William Gilbert's Renaissance Philosophy of the Magnet

Table of contents :
Table of Contents
Preface
Note on the Text
Introduction
Chapter One
Chapter Two
Chapter Three
Chapter Four
Chapter Five
Chapter Six
Chapter Seven
Conclusion
Appendix: Gilbert and Mathematics
Bibliography

Citation preview

WILLIAM GILBERT'S RENAISSANCE PHILOSOPHY OF THE MAGNET

By Charles D. Kay A.B. Princeton University, 1972 M.A. University of Pittsburgh, 1977

Submitted to the Graduate Faculty of Arts and Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy

University of Pittsburgh 1981

Table of Contents

Page

Preface ............................................................

v

Note on the text..................... ............................. viii Introduction - Overview and Bibliographic Survey ................. 1

The Background Chapter 1 - Gilbert1s life; Survey of the history of magnetism and electrics.......................................... 25 Chapter 2 - Textbooks, Aristotle & Medical Education .............

60

The Argument of De Magnete Chapter 3 - Gilbert’s Aims, Method, discussion of electrics . .

82

Chapter 4 - Magnetic Form and Anima............................... 107 Chapter 5 - Gilbert’s Contemporary Sources ........................ 130

The Make-up of the Universe Chapter 6 - Matter, Medicine and Terra

Matrix................... 150

Chapter 7 - Astronomy.............................................

167

Conclusion......................................................... 189 Appendix - Gilbert and Mathematics and

De Magnete................. 193

Bibliography ...................................................... 209

LIST OF ILLUSTRATIONS Figure

Page

1- The EarthTs magnetic field pictured against its axis of rotation............................................ 8 2.

Lines of equal geomagnetic declination ("variation”).

3.

Lines of equal geomagnetic inclination ("dip")

4.

How the power dwells in the lodes tone................... 114

5.

a.

from De Magnete, p. 73

b.

from De Magnete, p. 74

c.

from De Magnete, p. 82

. . . .

10 11

How the orbis virtutis conforms to the shape of the lodestone (from De Magnete, pp. 76-77)

6.

.

............... 117

Declinations of a magnetic needle..................... 120 a.

from De Magnete, p. 189

b.

from JDe Magnete, p. 189

Rotation and Declination of a terrella c. 7.

from De Magnete, p. 190

Diagram of motions in magnetic orbes.................. 122 from De Magnete, p. 206

8.

9.

Effluvia surrounding heavenly bodies ............... a.

from De Mundo, p. 38

b.

from De Mundo, p. 68

. .

Vacuum between heavenly bodies .............................

153

180

from De Mundo, p. 213 10.

The Solar System (from I)e Mundo, p. 202)............. 182

11.

The Face of the Moon (from De Mundo, facing

12.

Determination of the dip/latitude relation

p.

172) . .

185

.............

200

.............

202

adapted from De Magnete, p. 198 13.

Determination of the dip/latitude relation adapted from J)e Magnete, p. 198

14.

Instrument for calculating latitude from observed mag­ netic dip (from De Magnete, facing p. 200)............... 204

V

PREFACE

This dissertation began as an attempt to show that the thought of William Gilbert, whose De Magnete was the principal scientific achieve­ ment of Elizabethan England, has been inadequately portrayed in the cur­ rent historiography of science which views him as an early empiricist who, rejecting the worn-out view of Aristotle and the Scholastics, intro­ duced an experimental method which anticipated the philosophy of Francis Bacon and the ideology of the later Royal Society of London. It was thought that by examining the largely ignored posthumous work De Mundo a better insight would be afforded regarding Gilbert's broader intel­ lectual framework and his strong ties to Aristotle and Neoplatonism. In addition, it was hoped that this later work would show how the more speculative and metaphysical portions of Be_ Magnete formed an integral part of his overall philosophy and were not indicative of any duality or weakness of intellect. As I proceeded in this investigation, however, two things became quickly apparent:

first, De Mundo was not a coherent

work of sufficient significance to achieve the goal I had set, and second, De Magnete itself would provide sufficient evidence of the broader phi­ losophy and traditional connections once the inadequate English trans­ lations are put aside and the Latin text examined. The result has been a reinterpretation of Gilbert's major work which views it not as the anticipation of the seventeenth-century but as the culmination of the sixteenth.

Gilbert* s use of experiment was novel, but it was not identical with the methods professed by Boyle and Newton. The experiments de­ scribed in De. Magnete are basically of two types:

what Gilbert tends

to call demonstrations, similar in style and illustrative function to the anatomical demonstrations he would have seen in medical dissections, and experiments which tested the phenomena in order to set up limits within which it was permitted to hypothesize freely, in accordance with the generally accepted principles of philosophy. Gilbert*s work was not a Baconian natural history, and it was not his purpose merely to establish the empirical phenomena or even to argue that the Earth itself is a great magnet, although the later was indeed an important part of his philosophy. A careful reading of De Magnete reveals a continuous argument within its pages to establish a theory of the primacy of an elemental earth-matter, homogeneous with the Earth, and which exhibits a magnetic nature:

i.e., a uniquely ordered, effused form which es­

tablishes the geometry of the orb and unites it with homogeneous matter by a joint entelechy or a unity of form. This theory forms the basis of a general cosmology where the magnetic form or anima of the Earth re­ lates to the analagous forms of other heavenly bodies to order the cos­ mos. I believe De Magnete leads consistently and directly to this con­ clusion if is read from a non-Whiggish perspective. The present dissertation is primarily an exposition of these views a new reading of Gilbert which permits his own intentions and accomplish­ ments to become more obvious. With this reading as a foundation it will be possible to exhibit Gilbert's general overriding metaphysic and the traditional ties of his thought. This is not accomplished within these pages, however. Here there is only the beginning. I have, for example.

emphasized Gilbert*s Aristotelian links here not because there were not others, or that Neoplatonism was insignificant, but because they are far easier to establish and are sufficient to illustrate the positive role of traditional philosophy generally denied in Gilbert historiography. The subtle divisions of Neoplatonism, the metaphysics of light, the mas­ sive works of Cardano and Patrizi, have not been adequately presented in the literature, and it will take much longer to evaluate their impact on Gilbert's work. Here certain ties are pointed out and some earlier views rejected, such as the supposed connection of Gilbert with Bruno, Hermeticism or the craft tradition. I hope to provide a new, alternative reading of De Magnete, an outline of its general heritage, discusion of its Aristotlian sources, and suggestions on medical, Neoplatonic and iatrochemical influences which need further investigation. In completing this dissertation I would like to thank the members of the University of Pittsburgh faculty who have served on my disserta­ tion committee, and those several other individuals who have provided help and encouragement along the way.

viii

NOTE ON THE TEXT Throughout this dissertation, several conventions have been adapted. The frequent quotations from GilbertTs work will be referenced in the body of this text by the page number in parentheses for passages quoted from De_Magnete, and an underlined page number in parentheses for quota­ tions from De Mundo. In both instances, pages refer to the original Latin editions, but the pagination of the Thompson translation of De Magnete is designed to coincide with the original. There is no English version of D

From the construction, Z-ONL = Z-MNL +Z-0NM Z.SN0 = 90° -^ONM So it remains to find^MNL and^-ONM: In equilateral triangle LMN, Z.LMN = 0 + 90 90° - 0 therefore ^MNL = 1/2 (180° -Z.LMN) =

Finally, using the law of cosines for triangle OMN: __ __ ________ ___ on -l o NM = 1 , OM =/3 , ON = NL = 2 sin --------NM2 + QN2 - MO2 cos /- ONM = 2 NM x ON

2

204

FIGURE 15

205 = 2 sin2 (frO + 9)/2) - 1 2 sin (©0 + ©y2) 2 So that Z.ONM = arccos ?. s l . n — j . 1. 2 sin ((90 + 9>2) Although this seems rather complicated, a table of numerical values was calculated by Henry Briggs in 1602. Briggs^ was one of the earliest proponents of logarithms in England, professor of geometry at Gresham College, and thoroughly versed in trigonometry. The computation of a table of declinations according to the solution above would not have been very difficult if taken step by step: For any given 9, find

90+9

using a table of sines find sin

+

^ = n 2

and using logarithms calculate the value of

2 n - 1 2n

and use a table of cosines to find the corresponding angle ot. The declination is found by adding the quantity (90 -ok) to the |^th part of^°-~

Q

+

Unfortunately, Gilbert gives no indication of how such a relation was conceived originally. The conversion to an instrument (fig. 14) in­ volved a rather straightforward encoding-decoding procedure much like that found in the astrolabe or the more recently invented sector, both 20

of which were probably familiar to Gilbert. The origin of the rela­ tion described in figure 13 is obscure. One thing is sure:

it must

have involved a series of careful measurements since the relation is very close to that which holds for an ideally magnetized sphere.

21

Gilbert also describes at great length instruments involved in making such measurements. Gilbert apparently believed that at 45° latitude, the magnetic needle was directed to the equator on the opposite side of the sphere (i.e. I) in fig. 13). This is the declination most frequently used in his illustrations, probably because it is so easy to draw. It

206

may have also played a role in devising the relation in figure 13, since it is the only simply constructed declination except those at the equator and pole. With N at 45°, line NO falls on C^, and RT coincides with J), so that the declination is directed along the bisector of^LCNL between the two poles. At a latitude of 0°, the direction of the needle is along tangent AB. If Gilbert attempted to include the poles in deter­ mining the declination here, he may have struck upon the arc LCB about A, thus defining 1$. Gilbert had discarded the theory that the declination was a re­ flection of the balance of the strength of the two poles, but beginning with this assumption, and examining the situation at 0°, 45°, and 90° he may by trial and error have come up with his final formulation. Gilbert may well have had assistance in this investigation, but when Blundeville republished the results in 1602, he attributed it to Gilbert alone, and when after Gilbert’s death Wright claimed to have written a certain portion of De Magnete he did not lay claim to anything in Book V.

207

NOTES

1. Galileo Galilei (1632/1967), p. 406. Galileo encountered De Magnete soon after it was published in 1600 receiving a copy as a present from "a famous Perepatetic philosopher ... I think in order to protect his library from its contagion" (p. 400). His own opinion of the work was considerably different, expressing in the words of Salviati "the highest praise, admiration, and envy for this author." (p. 406). There is little doubt that Galileo was greatly impressed by Gilberts work and used it as a point of departure for his own brief study of magnetism. At one point, Galileo misread a portion of Gilbert’s text and quoted the wrong value of the distance from the earth to the moon; Rosen (1952), p. 344-348. See also Wisan (1978), p. 32-34. 2. In fact, the criticisms began even earlier from English navigator-scientists such as Ridley and Borough. Their wish, however, was for more navigational and astronomical mathematics not mathematical treatment of the magnet. 3. Lindsay (1968) p. 137. Lindsay’s reference to "magnetic field" is typical of much current historiography which places Gilbert at the beginning of the history of modern "electromagnetism," adopting a pro­ spective utterly foreign to Gilbert’s own (Cf. Roller (1959), p. 148150). 4.

E.g., A. Koyre, A. N. Whitehead, E. Cassirer.

5.

Cf. Kuhn (1978), p. 31ff.

6.

Koyre (1939/1978) p. 188.

7.

King (1959), p. 123f, see also p. 138.

8.

Abromitis (1977) pp. 126-128.

9.

Dijksterhuis (1961), p. 395.

10.

Cf. Schmitt, (1973), p. 177.

11. For an attempt at a fairer treatment of non-mathematical sciences see Kuhn’s essay cited above (n.5). See also Laudan (1977), ch. 5 for a discussion of the role of normative philosophy of science in the history of science.

208 12 .

Zilsel (1941), p. 30f.

13.

Roller (1959), p. 119f.

14. See Palter (1972), 544-558. See Heilbron (1980) p. 87-97, 133 for failures and Coulomb’s success. 15. Newton (1687/1947), p. 414, emphasis added. See Palter (1972) for an interesting attempt to measure the force published in a note to this text in the Geneva edition of Principia (1739). 16.

Cf. biography in Chapter 1 above.

17. Roller (1959), p. 119, uses such trivial examples as indicative of Gilbert’s lack of mathematics while completely glossing over the other examples given below. 18. The following derivation owes something to Lindsay (1940), (esp. p. 278-281. omitted from his (1968)). However, it has been com­ pletely reworked to avoid the use of radians and unnecessary complica­ tions such as square roots. Lindsay (p. 279n7) also misunderstands the way curve FR’ is generated for the purposes of the instrument. 19.

On Briggs see Taylor (1954).

20. On the sector see Drake (1976). Thomas Hood published the first description of the sector in 1598. Cf. also North (1974). Gilbert made astronomical observations and used ’’dials” as an undergraduate at Cambridge. 21. The ideal relation derived first by Gauss in 1839 is tan 4* = 2tan 9.