's theory. I am completely convinced of the validity of your "law of entire equilibrium." But I can not agree with your opinion that this law proves the incorrectness of my derivation of Planck's law. That this line of argument may not be so easily applied here is due to the fact that no mechanism is imaginable which catalytically favors the spontaneous emission [freie Ausstrahlung], but not the stimulated absorption and stimulated emission [positive und negative Einstrahlung]. One must re­ gard spontaneous emission and stimulated emission, on the one hand, and stimulated absorption, on the other hand, as inverse processes. I do not agree with your distinction that according to the law of mass action stimulated emission is regarded as a reaction in which two quanta are involved (Z m + hv = Z n + 2hv). I think that the law of mass action ceases to be applicable in its simple form in the non-Wienian radiation region, or for degenerate gases. In formulating my [1917] theory, I myself found the non-evident reversibility of my statistical mechanism unpleasant, and I have empha­ sized this point in lectures. But this is not in fact an objection. To see this one only has to consider the radiative equilibrium state of an oscilla­ tor in a Jeanian radiation field, where one can operate with classical theory, and where one can use considerations completely analogous to those in my paper. In so doing one is certain from the very beginning that one is to remain in the region of strictly reversible processes. (Mechanics and Maxwell's equations). If one considers an oscillator of energy E during a short time 7, such that during this time the percentage change in E is infinitely small, its energy changes 1) by spontaneous emission 2) by absorption of radiation (work done by the external radiation field on the oscillator). The sign in front of the absorbed radiation de­ pends on the phase of the oscillator, and is therefore just as probably positive as negative. My theory is nothing but the appropriate transformation of this idea into quantum theory. In view of this consideration, it is actually impos­ sible to omit the stimulated emission, and it is therefore in no way an ad hoc assumption. Otherwise the theory would not have satisfied me.

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LEWIS ON DETAILED BALANCING

I hope this convinces you. Please let me know what you think about it. Meanwhile, I remain, with best wishes, your A. Einstein85 Einstein's criticisms were clearly devastating. The thrust of his remarks on Lewis's direct interaction theory of radiation was that if two atoms A and C were in virtual contact (in Lewis's sense) via a mirror B, they would not in general be in virtual contact in the absence of the mirror: the two four-dimensional distances SAB ^ BC ma Y be individually zero, without having the direct four-dimensional distance S equal to zero, as may readily be seen by an example.86 Hence, on Lewis's theory, the radiative coupling between two atoms A and C could be radically different depend­ ing on whether or not the transmitted quanta were reflected from a mirror—a consequence which is inconsistent with some of the simplest optical phenomena. Einstein's remarks on the conclusions Lewis drew from his law of entire equilibrium were equally devastating. The correspondence between classi­ cal and quantum radiative processes, which Einstein had already hinted at in his 1917 paper, and which clearly revealed the need for the stimulated emission term, was the same correspondence that Van Vleck had empha­ sized in his 1924 paper and which Fowler had drawn to Lewis's atten­ tion. 87 As a corollary, Einstein's remarks were in sharp disagreement with Fowler's suggestion that Bose's derivation of Planck's law seriously weakened the classical-quantum link. Lewis took Einstein's criticisms very seriously. When he answered Einstein's letter on 3 November 1926, he opened on a note of capitulation: "Owing to our isolation here [at Berkeley] I am afraid I spend a good deal of time puzzling out questions which have already been solved by others. I wish that I could hear more frequently the informal opinions of those who are studying the same problems that I am." 88 In spite of his pub­ lished promise, Lewis never developed his theory of light further along anc

s

j

the lines he had indicated. Rather, his researches on radiation theory took 85 Einstein to Lewis, 22 August 1926, Lewis Correspondence, Berkeley. Lewis attached so much importance to Einstein's handwritten letter that he had a type­ script of it prepared. The translation is my own. I wish to thank Dr. Otto Nathan, Trustee, Estate of Albert Einstein, for suggesting three changes in it.

86 LeE s\b = (x/i ~ Xb) 2 ~ {cty\ - cts) 2 , with analogous definitions for S [k; and s/jC> ant ^ suppose for example that (in units of distance) χ a = 3, Χβ = 2, X(; = 1, c t \ = 2, ctft = 3, and etc ~ 2. Then Sab BC = but sac = 2=/=0. y

= s

87 88

See references 21, 32, and 33. Lewis to Einstein, 3 November 1926, Lewis Correspondence, Berkeley.

ROGER Η. STUEWER

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quite a different turn, 89 although his ultimate views on the subject were determined by his firm belief in the symmetry of time. Lewis also recognized the force of Einstein's criticisms of his law of en­ tire equilibrium as applied to radiative processes. He admitted to Einstein: "I can not so easily dispose of your argument regarding 'negative EinstrahIung' [stimulated emission]. While I do not believe that there is any energy in the undulating field of radiation, the existence of such a field can not be ignored, for it is by means of this field that we can predict all of the phenomena of interference." Thus, even if the field were an energyless probability field, "there would still be a phenomenon relating to the prob­ abilities quite analogous to the 'Einstrahlung' [absorption] and 'AusstrahIung' [emission] of energy, and it might be argued that these have to be taken into consideration just as you have done." 90 In the end, however, Lewis could not bring himself to fully admit the validity of Einstein's concept of stimulated emission. He could not con­ vince himself that it would be "possible to reconcile this idea of reversibil­ ity to the last detail with the classical picture of radiation," because he could not understand how spherical waves could be observed to spread out from a source without ever being observed to contract back into it. He hinted that he might have to abandon his earlier assumption that the proba­ bility of transmission of radiation depends only upon the relative phases and polarization of the emitting and absorbing atoms; "other similar pro­ cesses" might also have to be taken into account. These processes in turn would perhaps produce those equilibrium conditions which Einstein in 1912 had termed "aussergewohnlich," 91 and which would correspond to an "extended thermodynamics." 89lt is worth remarking that if Lewis had not preserved his correspondence, we would have very little idea of why he redirected his research program, since he does not discuss this point in his published papers. ^Lewis to Einstein, 3 November 1926, Lewis Correspondence, Berkeley. ^ 1 In this connection Lewis later cited Einstein's papers "Thermodynamische Begriindung des photochemischen Aquivalentsgesetzes," Annalen der Physik, 38 (1912), 881-884, and "Deduction thermodynamique de la Ioi de !'equivalence photochimique," Journal de physique, 3 (1913), 277-282. The second paper is not a translation of the first. Lewis brought out what he meant by these "aussergewohnlich" states by considering a box containing radiation and having perfectly reflecting walls, one of which is so thin that radiation pressure fluctuations can cause it to undergo a sort of Brownian motion. At thermal equilibrium there would be no interchange of energy on the average between the enclosed radiation, the thin wall, and the outside surroundings; but, Lewis argued, the radiation would have a definite frequency distribution owing to the Doppler shifts it experiences in its approach to equilibrium. "Thus," Lewis concluded, "the radiation may have any number of different states of

498

LEWIS ON DETAILED BALANCING

Lewis had already begun working along these lines, for in his letter to Einstein he included a copy of a new paper giving the "briefest outline" of his ideas. "It is pretty extreme quantum theory," Lewis remarked, "but I think you may find it amusing, and the extended thermodynamics which I discuss there might be built up quite without regard to the 'photon' hypothesis." 92 5. THE CONSERVATION OF PHOTONS Lewis published his "pretty extreme quantum theory" and its associated "extended thermodynamics" in a long letter to the editor of Nature dated 29 October 1926, 93 and in two papers he communicated to the Proceed­ ings of the National Academy of Sciences on 6 April and 18 April 1927. 94 Einstein's criticisms had forced him to reevaluate his ideas on the nature of radiative processes and to drop some of his ideas altogether, but neither his interest in the subject nor his research on it had been truncated. The major feature of radiative processes which Lewis felt could with­ stand Einstein's criticisms was that "a new kind of atom" was involved in them. This "atom" had to be "an identifiable entity, uncreatable and indestructible, which acts as the carrier of radiant energy and, after ab­ sorption, persists as an essential constituent of the absorbing atom until it is later sent out again bearing a new amount of energy." 95 It was for this "atom," this "entity," that Lewis coined a new name: It would seem inappropriate to speak of one of these hypothetical enti­ ties as a particle of light, a corpuscle of light, a light quantum, or a light quant, if we are to assume that it spends only a minute fraction of its existence as a carrier of radiant energy, while the rest of the time it remains as an important structural element within the atom. It would also cause confusion to call it merely a quantum, for later it will be necessary to distinguish between the number of these entities present in an atom and the so-called quantum number. I therefore take the liberty equilibrium, all at the same temperature, according to the amount of energy originally in the enclosure, and only one of these states coincides with the state of black body radiation, which is alone considered in the classical [i.e., Planck's] thermodynamics of radiation." The other states presumably were the "aussergewohnlich" states. See Lewis's paper "A New Equation for the Distribution of Radiant Energy," Proc. Nat. Acad. Sci., 13 (1926), 473. 92 Lewis to Einstein, 3 November 1926, Lewis Correspondence, Berkeley. 93 Gilbert N. Lewis, "The Conservation of Photons," Nature, 118 (1926), 874-875. 94 Gilbert N. Lewis, "The Entropy of Radiation," Proc. Nat. Acad. Sci., 13 (1926), 307-313, and "New Equation" (reference 91), pp. 471-476. 95 Lewis, "Conservation" (reference 93), p. 874.

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of proposing for this hypothetical new atom, which is not light but plays an essential part in every process of radiation, the name photon.96 Lewis attached six major properties to his "photon": (1) In any isolated system the total number of photons is constant. (2) All radiant energy is carried by photons. . . . (3) All photons are identical. . . . (4) The energy of an isolated photon, divided by the Planck constant, gives the frequency of the photon, which is therefore by definition strictly monochromatic. . . . (5) All photons are alike in one property which has the dimensions of action or of angular momen­ tum, and is invariant to a relativity transformation. (6) The condition that the frequency of a photon emitted by a certain system be equal to some physical frequency existing within that system, is not in general fulfilled, but comes nearer to fulfilment the lower the frequency is. 97 Clearly, Lewis's "photon" was not Einstein's light quantum. Lewis stated that his "photon" "is not light but plays an essential part in every process of radiation." The most striking aspect of Lewis's concept was his conten­ tion that in "any isolated system the total number of photons is constant." He considered this property to be central to his concept, entitling his article "The Conservation of Photons." Indeed, this property would soon become the basis of the "extended thermodynamics" he mentioned to Einstein. First, however, Lewis felt compelled to allay two possible "serious objections" to it. The first arose out of the thermodynamics of black body radiation. Consider a Hohlraum containing black body radiation of definite energy E and temperature T, where E ~ X4, and imagine that the Hohlraum undergoes a free expansion which increases its volume by a factor of 16 = 2 4 . This implied, Lewis asserted, that if the radiation were then "brought to a new temperature equilibrium by introducing an infinites­ imal black body," the total number of photons present would change by a factor of 2. 98 To now insist on photon conservation, Lewis had to reject a postulate "tacitly employed" by Wien and Planck, but one "which is sup­ ported by no experimental facts; namely, if an infinitesimal black body is introduced into a hohlraum, the radiation will come to a certain tempera­ ture, and then no further change will ensue when a large black body of the same temperature is introduced." By "dispensing with this postulate, and 16 Ibid. 98 Lewis

9 1 Ibid.

actually said that the number of photons would double, but his argument here is not very clear to me; rather than lose his main point, I stated his conclusion in a neutral way.

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LEWIS ON DETAILED BALANCING

adding a new variable, the number of photons . . . , we obtain a greatly enlarged science of thermodynamics" 99 and one which by implication was consistent with photon conservation. The second objection arose out of spectroscopic considerations. Since an electron can undergo a transition from an upper to a lower energy level either directly or through various intermediate levels, it could be asked if the total number of photons emitted in both cases are equal. The answer was simple: the existence of "superfine structure" proved to Lewis that the upper and lower levels "must be multiple," and hence that both transi­ tions could result in the emission of the same number of photons, which again would preserve photon conservation. Consequently, "The rule that one, and only one, photon is lost in each elementary radiation process, is far more rigorous than any existing selection principle, and forbids the majority of processes which are now supposed to occur." 100 Lewis suggested that these "inhibited" processes, if they existed, would be found particularly "at very low temperatures," and he indicated that he had already initiated experiments to test this prediction. This remark caught P. W. Bridgman's eye, and on 24 April 1927 he commented on it in a letter to Lewis: Your photons interest me very much, and I shall want to see how the new thermodynamics which you promise works out; and also of course whether you get any new experimental results at low temperatures. I can't help having a feeling, however, that the solution of our many present difficulties with the nature of Ught will be found at least partly in inventing new ways of thinking about things, particularly in thinking about time, rather than by inventing new quasi-material structures. 101 Bridgmen was unaware that it was precisely because Lewis had begun to think anew about time that he had begun to think anew about microscopic reversibility and, ultimately, about the nature of light itself. Even before receiving Bridgman's letter, Lewis had returned to still another problem in radiation theory, the derivation of Planck's law, which was intimately related to the issue of photon conservation and the significance of photon conservation for the "extended thermodynamics" he hoped to develop. In early April 1927, Lewis derived Planck's expression for the entropy of black body radiation 102 (which of course was tantamount to deriving Planck's law) in a way that seemed to Lewis to be "even more fundamenloo Ibid., p. 875. "Lewis, "Conservation" (reference 93), p. 874. to Lewis, 24 April 1927, Lewis Correspondence, Berkeley. 102 Lewis, "Entropy" (reference 94), p. 307-313. 101 Bridgman

501

ROGER Η. STUEWER

tal" than Einstein's 1917 derivation—a remark which clearly indicated Lewis's continuing skepticism toward Einstein's concept of stimulated emission. Lewis did not regard his derivation as entirely satisfactory, how­ ever, because he had not explicitly used his law of photon conservation in it; he succeeded in a second approach to the problem 103 less than two weeks later. Lewis considered an enclosure of volume V containing radiation of fre­ quency v, energy density u v , entropy density s v , photon density n v = u v lhv, and made the following three assumptions: first, that the total energy u = V / 0 °° u v dv is constant or, in other words, that du/ V = /0°° Su v dv = 0; second, that the radiation is in thermal equilibrium, its total entropy 5 = V/ 0 °° s v dv a maximum or, in other words, that ds/V = /0°° hs v dv = /0°° (ds v /du v )8u v dv = 0; and third, that the total number of photons JV = V

n v dv = V /0°° (u v lhv)dv is constant or, in other words,

that dN/V = / 0 °° (IIhv)Supdv = 0. Taken together, these three assumptions imply that 9Sv

X1

.-α=-1+χ2ί hv

(5.1)

Ou v

where λι and X 2 are constants independent of frequency but not in gen­ eral independent of temperature. They may be evaluated either by purely mathematical techniques or, Lewis argued, by starting from a considera­ tion of Wien's law, u v ~ v 3 e'^ v . Lewis chose to follow the second route. The proportionality constant in Wien's law had been "evaluated by Planck as 87Thlc 3 " This constant corresponded to "the particular kind of equilibrium" known as black body radiation, but, as Lewis contended later, if "the law of conservation of photons can be established" it would be "doubtful" that black body radiation "is as definite a thing as has been supposed." 104 "In order to include all of our new types of equilibrium we may introduce a new quantity γ which is constant only when the number of photons is constant. If J = 1 for the case of black body radiation, then in general J will give the ratio, at any frequency, between the actual energy density and the energy density in a black hollow at the same tempera­ ture." 105 Lewis therefore multiplied Planck's proportionality constant by 103 Lewis, "New Equation" (reference 91), pp. 471-476. Joan Bromberg has pointed out to me that in 1927 Dirac and Jordan were also willing to alter Planck's law by assuming that the number of photons is constant. To my knowledge, Lewis was uninfluenced by this work. 104 IfctU, p. 476. 105ibid., p. 474.

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LEWIS ON DETAILED BALANCING

γ, obtaining a "generalized" Wien's law given by (52)

In his preceeding paper Lewis had calculated an expression for the entropy density s v which was "essentially identical with that of Planck" and which by differentiation implied that 9s v k 1 fe / 8 nhv3 \ — = In —-- + — In [ —χ +1 , buv hv 8πββ hv \c uv J

(5.3)

where β is a constant and e the base of the natural logarithms. Taking the high frequency limit of equation (5.3) and eliminating u v , using equation (5.2), Lewis obtained the following expression: ds k 1 1 r— = — In + —. duv hv γδπβε T

(5.4)

Bycomparing equations (5.1) and (5.4), Lewis readily determined the tem­ perature dependent constants λι and A 2 . At the same time, by comparing equations (5-3) and (5.4), he concluded that 8nhv3

1

u v = —— c

,

(5.5)

LeUvIkT _1 J

which represented his "general expression for the distribution law." 106 In Lewis's "general expression," different values of J corresponded to different equilibrium states. "It is true," Lewis wrote, "that I have been led to the discovery of these new equilibrium states through an attempt to find a law of conservation of photons, but their existence does not yet prove that such a law obtains." Nevertheless, if "it later proves possible to show that in absorption and emission of light the photon acts as an indes­ tructible and uncreatable atom, then we shall find, not only in the thermo­ dynamics of radiation, but also in the thermodynamics of all substances, great fields of equilibria hitherto unsuspected, in which the individual states differ from one another with respect to the new variable, the num­ ber of photons." 107 Lewis's concluding words and entire derivation prove that by April 1927 he still had not taken Fowler's advice and familiarized himself with either Bose's derivation of Planck's law or Einstein's subsequent applications of Bose-Einstein statistics to gas theory. 108 If he had, he could not have i06 Ibid.,

p. 475.

107 Zbici.,

pp. 475-476.

108 See

reference 37.

ROGER Η. STUEWER

503

missed seeing that his central assumption of photon conservation and the resulting introduction of his quantity 7 directly conflicted with a central assumption in Bose's derivation; namely, that the total number of photons is not constant. Lewis's "indestructible and uncreatable" photon was a chemist's atom and not a physicist's light quantum, a fatal flaw in Lewis's work. For although Lewis's term "photon" was promptly assimilated into physics, his "photon" concept was not. In October 1927, ten months after Lewis had introduced both his term and his concept, the fifth Solvay conference was held in Brussels. Throughout the almost three hundred printed pages of conference reports and discussions109 Lewis's term "photon" was frequently used—indeed, it appeared in the title chosen for the reports and discussions, Electrons et Photons—but his "photon" con­ cept was never elaborated. Thus, within a period of only ten months, the meaning of Lewis's term had changed radically: it no longer denoted Lewis's atom, but Einstein's light quantum. Perhaps the foremost advocate of this altered meaning at Brussels was Arthur H. Compton, who only two months later would travel to Stock­ holm to receive the 1927 Nobel Prize in Physics for his discovery of the Compton effect. 110 Understandably, Compton's advocacy of Lewis's term carried a great deal of authority. He adopted it at Brussels with the follow­ ing words: In referring to this unit of radiation I shall use the name "photon," sug­ gested recently by G. N. Lewis. This word avoids any implication re­ garding the nature of the unit, as contained for example in the name "needle ray." As compared with the terms "radiation quantum" and "light quant," this name has the advantages of brevity and of avoiding any implied dependence upon the much more general quantum me­ chanics or quantum theory of atomic structure. 111 It is this meaning—Einstein's light quantum and not Lewis's atom—that the term "photon" has assumed ever since. The only time Lewis's work 109 Institut International de Physique Solvay, Electrons et Photons—Rapports et Discussions du Cinquieme Conseil de Physique Tenu a Bruxelles du 24 au 29 October 1927 sous Ies Auspices de I'Institut International de Physique Solvay (Paris, 1928). 110 See Stuewer, Compton Effect (reference 5). 1 1 1 Arthur H. Compton, "Some Experimental Difficulties with the Electromagnetic Theory of Radiation," Journal of the Franklin Institute, 205 (1928), 156-157. This article is the original (English) version of Compton's Solvay address. In a letter of 11 August 1949 to Samuel Glasstone, Compton stated that the use of Lewis's term "photon" became immediately common in the United States and Europe with the meaning which he assigned to it.

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LEWIS ON DETAILED BALANCING

was at all mentioned at Brussels was after Louis de Broglie's paper, when L. Brillouin pointed out that, according to de Broglie's most recent theory of light, the experiment that Lewis had proposed should actually yield a negative result. 112 By the time of the fifth Solvay conference profound changes had taken place in physical theory. Both matrix mechanics and wave mechanics had been created, the Davisson-Germer and Thomson experiments had just established the existence of electron waves, and only one month earlier Bohr had first enunciated his principle of complementarity in Como. 113 Lewis himself was fully aware of these developments, but his initial reac­ tion to them was mixed, as his contemporary correspondence with A. F. Joffe in Leningrad reveals. 114 Lewis wrote Joffe that he felt that the dis­ covery of electron diffraction did not really help in understanding the dual nature of light. It only made the problem "a larger one," because now one had to explain why neither electrons nor pho' ons can "pass to a cer­ tain forbidden spot in an interference field." Nev theless, he told Joffe, he was becoming "a little more acquainted" wit! the "new mechanics," although the mathematics involved in it was "rather beyond the powers of an old-fashioned chemist." 115

6. THE SYMMETRY OF TIME Lewis's conviction that time is symmetric was central to his research program for at least five years, 1925-1930. He expressed his confidence in the validity of the principle at the end of the period in the following words: "throughout the sciences of physics and chemistry, symmetrical or two-way time everywhere suffices. As a philosophic speculation this view has received some attention, but I shall be much disappointed if it can not ^''•Electrons et Photons (reference 109), pp. 139-140. a full discussion, see appropriate sections in Max Jammer's Conceptual Development of Quantum Mechanics (reference 5). Also s^e Richard K. Gehrenbeck, C. J. Davisson, L. H. Germer, and the Discovery of E ?ctron Diffraction (Ph.D. Thesis, University of Minnesota, 1973). 114 Joffe had just returned to Leningrad after one yea· as a visiting professor at Berkeley. Joffe wrote to Lewis on 16 June 1927 and 6 November 1927, while Lewis wrote to Joffe on 27 October 1927 and 31 December 1°27. See Lewis Correspon­ dence, Berkeley. 115 Lewis to Joffe, 27 October 1927, LewisCorrespond- nce, Berkeley. That Lewis did in fact soon begin to familiarize himself with the "m mechanics" may be seen from his paper "The Quantum Laws and the Uncertainty Principle of Heisenberg," Proc. Nat. Acad. Set., 15 (1929), 127-139 (with Joseph E. Mayer). 113 For

505

ROGER Η. STUEWER

also be accepted as the statement of a law of physics, of exceptional scope and power, directly applicable to the solution of many classical and modern problems of physics." 116 The conclusions Lewis drew from this principle were not always ac­ cepted by his contemporaries, but neither were they ever rejected as un­ worthy of consideration. In one instance, in the case of Lewis's direct particle interaction theory of light, two decades had to pass before Ein­ stein's criticisms were surmounted and Lewis's basic ideas vindicated: in 1945 Wheeler and Feynman dispensed with Lewis's assumption that the interaction takes place between a single emitter and absorber, and postu­ lated instead that sufficiently many particles are present to absorb com­ pletely the radiation emitted by the source. 117 Wheeler and Feynman emphasized this point when they evaluated Lewis's contributions: "Lewis went nearly as far as it is possible to go without explicitly recognizing the importance of other ab sorbing matter in the system, a point touched upon by Tetrode, and show,· '. . . [by us] to be essential for the existence of the normal radiative mechanism." 118 It is difficult to understand why Lewis so persistently rejected Einstein's concept of stimulated emission until one realizes the strength of his con­ viction that time is symmetric. As late as 1930, when Lewis published yet another derivation of Planck's law, 119 this time one which was similar to 116 Lewis

"Symmetry of Time" (reference 16), p. 570. Archibald Wheeler and Richard Phillips Feynman, "Interaction with the Absorber as the Mechanism of Radiation," Reviews of Modern Physics, 17 (1945), 157-181; "Classical Electrodynamics in Terms of Direct Interparticle Action," Rev. Mod. Phys., 21 (1949), 425-433. In their first paper, Wheeler and Feynman presented a causal paradox related to Lewis's and to a similar one by Tetrode (1922). For comments on this paradox, see Mary B. Hesse, Forces and Fields (Totowa, New Jersey, 1965), pp. 279-285. Also see Carlton W. Berenda, "The Determination of Past by Future Events: A Discussion of the Wheeler-Feynman Absorption-Radiation Theory," Philosophy of Science, 14 (1947), 13-19. 118 Wheeler and Feynman, "Interaction" (reference 117), p. 159, n. 10, where Tetrode's 1922 paper is also cited. 1

117 John

119 Gilbert

N. Lewis, "Quan;um Kinetics and the Planck Equation," Phys. Rev., 35 (1930),

1533-1537. Lewisconsiderec a Hohlraum of volume V containing radiation at temperature T and a single atom with oi : y two energy levels, A and B, such that Eg -

= hv. He took ~~Eg Ik'l' ~EIk'V the relative probability of finding the atom in these levels to be ΡβΙΡλ ~ Ie ~ e

e

~hvjkl ^

anc

i .| l e

num

ber of photons dn in each "skeleton position, or cell," which had been

found "by several different methods," to be SiitVv 1 dv/c 3 . If, now, the atom undergoes a transition from B to A, a -e«|ll Q m containing m photons will lose a photon to cell Q m +i, and if q m and q m +i are the ^spective probabilities that the cells will contain m and m + 1 photons, symmetry of time demanded, Lewis argued, that P g q m = P ^ q m + i , or PgIPyi = qm+ilqm ~ e

By

normalization of the probability, one has that Σ ^ _ 0 q m =

506

LEWIS ON DETAILED BALANCING

de Broglie's of 1922, Lewis motivated his discussion by asserting that: "Without in any way minimizing the value of this conception [Einstein's concept of stimulated emission], which indeed seems necessary to an un­ derstanding of radiation from the standpoint of field-theory, one may doubt whether it was necessary, or even legitimate, to combine this method of treatment with a totally different method based upon the kinetics of light quanta, or photons; especially as Einstein's treatment seems to be incompatible with the principle of the symmetry of time. ))120

L ew J s then went on to derive Planck's law from assumptions

which involved "no suggestion" of stimulated emission. The extent to which Lewis regarded the symmetry of time as a funda­ mental principle of nature became fully evident on 17 April 1930, when he received the gold medal of the Society of Arts and Sciences in New York City, and chose as the subject of his acceptance speech "The Sym­ metry of Time in Physics." 121 In this long address, Lewis presented a panorama of physical phenomena—mechanical, thermodynamical, radia­ tive, electrodynamical—which he took to support the principle. "We shall see," he promised, "that nearly everywhere the physicist has purged from his science the use of one-way time, as though aware that this idea intro­ duces an anthropomorphic element, alien to the ideals of physics. Never­ theless, in several important cases unidirectional time and unidirectional causality have been invoked, but always, as we shall proceed to show, in support of some false doctrine." 122 "To lighten the discussion," Lewis imagined an early protagonist of the symmetry of time, Dr. X, who kept notebooks in which he commented on relevant developments in physics as they occurred. Dr. X's first entry dealt with the progressive geometrization of kinematics which culminated in the work of Minkowski: "If this geometrical view of kinematics is correct