History of Technology Volume 2: Volume 2, 1977 9781350017368, 9781350017399, 9781350017382

Table of contents :
Cover
Half-title
Title
Copyright
Contents
Preface
Samuel Brown: Britain's Pioneer Suspension Bridge Builder
Introduction
The beginning of suspension bridge building in Britain
Enter Samuel Brown (1776-1852)
The Union Bridge across the Tweed at New Waterford
Suspension Piers
Two Decades of Bridge Building
Conclusions
Notes
The Banū Mūsà and their 'Book of Ingenious Devices'
Life and Works of the Banū Mūsà
The Book of Ingenious Devices (Kitāb al-Hiyal)
List of Models
Motifs
Models
Conclusion
Notes
A Note on Roman Metal Turning
Notes
Old Dams in Extremadura
Spanish Dams
Extremadura
The Dams
Why were they built?
Chief Characteristics of the Dams
Dating
Conclusion
Notes
The Vocabulary of Technology
Notes
Museums, History and Working Machines
Running Prime Movers
Production Machines
Notes
The Use of Models in Nineteenth Century British Suspension Bridge Design
Introduction
Suspension bridges
Notes
The Origins of the Water Turbine and the Invention of its Name
Introduction
The vertical water-wheel
The horizontal water-wheel
The reaction wheel
Claude Burdin (1790-1873)
Benoît Fourneyron 1802-1867
The invention of the word 'turbine'
Notes
The Contributors

Citation preview

1

H i s t o r y

o f

T e c h n o l o g y

1

History of Technology Volume 2, 1977

Edited by A. Rupert Hall and Norman Smith

Bloomsbury Academic An imprint of Bloomsbury Publishing Plc LON DON • OX F O R D • N E W YO R K • N E W D E L H I • SY DN EY

Bloomsbury Academic An imprint of Bloomsbury Publishing Plc 50 Bedford Square London WC1B 3DP UK

1385 Broadway New York NY 10018 USA

www.bloomsbury.com BLOOMSBURY, T&T CLARK and the Diana logo are trademarks of Bloomsbury Publishing Plc First published 1977 by Mansell Publishing Ltd Copyright © A. Rupert Hall and Norman Smith and Contributors, 1977 The electronic edition published 2016 A. Rupert Hall and Norman Smith and Contributors have asserted their right under the Copyright, Designs and Patents Act, 1988, to be identified as the Authors of this work. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage or retrieval system, without prior permission in writing from the publishers. No responsibility for loss caused to any individual or organization acting on or refraining from action as a result of the material in this publication can be accepted by Bloomsbury or the authors. Articles appearing in this publication are abstracted and indexed in Historical Abstracts and America: History and Life. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. History of technology. 2nd annual volume: 1977 1. Technology – History – Addresses, essays, lectures I. Hall, A. Rupert II. Smith, Norman, b. 1938 609  T15 ISBN: HB: 978-1-3500-1736-8 ePDF: 978-1-3500-1738-2 ePub: 978-1-3500-1737-5 Series: History of Technology, volume 2

C o n t e n t s Preface

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E M O R Y L. K E M P S a m u e l B r o w n : Britain's Pioneer Suspension Bridge Builder

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D O N A L D R. H I L L T h e B a n u M u s a a n d t h e i r 'Book o f I n g e n i o u s D e v i c e s '

39

J. F . C A V E A Note on R o m a n Metal Turning

77

J. A. G A R C I A - D I E G O Old D a m s in Extremadura

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G. H O L L I S T E R - S H O R T The Vocabulary of Technology

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RICHARD HILLS M u s e u m s , History and Working Machines

157

DENIS SMITH The Use of Models in Nineteenth Century British Suspension Bridge Design

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N O R M A N A. F . S M I T H The Origins of the Water Turbine and the I n v e n t i o n o f its N a m e

215

T h e Contributors

261

P r e f a c e I t is more by accident than editorial design that in this, the second volume of History of Technology, each of two themes is explored by pairs of authors. T h e problem of technology's vocabulary is the theme of D r . Hollister-Short's paper and it is prominent in the piece on water turbines. T h e infrequently studied history of early suspension bridges is presented from two diflFerent angles by Professor K e m p and Denis S m i t h : through the life and work of Samuel Brown by the first author; as part of the development of structural models by the latter. I n addition it is pleasing to have been able to realize an aim expressed in our first editorial. Assembled in this volume are three articles on the pre-industrial period and covering aspects of the technology of the Romans, Islam and Spain between the sixteenth and eighteenth centuries. D r Hills' remarks on the problems of operating old machinery as a proper part of the activities of museums we hope will not be the last contribution in this vein. W e shall welcome contributions to the journal from historians of engineering and technology around the world and material to be considered should be addressed to us, at the D e p a r t m e n t of History of Science and Technology, Sherfield Building, Imperial College, L o n d o n S W 7 . F r o m the same source can be obtained an author's guide for the preparation of manuscripts. A. R U P E R T H A L L N O R M A N A. F . S M I T H

S a m u e l B r i t a i n ' s

B r o w n :

P i o n e e r

B r i d g e

S u s p e n s i o n

B u i l d e r

E M O R Y L. K E M P Introduction HISTORIC SIGNIFICANCE T h e construction of long-span suspension bridges is a notable feature of the general development of civil engineering in the nineteenth century and worthy of study by historians in its own right. It has an even broader significance in the history of technology since it provides an example of the transformation of a primitive idea into very large and useful engineering structures which could fully utilize the tensile strength of iron. It may also be identified as one of the earliest combinations of analytical and experimental techniques to solve important structural engineering problems and it provides an excellent illustration of the transfer and development of a specific technology between engineers and between nations. It has its place, too, as an illustration of the important struggle to resolve the confusion between the concepts of strength and stiffness and the different effects caused by static and dynamic loads on flexible structures. T h e s e subtle concepts were only dimly recognized by nineteenth-century engineers and hence no really satisfactory design method was established to deal with those unique and puzzling modes of behaviour until m u c h later. As a result a n u m b e r of serious failures occurred which cost many lives and the total or partial destruction of a large n u m b e r of important bridges. Very little was learned from these early bridge failures. T h e problem of stiffened suspension bridges was not solved until the end of the nineteenth century and that of dynamic loading not until after the collapse of the T a c o m a Narrows bridge in 1940. AN ANCIENT LINEAGE Suspension bridges have been built for centuries in the Himalayas and in the Andes. W i t h a well developed iron industry in China dating from ancient times it is not surprising that iron chains were introduced into suspension bridge building in China and T i b e t before the Christian era. Details of these bridges were brought to E u r o p e by Jesuits such as A. Kircher and other travellers to China in the sixteenth century. Despite suggested designs such as those

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of Verantius this type of bridge was not employed for permanent structures in E u r o p e until m u c h later. Nevertheless a n u m b e r of temporary suspension bridges using rope and ordinary chain were built for military purposes as early as the sixteenth century and military engineers continued to build t h e m as late as the Napoleonic Wars and probably even later. 1 T h e W y n c h (or Winch) bridge of about 1741 has often been cited as Britain's first iron suspension bridge. However, there may well have been others as old or older. Smeaton refers to one as the Ripon Chain Bridge and there is an account of an unusual iron bridge at Kirklees constructed in 1774 which may have been a suspension bridge. 2 A l t h o u g h the A n d e a n bridges were of great antiquity, information on t h e m was not available in Europe and N o r t h America until the eighteenth century. 3 N o n e of t h e m used iron for the suspending cable but at least one, the bridge at Penipe, Chile, over the River M a y p o , had a level deck suspended from the catenary cables. JAMES FINLEY AND THE MODERN SUSPENSION BRIDGE Given that knowledge of the suspension bridges of both the Himalayas and the Andes was available in Europe by the middle of the eighteenth century and that there was by that time a tradition of military suspension bridges, one might expect the next important development to take place there. I n fact, the modern era of suspension bridge building begins with the construction of a modest bridge of 70-feet span across Jacob's Creek in western Pennsylvania. T h i s bridge, built in 1801 by James Finley, incorporated all of the basic elements of the modern suspension bridge. Finley patented his invention in 1808 and by 1820 nearly fifty bridges had been built on his pattern. T h e essential elements of his system were a catenary chain composed of hand-forged wrought-iron links, and iron suspenders supporting a level deck which was stiffened with two longitudinal trusses on either side of the roadway. 4 A significant aspect of Finley's work was his experimental investigation of the strength of the catenary chain and his experimental method of determining the geometry of the loaded chain. H e obtained strength values for various sag/span ratios of the cable and observed that the force in the chain decreased away from the towers and reached a m i n i m u m at midspan. T h u s , Finley was the first suspension bridge builder to have any idea of the forces in a suspension cable. Although the mathematical solution of the catenary and the solution of the forces in a funicular polygon were known m u c h earlier these solutions were applied to masonry arches and not to suspension bridges. 5 Although chain-link suspension bridges on the Finley system continued to be built until his death in 1828 and very likely even

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after that t i m e , the next i m p o r t a n t developments in this technology occurred in Europe and not in the United States. T h e influence of Finley's work was felt first in Britain and then in France as a result of several publications on his 'ingenious' system which appeared between 1808 and 1811. I n both countries there was a n u m b e r of innovations which resulted in important changes, principally in the analysis and construction of the suspension chains or cables. T h u s , when the m o d e r n long-span wire suspension bridge was introduced into the United States by Ellet in the 1840s it was referred to as the ' F r e n c h ' system. The beginning of suspension bridge building in Britain Telford's suspension bridge across the Menai Straits, in N o r t h Wales, completed in 1826 with a span of 580 feet, is the outstanding example of the use of the eye-bar suspension chain. T h i s improved type of chain was a major British contribution to suspension bridge design and its use permitted bridges of more than twice the span of Finley's to be built economically. It ushered in a new era of long suspension bridges. However, it is not with the monumental Menai Bridge that the modern history of British suspension bridges begins: rather, it begins with a n u m b e r of smaller bridges built in the lowlands of Scotland on quite different principles and in all b u t one case, constructed of wire cables. It was this earlier period, which saw the experimental work on the chains for a bridge which was never built and the adoption of iron for anchor chains and standing rigging for ships of the Royal Navy, which led to the development of the eye-bar chain for suspension bridges. SUSPENSION BRIDGES ON THE TWEED A group of cable-stayed bridges was built across the T w e e d and its various tributaries, beginning in 1816. I n concept these bridges bear some relationship to one proposed by Verantius in 1617, (Fig. 1) and an even closer resemblance to a fan-type cable-stayed bridge proposed by Poyet, about 1790. Although there are such p r e c e d e n t s for c a b l e - s t a y e d b r i d g e s t h e r e is insufficient information on these border bridges and their builders to establish any direct links with the earlier proposals, even though D r e w r y states that they were inspired by Poyet. T h e s e small and obscure structures may well have been the first iron cable-stayed bridges ever built. After discussing the Menai Bridge, the proposed Runcorn Bridge and the W y n c h Bridge over the Tees, Robert Stevenson in 1821 described the first of the T w e e d bridges. T h e next malleable iron-bridges which we know of in this country, were those executed on the river T w e e d , and its

Figure i. A cable-stayed bridge as proposed by Verantius in 1617.

Figure 2. Sketches of'bridges of suspension' as presented by Robert Stevenson in 1821.

Emory L. Kemp

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tributary streams of Gala and Etterick. M r Richard Lees, an extensive woollen-cloth manufacturer at Galashiels, whose works are situated on both sides of Gala-water, conceived the idea of forming a foot-bridge, of slender iron-wires, for the convenience of communicating readily with the different parts of his works. T h i s gangway, or bridge, was erected in the m o n t h of November 1816; its extent is i n feet, and it cost about £ 4 0 . T h o u g h only of a very temporary, and even imperfect construction, yet being the first wire-bridge erected in Great Britain, it deserves our particular notice, as affording a useful practical example of the tenacity of iron so applied, and of its utility in many situations, and particularly in an inland country such as the vale of the T w e e d , where the carriage of bulky materials, of every description, is extremely expensive. 6 Earlier, in April 1816, a very similar but m u c h longer (408-feet span) foot-bridge was erected by Hazard and White over the Schuylkill River near Philadelphia. N o illustration or other details of the Galashiels Bridge are known to exist. Although it afforded 'a useful practical example of the tenacity of iron so applied' it was not the harbinger of interest in the use of wire for suspension bridges in Britain, nor did the cable-stayed type persist except in a few isolated cases. At about the same time several other wire bridges were built and are described by Stevenson: the wire bridge of Kingsmeadow, on the estate of Sir J o h n Hay, Bart., of which we have given a sketch in Fig. [2] T h i s foot-bridge is thrown across the T w e e d , a little below Peebles. It is n o feet in length, and 4 feet in breadth, and is ornamented with a handsome lodge or cottage, as will be seen delineated on the sketch. T h i s work was contracted for and executed by Messrs. Redpath and Brown, of E d i n b u r g h , in the summer of 1817, and cost about £ 1 6 0 . It may be described as consisting of two hollow tubes of cast-iron, which are erected on the opposite sides of the river, set 4 feet apart, into each of which a corresponding bar of malleable iron is fitted, and to these the suspending wires and braces are respectively attached by screw-bolts. T h e s e hollow tubes of cast-iron measure 9 feet in height, 8 inches in diameter, and 3/4ths of an inch in thickness of metal. T h e malleable iron-bars, which are inserted into these hollow tubes, form the points of suspension, measure 10 feet in height, and 2^ inches square. T h e roadway is formed with frames of malleable iron, to which deal boards, measuring 6 inches in breadth, and i^ inch in thickness, are fixed with screw bolts. T h e side rails are neatly framed with rod-iron, on which a coping, or hand-rail of timber, is fixed. T h e roadway

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Samuel Brown: Pioneer Suspension Bridge

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here is suspended by diagonal wires, in a manner different from the catenarian principle, as will be seen by comparing Fig. [2.1] with Figs. [2.2,2.3, and 2.4.] T h e chain-suspending wires of Fig. [2.2] are of the strength known to artists as N o . 1 of the wire-gauge, measuring about 3/ioths of an inch in diameter. T h e back or landward braces are made of bolt-iron, 3/4ths of an inch in diameter, formed into links of from five to six feet in length. T h e screw-bolts are one inch in diameter, and are all 42 in n u m b e r , by which the whole of the suspending rods and wires may be tightened, and set u p at pleasure. W h e n thus braced, the roadway of the bridge is found to have little or no vibration, having only such a tremor as rather tends to convey the idea of firmness and security. As a proof of the strength of this, when newly finished, it was completely crowded with people, without sustaining any injury. About the same time the H o n . Captain Napier replaced a rope suspension bridge over the Etterick at Thirlstane Castle with a wire bridge of 125-foot span. T h e bridge was based on the cablestay principle and Stevenson reports that it looked very similar to his sketch of the Kingsmeadow Bridge. THE DRYBURGH BRIDGE Although not built of wire, b u t rather with bars, the D r y b u r g h Bridge was also cable stayed and should be considered with the other T w e e d bridges as one of the same genre. T h i s bridge, with its 260-feet span and 4-feet width, was the most impressive of the group. It is the first known example of a hook and eye-bar chain being used in a practical structure. Quoting Stevenson again: T h e bridge at D r y b u r g h is 260 feet between the points of suspension, and is four feet in breadth. It was executed by Messrs. John and William Smith, builders and architects near Melrose, at the expense of the Earl of Buchan, as proprietor of the ferry, and has altogether cost his Lordship about £720. T h i s bridge is constructed for foot passengers and led horses. It was originally begun on the 13th of April 1817, and was opened to the public on the 1st day of August following, having required little more than four months for its erection. It is observed by M r . J o h n Smith, one of the gentlemen above alluded to, that when the original bridge of D r y b u r g h was finished, u p o n the diagonal principle like Fig. [2.2] it had a gentle vibratory motion, which was sensibly felt in passing along it; the most material defect in its construction arising from the loose state of the radiating or diagonal chains, which, in proportion to their lengths, formed segments of catenarian curves of different radii. T h e motions of these chains were

Emory L. Kemp

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found so subject to acceleration, that three or four persons who were very improperly amusing themselves, by trying the extent of this motion, produced such an agitation in all its parts, that the longest of radiating chains broke near the point of its suspension. O n another occasion, in a very high wind, one of the horizontal chains, stretched under the beams of the roadway, gave way. But, on the 15th of January 1818, after this bridge had been finished about six m o n t h s , a most violent gale of wind took place, when the vibrating motion of the bridge was so great, that the longest radiating chains were again broken, the platform blown down, and the bridge completely destroyed. Messrs. Smith happened unluckily to be home at the time of the accident, b u t on examining a n u m b e r of persons who saw it, they all concurred in stating, the vertical motion of the roadway of the bridge before its fall, was as nearly as may be equal to its lateral motion, and was altogether concluded to be such as would have pitched or thrown a person walking along it into the river. T h e eyes, formed on one end of the rods or links of the chains of this bridge, were welded, b u t the other end was simply turned r o u n d , and fixed with a collar, as shown in the connecting diagrams, marked b in Fig. [2.3] It further deserves particular notice, that after the bridge fell, and on a careful examination of the roads or links, not more than one or two instances appeared of the iron having failed at the welded end, b u t had uniformly broken at the open eye of the link, as shown in the diagrams b , b above alluded to, — a mode of construction which had been recommended to Messrs. Smith, by an experienced blacksmith. T h e sudden destruction of the bridge, created a great sensation of regret throughout all parts of the country, and was considered an occurrence of so m u c h importance in the erection of chain-bridges, that several of the gentlemen of Liverpool, interested in the proposed bridge at Runcorn, made a journey to Scotland, for the express purpose of inquiring into the circumstances of the misfortune. T h e utility of D r y b u r g h Bridge, when compared with a troublesome ferry, even on the short experience of six m o n t h s , had given it such a decided preference to the boat, that his L o r d s h i p , without hesitation, directed that it should be immediately restored. T h i s was accordingly done, after a better design, for the additional sum of about £ 2 2 0 , and in less than three months it was again opened to the public. According to legend the re-building of this bridge launched Samuel Brown on his career as one of the earliest and most prolific of Britain's suspension bridge builders. Sir J o h n Rennie and

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Samuel Brown : Pioneer Suspension Bridge

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several later writers attribute the re-building to Brown, but none of the contemporary chroniclers, Stevenson, Drewry, Bender, nor Brown himself mention his involvement in any way with the reconstruction of the D r y b u r g h Bridge. 7 T h o s e that have espoused Brown's involvement in the re-building have been puzzled by the use of combined stay-cables and a catenary cable. T h e explanation seems straightforward. T h e deck and longest rods were destroyed in the storm. However, the pairs of shorter rods were not broken and were simply re-used. Instead of replacing the pair of long stays a continuous catenary was used. Writing in the first publication of the Institution of British Architects in 1836, Messrs. Smith, the original builders, stated 'we restored it in the summer of 1818, in its present form, and it has stood very well ever since.' T h e y record costs as about £ 5 6 0 for the original bridge and £ 2 4 0 for the re-construction. 8 E n t e r S a m u e l B r o w n (1776-1852) NAVAL OFFICER AND BRIDGE BUILDER It was not, therefore, with the re-building of the D r y b u r g h Bridge but rather with the completion of the U n i o n Bridge over the T w e e d on 26 July 1820 that Samuel Brown came to the fore as a builder of suspension bridges. At the time it was the greatest suspension bridge ever constructed with a clear span 437 feet between towers and the first such bridge in Britain designed for carriages. Appropriately, it was also his most lasting work and is still extant. Although the Union Bridge was constructed in less than a year it represents more than a decade of work on Brown's part, dating back to 1808. Samuel Brown, born in L o n d o n , was the eldest son of William Brown of Borland, Galloway and his mother was the daughter of the Rev. Robert Hogg of Roxburgh. T h u s , like so many early British engineers, he was of lowland Scots stock. H e entered the Royal Navy in 1796 and had an active and distinguished career in the French Wars. H e served in various ships and was at sea almost continuously until his last full-time duty which he began in the English Channel in August 1806. H e then had several short appointments in 1807 and 1809 and was advanced to the rank of commander in August 1811. Apparently, like so many of his naval colleagues at t h e t i m e , he was u n a b l e to obtain further appointments at sea and in May 1812 he was promoted to the rank of captain retired. I n 1837 he was knighted by Queen Victoria. I n Brown's patent of 1817 for the construction of bridges, he states that in 1808 he made a series of experiments on the comparative strength of bolts and bars and of chains of various designs. 9 About this time, while still on active duty in the Navy, he urged the adoption of iron standing rigging and iron chain for use

Emory L. Kemp

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in warships. I n 1813 he constructed a prototype bridge at his Isle of Dogs cable manufactory. It was 105 feet long and capable of supporting carriages. Both T h o m a s Telford and J o h n Rennie visited Brown's bridge. I n his Runcorn Bridge Report Telford refers to his visit in 1817, saying: Captain Brown had constructed a model, one h u n d r e d feet in length, at his patent chain-cable manufactory, opposite Deptford. Your solicitor and I examined this model, and drove a hackney-coach over it. 11 Rennie (the elder) was also taken over the bridge in a carriage and afterwards reported it to be safe and evincing very little vibration. F r o m the patent specification it is difficult to determine when Brown turned his attention from testing and developing iron chain, in a general way, to consider specifically the application of chain to suspension bridges. It was clearly sometime between 1808 and 1813. Finley's Port Folio article was followed (in 1811) by Pope's book on bridges which popularized Finley's 'ingenious invention'. 1 2 I n the absence of more definitive information one can only speculate, but it seems likely that Brown was engaged in the manufacture of chain for naval purposes when he became aware of Finley's work and saw how his tests on chain and improved methods of making it could be readily applied to the construction of suspension bridges. If this is the case he probably started work on suspension bridges about 1812 and produced his test bridge the following year. Brown says in his Patent specification of 1817: T h e plans which I have adopted for removing and remedying the foregoing objections have not been hastily formed, b u t have been deduced from a series of experiments which I made on the comparative strength of bolts and bars and chains of different descriptions in the year One thousand eight h u n d r e d and eight. A b o u t that p e r i o d I m a d e d r a w i n g s and calculations of the strength of bridges of suspension on the precise principle of the design which is the subject of the above recited Patent. A variety of the important engagements prevented me from making any experiments upon the design itself on a scale commensurate to its importance till One thousand eight h u n d r e d and thirteen, when I constructed a bridge of straight bars for this purpose on my own premises, where it still remains. T h e span or extent of this bridge is one h u n d r e d and five feet, and although the whole of the iron work weighs only thirty-seven h u n d r e d weight, it has supported loaded carts and carriages of various descriptions. RUNCORN BRIDGE PROPOSAL AND BRIDGE PATENT For the next three or four years Brown was engaged in developing

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Samuel Brown: Pioneer Suspension Bridge

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his suspension bar system which he patented in 1817 a year after his patent for chains. T h e result of Brown's work was not only a patent b u t a proposal, submitted with other competitive designs, for a bridge across the Mersey at Runcorn. Brown presented a bold design for a 1,000-feet span bridge in his patent specification as well as submitting a similar design for the Runcorn project. Telford had been involved with the project as early as 1814 and when it was revived in 1816 he served on the selection committee. I n his mind a suspension bridge was the only solution and he warmly endorsed Brown's proposal. According to Professor Peter Barlow who was at Woolwich at the time neither Brown nor Telford knew of each other's work until the Runcorn proposals were submitted. 1 3 Although the bridge was never built, Brown's proposed design had an important influence on the use of eye-bar chains on the Menai Bridge and set the pattern for all of his subsequent designs. Both Brown and Telford experimented with suspension chains in m u c h the same way as Finley. I n many accounts it has been stated that as a result of Brown's Runcorn design and his patent Telford adopted Brown's eye-bar chain for the Menai and Conway Bridges. T h i s is not strictly true, although he did abandon his bundled-bar scheme, where each continuous bar was made u p of shorter lengths butt-welded together, for the eye-bar system. H o w e v e r , B r o w n did not specifically p a t e n t t h e eye-bar suspension chain b u t rather he presented a n u m b e r of possibilities: I employ a combination of straight bars, bolts, or rods, joined or united at their ends either by side plates and bolts, coupling boxes, welding or other suitable methods, so that these bars, bolts or rods so joined become in effect one entire length or piece the whole extent or length of the bridge, and support their proper proportion of the tension of the direct line of curve. H e further states that iron is most efficient in direct tension and in fact his patented systems of bars, which were loaded at their ends, are m u c h more efficient than the Finley type of link chain. T h i s conclusion is the most important factor in his entire specification. M a n y believe that he patented the flat eye-bar chain for suspension bridges, b u t this could hardly be the case: such chains were already in common use at the time for other purposes and a previous patent in 1805 by Hawks would have precluded any such attempt. T h e wording of Brown's specifications, in fact, is so vague that, apart from what may be deduced from his observation on the efficiency of suspension members joined to act in direct tension it is difficult to know just what he is patenting. T h e various types of joints illustrated in his specification are shown in Fig. 3. T h e essential difference between the chains used by Telford

11

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Figure 3. The Trinity Suspension Pier and details of Brown's patent chains. and those used by Brown is that in the latter case each round eyebar comprised a separate chain whereas Telford's chains were each composed of a n u m b e r of flat eye-bars pinned together to form a single chain. It was Telford's improvement of the eye-bar chain that became the standard design that has survived to this day. All the available evidence suggests that Brown persisted in using his chain for all the bridges he built and for those in which he supplied the iron work, except the H a m m e r s m i t h Bridge which was designed by William Tierney Clark, in the Telford tradition, and for which Brown supplied part of the ironwork. While Brown objected to link chains because of their lower efficiency compared with his end-connected bars, he objected to the use of wire on quite different g r o u n d s : A bridge of wires, being the most complicated of any, is the most objectionable. Where they are intended merely for the accommodation of foot passengers they may be easily contrived and constructed, b u t one composed of such slender and ductile materials, of sufficient strength to support the weight of loaded carriages, must consist of such a multiplicity of parts that an united effort by their proper adjustment is not

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Samuel Brown: Pioneer Suspension Bridge

Builder

to be expected. T h e lack of durability is of itself an insuperable objection to wire bridges, as well as all others constructed of such slender filaments. T h e immense surface exposed to the action of the atmosphere would infallibly cause a rapid decay, and the common preventatives of corrosion could not be made generally beneficial because it is impossible to apply any composition to the interstices and crossings of the wires or seams of the filaments where they are most liable to be effected; and as the defects cannot be there observed, the bridge might be in a state of dangerous insecurity while it indicated no appearance of decay. T h e prejudice against the use of wire for permanent suspension structures was to continue in Britain, with few exceptions, until recent times. Despite the stated disadvantage of wires, their successful use proved, later in the century, that this type of cable was the only one suitable for really long-span bridges. T h u s , just as the eye-bar chain replaced the link chain as a more suitable structural element, the spun-wire cable superseded the bar chain. T h e U n i o n B r i d g e a c r o s s t h e T w e e d at N e w W a t e r f o r d A COMPLICATED HISTORY T h e history of the U n i o n Bridge is interwoven with legendary information concerning the D r y b u r g h Bridge and the 'Kelso Bridge 5 . M a n y writers on the history of technology indicate that the U n i o n Bridge was blown down six months after its completion. T h e r e is absolutely no contemporary evidence that this is true. Stevenson is most laudatory in his account of the bridge and Brown, writing in 1826, states that it had given entire satisfaction since it was constructed. It is difficult to imagine how a calamity to the greatest suspension bridge in the country could go unnoticed in the popular press or in engineering journals. 1 4 T h e conclusion is inescapable that this is a case of mistaken identity and that in the reporting of the collapse the D r y b u r g h Bridge was somehow confused with the U n i o n Bridge. A further complication is provided by accounts of the 'Kelso Bridge 5 , which is mentioned by several writers, including Bender, Jakkula and Tyrell and which was reported to have been completed in 1820. T h e r e is no firm evidence that this bridge ever existed and none of the early writers mention it. T h e U n i o n Bridge was built with a clear span between towers of 437 feet but the deck length was only 367 feet (see Fig. 2.4). It is possible that failure to associate these two different dimensions with a single bridge led to the assumption that there were two bridges, and that the 'Kelso Bridge 5 owes its notional existence to this fact.

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THE UNION BRIDGE Brown's early investigations and the development of iron chain manufacturing techniques coupled with his patent on suspension bridges and the Runcorn Bridge proposal provided him with the experience and reputation to be a most logical choice to build the Union Bridge. It also appears that his navy connections may have been instrumental in his appointment. His patron was probably Admiral Milne. F r o m 1803 Admiral David Milne (1763-1845) served for several years as officer in charge of the F o r t h District of the Sea Fencibles. I n 1811 he was at sea again; in 1814 he was promoted to flag rank and in 1816 he was appointed commander of the N o r t h American station returning to England in the summer of 1819. Less than a year later he was elected M e m b e r of Parliament for Berwick-upon-Tweed. Milne was impressed with Brown's work for the Navy and having strong connections in Berwick-uponT w e e d , as witnessed by his election to Parliament, he was probably partly responsible for Brown's appointment. H e later served on the committee reviewing Brown's proposal for a suspension bridge at N o r h a m over the T w e e d . By good fortune Brown's U n i o n Bridge, which was his most impressive work, is still extant in essentially its original form except for the deck, which has been renewed on several occasions, and the addition of wire ropes to assist the main chains. W i t h a main span of 437 feet it marked the beginning of long-span suspension bridges in Britain and was the first such bridge in the country to carry road vehicles. Details as given by Stevenson are shown in Fig. 2.4. Briefly, the timber roadway was 18 feet in width and composed of 7 - b y - i 5 inch main joists on which there was a plank floor 12 inches wide by 3 inches thick. T h e floor joists were supported on a 3-inch deep by f-inch thick iron bar which extended one on each side of the roadway, the entire length of the bridge. T h i s longitudinal bar was a favourite detail of Brown and occurred on many of his bridges and piers. T h e s e bars provided longitudinal continuity for the deck and were used to connect the suspenders to the deck. T h e wrought-iron suspenders were connected to these bars on each side by a special 'spear' or bolt which formed a cleavis arrangement. T h e suspenders were, in t u r n , carried by the main chains by means of the shackle and cap fitting (shown in Fig. 2.4). I n conception the chain-suspender-stringer system was the same as Finley's patented method. T h e entire iron work was made of the 'very best Welch iron'. T h e chain rods were about 2 inches in diameter and about 15 feet long with eyes 'strongly welded and neatly finished at each end'. T h e arrangement of three chains, each of a pair of bars on each side, with staggered joints permitted a suspender spacing of 5 feet. By supporting the suspenders at the

14

Samuel Brown: Pioneer Suspension Bridge

Builder

joints in the chains, bending of the rods was avoided because members which are pin-connected at the ends sustain axial tension loads only. T h e parapet, composed of a 6-inch square iron mesh, was 5 feet high on each side of the roadway. F r o m its design and description it is clear that it was intended as a safety fence for foot passengers rather than as a stiffening truss. As a result the bridge deck was essentially unstiffened and probably owes its longevity to its isolated and protected position rather than to any special merit of design. T h e bridge is unsymmetrical with a masonry tower on the Scottish side, b u t on the English side of the river the tower is actually built into the hill side (see Fig. 2.4). T h e roadway makes an ' L ' junction on this side and thus the deck is only 367 feet in length whereas the span between saddles is 437 feet. Various dimensions are reported in the literature, b u t the ones stated above are taken from Brown's drawing of the bridge and conform with the approximate dimensions given by Stevenson. T h e versed sine or sag of the middle pair of chains is about 26 feet and the end slope of the chains at the towers was reported as 12 degrees. Quite unexpectedly the bridge was load tested on the very day of its opening when a crowd of 700 enthusiastic people forced their way on to the structure. Stevenson computes the capacity of the chains by assuming that the average person on the bridge weighed 150 p o u n d s which would have produced a live load of just under 47 tons. T h e total dead load of the bridge was estimated at 100 tons of which the chains made u p 5 tons. Using a combined load of 147 tons rounded off to 150 tons it was found that the load in the chains was 370 tons which is considerably lower than the estimated capacity of 12 times 92 = 1,104 tons. However, the strength of wrought iron is usually based on a fraction of the yield point and not on the r u p t u r e strength. Using a third as the factor of safety against yielding the resulting safe total load is 240 tons. A safe stress of si tons per square inch, commonly used for wrought iron in the 1820s and 1830s, gives a capacity of 207 tons. Brown usually used more than twice this value, 10-12 tons per square inch, which gives a capacity of 415 tons, just in excess of the 370 tons required to support the opening-day crowd. T h u s , by the standards of Telford, Brunei and what came to be considered safe and sound practice, Brown's bridge lacked a sufficient margin of safety against gravity loads. T h e strength of the cables could have been increased by increasing the n u m b e r or area of the cables or by increasing the sag/span ration. As Bender notes, engineers at the time were unwilling to use Finley's suggested ratio: Finley expressly advocated the construction of platforms of one piece, b u t Navier and his followers supposed a perfectly

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movable floor. Finley applied 1/7, Navier 1/12 to 1/15 of the span's deflection. Finley prevented the undulations by his stiff platform; Navier believed he could prevent greater deplacements [sic displacements] by flat catenaries. This is the great antithesis of these two celebrated engineers, and every scientific bridge-builder must concede that Finley stood much nearer to the perfect solution of this problem than Navier. 15 Not only did most engineers believe that flatter catenaries would increase stiffness but also that such a practice would reduce tower heights and cable lengths and thus make a significant saving in materials. Brown was not alone in using substantially higher design stresses. However, it is likely that he did not appreciate that the useful limit of the material was its yield point. Through a series of failures evidence began to accumulate which indicated that the deck stiffness was the key factor in the behaviour of suspension bridges. Rendel was quite conscious of this matter of stiffness when he re-built Brown's Montrose Bridge in 1839. 16 As we have seen no satisfactory method of analysis of the stiffened suspension bridge was available until nearly the end of the century. In the first four decades of the nineteenth century attention was directed most towards perfecting the design and construction of the main chains which were considered the primary structure. The entire structure was not thought of as a composite one. Ellet and other engineers felt that composite action was undesirable and without question complicated the action and invalidated the simple elegance of the mathematical solution of the unstiffened suspension bridge. Brown continued to build unstiffened bridges, little changed from the Union Bridge, until the 1840s. N o n e of his subsequent structures were to achieve the clear span of the Union Bridge, although he was involved in numerous bridge projects for more than two decades after the completion of the Union Bridge. N o provisions were made in either the strength of the cable nor the stiffness of the deck against wind loading by any of the designers during this early period. This serious defect was to cost Brown and others dearly in the total or partial destruction of a number of bridges caused by wind action. As early as 1821 Stevenson very perceptively adds the following caution: But the effect we have to provide against in bridges of suspension is not merely what is technically termed deadweight. A more powerful agent exists in the sudden impulses, or jerking motion of the load . . . Hence also the effects of gusts of wind, often and violently repeated, which destroy the equilibrium of the parts of a bridge of suspension; and the

16

Samuel Brown: Pioneer Suspension Bridge

Builder

importance of having the whole roadway and side-rails framed of the strongest possible manner. 1 7 Suspension Piers A UNIQUE IDEA Brown's next two projects were not suspension bridges in the accepted sense of the term but a totally new application of the suspension principle, namely to the construction of landing piers. I r o n piers for landing stages, p r o m e n a d e s and places of amusement were very m u c h part of the Victorian seaside resort. D u r i n g Queen Victoria's reign dozens were built, b u t Brown, in the 1820s, was one of the first to use iron for the superstructure and only he constructed piers as multispan suspension bridges. 1 8 TRINITY SUSPENSION PIER T h e design and construction of the Trinity Pier is described and illustrated in a letter from Brown published in the Edinburgh Philosophical Journal in 1822. 1 9 Brown credits L i e u t e n a n t Crichton, R.N., who was the manager of the L o n d o n , Leith, E d i n b u r g h and Glasgow Shipping Company, with successfully promoting the construction of a new pier at Trinity on the Forth near E d i n b u r g h rather than being involved in extensive litigation to establish the right to land at Newhaven. T h e pier was intended to serve as a landing stage for the increasing steam ship traffic. F r o m M a r c h to July 1821 Brown was involved in driving pileclusters to support the towers and to act as the off-shore landing stage. T h e total length was 700 feet consisting of three 209 feet long clear spans (see Fig. 3). T h e walkway was 4 feet wide, was suspended from a round eye-bar chain in which Brown had made several improvements over his previous designs. Recognizing that the tensile forces in the bars increases towards the towers he was the first to build a chain which approximated, by discrete steps, a tendon of uniform strength. T h i s was done by using bars 2, if, and i f inches in diameter instead of bars of constant diameter. T h e s e were united by side-plates and bolts of proportional strength. With this innovation he anticipated Dredge's tapered chain system by more than a decade. 2 0 T h e versed sine of the cables was 14 feet which resulted in a sag/span ratio of approximately 1:15 which, like the Union Bridge, was quite a flat catenary. T h e pier was very lightly constructed with an unstiffened deck and high working-load stresses in the chains but nevertheless it survived until 1898 when it was wrecked in a storm. After describing the cast iron towers and the stone tower on the shore. Brown says: T h e back stay-bars form an angle of 45 degrees; the extremities are sunk about 10 feet below the surface of the

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ground, and secured in hard clay by cast iron plates, on the principle of a mushroom anchor. The outer back-stays are carried in the same angle over the standard of the outer-pierhead, and are morticed into a rider, which is bolted to the piles; and these riders are backed by spur-shores to resist the drag of the bridge. The deck-suspension system was similar to the Union Bridge with the suspenders attached to a pair of 3-inches by f-inches thick longitudinal bars, one on each side of the bridge deck and running the entire length of the span. Transverse beams rested on these bars and they in turn supported a 2-inch thick plank deck. A 4-feet high railing using the suspenders as verticals was provided for safety but it added very little to the deck stiffness. Brown's letter ends with a brief justification of the use of such piers and the particular advantages in constructing one at Deal. However, his promotion of the Deal Pier was in vain and the project was abandoned in 1824. BRIGHTON CHAIN PIER According to Bishop this pier was constructed to 'afford accommodation for the ever increasing passenger traffic between England and France'. 21 In addition, Brighton was a growing and fashionable seaside resort which meant that the pier could also serve as a promenade. The traffic to and from London in this prerailway age amounted to fifty coaches per day. In 1821 a prospectus was issued for a £27,000 joint stock company. T h e prospectus contained two reports from the directors of the Trinity Pier Company at Leith to the effect that they were entirely satisfied with Brown's services. Later Brown and his family subscribed £17,200 in shares for the proposed pier. Among others, the Duke of Wellington pledged £300. On 18 September 1822 construction began and the pier was opened on 25 November 1823. The opening ceremonies were a great success although the directors were disappointed that no members of the royal family were able to be present. At this time Telford's Menai Straits Bridge was under construction and with the completion of the Brighton Chain Pier the suspension bridge had moved out of its narrow confines of the Tweed Valley and was attracting nation-wide attention. The Brighton Pier was not nearly as significant from the technological point of view as the Union Bridge, finished three years before, but one should not underestimate its promotional value at the time. Exactly one year after the opening what was to be called 'the birthday storm' broke on Brighton, but severe as it was the pier 'stood like a rock'. The pier was constructed on an exposed part of the coast and on a visit to Brighton to inspect the Pier in November

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Samuel Brown: Pioneer Suspension Bridge

Builder

1830, Brown was asked to consider the possibility of creating a breakwater by filling in the pierhead with rock and extending the rock fill on each side of the pierhead. T h i s scheme was not executed and the pier remained unmodified and unprotected from the sea. A very severe storm struck Brighton on 15 October 1833 and caused considerable damage to the pier. T h e deck suffered from the dynamic action of the wind, which according to eye witness r e p o r t s involved a c o m b i n a t i o n of flexural and torsional displacements which caused the third span to collapse (as shown in Fig. 4). Apparently, the unstiffened deck reached a resonant frequency which produced ever-increasing amplitudes until the suspenders broke and the deck collapsed. T h e pier was repaired only to be struck by a 'hurricane' in 1836 which damaged the towers and caused the deck of the third span to fail. It was again repaired in time for the young Queen Victoria to visit in 1837. Thereafter, through neglect it gradually fell into disrepair and was purchased in 1889 by the Marine Palace and Pier Co. F r o m this time it was doomed because the new company intended to raze it and build a new pier. However, before it could be demolished by the hand of m a n it was completely destroyed in a storm on 15 December 1896. T h e pier was quite similar to the T r i n i t y Pier with three spans each of approximately 250-feet length with each chain rising over a 25-feet high cast-iron tower. At the inner end the chains were anchored 54 feet into the cliflf face and terminated at an iron plate weighing nearly three tons. T h e anchorage excavations were filled

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u p with stone and brick work. At the outer end the chains were carried to rock where the ends were properly secured by bolts and keys. T h e chains consisted of 170 links, each being 10 feet long and 6 inches in circumference (i.e. 2 inches in diameter) and weighing one hundredweight. T h e r e were four chains on each side of the 13feet wide deck. T h e deck and suspender details were similar to the Trinity Pier and are beautifully illustrated by Weale. 2 2 Two Decades of Bridge Building After the completion of his two piers and the U n i o n Bridge, Brown actively promoted the suspension bridge idea across the length and breadth of Britain. H e was involved in the design, erection and supply of iron work for at least eighteen bridges in the two decades following 1823. And even though the exact n u m b e r of his projects remains unknown and many details are lacking, it is still possible to present a very full account of Brown's work.* NORTH AND SOUTH SHIELDS BRIDGE PROPOSAL 1825 After the Deal Blackwater Pier proposal Brown was involved in the design of a proposed bridge across the T y n e . I n 1825 William C h a p m a n proposed a major three-span suspension bridge from N o r t h to South Shields. 2 3 T h e design, which featured side spans of 440 feet and a main span of 880 feet, was based upon an earlier design of Brown. T h e first proposal was for a bridge with a main span of 800 feet and a sag of 56 feet resulting in a sag/span ratio of 1:14.3 which was typical of Brown's earlier designs. T h e main span was t h e n increased to provide a better location for the tower foundations. C h a p m a n proposed a sag of 70 feet and a main span of 880 feet yielding a more satisfactory sag/span ratio of 1:12.6. T h e modified design had Brown's approval and presumably he would have supplied the iron work for the bridge. T h e first estimated cost was £93,000 but this was increased to £110,000 when the main span length was increased. A company was formed to erect the bridge, b u t it was never built. WARDEN BRIDGE 1826 T h e W a r d e n Bridge, over the South T y n e River, was built by Brown in 1825-6 and the cost of its construction, some £50,000, was defrayed by him. It was a road bridge of about 315-feet span with a width of 20 feet. T h e design was very similar to the U n i o n Bridge. T h e suspenders were connected, on each side of the deck, to longitudinal iron bars running the entire length of the deck. T h e *I am particularly indebted to Mr Francis Cowe of Berwick-upon-Tweed and to Mr Gordon Miller of Kingston-upon-Thames for information on many of Brown's lesserknown bridges. Except for Mr Cowe's article on the Union Bridge (Country Life 6 July 1961) this information is unpublished.

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Samuel Brown: Pioneer Suspension Bridge Builder

suspenders and transverse timber floor joists were spaced at 5-feet intervals. A timber deck and wearing surface were supported by the joists. The bridge has also been called the Hexham Bridge and the West Boat Bridge and its dates of construction given variously as 1820 and 1825. Little is known of its early history except that it was a toll-bridge. It was adopted by the County of Northumberland in 1876 and in 1877 the deck was rebuilt with new timber flooring and a new wearing surface. The suspension bridge survived until 1903 when it was replaced by a stone structure. Nothing of it remains at the site, but the County Surveyor's Office has plans showing the bridge before and after the alterations of 1877. I n addition, the Newcastle University Library had a print of the bridge dated 1829. In 1924 Moncrieflf published a brief description of the bridge and accompanied it with a plan and elevation. 24 WELNEY BRIDGE 1826 On the 7th September, 1825, the Bedford Level Corporation granted a lease of a strip of land at Welney (a village on the western border of the county), forming part of the bank of the Hundred Foot River to the late Rev. William Gale Townley for a term of 99 years. The late Rev. Townley covenanted with the Corporation to erect a suspension bridge across the Hundred Foot River on the land leased to him, and the Corporation at the same time granted certain priviliges for taking tolls in accordance with a scale set out in the schedule of the lease. The bridge erected by the Rev. Townley was a wrought iron suspension bridge with a wooden floor. The span was 191 feet, width of carriageway was 7 feet 6 inches, with a footpath each side of 3 feet, 4 inches. The bridge has stood until it was recently demolished. At no time was it possible to take the heavier forms of traffic such as traction engines over it, and during the last few years weights have been restricted to 3 tons, so that the bridge has always formed a weak link in the route between Wisbech and Ely. 25 T h e bridge was erected for £3,000 to a design by Brown. It was opened on 16 August 1826 and replaced by a concrete bridge in 1926 or 1927. BROUGHTON BRIDGE, 1825 A very serious and alarming accident occurred on Tuesday last, in the fall of the Broughton suspension bridge, erected a few years ago by John Fitzgerald, Esq., whilst a company of the 60th Rifles were passing over it; and although fortunately no lives were lost, several of the soldiers received serious personal injuries, and damage was done to the structure which

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will require a long time and a very considerable expense to repair... Shortly after they got upon the bridge, the men, who were marching four abreast, found that the structure vibrated in unison with the measured step with which they marched; and, as this vibration was by no means unpleasant, they were inclined to humour it by the manner in which they stepped. As they proceeded, and as a greater number of them got upon the bridge, the vibration went on increasing until the head of the column had nearly reached the Pendleton side of the river. They were then alarmed by a loud sound something resembling an irregular discharge of fire-arms; and immediately one of the iron pillars supporting the suspension chains . . . fell towards the bridge. These excerpts from the Manchester Guardian of Saturday, 16 April 1831 illustrate the vulnerability of unstiffened suspension bridges to dynamic loads which cause resonant responses in the structure and result in increasing amplitudes of the deck and ultimately in the destruction of the roadway and failure of some or all of the supporting suspension members. T h e collapse of the Broughton Bridge was just one of a number of such failures that occurred between 1829 and 1839. These collapses had a significant influence on the subsequent history of suspension bridge building in Britain. The country's most prolific suspension bridge builder was also involved in several serious failures which dampened the enthusiasm of engineers to use or improve this type of structure. The Broughton Bridge was built for John Fitzgerald on private property. The foundation stone was laid in October, 1825 and the bridge was completed the next year. The interesting point about the history of the bridge is that a paper devoted exclusively to an evaluation of its strength was published before it collapsed. It was written by Eaton Hodgkinson who had already gained a considerable reputation for his work on the strength of materials. 26 He describes the bridge as having a span of 144 feet 6 inches and chains composed of two double wrought-iron cables. These pairs of rods were coupled by three small elliptical links and two bolts. T h e suspenders were attached at the coupling points and carried the unstiffened deck. Gies credits the design and erection of the bridge to Brown, but none of the contemporary sources, including Hodgkinson, mention Brown or any other designer by name. 27 Nevertheless, the details of the chains and general appearance of the bridge suggest that Brown may well have had a hand in its design. One unusual feature, which M. I. Brunei had used earlier in his Isle of Bourbon bridges, was the suspension of the chains in the cast-iron towers by a short link rather than by running them over the tower-tops on saddles. Hodgkinson examined all aspects of the static strength of the

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Samuel Brown: Pioneer Suspension Bridge

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bridge and said that it would fall in the following m o d e s : F r o m the preceding inquiry it appears, that were the bridge overloaded it would give way, — ist in the pier . . . 2nd in the side chain, — 3rd in the top link of the catenary, — 4th in the succeeding ones and 5th at the bottom of the suspending link in the tower. T h e paper was read on 8 February 1829. After the collapse, Hodgkinson investigated the failure and concluded that the 2-inch anchor bolt, which was not visible on his previous investigation, had failed. T h i s was a design error; the joints in the pairs of 2-inch diameter rods were composed of three short links and two bolts except at the anchorage where there was only one link. T h e strength of the bolt in this anchorage was only a quarter of the strength of the chain itself. Hodgkinson prepared an appendix to the paper devoted to the collapse. His paper gives a good idea of the state of analysis and design of suspension bridges in the 1820s in the hands of an acknowledged expert in structural analysis and strength of materials. It was most unfortunate that he was not consulted on the Broughton Bridge before construction started and on other suspension bridge projects where his advice could certainly have prevented failure of a n u m b e r of bridges of questionable design. MONTROSE BRIDGE, 1829 T h e Commissioners of the Montrose Bridge authorized George Buchanan's report on a new suspension bridge to be printed and circulated for their information. T h e authorization was given on 28 February 1823 and the report printed in 1824. 28 T h e proposal was to replace a timber viaduct over the South Esk River with a suspension bridge whose span would be such that the channel, with its swift currents and high tidal flow, would not be obstructed. T h e report was quite comprehensive and dealt with all aspects of the construction including a cost estimate of £12,623. With the advice of Professor Leslie, of the College of E d i n b u r g h , Buchanan used a sag/span ratio of 1:8 and showed that his design would result in half the cable force of previous Brown designs which used a ratio of about 1:14. T h e r e are a n u m b e r of interesting points in Buchanan's proposal which are worth mentioning briefly, if only as a contrast to Brown's rival design. T h e proposal was for a span of 420 feet between towers and an overall deck width of 30 feet, sufficient for two footpaths and a 20feet carriageway. T h e chains were to be i^-inch diameter rods with upset ends which were coupled together with coupling boxes or sockets of cast iron similar to those proposed by Brown in 1817. T h e two chains, one on each side of the deck, consisted of thirty-

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six bars in each chain arranged in a compact square 6-by-6 inches. A unique feature was the provision of a narrow 20-feet wide draw span at one end of the roadway to permit the passage of ships. In order to support the deck at the opening Buchanan proposed to use one of the wood piers of the viaduct. Rather than use heavy transverse timber joists for the deck it was proposed to use light iron members trussed with a suspension chain and vertical compression struts under the deck. T h e roadway was to be formed with iron plates and a tar and gravel wearing surface. Buchanan was concerned about the action of the wind and other moving loads. He made provision for these loads by extending under the roadway a series of malleable iron plates running the length of the bridge, by binding the roadway very firmly to the chains, 'binding these latter all together into one great mass or cable of chains, so that any load or heavy body moving along the bridge, acts, not on one, but on all the chains together' and by provision of horizontal rods attached to the main chain and carried back to the towers. He did not give serious attention to stiffening trusses for the deck which would have been the only effective means of resisting the wind loads. On 8 July 1823 Brown, who was residing in Brighton at the time, submitted a letter, brief specification and one plan together with a cost estimate to the Commissioners of the Montrose Bridge. 29 The one-page specification and plan sheet give details of the bridge, but no indication of the design assumptions. The following dimensions are from the specification: T h e bridge is to be 28 feet wide between the railing, and 418 feet in length, or thereabout: there are to be 3 rows of principal suspending chains over each other: each row to consist of 3 chains parallel . . . one of the bolts of the above chains 2% inches in diameter, and 15 feet long — or 20 feet long, if I prefer that l e n g t h . . . . the main beams of cast iron; it is to be 10 inches deep at the ends where it rests on longitudinal bars and rise with a regular curve to the centre where it is to be 15 inches deep; it is to be 1 inch thick throughout between flanges, and 28 feet 6 inches long. These beams were of T cross section, placed 5 feet on centres. Details were given of the suspenders, anchorages, towers, draw span and railings, which were ornamental and not structural. T h e deck is not shown on the drawing and is vaguely described by Brown: The plates which are to form the covering or road need not be shewn by a drawing; they will be a cast in suitable lengths for bolting or screwing down on the beams. Their thickness will be decided by some experiments which I am about to make.

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Samuel Brown: Pioneer Suspension Bridge Builder

Brown estimated the cost at £12,500 which was very slightly less than Buchanan's estimate. However, Brown used only 71.6 square inches total in the cross section for his chains with a sag/span ratio of about 1:10 compared to 124 square inches total in Buchanan's chains with a sag/span ratio of 1:8. Buchanan's design was altogether a more thorough and substantial piece of engineering, but Brown's design was accepted and he constructed the bridge during 1829. It was finished in December of that year. As we have seen, in Brown's original design, he intended to use round bars for the chains in sets of three bars, one such chain being on top of another in three levels. However, when the bridge was built flat eye-bar chains were used, consisting of four 5-by-i inch flat bars approximately 10 feet long. There were two rows of chains stacked vertically on each side of the deck, giving a total area of 80 square inches. This was only a slightly better arrangement than the original proposal and the chains were decidedly under strength for the type of loads one might expect on such a bridge. T h e deck was altered from an all-iron one to a timber deck resting on cast-iron transverse beams. It was essentially unstiffened. The timber deck consisted of 3-inch planks covered by a i^-inch flooring and on top of this a tar and gravel wearing course was laid. On 19 March 1830 a crowd of people, estimated at 700, was watching a boat race and bodily moved from one side of the bridge to the other as the race proceeded. This shift in live load caused one of the chains to break plunging most of the people into the river with a 'great loss of life'. It should be noted that Buchanan had designed his bridge to carry 7,000 people. A subsequent investigation of the disaster, under the direction of Telford, recommended strengthening the bridge by increasing the number of chains. However, before the work could be taken in hand Telford died and J. M. Rendel (1799-1856) took over the responsibility for repairing the bridge. As a young man Rendel left Okehampton and served as a surveyor under Telford. He was later involved in the Runcorn Bridge proposal and in the design of a suspension bridge at Saltash which was not built. Thus, he was well known as one of Telford's assistants and as having had some experience with suspension bridge design. In the Minutes of Proceedings of the Institution of Civil Engineers, for April 1841 Rendel reported: . . . it was discovered that the intermediate or long links of the chains bore so unequally upon the saddles as to be bent and partially fractured. After a minute personal inspection he concurred in Mr Telford's idea of the necessity of increasing the strength of the bridge, but instead of augmenting the number of chains, he advised the addition of two bars in width to each . . . by which means the required strength might be gained.

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Rendel's addition of extra bars to each chain not only provided the increased strength, but it allowed a better bearing of the chains on the saddles and was thus a superior way of repairing the bridge than the method suggested by Telford. With regard to the deck, Rendel comments: In the author's report on the state of the bridge, he noticed what he deemed defects in the construction of the roadway, but as there was no positive symptom of failure, it was allowed to remain. He conceived, that in the anxiety to obtain a light roadway, mathematicians and even practical engineers had overlooked the fact, that when lightness induced flexibility, and consequently motion, the force of momentum was brought into action, and its amount defied calculation. On I I October 1838 the roadway of the renovated structure was destroyed by a 'hurricane 5. T h e strengthened chains, saddles and other features of the main supporting elements held firm and were undamaged. Considerable interest was taken in this structural failure. Col. C. W. Pasley, R.E. as well as Rendel reported on the collapse and related problems associated with wind action on suspension bridges to the Institution of Civil Engineers. Pasley said: . . . This rise and fall of the roadway is prevented in the Hammersmith Bridge by four lines of strong trussing along the whole length of the roadway, firmly connected to the bearers below; no similar trussing exists in the Menai, the Montrose, or any other suspension bridges which Col. Pasley has seen, or in the Brighton Pier. The damage done to the latter, in November, 1836, is attributed, by Lt. Col. Reid, who witnessed it, to the action of the wind on the under surface of the roadway, and not to the lightning. T h e rise and fall of the platform of the Menai Bridge is confidently stated to be three feet in ordinary gales, so that unless some similar trussing be employed, it may reasonably be expected that this bridge will be seriously injured in a hurricane. 30 His prediction about the Menai Bridge was fulfilled in 1839 when it was damaged in a storm. The vertical oscillations noticed on a number of these bridges were associated with flexural resonance of the deck described at the time by Pasley and others as being caused by wind underneath the deck. Although unable, as he stated, to calculate the stiffness required in the deck of the Montrose Bridge, Rendel nevertheless proceeded to design a new deck. It was very stiff, with two 10-feet deep stiffening trusses joined to the deck at the mid-height of the truss. This trussing was designed to prevent excessive vertical deflections along the length of the deck. The lateral motion caused

26

Samuel Brown: Pioneer Suspension Bridge Builder

by the wind on the platform was resisted by a horizontal truss just under the deck. Diagonal 2-inch planking formed the bottom two layers of the deck with one 2-inch longitudinal and one i^-inch transverse layer of timber on top of these. This laminated deck rested on the horizontal truss which was composed of 6-inch square timbers. A tar and gravel wearing surface, similar to Brown's original design, was installed on the timber deck. By the time Rendel had finished his work on the Montrose Bridge it was virtually a new bridge built to a new design. This much improved structure survived until 1931 when it was replaced by a concrete bridge. T h e failure of the Montrose Bridge provided dramatic evidence of the behaviour and strength of the component parts of a suspension bridge. Rendel successfully reinstituted Finley's idea of a stiffening truss, corrected the weakness in the suspension cable and provided a stiff and strong platform to resist wind and moving loads on the deck. At the time many engineers were interested in the details of the Montrose Bridge failures and deeply concerned about the puzzling behaviour of such structures under dynamic loads. Rendel had given an insight into the problem and a practical means of designing a suspension bridge to resist dynamic loads. However, few were willing to follow his lead at the time. CLIFTON BRIDGE OVER THE RIVER AVON, 1829 The Avon Gorge at Bristol provided an outstanding site for a major bridge. As early as 1753 a Bristol merchant established a bequest for a new bridge. By 1829 sufficient funds had accumulated to advertise for designs. All of the designs submitted were rejected and Telford, judge of the competition, then submitted his 'Gothic Design' which after wide initial acclaim was also rejected by the Bridge Committee. A second competition was held with Davies Gilbert, president of the Royal Society, and John Seaward as the judges. They selected four designs, one of which was Samuel Brown's proposal. Body lists the following details of these designs: Competitor Span Weight Area of Chain Tension Tensile Stress (feet) (tons) (square inches) (tons) (tons/sq. inch) I. K. Brunei 630 1468 470 1966 4.20 J. M. Rendel 780 1378 300 1861 6.25 W. Hawks 630 1226 288 2022 7.00 Samuel Brown 780 1709 324 2700 8.33 Although Brown was using lower stresses than in his earlier designs his stress level was considerably higher than any of the other designs and in excess of the 5^ tons/sq. inch recommended by the committee. Nevertheless, his design was selected as one of the four final designs. Details are lacking on Brown's proposal to enable us to determine if any improvements had been made in this

Emory L. Kemp

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design compared to his earlier bridges. However, we do know that his design stress of 8.33 tons/sq. inch was less than three-quarters of the value he had used previously. T h e committee's selection did not follow the above order. In order of merit the designs were considered to be: 1. W. Hawks 2. I . K . B r u n e i 3. Samuel Brown 4. J. M. Rendel Telford's design was not listed. After a very persuasive argument ranging from aesthetics to technical merit Brunei convinced the entire board that his design should be accepted. By not having been selected to build the Clifton Bridge Brown lost the opportunity to sustain or increase his national reputation as a leading suspension bridge builder. He would try again with a proposal for the Lambeth Bridge but it too was not successful. A new generation of engineers assumed the leadership and carried on in Telford's tradition of suspension bridge building. After the Clifton proposal Brown's remaining work was located, with one or two exceptions, in the North of England and in Scotland, all of these later projects being for bridges of relatively modest spans. With his failure to secure the Clifton Bridge contract he was no longer in the forefront of suspension bridge builders. However, the Clifton Bridge would probably have been a mixed blessing to Brown since it was beset with many difficulties. Started in 1831 it was not completed until 1864 after the deaths of both Brunei and Brown. It was the last major British suspension bridge to be built for almost a century. 31 STOCKTON RAILWAY BRIDGE OVER THE TEES, 183O In 1830 Brown built the first suspension bridge for railway traffic to carry coal wagons across the Tees. The bridge had a main span of 281 feet, and a cable sag of 28 feet giving a sag/span ratio of 1:10, considerably more than in his previous bridges. The improved efficiency resulting from this configuration did not prevent this bridge from being quite unserviceable for its intended use. T h e deck was stiffened with light trusses which were entirely too flexible for railway loadings. According to Stephenson, when commenting some years later on the suitability of suspension bridges for railway traffic: I do not think that a railway bridge could be made on the suspension principle; we have one at Stockton, which I replaced . . . and it was fearful when an engine went onto it. I have been informed that the wave on the bridge was two feet high. I do not say that from having seen it myself, but I have heard it stated, that when an engine and train went over the

28

Samuel Brown: Pioneer Suspension Bridge Builder first time, there was a wave before the engine of something like two feet, just like a carpet. 32

As a temporary expedient a pier was placed under the deck at midspan so that horse-drawn wagons could continue to use the bridge. By 1841 the bridge was abandoned and only the cables remained. Stephenson replaced the bridge with a cast-iron span in 1842. T h e unfortunate history of this bridge had an adverse influence on subsequent suspension bridge building in Britain. It was built during the decade when civil engineers were increasingly turning their attention to railway construction and this bridge convinced a number of leading engineers that suspension bridges were unsuitable for railway traffic. With the completion of Roebling's combined road/rail bridge across the Niagara Gorge in 1855 there was renewed British interest in building railway suspension bridges. This issue was the subject of a lively debate at the Institution of Civil Engineers at the time but no railway bridges were built on the suspension principle in Britain after Brown's first effort. BATH CHAIN BRIDGE, 183O During the same year as the Clifton and Stockton projects Brown was also involved in supplying the ironwork for the Bath Chain Bridge, designed by T . Shaw and erected in 1830. The bridge was of modest proportions but nevertheless Drewry gives detailed information on it. The span of the cable between the points of suspension was only 118 feet with a sag of about 10^ feet. This resulted in a sag/span ratio of 1:11.5 which was even more favourable than that of the ill-fated Stockton Bridge. The roadway was 9% feet wide and consisted of a pair of longitudinal timbers supported by suspenders which passed through the beams and were fastened with a washer-and-key system. T h e 'side bearers' were made of two 4-inch by 10-inch timbers bolted together to form a 20-inch deep beam. On these 'side bearers' the cross-joists were laid and these supported the plank deck. T h e interesting feature of Drewry's remarks are the calculations of the static strength of the bridge. It was warranted to carry 12 tons live load, which together with the weight of the bridge gave a maximum load of 20 tons. With a sag/span ratio of 1:11.5 Drewry computed the cable tensile force as 28 tons (20 times 1.4). However, if the footbridge had been completely crowded with people the live load would have amounted to some 35 tons and the total load to 43 tons. This loading would, in turn, have resulted in a total tension in the cable of 60 tons. T h e cable area was reported as 4.8 square inches. Drewry used

Emory L. Kemp

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a stress of 9 tons per square inch 'before stretching' and calculated a cable force of 43.2 tons. This is quite adequate for the warranted load, but only about two-thirds of the capacity required for the bridge when fully loaded. The figure of 9 tons/sq. inch was not likely to have been the yield point of the cables but rather a safe stress which was determined as a fraction of the yield. Drewry explains his justification of this stress: It is said that iron has been found to stretch at 10 tons per sq. inch the amount of the stretching being equal to about 1/1630th part of the length of the bar. And that it will bear 9 tons per square inch without stretching at all. Nine tons per square inch are accordingly now taken as the strain that the chains of a suspension bridge may bear continually without injury, and it is prudent to proportion them for the strain. But we may, at the same time, conclude from the experiments first cited, and from the almost imperceptible amount of stretching at 10 tons per square inch, that iron bars will bear 12 or 14 tons per square inch, for a time without being injured, although they ought not to be loaded with that strain continually. 33 This stress is approximately the value used by Brown in his Clifton suspension bridge proposal which was nearly twice the 5^ tons per square inch recommended by the committee. T h e 60-ton cable load for the Bath Bridge would have produced a stress of 12^ tons per square inch which was probably below the yield but it did not incorporate a safety factor of two or three as implied by the use of a value such as 5^ tons per square inch. At best it was a marginal design. Drewry concludes his remarks by saying: T h e bridge is, however, not likely to be ever loaded with more than the weight it is warranted for, as it is private property, and carriages are not allowed to cross it, and moreover it does not communicate with any great thoroughfare. In the absence of building code requirements each designer had to use his own judgement, tempered by what was common practice at the time, on the safety of a particular design. This judgement included selecting appropriate design stresses, a suitable method of analysis and an appropriate live load. Thus, rather than consider the actual yield point of the iron in terms of the stresses induced in the Bath Bridge when fully loaded with people, Drewry considers the loading as very unlikely, despite the fact that several suspension bridges did collapse under just such loadings. It seems a cavalier manner of dismissing what appears to have been a serious shortcoming in the design strength of the bridge.

30

Samuel Brown: Pioneer Suspension Bridge

Builder

WELLINGTON BRIDGE OVER THE DEE AT ABERDEEN, 183O-I At the opening of the Wellington Bridge, or as it was called at the time the Craiglug Bridge, the Aberdeen Journal remarked: It is with great pleasure we have to announce the completion of this elegant structure. T h e iron and carpenter work was on Friday last taken off the hands of the Contractor, Captain Samuel Brown, R . N . , the Inventor and Patentee of the Suspension Bridge. T h i s erection, although comparatively of a small span, does infinite credit to that gentleman's genius and talents, not only in the light and elegant appearance of the design, b u t in the neat and substantial execution of the workmanship. T h e span, or distance between the piers is 215 feet, and the width of the carriageway is 15 feet, having a footpath on each side of 2^ feet broad. T h e platform is suspended from four main chains, having three bars in each, joined together by side plates and bolts at every ten feet. A suspension rod is attached to each joint for supporting the cast iron beams, to which planking forming the roadway is bolted. O n this a second tier of planks is spiked, on which is laid the composition of coal-pitch, broken stones, etc. (that invaluable discovery of Captain Brown's), which is not only impervious and impenetrable, b u t which deafens the sound arising from the tread of horses, which often times is dangerous and at all time a disagreeable accompaniment to wooden platforms. T h e r e is now a pontage of a halfpenny to every foot passenger levied at this bridge, but in consequence of the approaches not being completed, horses and carriages are yet prevented from passing. N u m b e r s of strangers and inhabitants of the town go daily to visit it, and are all unanimous in their opinion of the utility and beauty of the erection. T h e approaches were completed and the bridge opened to road traffic in the beginning of M a y 1831. Earlier, in M a r c h , the Trustees of the bridge named it in honour of the D u k e of Wellington. Work on the bridge was begun in August of 1829 by the local contractor, Robert M e a n s , builder. After only six weeks the foundations of the north towers were completed. T h e entire structure was finished, except for the approaches, in N o v e m b e r 1830. T h e deck was supported by cables on each side and these were composed of three flat eye bars, each 3 inches by i^ inches wrought iron. T h e eye bars were connected by four 6-inch by i^-inch links having two 2-inch diameter pins. T h e cables were supported by granite towers and had a sag of 18 feet. T h e original transverse deck beams of cast iron were replaced by steel joists and the wrought iron suspenders by i f - i n c h diameter steel rods. T h e deck was also renewed with a 3-inch pine floor and pine floor beams.

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T h e alterations cost £3,427 and reduced the dead load by about 100 tons. Even with this reduction in weight the live load was restricted to vehicles of 8 tons or less. The bridge is now the property of the City of Aberdeen. FOCHABERS BRIDGE OVER THE SPEY, 1831 This bridge, which was completed in 1831, had a main span of 360 feet. It was proposed by A. Mitchell to a design of Brown and with his approval. It was extant in the 1960s but details are lacking on the structure and its history. It is probably this structure which is also known as the Boat O' Brig. This appears to be a more correct designation since the bridge at Fochabers was never constructed on the suspension principle. The Boat O' Brig is the next bridge downstream on the Spey from Fochabers. FINDHORN BRIDGE, 1832 There is some confusion over Brown's next bridge. It was built in 1832 with a span of 254 feet, according to Cowe, and survived until 1883. In the literature a bridge at Forres over the Spey is also credited to Brown. However, Forres is not on the Spey and this bridge is certainly the same as the Findhorn Bridge. Drewry gives the following details of the bridge which was under construction when he wrote his book: This is a bridge now in course of erection, and nearly completed, under the direction of Captain S. Brown, R.N., over the River Findhorn, in the North of Scotland. T h e span is about 300 feet. T h e breadth of the platform is 23 feet: and the bridge is calculated to bear 250 tons in load, besides its own weight. T h e main chains will contain twelve lines of bars 9 feet 8 | long, out to out; 4 inches broad by i £ thick: 49^ square inches of iron in all, united by coupling plates i 8 | inches long, and bolt-pins i \ diameter. The coupling plates are 5 ! broad in the middle, and 7 ! broad across the ends, where the bolt-holes are drilled out, so as to allow 2f metal all round the holes. T h e ends of the main chains will be held by keys rounded on one side, 2 feet long, 3 inches broad, and 4 inches deep. The entire weight of ironwork suspended will be about 76 tons. 3 4 Regrettably, Drewry does not report the sag of the chains nor the exact span of the bridge from tower to tower so that it is impossible to evaluate the strength of the chains in terms of the total design load. NETHERBYRES BRIDGE, 1834 Netherbyres was a house purchased by Brown about 1824. In order to provide better access to his property Brown constructed

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Samuel Brown: Pioneer Suspension Bridge Builder

what was then called a 'bridge of tenacity'. One of the earliest proposals for this type of bridge was made by Stevenson and is shown in Fig. 2.5. T h e Netherbyres Bridge was removed in recent times leaving no trace except for the anchorages. KALEMOUTH BRIDGE, C. 1836 Apart from the Union Bridge this is probably Brown's only surviving structure in substantially original form. It was constructed over the Teviot near Eckford. Local records indicate that the bridge was erected a few years before 1836, by William Mather of Kalemouth. All other details of its history are lacking. A recent inspection of the bridge revealed that it is approximately 180 feet long, with a clear inside width of 15 feet. The deck is composed of 2^-inch timber flooring on longitudinal stringers 4 inches deep. It is stiffened somewhat by a pair of timber trusses on either side. The trusses are divided into panels approximately 5 feet long and 2 feet 6 inches deep with 4-by-4 inches square diagonal members and 5-by-5 inches verticals and chords. The suspenders pass through the verticals and are fastened to 16-inch deep longitudinal timbers. Pairs of if-inch diameter rods form the cables to which the i-inch diameter suspenders are attached. In the case of this bridge and unlike all his others. Brown attached the suspenders not only at the joints of the bars but also at the middle of each pair of bars. This method of construction induces bending in the bars and is a most unsatisfactory arrangement. With a suspender spacing of only 5 feet rather short bars would have been needed if Brown had not resorted to use of bars spanning two truss/suspender spaces. T h e chains pass over the stone towers and have a sag of about 13 feet 9 inches which gives a sag/span ratio of 1:13.1. T h e bridge still serves local traffic and has a 3-ton load limit. LAMBETH BRIDGE, 1836 For more than a decade from 1835 or 1836 until 1847 Brown was interested in erecting a major bridge across the Thames at Horse Ferry. However, nothing was constructed on the site until ten years after Brown's death when Peter Barlow erected what was to be called the Lambeth Bridge. NORHAM AND LEITH DOCKS, 1837 In 1837 Brown proposed a suspension bridge at Norham over the Tweed and he prepared a proposal for new docks at Leith. Neither project reached the construction stage. T h e Norham Bridge was approved but a cheaper wooden bridge was erected between 1838 and 1841.

Emory L. Kemp

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EARITH SUSPENSION BRIDGE, 1844 T h i s bridge was one of the last structures to be erected by Brown and it survived until the 1930s. It was constructed over the River Great Ouse. Details of its history and construction are confusing. T h e r e is some correspondence in the Huntingdonshire Records Office, dating from 1842-4 between the Clerk of the Peace, Brown and others regarding the proposed suspension bridge at Earith and there is also an official deed of agreement for the erection of such a bridge, dated 1843. However, the resulting bridge was a lenticular truss with an iron compression chord curved in elevation and a curved tension chord composed of eye-bar chains. T h i s type of structure was used by Brunei for his Saltash Bridge and by others. I t is a complicated arrangement and one which Brown would hardly have used on grounds of economy; equally, it would have involved design difficulties which he probably could not handle. Although information is lacking, therefore, it seems likely that Brown was asked to supply the iron work for someone else's design. T h i s bridge may well be one of the earliest examples of this special truss system and additional information on its history and construction would be welcome. Conclusions F r o m the information now available on Brown, what conclusions can be reached about his contribution to suspension bridge technology in its formative years ? Like Finley in America, Brown was the first in the field in Britain and his pioneering work on chains influenced, in a most striking way, all subsequent developments of this technology in Britain. H e firmly established the use of bar chains with link pins for suspension bridges which became the British standard for the entire period during which suspension bridges were built in Britain in the nineteenth century. Brown was unquestionably the most prolific suspension bridge builder Britain has ever seen. W i t h the completion of his Union Bridge in 1820 he ushered in a new era of long-span bridges which were a decided improvement on Finley's link chain system. His u n i q u e a p p l i c a t i o n of t h e s u s p e n s i o n p r i n c i p l e to p i e r s demonstrated not only the technique's versatility b u t also his own ability to adapt a known technology to solve novel engineering problems. W e do not know the circumstances of his first interest in suspension bridges, b u t here again we see him applying his ideas by experimental studies, such as his prototype bridge in 1813, and then using the results of his study to design important engineering structures. It appears that the completion of the Brighton Pier marked the zenith of Brown's career as an engineer. His U n i o n Bridge was still

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Samuel Brown : Pioneer Suspension Bridge Builder

the greatest in the land and indeed in the world in 1823. With the Brighton Pier he gained international technical as well as national popular recognition for the suspension principle and as a result for himself. The suspension bridge was no longer a parochial building form of the Tweed Valley but a new technology based on the efficient use of iron. Several years later Telford completed the Menai and Conway Bridges and Clark carried on the tradition with his bridges at Hammersmith, Marlow, Shoreham and his greatest work, the Budapest Bridge. Brown proposed a number of major bridges but he was unsuccessful in securing contracts for any of them. Meanwhile, the age of the craftsman-engineer was coming to an end and the dayspring of the heroic period of Victorian engineering was fast approaching. By the middle of the decade it was becoming common to apply the elegant theory of the catenary to suspension bridge design, especially to that of the major spans. Brown, without the benefit of any formal education in engineering or mathematics and very much the self-taught engineer, depending on the 'practical' approach to design, was not equipped to keep pace with these developments and become a more broadlybased civil engineer. He stuck to the suspension bridge of the type represented so well in the Union Bridge, and lost his leadership of the field. It was not only the matter of analysis but one of craftsmanship and approach to design which distinguished Brown's designs from those of Telford and others. His designs were decidedly lightweight compared to others and this probably reflects an attempt to achieve the greatest possible design economies. The result was the use of flat catenaries for his chains together with high stresses in the bars. In addition, in his designs and in his descriptions of the construction of his bridges one sees neither the same meticulous regard for details in the anchorages and tower foundations nor the proof testing of all the structural elements which insured the highest standards of workmanship and greatest safety in the bridges built by Telford, Clark and others responsible for major spans. Thus, it is not surprising that with low margins of safety several of his bridges (e.g. Brighton, Stockton and Montrose) failed. These failures together with those of other builders cast serious doubts on the safety and suitability of the suspension type of bridge. With engineering more and more concerned with railway construction the failure of the Stockton Bridge convinced many engineers that suspension bridges were not suitable for railways without their ever giving the matter a fair evaluation. Rather than face the problem of the strength and stiffness necessary to insure a satisfactory structure for railway traffic, engineers used other types of bridge structures.

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Brown continued to build numerous bridges for local needs until the 1840s. Many of these served long and well and were a sound investment for their backers. Just as his early development of the improved chain bridge resulted in a superior structure to the Finley type of bridge using link chains, so Brown's designs were overshadowed by the achievements of others. Nevertheless, he played a key role in the development of suspension bridges and should be considered the father of the eye-bar suspension bridge which became the 'British' type throughout the nineteenth century. I was fortunate to have been selected as a Fellow of the American Council of Learned Societies for the academic year 1975-6 which enabled me to study many aspects of nineteenth-century civil engineering. The work on Samuel Brown was just one part of this larger effort. I am also very much indebted to Mr Francis Cowe of Berwick-upon-Tweed and to Mr Gordon Miller of Kingston-upon-Thames for their help in supplying information on many of Brown's less well-known bridges. This information has added an important new dimension to the history of suspension bridges in Britain. A great deal of time was spent in the congenial atmosphere of the Library of the Institution of Civil Engineers. I am most grateful for the assistance of the staff in my study of early suspension bridges. Mr Alan Butcher has been most helpful in my study of bridges and I am indebted to him and the Science Museum for the illustrations used in the text. Notes 1. Needham, J., et al., Science and Civilization in China, Vol. 4, Cambridge Univ. Press, 1971. In this fascinating and voluminous account of Chinese science and technology, Needham records twenty-four iron suspension bridges constructed from A.D. 65 to A.D. 1706. Many of the features of modern suspension bridges had been developed by the fifteenth century. See also Kircher, Athanasius, China Monumentis . . . Amsterdam, 1667. Verantius, Faustus, Machinae Novae, 1617. Douglas, Sir Howard, Military Bridges, 3rd Ed., John Murray, London 1853. 2. Cumming, T. G., Description of the Iron Bridges of Suspension Now Erecting Over the Strait of Menai, at Bangor, and Over the River Conway ... John Taylor at the Architectural Library, London, 1824. Drewry, C. S., A memoir on Suspension Bridges, Longman et al., London, 1832. Stevenson, Robert, 'Description of Bridges of Suspension', Edinburgh Philosophical Journal, Vol. 5, No. 10, 1821, pp. 239-40. Smeaton, John, Reports of the Late John Smeaton, London, 1837. 3. Juan, George and DeUllos, Antonio, Voyage Historique de VAmerique Meridionale, Spanish 1748; transl. into English, London, 1758. An excellent description of the bridges built by the Incas. Robertson, William, The History of America, Vol. Ill, pp. 250-1,450n.; London, 1780. An account of the suspension bridges built by the Peruvians using natural plantfibresfor cords. The work features the Apurimac Bridge which was built on the main route to Cuzco. 4. Finley, James, 'A Description of the Patent Chain Bridge', The Port Folio, 3, No. 6 (1810), pp. 441-53. See also Pope, Thomas, A Treatise on Bridge Architecture, New York, 1811. 5. In the seventeenth century Hooke and later James Bernoulli published the solution of the catenary and in 1586 Simon Stevin published his work on loaded strings and established the basis of the funicular polygon. The terms 'catenary' and 'cable-stayed' are frequently used in the literature and require some explanation. Aflexiblecable of uniform weight supported at its end will assume an equilibrium curve called a catenary. A weightless cable supporting a level deck and live load

36 Samuel Brown: Pioneer Suspension Bridge Builder of uniform weight per horizontal distance will assume the shape of a parabola. The same weightless cable supporting a loaded deck at discrete suspender points will take the shape of a funicular polygon which will be sensibly the same as a parabola if the suspenders are closely spaced. Obviously, in practical cases the cable lies somewhere between the catenary and a funicular polygon if the weight of both the cable and deck are significant. This entire class of cable profiles is often referred to as a catenary. Cable-stayed bridges, on the other hand, employflexibletension members in a different manner. Each support point on the deck is carried directly to the tower by a straight tension rod or cable. Each cable is thus independent of the others except for its interaction through the deck structure. There are a number of possible cable configurations. Two of the most popular are the fan type with all of the cables passing over the tower top and the harp type with all of the cables parallel, which means they meet the tower at different levels. Cable-stayed bridges werefirstused in the Scottish border country in the second decade of the nineteenth century but were quickly superseded by the conventional catenary bridge. They had a brief revival by Motley, who constructed the Twerton Bridge at Bath on this principle and by Clive, who proposed a unique criss-cross cable-stayed bridge which was never built. The idea then lay dormant for more than a century until it appeared in modern garb after the Second World War,firstin Germany and then elsewhere. 6. Stevenson, 'Bridges of Suspension'. 7. Rennie, Sir John, 'Presidential Address', Institution of CivilEngineers Proceedings, Vol. 5, Session 20 January 1846, Suspension Bridges section p. 32. Bender, Charles, 'Historical Sketch of the Successive Improvements in Suspension Bridges to the Present Time', Transactions, American Society of Civil Engineers, Vol. 1, 1872. 8. de Mare, Eric, The Bridges of Britain, Batsford, London, 1954. In this reference the author quotes the builders, Messrs. Smith, on the construction and re-construction of this bridge. The Smiths' statement appeared in an obscure paper: Smith, John & Thomas, 'On Whinstone Constructions etc.', Transactions of the Institute of British Architects, Vol. 1. London, 1836, pp. 58-9. 9. Brown, Samuel, 'Construction of a Bridge by the Formation and Uniting of its Component Parts', British Patent No. 4137, 10 July 1817. 10. In connection with the successful completion of the Brighton Chain Pier, Brown was presented with an engraved silver vase, which Bishop describes as 'encircled by chain cables (resembling those invented and introduced in the Naval Service by Capt. Brown in 1810). The handles of the vase represented two improved anchors, adapted expressly for the use of the chain cables'. 11. Telford, Thomas, Report of the Select Committee . . . The Proposed Bridge at Runcorn, printed by J. and J. Haddock, Warrington, 8 April 1817. 12. See note 4. 13. Hopkins, H. J., A Span of Bridges, David & Charles, Newton Abbot, 1970. On page 186 Hopkins quotes the following, attributed to Peter Barlow: It seems to have been a complete surprise to Telford to find that anyone had approached the problem in the same way as himself and had studied it so deeply. He accordingly disclosed his own designs and calculations to Brown. Brown reciprocated and various modifications and improvements were worked out in a joint scheme which was unanimously accepted by the committee. 14. Tyrell, G. H. History of Bridge Engineering, published by the author, Chicago, 1911. Jakkula, A. A. A History of Suspension Bridges in Bibliographic Form, Texas, A. & M., College Station: Texas Engr. Exp. Station, Bulletin, 4th ser., Vol. 12, No. 7, July 1941. Rennie's address contains many errors on current bridge practices and it may be that this error originated with him. Brown, Samuel, 'Description of the Trinity Pier of Suspension at Newhaven near Edinburgh', Edinburgh Philosophical Journal, Vol. 6, No. 11, 1822. 15. Bender, 'Historical Sketch'. 16. Rendel, J. M. 'Memoir of the Montrose Suspension Bridge,' Proceedings, Institution of Civil Engineers, April 1841, pp. 122-9. 17. Stevenson, 'Bridges of Suspension'.

Emory L. Kemp 37 18. James, J. G., 'Ralph Dodd, the Very Ingenious Schemer', presented to the Newcomen Society on 14 January 1976, credits Ralph Dodd with originating the idea of a suspension pier. 19. See note 14. 20. Dredge, James, 'Construction of Suspension Chains for Bridges, Viaducts and Aqueducts, and Other Purposes, and Construction of such Bridges, Viaducts or Aqueducts. British Patent No. 7120, 17 June 1836. 21. Bishop, J. G. The Brighton Chain Pier . . . with a Biographical Notice of Sir Samuel Brown, published by Brighton Herald Office, Brighton, 1897. 22. Weale, John, The Theory, Practice and Architecture of Bridges of Stone Iron and Wire, John Weale, Arch., Lib., 1839-43, 4 Vol., London. 23. Chapman, William, Report on the Projected Patent Wrought Iron Suspension Bridge, across the River Tyne, Pub. Newcastle, 1825 (part of the Telford Bequest, Institution of Civil Engineers.) 24. Moncrieff, J. M., 'Discussion of the Menai Bridge', Proceedings of the Institution of Civil Engineers, Vol. CCXVII, 1923-4. 25. Eastern Daily Press, 23 June 1927. 26. Hodgkinson, E., 'On the Chain Bridge at Broughton', Memoirs of the Manchester Literary and Philosophical Society, Vol. 5, second series, 1831. On Hodgkinson himself see Warburton, P., 'Eaton Hodgkinson Mathematician and Engineer', Chartered Mechanical Engineer, Vol. 21, No. 9, Oct. 1974. 27. Gies, Joseph, Bridges and Men, Cassell, 1964. 28. Buchanan, George, Report on the Present State of the Wooden Bridge at Montrose, and the Practicability of Erecting a Suspended Bridge of Iron in its Stead, Montrose, 1824. 29. Brown, Samuel, A Bridge of Suspension over the River South Esk, the author, Brighton, 8 July 1823. 30. Pasley, C. W., 'On the State of the Suspension Bridge at Montrose, after the Hurricane of October, nth . . .', Proceedings, Institution of Civil Engineers, Vol. 1, 1839, pp. 32-3. 31. Body, Geoffrey, Clifton Suspension Bridge, Moonraker Press, Bradford-on-Avon, Wilts. 1976. 32. Evidence given in 1848 for: 'Report of the Commissioners Appointed to Inquire into the Application of Iron to Railway Structures'. Par. Paper, 1123, XXIX, 1849. 33. Drewry, Memoir on Suspension Bridges. 34. Ibid.

T h e B o o k

B a n u of

M u s a

a n d

I n g e n i o u s

t h e i r

D e v i c e s

D O N A L D R. H I L L T h e spread of Islam beyond the borders of Arabia began in A.D. 634 with the invasion of Spain and Iraq by large raiding parties. T h e success of these forces against the armies of the Byzantine and Persian empires was facilitated by the exhaustion of the two empires after a prolonged war between themselves and — in Syria, Egypt and Iraq — by the hostility of the indigenous populations to their imperial masters. Very soon the campaigns became wars for permanent conquest, fed partly by the desire for booty and partly by genuine religious fervour. By about A.D. 645 Syria, Egypt, Cyrenaica, Iraq and Mesopotamia had been effectively subjugated. Resistance was stiffer in the Iranian heartland and in the Berber country of north-west Africa b u t the first was conquered by about A.D. 656, the second by the end of the seventh century. T h e conquests were then extended into Spain and Central Asia, and by the middle of the eighth century the Arab empire had attained its greatest expansion, stretching from the A m u Darya river (Oxus) to the Pyrenees, and including the Mediterranean Islands of Cyprus and Sicily. At first the conquests were directed by the Caliphs from Medina, b u t in A.D. 660 the Umayyad dynasty assumed power and made their capital in Damascus. I n A.D. 750 the Umayyads were in t u r n overthrown by the Abbasids and the centre of gravity of the empire shifted to Iraq, where the second Abbasid Caliph, al-Man§Ur, built the splendid new city of Baghdad as a fitting capital for his empire. T h e Abbasids were only able to maintain the empire as a cohesive unit for about one h u n d r e d and fifty years, after which it split u p into a n u m b e r of separate states, some nominally owing allegiance to the Caliphs b u t all virtually independent. I n the second half of the ninth century the Caliphs themselves became the puppets of their T u r k i s h military commanders and never regained temporal power. I n the eleventh century Baghdad was incorporated in the Seljuk empire and was finally destroyed by the Mongols u n d e r H u l a g u i n A.D. 1258. I n the period from the early conquests to the end of the Umayyad dynasty the Arabs were concerned with conquest, with the pacification of the occupied lands, and with the setting u p of administrative, fiscal and legal systems. T h e Arab conquerors formed a ruling elite, in receipt of financial and other privileges that were denied the conquered population, even when these

40

The BanTL Musd and their 'Book of Ingenious Devices'

became Muslims, although in this case discrimination was contrary to the teachings of the Koran. Islam slowly became the faith of the majority and Arabic superseded the native languages everywhere, except in Spain and Iran, although even in those countries Arabic became the main vehicle for written communication and remained so for several centuries. T h e Arabs were never more than a small minority of the population of the empire and as they intermarried with women from the native populations the numbers of those who could claim pure Arab descent diminished, while the status of the indigenous peoples gradually improved. The Empire of the Arabs became the Worldof Islam. It was by no means a homogenous world: racial and linguistic differences remained, there were sizeable minorities of Christians, Jews and other religious groups, and the Muslims themselves were split by religious schisms, the deepest and most enduring of which was that between the orthodox Sunni believers and the Shia, followers of c All the son-in-law of the Prophet. Nevertheless, and despite the political break-up, Islam was a real entity, held together by the bonds of religion and language. We speak of Arabic science, engineering, medicine, philosophy and so on, because the books were written in Arabic and the beginnings of intellectual activity in Islam were due to the encouragement of Arab patrons. The scholars were of diverse origins, although in many cases their descendants would today be considered, and would consider themselves, Arabs. Arabs, Greeks, Persians, Jews and Sabeans from Mesopotamia, all made notable contributions to the origins and growth of Arabic science and technology, the foundations of which were laid in ninthcentury Baghdad during the Abbasid Caliphate. 1 T h e Caliph alMa'mun is generally regarded as the main founder of Arabic science, and there seems little doubt that without his encouragement the first steps would have been slower and less certain. Intensely interested in ancient learning and its 'verification', he founded an academy in Baghdad known as the House of Wisdom (bayt al-Jiikma),2 and supervised the collection of manuscripts from Byzantium, Iran and India, which were then translated into Arabic, usually with high competence, in the House of Wisdom. Most emphasis was placed upon Greek works, sometimes received in Syriac versions, and most of the major Greek writings on mathematics, astronomy, mechanics, medicine and philosophy passed into Arabic during the course of the ninth century. Some of these works are now preserved only in Arabic versions. There were also significant transmissions from Iran and India and the importation from India of 'Arabic' numerals, the concept of zero being of the greatest importance for the future of mathematics and science. T h e translators wrote commentaries and criticism of many classical works, such as Euclid's Elements, the

Donald R. Hill

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Conies of Apollonius and Ptolemy's Almagest. M a n y of t h e m were also scientists in their own right and composed original works of considerable value. By the end of the ninth century the great work of assimilation was complete, and learning had appeared in a new guise, in which Greek, Indian and Iranian elements were merged with Arabic additions to form a recognizably new science. I n the same period the language itself had been transformed into a subtle and flexible instrument for the expression of philosophical and scientific thought. For the ensuing five centuries Arabic science flourished and developed, albeit sporadically, throughout the Islamic world, from Andalusia to Central Asia. I n medieval Europe, notably in twelfth century Toledo, where there was a school of translators not unlike a l - M a ' m u n ' s House of Wisdom, many Arabic works were rendered into Latin and became a potent force in the cultural revival known as the Renaissance. Life a n d W o r k s o f t h e B a n u M u s a T h e Banu (sons of) M u s a were among the most important figures in the intellectual and political life of ninth century Baghdad and played a key role in the founding and development of Arabic science and technology. Fortunately we have a good deal of information about them in biographical and historical works, the most important of which are listed briefly below, with the abbreviations used in references given in parentheses after each source. (In other words each Arabic source is given a letter reference, e.g. F , Q, K , H , A and so on, and these are used in this paper in association with page n u m b e r s . T h u s H.264 signifies page 264 of Bar Hebraeus', History of the Dynasties.) Separate articles are devoted to the BanU M n s a in several works, of which the earliest is the Fihrist of I b n al-NadTm, 3 composed A.D. 988, p p . 378-9 (F). I b n al-Qiftl, 4 A.D. I 172-1248, p . 208 draws some of his material from I b n al-NadTm and some from unknown sources (Q). Additional information is given by I b n Khallikan, A.D. 1211-1282, p p . 161-3 in his Biographies of Illustrious Men (K),5 and by Bar Hebraeus, A.D. 1226-1289, History of the Dynasties,6 p p . 264-7 (H). A b u ' 1-Fid3', A.D. 1273-1331, Universal History, Vol. I, Bk. 2, p . 49 provides what is virtually a copy of I b n KhallikSn's article (A). 7 T h e r e are other works which do not contain separate entries on the BanU M u s a , b u t rather a n u m b e r of scattered references to their activities. Perhaps the most important of these is the great history of al-TabarT, A.D. 839-923, Series I I I ( T ) . 8 Al-TabarT was living in Baghdad while the brothers were active in the political and intellectual life of the city and his mentions of them, though brief, therefore have particular value. Of a similar nature are a n u m b e r of references in the first volume of the biographical dictionary of I b n Abi U§aybi c a, A.D. 1196-1270, 9 which are of

42

The Banu Musd and their 'Book of Ingenious Devices'

interest for the light they throw upon the relationships of the brothers with the Caliphs and with other scholars (U). Finally, there are a number of references to the brothers' astronomical studies in Ibn Ynnus, d. A.D. 1009 (Y), 10 and in the Chronology of al-BlrnnT, A.D. 937-c. 1050, (B). 11 T h e three brothers were called, in order of seniority, Muhammad, Ahmad and al-tlasan. We do not know their dates of birth but Muhammad died in January 873 (F.K.) and could hardly then have been less than seventy years old because the youngest brother al-Hasan was already a brilliant geometrician in the reign of al-Ma'mnn (813-33) (H.264). Their father, Mnsa bin Shskir, is usually described as al-Munajjim meaning either astronomer or astrologer, although in his youth he is said to have been a resourceful highwayman who made the roads in KhurUsUn unsafe (H.264). By all accounts, however, he became a noted astronomer and a close companion of al-Ma'mnn when the latter was residing at Marw in Khur£sUn before he became Caliph in 813. When Mnsa died he committed his sons to the care of al-Ma'mun who entrusted Ish^q b. Ibrahim al-Musa c bT with their guardianship. Ish^q sent them to the House of Wisdom where their tutor was YahyS" b. AbT Man§nr and they completed their education in that establishment. In general they were said to have been skilled in geometry, ingenious devices (J}iyal)> music and astronomy. According to Ibn al-NadTm and Ibn Khallikan their weakest subject was astronomy, but this seems to conflict with the opinions of Ibn Ynnus and al-BTrunl, both good judges, who spoke highly of the accuracy of the BanU Musa's astronomical observations. Muhammad, who was the most influential of the brothers, specialized in geometry and astronomy, and excelled Ahmad in all the sciences except in the construction of ingenious devices. AlIJasan was a brilliant geometrician with a retentive memory and great powers of deduction. A rival once tried to discredit him in front of al-Ma'mun by saying that al-Iiasan had read only six of the thirteen books of Euclid's Elements. Al-Hasan replied by saying that it was unnecessary for him to read the remainder because he could arrive at the answers to any of Euclid's problems by deduction. Al-Ma'mnn acknowledged al-Hasan's skill, but did not excuse him, saying 'laziness has prevented you from reading the whole of it — it is to geometry as the letters a, b, t, th 1 2 are to speech and writing.' (H.264). Al-IJasan is rarely mentioned by name elsewhere in the sources and may have preferred to devote his time to scholarship, whereas his brothers were involved in a variety of undertakings. At the time of their entry into the House of Wisdom the BantE Mnsa were poor and needy (H.264) but under the successors of alMa'mnn they became wealthy and influential. They devoted much of their wealth and energy to the quest for the works of ancient

Donald R. Hill

43

writers, and sent missions to Byzantium to seek out such material and bring it to Baghdad (F.Q.). Muhammad is said to have made a journey to Byzantium in person. T h e renowned translator Thubit b. Qurra accompanied Muhammad on his return to Baghdad and began his studies in Muhammad's house (F.380. U.215). T h e brothers used to pay about five hundred dinars a month to a group of translators who worked in the House of Wisdom (U.187). T h e most outstanding of these translators were Thabit b. Qurra and Hunayn b. Isfraq, both of whom were proficient in Greek, Syriac and Arabic. They rendered numerous works into Arabic and made important original contributions. 13 Muhammad was on friendly terms with these men, particularly with IJunayn, who translated and composed books at the request of his patron ( U . 1 0 2 , 1 9 3 , 1 9 9 , 205). Several of these works were on medical subjects, which indicates that the brothers' interests were not confined to the physical sciences. Indeed, ThEbit b. Qurra wrote a report on atmospheric phenomena that had been observed by himself and the BanU Musa (U.219). Apart from their role as scientists and patrons of scientists, the Banu Musa, particularly Muhammad, were employed by the Caliphs on various undertakings, and became involved in the turbulent political life of Baghdad. One of their earliest tasks, carried out on the orders of al-Ma'mun, was to check the circumference of the earth, given by the ancient writers as 24,000 miles. T o do this they went to the level desert of al-Sinjar in northern Iraq, accompanied by a group of observers. They set up a base point from which they measured the altitude of the Pole Star, and then walked due north in a straight line, using a rope for measuring and marking their route by pegs, until the altitude of the Pole Star had increased by one degree. They then repeated this procedure towards the south, after which they went to the locality of al-Kofa in southern Iraq and carried out similar measurements. T h e value they arrived at was 66f miles for one degree of latitude, giving the circumference of the earth as 24,000 miles. (K.A.) Muhammad and Ahmad later became concerned with public works. They were among a group of twenty men responsible for the construction of the new town of a JacfarT for the Caliph alMutawakkil (T.1438) and are mentioned as having directed the excavation of a canal between Ba§ra and Wa§it (T. 1747). In this field, as in others, they did not take kindly to competitors and are said to have plotted against anyone who rivalled them in knowledge (U.207). T h e y became enemies of the famous philosopher al-KindT (T.1502) and caused him to lose the favour of al-Mutawakkil who ordered him to be beaten and allowed the brothers to confiscate his library (U.207). According to the account of Ibn AbT Usaybi c a (207-208) the envious nature of the brothers almost led to their downfall. They had also alienated al-

44

The Banu Musd and their 'Book of Ingenious

Devices'

Mutawakkil from Sanad b . All, a good engineer and a friend of alKindT. W h e n al-Mutawakkil commissioned the brothers with the excavation of a canal known as al-Ja c fariyya, they subcontracted the work to A h m a d b . KathTr al-Fargh^nT 'whose knowledge was greater than his achievements, because he never completed a work'. Al-FarghunT made a serious error in his levelling, such that the canal would never have filled to the required depth. W h e n r u m o u r of this reached al-Mutawakkil he threatened to crucify M u h a m m a d and Atimad on the banks of the canal if the report proved to be true. I n desperation they turned to Sanad b . cAlT who would only give his assistance if they undertook to return alKindT's books to him. W h e n this had been done, Sanad said that he would tell the Caliph that no mistake had been m a d e ; because the Tigris was at its highest level the error would not be detectable for four m o n t h s , and the astrologers had predicted the death of alMutawakkil before this period had expired. Within two months t h e Caliph was assassinated and the conspirators escaped retribution. I n his last years M u h a m m a d was deeply involved with palace politics, in the period during which T u r k i s h commanders were assuming effective control of the state. After the death of alMunta§ir he successfully campaigned for the nomination of alM u s t a cTn in preference to A h m a d b . al-Mu c ta§im, because the latter was a friend of al-KindT (T.1502). W h e n Baghdad was besieged by the army of the Caliph's brother Abu Ahmad, M u h a m m a d was sent by al-Musta c Tn's commander c Abd Allah b . T ^ h i r to estimate the strength of the enemy forces ( T . 1557-8). H e was at al-Musta c Tn's side when the Caliph addressed the rebellious populace (T.1634) and he was one of a delegation sent by I b n T ^ h i r to Abu A h m a d ' s army to ascertain the terms for alMusta c Tn's abdication. (T.1641). T h e s e reports are interesting for the information they give us about M u h a m m a d ' s standing in the courtly circles, b u t his political activities were not of the first importance since it was of little m o m e n t who occupied the Caliphal throne when real power lay elsewhere. T h e role of the BanU M u s a in fostering the work of translators and scientists can hardly be overestimated, b u t their own scientific achievements were far from negligible. Al-BTrunT mentions their calculations for the length of the solar year (B.61) and I b n Y u n u s tells us that he made use of their astronomical observational records, which were numerous and accurate (Y.42, 62, 98, 132, 133, 142, 146, 148). A list of their works is given by I b n al-NadTm and I b n al-QiftT, as follows : 14 1. Book on the steelyard (qarasfun). (F.Q.) 2. Book of Ingenious Devices (hiyal) — by Ahmad. (F.Q.) 3. Book on the long, curved figure (i.e. the ellipse) — by alliasan. (F.Q.)

Donald R. Hill

45

4. Book of the first movement of the sphere (spheres in Q) — by M u h a m m a d . (F.) 5. Book on conic sections — by M u h a m m a d . (F.Q.) 6. Book of the T h r e e [?] — by M u h a m m a d . (F) 7. Book of the geometrical shape, as demonstrated by Galen — by M u h a m m a d . 1 5 (F.Q.) 8. Book of the Parts (proportions?) — by M u h a m m a d . (F.Q.) 9. Book in which it is demonstrated by didactic means and by geometrical method that there is no ninth sphere outside the sphere of the fixed stars — by Atimad. (F) I n Q this reads: denial of a ninth sphere — by A ^ m a d . 10. Book on the beginning of the world — by Atimad. (F) I n Q this reads: on the first of causes. 11. Book on the question p u t to Sanad by c All by Atimad b . M u s a . (F.Q.) 12. Book on the nature of speech (Kalam) — by M u h a m m a d . (F) 13. Book on the questions discussed between Sanad b . \Ah and Atimad b . M u s a . (F) 14. Book on the measurement of the sphere, division of an angle into three equal parts, and calculation of the mean proportional between two quantities. (F.Q.) 15. Astronomical tables — as mentioned by a l - B l r u n l and I b n Yunus. 16. T w o works on time, edited by T h a b i t b . Qurra. (Q.117) 17. A work on war engines (Hajji Khalifa I, 394). 18. O n the sphere. (Hauser 10. Without exact references.) 19. O n the construction of astrolabes. (Hauser 10. Without exact references.) 20. Description of a musical automaton, (E. Wiedemann. Amari Festschrift (1909) 169-80. Wiedemann made his translation from a text published by Professor Cheikho in Bayrut, b u t gives no details.) T h e most important of these works apart from the Book of Ingenious Devices was known in the medieval west as On the Measurement of Plane and Spherical Figures, in a Latin translation by Gerard of Cremona, Liber triumfratrem etc. T h i s was probably N o . 14 above —- see Suter 2 1 . T h e Latin text was published by M . Curtze (Nova Acta der KaiserL Leop. Carol Deutschen Akad. der Naturf., 49, N r . 2, 1883) T h e B o o k o f I n g e n i o u s D e v i c e s (Kiffib al-Hiyal) T h i s work enjoyed a great reputation in medieval Islam. T h e earliest reference we have is the Fihrist 'Book of Ingenious Devices (hiyal) by the BanU M u s a b . Shskir the astronomer, and it contains a n u m b e r of movements'. (F.397.) I b n al-QiftT says that 'their

46

The BanU Musa and their 'Book of Ingenious Devices'

book on fyiyal is marvellous and famous' (Q.208). Bar Hebraeus is the first to mention Afcmad as having been concerned largely with this subject: he says. 'Atimad was lower than him [i.e. Muhammad] in all the sciences except in the construction of friyal, in which things were revealed to him such as had been revealed to no-one [else]' (H.264). Ibn KhallikSn, having mentioned at the beginning of his article that the BanU Musa were famous for their book on hiyaU says later 'their book on fyyal is wonderful and rare, and includes every strangeness. I have studied it and found it the best and most delightful of books. It is one volume.' (K.161-2.) Ibn KhaldUn (A.D. 1332-82) writes 'there exists a book on mechanics that mentions every astonishing remarkable and nice mechanical contrivance. It is often difficult to understand, because the geometrical proofs occurring in it are difficult. People have copies of it. They ascribe it to the Banu Shakir.' 16 T h e only comment we have by a technical man is that of al-Jazan, 17 in the introduction to that section of his book (composed 1206) that deals with fountains. He says 'I did not follow the system of the BanU Musa, may God have mercy upon them, who in earlier times distinguished themselves in the matters covered by these subjects.' He goes on to make his criticism of the BanU Musa's fountains, which he considered to be unreliable; in particular he thought that the intervals between the changes of shape of the fountains were too brief. The only modern studies of major importance on the Book of Ingenious Devices are the papers published by E. Wiedemann and F. Hauser in the early years of the present century. Their joint paper deals with the large drink dispensers (Models 75-87), 1 8 and provides descriptions of the operation of the devices together with modified copies of the original illustrations with Roman lettering. Hauser's much longer work covers the remaining devices, and was based upon a translation and information on sources supplied by Wiedemann. 19 These papers are of considerable merit and allow anyone with technical training and a working knowledge of German to obtain a good understanding of the operation of all the devices. Hauser's work contains a great deal of information on the sources, on the life and works of the BanU Musa, a survey of similar works by Greek and Arab writers, a full description of the manuscripts, and transliterated Arabic equivalents of technical terms. Much of the credit for this presentation must be given to Wiedemann. Thereafter the treatment is much the same as in the joint paper — descriptions of the devices, modified copies of the illustrations, explanatory notes and drawings. In general the work of Wiedemann and Hauser achieves the purpose for which it was presumably intended: that of informing an audience of historians of science, and engineers interested in the history of their profession. Even in this context the information

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they provide on source material is inadequate, since proper references, including the edition and date, are never given. For a wider public Hauser's explanations of the principles — hydrostatic, aerostatic or mechanical — that are embodied in the devices are seldom adequate for a layman. Finally it must be said that there is no real substitute for a proper translation, (which Hauser considered unnecessary — p. 28) with faithful photographic reproduction of the original illustrations. Only when this is available can readers make their own estimate of the value of the BanU Musa's contribution to the history of technology. In view of the interest shown in the work in the Islamic world from the tenth to the seventeenth century it is somewhat surprising that we know at present of only three almost complete manuscripts and two fragments, compared for instance, with some fifteen copies of al-JazarT's masterpiece. The fragments are in Leyden (catalogue Vol. 3, N o . 1019 169 Gol) and N e w York (Spencer Collection, Risala'i Hakim Muhammad Yasin). One of the almost complete manuscripts is in the Vatican (No. 317) and another is in two parts, one in Gotha (Catalogue van Pertsch, Arab 1349) the other in Berlin (Catalogue Ahlwardt 5562). Fortunately the three manuscripts together permit full retrieval of text and illustrations of the one hundred devices called models (shakl) by the BanU Musa. T h e best manuscript is Topkapi Saray A. 3474. This contains only seventy-seven models; in particular the fountains and lamps are omitted. T h e text is accurate and the drawings are well executed with reference letters correctly positioned and corresponding to the references in the text.* T h e Vatican text is complete up to and including Model 90, although some of the leaves are out of sequence. Model 91 is missing completely, as is the beginning of Model 92. T h e text ends with Model 93 (no illustration), with the words 'the work is complete'. T h e Gotha/Berlin manuscript has more lacunae than the Vatican — in particular Models 11-18, inclusive, are missing — but Models 91-100 are complete. Both manuscripts begin with the words 'this is the Book of IngeniousDevicesby the BanU Musa'. In the Vatican text, however, there occurs the sentence, before Model 24, 'this is the second book of the work by Abu'l-IJasan Ahmad b. Musa', with similar remarks for the third and fourth books before Models 43 and 66 respectively. This therefore lends weight to the statements in our sources to the effect that A^mad was the principal author of this work. T h e first model is missing from the Topkapi M S . At the top of Folio 1 R are the words 'Book of *I am grateful to Dr. David King (see Note 41) for calling my attention to this manuscript. Unfortunately a microfilm of the MS did not come into my hands until this paper was about to go to press and I was not therefore able to use it. The loss is not great because, of thefivemodels I have described in detail, three are not included in A. 3474. The other two — Models 42 and 77 — can be adequately understood from the Vatican MS. I shall, however, be using A. 3474 as the principal basis of my forthcoming book.

48

The Banu Musd and their 'Book of Ingenious Devices'

Ingenious Devices and wonderful matters concerning water machines'. It seems likely that the original work contained one hundred devices, the same number that can be retrieved from the manuscripts, but one of the Models, N o . 94, is not by the Bann Musa, since its description includes remarks such as cas the Bann MOsa did'. Without further evidence, however, it must be assumed that the other ninety-nine models were from the hand of the brothers. All the manuscripts are written in legible naskhi (the most widely used type of Arabic script). In many cases the same errors occur in the Gotha/Berlin and in the Vatican M S S , and it is probable that both were copied from the same exemplar. There are far fewer errors in the Topkapi M S . Almost all the illustrations are sectionalized elevations, one to each model, no additional detailed drawings being provided. Once the conventions have been understood the drawings are quite easy to read. They are marked with letters of the Arabic alphabet, to which reference is made in the text, although in the Gotha/Berlin M S the letters are missing from the drawings. In the Topkapi M S the letters are accurately placed and correlate with those given in the text, which are themselves consistent throughout. In the other two M S S the lettering in both text and drawings is haphazard and inconsistent. All the descriptions are fairly brief: first a description of the purpose and operation of the device is given; then, with the words 'this is its example' (mithal), attention is drawn to the illustration and the construction is briefly described; finally a more detailed description of the operation is given — often it is only by reading this final section that the foregoing paragraphs can be fully understood. In many cases the chapter terminates with advice about the use of the device, for instance 'this device is suitable for use in baths, or places where taps are installed'. T h e most serious weakness in the work is the absence of any proper instructions for the manufacture of the devices. Dimensions are rarely given, materials of construction are mentioned in only one or two instances, assembly sequences, fittings and jointing are never mentioned, apart from general statements such as 'part A is soldered to part B'. The supports for tanks, installed inside vessels, are not shown — presumably the tanks rested on cross-pieces. This vagueness, which is in marked contrast to the meticulous instructions given by al-JazarT, not only detracts from the value of the work as an historical document, but also at times makes understanding difficult. This is particularly so in cases where results depended upon the achievement of a delicate balance of pressures, when the dimensions and positioning of the various components were critical. It is very probable, therefore, that the BanU Mnsa were not themselves skilled in metalwork, but that their devices were made

Donald R. Hill

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by craftsmen under their guidance, no doubt with the feedback of advice from the craftsmen if they considered a design to be impracticable. It could even be argued that the devices are merely abstract illustrations of the principles of machanics, but this is going too far. Most of the devices would certainly work and, in any case, the Caliphs and their circle would not have been content with unrealized paper concepts. Some of the models, however, are merely variant versions of others, with small additions and alterations, and it is possible that these were not made, but were suggested as refinements. T h e BanU Musa's approach was empirical and demonstrates a sophisticated use of hydrostatics, aerostatics and mechanics, without a matching explanation of the correct physical and mathematical uses of the phenomena, many of which had yet to be explained. There is nothing new about this, since man has frequently made effective use of natural phenomena before their causes had been identified. Many of the devices are intended to mystify the onlookers, and hence it was necessary to conceal from them the means by which the effects were produced. For instance, when two liquids were to be poured into a vessel, the first was poured in forcefully, the second gently; if it was desired to prevent a liquid discharging when a pitcher was tilted the operator had to cover a concealed airhole with his finger or with a piece of wax. T h e operator is usually referred to as 'he who understands how the device works' in contrast to 'those who are ignorant of how it works'. In the ensuing descriptions the former is designated 'the Adept', for the sake of brevity. Eighty-five of the one hundred devices can be classified as trick vessels, which produce a variety of effects, and embody a seemingly bewildering array of flow systems and assemblies. It would be impossible to give an adequate impression of the flavour of the book, and of the methods, simply by describing a number of selected examples, unless so many were chosen as to render this article overly long. It is felt, therefore, that the following method will provide a suitable substitute for fully representative sampling: first a full list of the models is given with brief descriptions of their functioning. Then descriptions of the ten most commonly used motifs are provided, with illustrations — close inspection of the work reveals that most of the devices use varied combinations of these motifs, with the addition of individual motifs and components, to produce the desired effects. An understanding of these concepts therefore permits rapid comprehension of most of the models. Finally, five representative models are described in detail, with illustrations, in one case with a full translation. In this way it is hoped to convey an appreciation of the BanU Musa's work — its value, merits and weaknesses.

50

The BanTt Musa and their 'Book of Ingenious Devices9

List o f M o d e l s T h o s e marked with an asterisk are described in detail later. Unless otherwise stated outlets are near the bottoms of the vessels. i. A beaker (ka's): demonstrating the action of a concentric siphon. 2. A pitcher (ibriq) with a spout: once interrupted, outpouring cannot be resumed. 3. A pitcher (ibriq) with a spout: once interrupted, inpouring cannot be resumed. 4. A jar (jarra) with open outlet p i p e : no water discharges while inpouring is in progress; discharge occurs whenever inpouring is stopped. 5. T w o basins (jam): by one is the figure of a small wild animal, by the other the figure of a lion. W h e n water is poured into the small animal's basin he drinks n o t h i n g ; when the lion's basin is filled both he and the other animal drink. 6. A basin (ijjana): the figure of a bull is placed by the basin with his muzzle in the water it contains and one then hears a sound, simulating the sound of a thirsty bull. 7. A trough (bawd) into which about 2 litres of water are poured. W h e n twenty or more small animals drink from it the water-level is not lowered, b u t when a bull drinks all the water disappears. 8. A pitcher (ibriq). Action as Model 3. 9. A pitcher (ibriq). Action as Models 3 and 8, except that a single interruption is possible. 10. A pitcher (ibriq). Action as Models 3 and 8. 11. A pitcher (ibriq). Action as Model 9. 12. A pitcher (ibriq) with a spout. W h e n the steward tilts it over a person's hands he can allow water to discharge, or prevent it from discharging. 13. A pitcher (ibriq) with a spout: hot and cold water are poured in, and do not mix inside the pitcher. According to the pourer's wish, hot, cold or mixed water can be discharged. 14. A pitcher (ibriq): by pouring in one or two ounces of wine the Adept can deceive his audience that the pitcher is full; he can also fill it completely and make them believe it to be e m p t y ; he can dispense from it as m u c h or as little as he desires. 15. A drinking vessel (kuz ibriq). Action as Model 14. 16. A jar (jarra) with two open outlet pipes, one above the other. One liquid issues from an outlet during inpouring, the second liquid issues from the second outlet when inpouring is stopped. 17. A boiler (milyUr) with an outlet t a p : hot water issues from the tap only so long as cold water is poured into the top of the boiler.

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18. A boiler (milyUr) similar to Model 17, except that it can be filled while the tap is open. 19. A jar (jarra) having a tap with three borings in its plug. Different measured quantities of three different liquids are poured in to the jar, and each can be extracted separately from the tap. 20. A fountain (fawwara) with variable discharge. 21. A jar (jarra). Action as Model 19, except that the liquid quantities are not measured. 22. A jar (jarra) with a tap. When the tap is opened it always discharges a known quantity. 23. A jar (jarra). Action as in Model 22. 24. A beaker (qadalj). T h e adept can deceive the audience into thinking it is full by pouring in one or two ounces of wine. 25. A jar (jarra) with a tap; two liquids are poured in but only the second can be drawn from the tap. 26. A beaker (qadaij). Action as in Model 14. 27. A jar (kuz) with an outlet pipe: during inpouring of a liquid, the pourer can, according to choice, allow the liquid to discharge, or prevent its discharging. 28. A jar (kuz, later jarra) with two outlet pipes, one above the other; during inpouring of a liquid, the pourer can allow discharge from either or neither of the outlets. 29. A whistle (sahlfcira): the whistle is at the top of a spherical vessel in whose underside is a perforated plate. When the vessel is plunged into water the whistle sounds. 30. A pipette (also safyfyara): upon lifting from the water, the water in the pipette may or may not be released, depending upon how it was immersed in the first place. 31. A flask (qinriina). Action as in Model 14. 32. A flask (qinriina) with two inlets (say A and B): wine is poured into A, water into B; when the flask is inverted water discharges from A, wine from B. 33. A jar (jarra) with an outlet pipe, from which the contents flow in equal measured quantities, with a distinct pause between each discharge. 34. A flask (qinnina) from which pure water, pure wine, or a mixture of both may be poured. 35. A flask (qinnina) from which only a known quantity of wine can be poured each time it is tilted. 36. A flask (qinnina) from which, at each outpouring, a known quantity, more than that quantity, of nothing, may be obtained. 37. A flask (qinnina) with an open top, from which alternate known quantities of wine and water can be poured. 38. A jar (jarra) with two diametrically opposed taps: liquid will only discharge from the tap that is opened first. 39. A jar (jarra) with a tap: it is first filled with wine, but water

52

The BariU Mtisa and their 'Book of Ingenious Devices'

discharges, not wine, as long as the water is poured into the top of the jar. 40. A jar (jarra). Action as in Model 39. 41. A jar (jarra) with an outlet pipe, from which wine discharges when inpouring of wine is stopped; when water is then poured in continuously, it discharges in place of the wine. 42. A jar (jarra) with three outlet pipes, one above the other: while wine is poured in nothing discharges, when inpouring is stopped wine begins discharging from the middle outlet. When water is poured in, it discharges from the middle outlet, wine from the other two; when inpouring of water is stopped, discharge of water ceases and wine again flows from the middle outlet — and so on. 43. A jar (jarra), with a tap, into which three different liquids can be poured, without mixing. When the tap is opened the liquids discharge in the sequence in which they were poured in. 44. A jar (jarra), its action similar to Model 43, but with an open outlet, which begins the sequential discharge after inpouring of the third liquid is complete. 45. A jar (jarra). Action as in Model 43, except that there is a pause between the discharge of the liquids. 46. A vessel (inay) or a jar (jarra). Action as in Model 43. 47. A jar (jarra), with an outlet pipe; as the liquid is poured in, it can be allowed to discharge, or prevented from discharging, as desired. 48. A jar (jarra) with two outlet pipes one above the other; according to the method of inpouring, the liquid can be made to discharge from one or other of the outlets. 49. A jar (jarra) with a tap: water and wine are poured into the same inlet. When the tap is opened a known quantity of water discharges, then the same quantity of wine, again the same quantity of water, and again the same quantity of wine. 50. A jar (jarra). Action similar to Model 49, except that it has an open outlet pipe. 51. A jar (kuz). Action as in Model 47. 52. A jar (kuz) with open outlet pipe: when water is poured in, wine previously poured in can be allowed to discharge or not, as desired. 53. A jar (kuz). Action as in Model 47. 54. A jar (jarra) with open outlet pipe: nothing discharges from it when a known quantity of wine is poured into it from a measuring vessel; when water is poured in a quantity of water, equal to the measured quantity of wine, discharges. 55. A jar (jarra), its construction similar to Model 54: wine, water, or wine mixed with water discharges when water is poured in. 56. A jar (jarra) with two outlet pipes one above the other:

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when inpouring of wine and water is stopped the liquids issue in known quantities, switching outlets after each discharge, until the jar is empty. 57. A jar (jarra) with two outlet pipes, which can be made to discharge alternately. 58. A jar (jarra) for wine and water with two diametrically opposed outlet pipes: when inpouring is completed the liquid that was poured in last begins to discharge from one of the outlets, and when this discharge is stopped the other liquid discharges from the other outlet, and so on. 59. A jar (jarra). Action as in Model 58. 60. A jar (jarra) with an outlet pipe: after wine has been poured in, wine, water, or a mixture of both can be drawn off. T h e result depends upon the rapidity of the inpouring of the water. 61. A jar (jarra) with an outlet pipe from which water and wine discharge alternately, as long as water is poured in continuously after the wine has been poured in. 62. A jar (jarra) with an outlet pipe from which, after wine has been inpoured, wine discharges as long as water is poured in, then water discharges as long as wine is poured in. 63. A jar (jarra). Action similar to Model 62, except that four liquids are used. 64. A jar (jarra) with two outlet pipes. Water and wine are first poured in separately before the jar is set before the audience. Then a mixture of wine and water is poured in and wine discharges from one outlet, water from the other. T h e audience is led to believe that the two liquids have separated inside the jar. 65. A jar (jarra). Construction and action similar to Model 64, but in this case the jar can be shaken without anyone detecting that it already contains wine and water. 66. A jar (jarra) with two diametrically opposed taps (say A and B). When both taps are opened wine discharges from A and water from B. When A is closed water ceases discharging from B and wine discharges in its place; when A is again opened, the situation reverts to the original one. 67. A jar (jarra). Action as in Model 66. 68. A jar (jarra). Action similar to Model 66. But the wine and water must be poured in in measured quantities. 69. A jar (jarra). Action as in Model 68. 70. A jar (jarra). Action similar to Model 58 but having a single outlet instead of two. T h e action is controlled by the operator. 71. A jar (jarra) with two outlet pipes, one above the other, and with two holes in the handle. It is filled with wine and water. When both holes in the handle are open, a mixture of wine and water discharges from both outlets; when one of the holes is closed wine discharges from one outlet, water from the other; if this hole is opened and the other closed the wine and water switch outlets.

54

The Banu Musa and their 'Book of Ingenious Devices'

72. A jar (jarra) with two diametrically opposed outlet pipes. Wine and water are poured into the jar. When inpouring is stopped wine discharges from one outlet, water from the other. As long as the hole in the handle is kept closed, the wine and the water switch outlets continuously. 73. A jar (jarra) with a tap. Either wine or water will discharge, depending upon whether a concealed hole in the handle is open or closed. 74. A jar (jarra) with two diametrically opposed pipes. When water is poured in, it discharges from one of the outlets; when an oil is poured in it discharges from the other. 75. A trough (ijjana) that always replenishes itself when men draw water from it or when animals drink from it. 76. A basin (jam) set beside a container. Wine is poured into the container and when inpouring is stopped, wine flows into the basin until it is full. When a quantity of wine is withdrawn, a like quantity flows into the basin. T h e same design can be used with water for a drinking trough for animals, or with oil for a selffeeding lamp. 77. A basin (jUm) or a trough (ijjana) beside a closed reservoir. When moderate quantities of liquid are taken from the basin, a like quantity runs into it from a pipe at the bottom of the reservoir; if, however, a large quantity is taken no replenishment occurs. 78. A basin (jUrri) or a trough (ijjana). Action similar to Model 76, except that the replenishment is from a pipe at the top of the reservoir. 79. A basin (jUm) or a trough (ijjana). Action similar to Model 77 but replenishment is from a pipe at the top of the reservoir. 80. A basin (jUm) or a trough (ijjUnd)> by a reservoir. Wine, water or a mixture of both may be made to discharge from the reservoir into the basin. 81. T w o basins (jam). A double version of Model 77. 82. T w o basins (jUm). Action similar to Model 81. 83. A basin (jUm) or a trough (ijjana) set beside a reservoir. A pipe discharges from the reservoir into the basin. If liquid is taken from the basin until it empties, the downpipe automatically refills it. 84. A basin (jUm) or trough (ijjana). Action as in Model 83. 85. T w o basins (jUrn) set on either side of a reservoir. From the upper part of the reservoir discharge pipes are directed into each of the basins. If wine (say) is poured into one basin the downpipe discharge wine into this basin, while water discharges into the other; and vice versa. 86. A trough (ijjana) or a basin (jam) set beside a reservoir, from the upper part of which a downpipe is directed into the trough. When a liquid is poured into the top of the reservoir it discharges into the trough. When inpouring is stopped discharge ceases; discharge resumes when inpouring is resumed.

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87. Another design to produce the action of Model 86. 88. A fountain {jawwHra — the same term is used for all the fountains). T h e water issues from the fountainhead in the shape of a shield, or like a lily-of-the-valley. T h a t is to say, the shapes are discharged alternately — either a sheet of water concave downwards, or a spray. 89. A fountain that discharges a shield or a single jet. 90. Fountain operated by wind or water, it discharges a single jet or a lily-of-the-valley. 9 1 . Fountain in which the action of Model 89 is doubled, i.e. there are two fountainheads one discharging a single jet the other a shield; they alternate repeatedly. 92. Fountain incorporating a worm-and-pinion gear. Action as in Model 90. 93. Fountain with one main fountainhead and two or more subsidiary ones. W h e n the main fountainhead ejects a shield the subsidiaries eject single jets, and when the main fountainhead ejects a single jet the subsidiaries eject shields. 94. Fountain with two fountainheads. Action is double that of Model 90. 95. L a m p (sifUj) with automatic feed. 96. L a m p with automatically extruding wick. 97. L a m p combining actions of Models 95 and 96. 98. L a m p with self-positioning windshield. 99. Bellows for removing foul air from wells. 100. G r a b for extracting objects from underwater. Motifs T h e motifs described below are those most commonly used to obtain t h e desired effects. Usually two or m o r e of these components are used in combination. 1. T h i s is a concentric siphon; pipe (a-cc) was probably joined to pipe (bd) by copper wires soldered to each pipe. Pipe (bd) passes through the floor of container (f), the joint being airtight. W h e n liquid is poured into the container it rises to point (b), the discharge of the first drop of water reduces the air pressure in space (ab) sufficiently to cause a continuous flow through pipe (bd) until the liquid level reaches (cc). T h i s siphon is very similar to those used in lavatory cisterns, except that in the latter case the partial vacuum is caused by the sudden raising of the bell covering the downpipe. T h e writer tested this device using plastic pipes of 9 m m . and 30 m m . internal diameter. It operated immediately, with rapid discharge; variations in distance (ab) had no noticeable effect on its operation. I n Arabic this siphon is called ka's al-cadl which can be translated approximately as the Cup of Equivalence. T h e

©

"nil

cUMc

tU, ..,„,, „ ^h

ft 2a

k

lb

f

a

[c

1

4^

d

t

6/7/8

Figure i. Motifs.

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c

word adl contains the concepts of equality, balance and justice and the expression therefore implies that the purpose of the siphon is to produce a balance of pressures. This idea is more readily explicable when considering the double concentric siphon (see Motif N o . 2). T h e ordinary bent tube siphon is used by the BanU Musa, but the concentric siphon is much commoner. 2. T h e double concentric siphon: used to prevent a liquid being poured into a container after the first pouring is stopped (Fig. 2a shows the conventional representation used in the M S S ) . T h e neck of vessel (1) is closed at its top and its root by plates (kk) and (mm). Joints between plates and neck, between plate (mm) and pipe (bd), and between plate (kk) and pipe (gh) are airtight. Vessel (1) is open to atmosphere. Liquid is poured in through pipe (gh), which must not be wide enough to allow air to enter. T h e liquid rises to point (b) (the air emerging through route (bde) into the vessel), pressure in space (ab) is lowered and the liquid flows through route (bde) since the liquid head (b-ee) is sufficient to maintain the flow. When pouring is stopped the liquid level in the neck falls and a liquid/air pressure balance is established; a second pouring is impossible because the end of pipe (bel) is closed, and the head in pipe (gh) is insufficient to break the air-lock in the neck of the vessel. 3. This is a device to permit two different liquids (usually wine and water) to be poured into the same vessel without mixing. T h e neck of the vessel is covered by a sieve-like plate (hh) beneath which is a soldered funnel (ab), whose end (b) is bent to the horizontal. Below (b) tanks (c) and (d) are installed; they have a common dividing wall (ee) and open tops. Pipes (f) and (g) are drawn simply to indicate that the tanks have outlets, probably valved, into the next part of the system. Wine (say) is poured into the top of the vessel 'copiously and forcefully 5 , and runs into tank (c). Water is then poured in 'gently, drop by drop' and runs into tank (d). T h e device is drawn as it is invariably shown in the manuscripts, and Hauser frequently says that (b) is too far to the left. This is probably not the case, since it would have been possible to pour in the second liquid slowly enough for it to be held by surface tension to the underside of the funnel and deposited into tank (d); only the last few drops would fall into tank (c). If, however, point (b) were to the right of plate (ee), then after pouring of the first liquid ceased, a large fraction of the contents of the funnel would fall into tank (d). 4. T h e assembly shown here demonstrates a method of opening a valve which is directly below the receiving vessel. Float (a) is in tank (k), into which the liquid is flowing. Rods (bd) and (cd) are soldered to the top of the float, and bent round the outside of tank

58

The BariU Musd and their 'Book of Ingenious Devices'

(k) as shown, and joined at point (d). A short valve rod connects the plug (e) of the valve to point (d). As the float rises valve (e) lifts from its seat (f). In the case shown here this would permit air to enter the sealed tank (g) and liquid could discharge from the narrow outlet (h). 5. This assembly has the same purpose as device N o . 2. Liquid is poured in at (a) and flows through the open valve seat (b) into the small tank (d) from which it overflows into the large tank (g). Tank (d) is soldered to the top of float (f). T h e valve rod carrying plug (c) is soldered to the top of the float and passes through tank (d). Tank (d) has a small hole (e) in the bottom of one of its sides. As long as tank (d) is full its weight prevents the float (f) from rising, but when pouring is stopped tank (d) empties through hole (e), the float then rises and closes the valve so that pouring cannot be resumed. This assembly is often used in conjunction with Motif N o . 4, so that when the float rises it also actuates a valve below tank (g). 6. 7. 8. The illustration combines three motifs. 6. T h e vessel is provided with a perforated cover (a) and the root of its neck is closed by a plate (gg). and a wide pipe (fb) closed at end (b) is soldered to the centre of the plate. All the joints are airtight. A narrow pipe (cd) runs vertically up pipe (fb); the top of it is bent and protrudes from pipe (fb) near its top — the joint between the two pipes is airtight. When liquid is poured in at (a) it flows along route (afcd) into the vessel and because end (c) of pipe (cd) is then blocked no air can enter the vessel from its top. 7. T h e vessel has a spout (k) to the root of which a concentric siphon (m) is fitted, its narrow pipe penetrating the wall of the vessel. This is to prevent air entering the vessel when liquid is poured out. 8. It also has a hollow handle that opens into it at (1) and in the handle is a small concealed hole at (h). If the server secretly covers hole (h) with his finger when making the motion of pouring there will be no discharge because no air can enter the vessel. (In fact one drop will come out, sufficient to lower the air pressure in the vessel slightly below atmospheric.) 9. A vessel is divided by a plate (kl) to which is fitted the seat (n) of a conical valve, the plug (m) which is soldered to the end of a rod (mhdc). T h e horizontal section of the rod turns about on an axle (de) which is supported by a vertical stanchion (de) whose lower end is soldered to plate (kl). T o the left-hand side of the rod is fixed a small tank (c). in the underside of which is a small hole (f): the lever arm is so designed that when tank (c) is empty the right-hand side is heavier and valve m/n is open. The tank is filled through the curved funnel (ab) and the liquid overflows from the tank and collects in the upper part of the vessel. When pouring is stopped tank (c) empties through hole (f), valve m/n opens, and the liquid

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runs into the lower part (g) of the vessel. (Fig. 9a shows the conventional representation of an axle.) 10. Conical valves. T h e s e are shown in Figs. 4, 5 and 9, and occur frequently throughout the book. T h e BanU M u s a were, to our knowledge, the first to use this component as a matter of course and in a wide variety of applications. It does not occur as a control device in the works of the Greek writers on mechanics, with the important exception of a treatise on a water-clock attributed to Archimedes, 2 0 extant only in Arabic manuscript versions. T h e earlier part of this treatise, including the description of a feedback control system incorporating a conical value, may indeed be of Greek origin, whereas the second part was probably added by a M u s l i m author. Al-JazarT uses a similar system and acknowledges his debt to 'Archimedes' (p. 17). Writing towards the close of the tenth century A b u c Abd Allah al-Khuw5rizmT, in this encyclopaedia of the sciences entitled the Keys of the Sciences (Mafutih al-^UtUm)^1 gives the following description of this component: ' T h e ground valve (bab matburi) has a male and a female — the male enters the female; it opens and closes. W h e n it is closed it is tight-fitting and has no outlet. Most of t h e m are coneshaped.' (p. 253 f). Al-JazarT tells us that they were made of cast bronze, and that the plug was ground into the seat with emery. H e adds 'every tap and ground valve is made in this way', (p. 20 f). AlKhuwUrizml's statement that 'most of t h e m are cone-shaped' implies that other profiles were used, and indeed the one in the 'Archimedes' clock is drawn with a curved profile. I n fact the operation of the valve depends mainly u p o n the position of the plug relative to the plane of the seat at the discharge point — the remainder of the seat is unimportant, b u t no doubt they were made as frustrums of cones to facilitate machining. I n m o d e r n practice the shape of the plug is chosen to suit the required pressure-drop characteristics, and may be conical, parabolic or another type of curve. Conical valves first appear in the West in the works of Leonardo da Vinci, and entered the general vocabulary of European engineering in the machine book of Agostino Ramelli published in 1588. T h e y are an essential component in machine design and instrumentation, since they provide a sensitivity in control systems that is unobtainable with plate-valves or clackvalves. Models (A) SMALL TRICK VESSELS

W i t h the exception of Models 5, 6, 7, 20 and 29, the first seventyfour of the devices are small trick vessels. Since many of these had to be lifted by an operator we can conjecture that the average size was of the order of 40 cm high by 30 cm in diameter; considering

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The BariU MUsd and their 'Book of Ingenious

Devices'

the n u m b e r of components installed they cannot have been m u c h smaller than this. I t will be noticed from the brief descriptions given in the List of Models, that there are a n u m b e r of recurrent effects, that several models may produce the same effects, or that one model is simply a more complex version of another. T h e ten motifs indicate how many of the results were obtained. Motif 2 was used so that inpouring could not be resumed once it had been interrupted, and if a second double siphon, its top higher than the top of the first, were introduced then one interruption is possible. Motif 5 could also be used to prevent a second filling and it had another purpose, also effected by Motifs 4, 5 and 9, of timing the opening of a valve at some point in the flow system. Motif 3 was the commonest method for permitting the inpouring of different liquids without their mixing inside the vessel, b u t M o t i f s was also used for this purpose. T h e drawing of Motifs 6, 7 and 8 is actually that of Model 12. W h e n hole (h) is covered with the finger or with wax, no liquid can be poured from the spout. T h e action can be doubled by running two pipes into the handle, each terminating at one end in a hole in the handle and at the other in a closed tank. T h e outlets from the tanks lead either into a spout or into an open or trapped outlet. Let the two holes in the handle be A and B , corresponding to liquids A and B : then when hole A is open liquid A discharges, when hole B is open liquid B discharges, when both are open a mixture of A and B discharges, and when both are closed nothing discharges. By considering the List of Models together with the Motifs it is possible to infer the construction of many of the models. A fuller idea of the Bann M u s a ' s style and presentation can, however, be obtained from the description of a typical Model, N o . 42. T h e illustration is traced from one of the M S S , the only alteration being that the Arabic letters have been replaced by R o m a n ones, as far as possible in accordance with the instructions in the text. A reconstruction has also been supplied. (A similar system is followed for the other four models described below.) M o d e l 42. Fig. 42 is from the Vatican M S , Folio 27. A jar (jarra) with three open outlet pipes. As long as wine is inpoured nothing discharges; when inpouring is stopped wine begins to discharge from the middle outlet; when water is poured in it discharges from the middle outlet, wine from the other two, when inpouring of water is stopped no more water discharges and wine again discharges from the middle outlet. And so on. A tank (a) is installed in the jar below the inlet. ( T o o far to the right in Fig. 42, moved to the centre in Fig. 42a). I n the tank is a float (t) to which are connected bent rods joined together at (s), from which point a vertical valve rod (sz) leads to the downward opening valve (z) (Motif 4). T h e seat of this valve is in a small tank (w) from which the middle outlet (k) protrudes. (Tank (w) is too large in Fig. 42,

o- a!

Figure 2. Models.

flJ-O^C

62

The BariU Musd and their 'Book of Ingenious Devices3

correctly drawn in Fig. 42a.) Tank (a) is connected to tank (w) by a pipe (edw) that comes out of tank (a) slightly below its top. (Too low in Fig. 42, correct in Fig. 42a). From tank (a) pipes (ab) and a wider pipe (jfrb) are led out, the first from the bottom of the tank, the second from near the centre (shown too high in Fig. 42, correctly in Fig. 42a). T h e purpose of pipe (jfrb) is to prevent the liquid from rising during inpouring to the outlet of pipe (edw). T h e purpose of pipe (ab) is to discharge the liquid from tank (a) after inpouring is stopped, but its rate of discharge should not be so great as to prevent float (t) from rising during inpouring. T h e two pipes have a common outlet in the seat of valve (b). Valve (b), discharges into tank (m) (badly drawn in Fig. 42) which has a small hole in the bottom of one of its sides. Tank (m) is supported on float (1) which rests in tank (k). T w o rods connected to float (1) are joined below tank (1) to a valve rod which terminates at the plug of valve (x). T h e two rods, the two valves (b) and (x), tank (m), float (1) and tank (k) thus constitute Motifs 4 and 5. Valve (x) opens into tank (th), from which outlets (f) and (t) are led out. (Pipe (th t) is incorrectly drawn in Fig. 42 — it should penetrate tank (th) as shown in Fig. 42a.) A wide pipe (§ sh) encloses tank th, and valve (z) is in its underside. (Incorrect in Fig. 42, correct in Fig. 42a.) A hole (sh), twice the diameter of outlets (t) and (k), is made near the bottom of pipe (s sh), into the interior of the jar. T h e operation is as follows: first wine is poured into the jar. It runs into tank (a), float (l) rises and closes valve (z). T h e wine flows out of tank (a) through pipes (ab) and (jfrb) and then through valve (b) into tank (m). It discharges from the small hole in tank (m) and from the rim of tank (m) into tank (k) whence it overflows into the interior of the jar and also into pipe ( s sh), where it collects. Because pipe ( § sh) and the interior of the jar are connected by hole (sh) the wine reaches the same level in both containers. N o discharge can take place, because float (1) cannot rise while tank (m) is full of water and hence valve (x) remains closed. When inpouring is stopped tank (a) empties through pipes (ab) and (jfrb), float (t) descends, valve (z) opens and the wine in pipe ( § sh) runs into tank (w) and discharges from outlet (k). Some wine runs from the interior of the jar into pipe ( § sh) through hole (sh), but insufficient to bring its surface to the level of valve (x), before tank (m) empties, lifting float (1) and opening valve (x). When water is poured into the jar it runs into tank (a) and raises float (1), so closing valve (z). The wine rises in pipe ( ? sh) until it is about the level of valve (x). It runs through valve (x) and discharges from outlets (f) and (t). T h e water cannot flow from tank (a) through pipes (ab) and (jhb) because valve (b) is closed; it therefore flows through pipe (edw) into tank (w) and discharges from outlet (k). When inpouring of water is stopped, the water-level in tank (a) falls due to the discharge through pipe (edw), and this fall is sufficient to allow

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float (j) to descend far enough to open valve (z). W i n e therefore again discharges from outlet (k), while nothing discharges from the other two outlets. T h i s model is fairly typical. T h e r e are an average n u m b e r of errors on the drawing b u t the text is reasonably clear. T h e relative proportions and positioning of the various components is crucial to the proper operation of the device. Lacking adequate dimensions we cannot be sure that Fig. 42a shows the exact relationships. It is intended, as are the other reconstructions, to assist the reader to understand how the device worked. (B) LARGE TRICK VESSELS

Models 5, 6, 7, 75-87 are larger types of trick vessel, although the first three incorporate some of the features of the smaller vessels. T h e general design of Models 75-87 consists of an open trough or basin placed beside a cylindrical vessel that contains the supply reservoir and the machinery. I n the simpler type, when liquid is drawn from the trough or basin it is replenished u p to its original level either through a concealed pipe or from a pipe discharging from the top of the main vessel. A refinement permits replenishm e n t if moderate quantities are withdrawn, b u t cuts off all further supply if a large quantity is withdrawn. T h e most elaborate of these models has this double-action, together with two basins instead of one. Model 77 is an example of a double-acting device with single basin. A full translation is given first. M o d e l 77. (Fig. 77 is from Vatican M S , Folio 63 R.) Construction of an empty basin or a trough, m o u n t e d on a plinth, into which two or three rafls [about 6-9 kg] of wine are poured and from which several times that [amount] is drawn without its diminishing. And if the Adept draws [wine] from it [in small amounts he can draw] many times [the amount poured in]. And if water is poured in instead of wine and a h u n d r e d , or more than that u p to a thousand or two thousand, animals approach it, then provided the animals approach it one by one, whenever each of t h e m quenches its thirst [the quantity it has drunk will return to the trough]. A n d if two or three animals approach the trough and drink from it simultaneously, all the contents of the trough will be exhausted. W e make for that the illustration of a vessel of handsome construction, circular like a cylinder if we wish, square [in crosssection] if we wish, or any other pattern whose shape we find pleasing. It is marked (jd lb). W e divide it by a plate ( k § ) . T h e basin from which one drinks is marked (sh.e) and we install it in the position we have illustrated. Inside the vessel we install a tank (wba) opposite the basin, and the top of this tank is level with the top of the basin, or approximately so. W e connect the bottom of the basin to the bottom of the tank by a pipe (eb) and its end (e) in the

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The Banu Musa and their 'Book of Ingenious Devices'

basin should be concealed, unnoticed and unseen. In tank (wba) we install a float (sz) that is immersed in the wine, as we have done elsewhere. Facing tank (wba) we make a hole (1) in plate (k §) and we suspend to this hole two ground valves, as we have illustrated, with two plugs, one (1) opening upwards, and the other (m) opening downwards. We connect the two plugs by a rod (lm) and the rod is extended until its other end is soldered to the float at position (m). Position (w) is opposite position (sh) and they should be in the [same] horizontal plane, and slightly below the top of the basin. T h e layout should be such that when the float rises to position (w) the plug (m) blocks the seat, and if the float approaches the bottom of tank (wba) the plug (1) blocks the seat. At position (f) we make a hidden hole for the escape of the air. It should be clear that if we pour any quantity of wine we wish into [upper] vessel (jkd 5), which is the reservoir, then place the basin in the assembly, and pour into it about two rails of wine, the wine flows into hole (e) and through pipe (eb) into tank (wba). Float (sz) rises, valve (1) opens and the wine discharges into tank (wba) and flows through the pipe into the basin until the basin fills up to mark (sh). At that juncture the valve plug rises and closes the valve (m) as we have explained. However if anything is drawn from the basin the float sinks and the wine flows to the amount that was extracted from the basin. And if the person is aware of how it works, he extracts the wine with a large cup (qadah)> so that the amount that he drinks exceeds that which flows from valve (1), whereupon float (sz) sinks, valve (1) is closed by plug (1) and everything remains in the basin [i.e. nothing more flows into the basin]. For this reason if the wine is replaced by water, and the animals drink one by one, whenever [one of them] quenches his thirst [the basin will be replenished]. If two or three approach and drink simultaneously, they will drink more than the discharge from valve (1), so float (sz) will sink, valve (1) will be closed from above, and nothing will flow from it, whereupon everything in the basin or the trough will be exhausted. And that is what we wished to explain. There are a number of lacunae in the Arabic text that corresponds to the first paragraph of the translation, as indicated by the additional phrases in square parentheses. Such omissions are not common in the Vatican M S . T h e only real fault with the illustration is that the valve is shown with insufficient travel; a more workable arrangement is shown in Fig. 77a. T h e operation is fairly clear from the text. When a small amount is withdrawn valve (m) opens and a like amount runs into tank (wba) and pipe (eb) balances the levels in tank (wba) and basin (s/*.e). When a large amount is withdrawn plug (1) drops into its seat and the reservoir is sealed. This model has been selected because it includes perhaps the

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earliest example of a double-acting conical control valve. In a similar model the double valve is replaced by a tap: a vertical rod soldered to the float has a ring on its upper end that passes over the handle of the tap. The tap is open when the handle is a certain angle above the horizontal and closed when the handle is at a certain angle below the horizontal. When only replenishment, and not cut-off, was required the valve or the tap was single-acting. (C) FOUNTAINS T h e fountains — Models 20, 88-94 — a r e * n most cases not described or illustrated clearly, particularly the design of the fountain heads. The single vertical jet is obvious enough; 'the Lily-of-the-valley' is discussed below under Model 92. The 'shield' is nowhere clearly described and we must therefore refer to al-JazarT (p. 164) where the shape is produced by the impinging of a jet on the lower, concave side of a dished plate. T h e water then descends into the pool in the shape of a dish, concave downwards. Model 20 is a simple fountain delivering a single jet whose height can be altered by varying the static head above the outlet. Model 88 describes the method of producing a shield (turs) or a lily-ofthe-valley {susari). T h e remaining models embody the idea of alternation: the fountain emits a given shape for a period, then changes over to emit a second shape, and so on. One way of doing this is to lead out two pipes from the fountain head, one inside the other. At the supply installation these pipes are separated, the narrow one entering one tank, the inside one entering another. As a refinement a second fountain head is added. Let the fountain heads be A and B, the shapes (a) and (b): then A emits (a) while B emits (b) and, when they switch over, A emits (b) while B emits (a). This is done by using two double pipes instead of one, but is essentially the same principle as the simpler version. A second basic method was the use of worm-and-pinion and special taps — this is described in detail for Model 92. For the first type the problem is to direct the flow now into one tank, now into the other. In model 89* this is achieved by running the water from supply channel (a) into a small tank (b) fixed to the end of a pipe balanced on an axle. While the axle is horizontal the pipe (bg) discharges into tank (k). On the balanced pipe, towards end (g) two small tanks (e) and (f) are suspended, and a small pipe from the main supply pipe drips water into tank (e). Tank (f) is connected to tank (e) by a small hole and has a narrow discharge pipe (w) in its bottom. When tank (e) is full the balanced pipe tilts, trough (b) lifts away from channel (a) which then discharges directly into the second main tank (t). Meanwhile tank (e) empties into tank (£) which in turn empties through pipe (w). When both are empty the pipe tilts back to the horizontal and * Models 89 and 90 are not illustrated here: however in the descriptions which follow the manuscript letter notations which cross-reference drawing and text have been left in.

C

n

about 50 cm. [!o

^?=tt=3=F

PLAN (ropes omitted)

SIDE

ELEVATION

END ELEVATION

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the discharge is again into tank (k). I n Model 90 a water-wheel or a wind-wheel is m o u n t e d at the top of a vertical axle u p o n which a tank (q) is centrally m o u n t e d ; (q) is over the two main tanks (g) and (b) and has a discharge hole at one side. As the Wind or water rotates the wheel, tank (q) rotates and discharges now into main tank (g), n o w into main tank (b). Model 91 is a doubled version of Model 88, except that the heads emit 'lilies' and single jets, whereas Model 88 emits a 'lily' and a 'shield'. Models 93 and 94 work on the same principle as Model 92, described below, except that Model 93 has one main fountainhead and several subsidiaries and Model 94 has two fountainheads, and the shapes emitted differ. M o d e l 92. Fig. 92 is from the Berlin M s , Folio 131 Verso. Fig. 92a is from Hauser, T a b l e X X , p . 159. A fountain that emits a straight jet or a lily-of-the-valley. Neither the text nor the illustration are clear, and reference should be made to Fig. 92a, which is a credible reconstruction. Even allowing for the use of conventions, the draughtsman seems to have found it difficult to show the combination of screw, pinion and tap. T h e action is as follows: the water enters through inlet (q) and pipes (j), the jets from which rotate vaned wheel (m). ( T h e water is presumably u n d e r a sufficiently high static head for it to fill chamber (webk) under pressure.) Wheel (m) turns screw (k) which rotates the pinion together with the plug of the tap. W h e n slit (b) in the plug of the tap (see Section B-B) is opposite the opening in the body that coincides with pipe (sa) the fountain emits a vertical jet. W h e n the plug of the tap rotates, bringing slit (b) in line with the opening in the body that coincides with pipe (f§), the fountain emits a lily-ofthe-valley. I n this and another fountain the purpose of pipes (y) and the shape of the lily-of-the-valley is not clear. As drawn, the most likely shape would be a spray. It is possible, however, that pipe (sa) passed through the top of the fountain and closed it completely; pipes (y) — say six of t h e m — were then passed to the outside through the wall of the vessel to produce separate fine jets. ( D ) LAMPS

T h e r e are four lamps, Models 95-98. Model 97, described below, combines the designs and functions of Models 95 and 96. Model 98 was a kind of 'Hurricane lamp' T h e lamp is installed inside a vertical half-cylinder that rotates in axles m o u n t e d on a stanchion. A vertical triangular wind-vane projects from the side of the halfcylinder so that the convex side of the half cylinder is always facing the direction from which the wind is blowing. M o d e l 97. Fig. 97 is from the Berlin M S . Folio 136 Verso. Fig. 97a is from Hauser, T a b l e X X I I , p . 171. T h e explanation in the text is

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The Banu Musd and their 'Book of Ingenious

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quite clear, b u t the illustration is not. T o o t h e d wheel (y) is too small, and both this and pulley (k) are erroneously shown on a vertical, instead of horizontal axle. T h e vertical pipe leading from (j) is mentioned b u t not shown, and there is no indication that the reservoir had to be at a higher level than the lamp. Discharge pipe (ae) should not be curved upwards, and should show a bird's head at end (e). T h e illustrations in the T o p k a p i M S show the figures of animals, birds, gargoyles etc., which are mentioned in the text, whereas the illustrations in the other two M S S nearly always omit these. N o doubt, in the environments where the M S S were copied, religious considerations prevented the representation of such figures. Finally, the two circles at the left of the illustration seem to serve no purpose. Inside the lamp the large toothed wheel (y) and the pulley (k) are m o u n t e d in the same horizontal axle. T h e toothed wheel meshes with the curved rack (mx) which runs in a groove at the bottom of the l a m p ; the wick is tied to a hole in the rack at (x). At (j) there is a second pulley and a hole through into the space below the reservoir. At (j) a vertical pipe is erected that passes through to the oil reservoir. Above this pipe is a pulley (b). A chain passes over pulley (k), u n d e r the pulley at (j) and over pulley (b). T o its end in the lamp a weight (s) is attached, and to its end in the reservoir a float ( t ) . T h e supply pipe to the lamp (aef) should not be wide enough to allow air to enter the reservoir while oil is flowing. O n the right of the reservoir are pipes (Is) and (wz) constituting Motif 6. T h e reservoir is filled at point (1), float (j) rises and the rack is drawn in direction (m). W h e n the oil reaches (a) it begins discharging through pipe (aef) into the lamp and continues to do so until it covers hole (j), at which juncture discharge ceases because no air can enter the reservoir. T h e wick is then lit, the oil in the lamp falls until hole (j) is uncovered, whereupon there is another discharge from pipe (aef). Float (t) descends and the rack moves in direction (x). And so on. (E) MECHANICAL GRAB

M o d e l i o o . Fig. ioo is from Berlin M S , Folio 143. T h e description in the text is very clear b u t the illustration is n o t ; reference should be made to Fig. 100a. T w o copper half-cylinders are connected by hinges (If) and ( i m ) . F o u r rings (k, y, s, §.) are soldered to the half-cylinders at the top of their convexities, ropes are tied to these rings and brought together at (x). Rope (xq) is the lowering rope and can be of any length, as required. Rope (bm) passes t h r o u g h a slot at point ( m ) ; short ropes (mu) and (mo) are tied or spliced to rope (bm) and tied to rings (u) and (o) respectively. (Rings (o) and (u) are not shown on Fig. 100, nor are the slight recesses in the half cylinders at (m).) T e e t h , which mesh together when the half-cylinders close, are fixed along edges (jb) and (bw) of the half-cylinders. T h e device is lowered into the water

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by rope (qx), rope (bm) being slack. W h e n the bottom is reached rope (qx) is slackened and rope (bm) is pulled, drawing the halfcylinders together. T h e device is then withdrawn from the water by rope (bm) and its contents examined on dry land. ( T h e ends of the half-cylinders were probably covered by plates b u t these have been omitted from Fig. iooa for reasons of clarity.) Conclusion If the Book of Ingenious Devices had been written in m o d e r n times the authorship would probably have been assigned to Afrmad, with due acknowledgements to M u h a m m a d and al-Hasan for their assistance and encouragement. T h e Arabic commentators are unanimous in ascribing the work to A h m a d and, after the mention of all three brothers in the opening of the M S S , only Atimad is mentioned thereafter. It is reasonable to suppose that A h m a d was the engineer of the family, al-Hasan the geometer, while M u h a m m a d took a general interest in all the sciences, was the main force behind the collection and translation of earlier works, and also involved himself in politics and public works. A h m a d ' s book was not intended to define and demonstrate basic principles of pneumatics, hydrostatics and mechanics, and should not be judged by its failure to do so. W e can be fairly sure, from the list of works written by the brothers or commissioned by them, that they were not unfamiliar with mathematical and scientific principles, and that A t i m a d ' s m e t h o d of presentation was therefore deliberate and not due to ignorance. W h a t he was concerned to do was to describe the machines that he had designed: whether they were constructed by himself or by a craftsman working under his guidance is not particularly relevant. Compared with the Greek works, they contain far less theory and a m u c h greater degree of engineering inventiveness. T h e r e is no reason to suppose that any of the one h u n d r e d devices included in the two main manuscripts, with the exception of Model 94, was not the work of Atimad, although Hauser suggests (p. 27) that the last eight were later additions. L a m p s similar to those described by Atimad occur in H e r o ' s Pneumatica, and since we are told that Model 97 was used in Christian churches and Magian temples, its use had probably been widespread for centuries before the Abbasid period. T h e bellows and the grab were probably designed to meet needs that arose during Atimad's involvement in civil engineering projects. T h e r e is no doubt that he was justifiably p r o u d of his ability as an engineer, and that, as Bar Hebraeus i m p l i e s , m a n y of t h e devices e m b o d i e d t e c h n i q u e s a n d mechanisms that were Atimad's own inventions. T h e book represents a marked advance in mechanical engineering, and this should be borne in mind when we consider its derivations. T h e documentary sources that may have been available to

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The BariU Musd and their 'Book of Ingenious Devices'

Ahmad were written in Greeks the most important being the Pneumatics of Philo, 22 the Mechanics23 and Pneumatics24 of Hero, and the treatise on a water-clock attributed 25 to Archimedes. In addition, there was a centuries old tradition in Syria, unbroken by the Arab conquest, for the construction of water-clocks and associated automata. 26 T h e knowledge of mechanics therefore came to Baghdad in Hellenistic guise, but it would be an oversimplification to postulate a Greek written tradition as the sole inspiration of the BanO Musa and their successors, although it was perhaps the main inspiration. T h e pre-eminence of the Greeks in the pure sciences cannot be questioned, and we are only becoming aware of their contribution to mechanical technology, 27 but in identifying the Greek elements in early Arabic mechanics we are faced with a number of problems, most of which can be attributed to our lack of knowledge of the scientific and technical advances made between the time of Hero and the time of the BanU Musa, a span of about eight hundred years. Our information is particularly meagre for Byzantium and SassUnid Iran. We know, of course, that the sciences flourished in Alexandria under the Roman Empire; one has only to cite the names of Hero (first century), Ptolemy (second century), Diophantos and Pappos (both third century) as evidence that Greek science was still full of vigour during this period. We have less knowledge about technology in Roman times — Vitruvius, writing during the reign of Augustus, is still the main documentary source. 28 There were also a number of anonymous improvements in the construction of machines for practical purposes. For instance, the chain-of-pots drawn by animal power through a set of gears became a really effective machine in the fourth or fifth century with the introduction of the ratchet-andpawl 29 and the siege engines operated by men hauling on ropes entered the Islamic area from the Far East towards the end of the seventh century. 30 T h e main flow of ideas, on present evidence, seems to have been from west to east. Thus the centre of learning at GondeshapUr (Arabic: JundaysEbUr) in south-western Iran was probably founded by Greeks, although it did not rise to eminence until the arrival of Nestorian Christians from Edessa and Nisibis in the sixth century. T h e language of instruction was Syriac, but there is a tradition that the introduction of medical studies, the main subject taught at Gond^shapOr, was due to an Indian. It may be considered as the centre through which Byzantine learning passed to Baghdad. 31 Of importance also were the Sabeans of IJarrUn in upper Mesopotamia, of whom Thabit b. Qurra was one. 32 They had preserved a large corpus of Greek scientific writings, also in Syriac, and were to be very influential in the development of Arabic science in Baghdad. It cannot be doubted, however, that there were significant advances in Iran and further east, although attestation is scanty. Writing in A.D. 1203, RicJwEn

Donald (

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b. al-Sa 5tT quotes a tradition to the effect that some of the techniques used in water-clocks were transmitted to Greece from Iran and were incorporated in clocks built in Byzantine Syria. 33 Certainly, many of the traditional crafts of Iran are of ancient origin 34 and it seems likely that metalworkers, for instance, would have moved from Iran into Baghdad when the city's cultural life began to flourish. We cannot say with certainty which of the Greek works were known to the BanU Musa, with the exception of Hero's Mechanics, translated by Qusta b. Luqa during their lifetime. 35 It is probable that other works of Hero were also available to them, since his reputation among the Arabs was already high in the tenth century. c Umar Ibn Muhammad al-Kindl (ca. 970) mentions Hero's writings on pneumatics, and that he constructed clocks; 36 Ibn alNadTm says that he wrote a book on automata (p. 397). T h e Arabic text of Philo's Pneumatics, as it exists in A.S. 3713, probably dates from the fourteenth century and contains late Hellenistic and Islamic additions, but the chapters by Philo himself may have been known in Arabic much earlier than this. Ibn al-NadTm knew of the 'Archimedes' water-clock, which he calls 'a book on the construction of an instrument that casts balls, by Archimedes' (p. 397). Again the existing manuscripts contain Islamic additions, but is possible that the earlier chapters were known to the Banu Musa. It is symptomatic of the difficulties that arise when attempting to untangle the Greek and Arabic traditions that the penultimate section of the 'Archimedes' contains 'snakes-andbirds', parerga, very similar to the motifs described in Chapter 40 of A.S. 3713 (195-8 in Prager), but the language in the 'Archimedes' section indicates that it was composed in Arabic. Problems of this kind, together with the Banu Musa's omission of any acknowledgement of the works of predecessors, makes identification of their sources and isolation of their own contribution a matter of some difficulty. It may be best to clarify the problem, for a start, by listing those models of the Banu Musa that have close counterparts in Philo and Hero; chapter numbers are taken from Hauser, Prager and Woodcroft. Banu Musa Description Hero Philo 1 Concentric Siphon 2 10 13 Hot and cold water dispenser — 7 Vessels that can be made to appear filled — 43-8 14,15,24 when unfilled, and vice versa Boiler that discharges hot water when cold 18 — 74 water is poured in Jar from which several kinds of wine can 21 32 21 be drawn from a single tap Water-operated whistle 48 60 29 Water-lifting pipette — 11 30 Vessel that discharges wine or water 34 59> 64, 65 23 separately or mixed

72 The BanU Musa and their 'Book of Ingenious Devices' BariU Mllsd Description , Hero Philo 75-87 Vessels that are constantly refilled 20,61 17,18,19 95 Lamp with automatic feed 71 20 Lamp with automatic extrusion of wick 33 — 96 T h e s e are not all the models where there are resemblances, b u t only those where the construction and the effects produced are very similar. M a n y of the BanU M u s a ' s devices are elaborations of basic ideas contained in the works of Philo or H e r o , or both, and these have not been listed above. Moreover, each of the three writers developed themes that were ignored, or dealt with only briefly, by the other two namely: the early chapters of Philo, demonstrating pneumatic theory; Hero's pyrotechnic and soundproducing devices; the BanU M u s a ' s fountains, and mechanical grab. Some components are common to all three. For instance, taps with multiple borings, bent-tube and concentric siphons, airvents. T h e double concentric siphon (Motif 2) does not appear in the Greek books, neither does the funnel with bent end (Motif 3) for pouring in different liquids — instead Philo used a rotary valve (Chs. 4 3 , 44). It should be evident from the foregoing, and from the high reputation enjoyed by H e r o among the Arabs that the BanU M u s a had access to the works of Philo and H e r o and possibly to the 'Archimedes' treatise and to later Hellenistic works. I n the light of recent investigations, it is permissible to speak of a Greek school of mechanical engineering, stemming from Ctesibius (300-270 B.C.) and continuing t h r o u g h Philo and H e r o , probably into Byzantium, whence it passed into SassSnid Persia. T h e school is represented, not only by writings that have survived, probably only a small part of the original corpus, b u t also by archaeological evidence such as the ' T o w e r of the W i n d s ' in Athens and the Antikythera geared computer. 3 7 I n SassSnid Persia the Greek system may have merged with Iranian, Indian and Chinese elements, and it was this composite tradition that came to the attention of the BanU M u s a in KhurSsSn and later in Baghdad. W i t h o u t knowing the full content of this system, we cannot be certain how many of A h m a d b . M u s a ' s original ideas are embodied in his work, b u t we can at least say that it differs markedly from the known writings of the Greek school. Apart from a greater concern with engineering at the expense of scientific theory, the main difference is the greater degree of automatic control, achieved by the use of conical valves and delay systems. T h i s preoccupation with automatic controls and timing came to be important in the west only in comparatively recent times. T h e r e are a n u m b e r of parallel examples in the history of technology of ideas having lain dormant for centuries, to reappear when the practical need for t h e m arose. T h i s is not to say, however, that the work of the BanU M u s a was without influence on the development of western machine technology in medieval times, b u t the influence was probably indirect.

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Over three hundred years later than the BanU Musa, al-Jazan composed his work, which represents the culmination of the Arab achievement in mechanical technology in the Middle Ages. AlJazarl's work incorporates all the significant devices and techniques of his predecessors, whose works he acknowledges in the appropriate places: 'Archimedes' for the water-machinery of his monumental water-clock (p. 17); Ibn Yunus for the design of a candle-clock (p. 87); the BanU Musa for fountains (p. 157); Hibat Allah b. al-Husayn 38 (d. 1139 or 1140) for musical automata (p. 170). Al-Jazan then describes the improvements — and they were real ones — that he made to the work of his predecessors and, in addition, describes a number of devices, techniques and components that are not to be found in their works. Almost all the ideas and techniques, usually thought of as typically Islamic, which later re-appeared in the West, can be found in al-Jazarl. A direct transmission of his work to Europe cannot, however, be postulated. There is no known medieval translation of it into a European language but, in any case, it is probable that the most important transmissions occurred before his book was composed. It is important to observe that al-JazarT records the assistance of a continuing tradition of machine technology from the time of the Bann Musa to his own day. He prides himself on being a part of this tradition (p. 15), and he mentions the engineering writings of such men as Hibat Allah, who otherwise is known to us only as maker of astrolabes. He also describes techniques, such as metal casting in closed mould-boxes in green sand, as having been long established in the Islamic world, although many of these were not known in Europe until later times. 39 He is therefore a valuable witness for the unbroken activities of Arab engineers throughout the medieval period, and a necessary witness, because as yet very few Arabic manuscripts have come to light. This continuity makes possible the assumption that Arabic knowledge of machines could have passed to the west at any time between the ninth and the thirteenth century. In fact, the most important transmission seems to have occurred in Spain during the twelfth century. It has been accepted for some time that the introduction of the water-clock into Christian Spain was due to Muslim influence, but the actual passage of knowledge was probably earlier than the Alfonsine tradition of the mid-thirteenth century, 40 and could have occurred by the inspection of existing Islamic clocks or by gaining access to Arabic writings — actual translation would have been unnecessary, because many scholars in this period were bilingual. T h e discovery of a hitherto unknown Andalusian M S on water-clocks and other machines is therefore of crucial significance. This Arabic M S is attributed to Abu c Abd Allah, known as Ibn Mu c adh, who worked in Cordova in the eleventh

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The BanU Musa and their 'Book of Ingenious Devices'

century — the copy itself is dated 1266. 41 It has not yet been fully studied, but it contains descriptions of thirty machines, including water-clocks, with illustrations that appear to be quite advanced; for instance, they show well-constructed gear-trains. There is no reason to doubt that this document, and others like it, was known in the Christian parts of Spain. Since the work of the BanU Musa was widely known and appreciated in medieval Islam it is probable that elements of their work were embodied in the writings and constructions of later Islamic engineers. The water-clock, with its gears, pulleys, cams, jackwork and automata is essentially similar to the tower clocks that appeared in Europe in the thirteenth century, undoubtedly as derivations from the water-clock; one has simply to consider the weight and escapement as replacements for the heavy float where fall is controlled by a uniform fluid discharge. T h e mechanical clock exerted a potent influence upon the development of machine technology. Although the BanU Musa did not construct waterclocks we can therefore assume an indirect influence by them, rather by Atimad, upon European technology, as follows: (1) Afrmad's ideas adopted by later Arabic engineers who constructed water-clocks; (2) transmission of Islamic water-clocks to Christian Spain followed by their dissemination throughout Europe; (3) invention of the weight-driven clock in Europe early in the thirteenth century; (4) influence of the techniques and mechanisms of the mechanical clock upon the development of machine technology. Other contributions, perhaps more direct, may be identified as research progress. ACKNOWLEDGEMENT The author wishes to express his gratitude to the Leverhulme Trust Fund for a Research Award to assist him in his research into medieval Islamic technology. Notes 1. The best general view of the growth of Arabic science from the ninth century onwards is given in: George Sarton, Introduction to the History of Science, Vol. I, Baltimore, 1927. 2. Article, bayt al-fyikma in Encyclopaedia of Islam. 3. Ibn al-Nadfm, Kitab al-Fihrist, ed. G. Flugel, Leipzig, 1871-2, 2 vols. Reprinted Cairo, A.H. 1348. 4. Ibn al-Qiftr, Kitab ikhbar al-( culama' bi akhbar al-hukaniti, Cairo, A. H. 1326. 5. Ibn Khallikan, Wafayat al-a yan, ed. Ihsan Abbas, Beirut, Vol. 5, undated. 6. Bar Hebraeus, Tarikh mukhtasar al-duwal, ed. A. Salihanf, Beirut, 1890. 7. Abu' 1-Fida', Al-Mukhtasarftakhbar al-bashar. Lithographic reproduction of Arabic text in School of Oriental and African Studies, London. From undated Cairo edition. 8. Tabari, Annalesf quos scripsit. . . etc, ed. M. J. de Goeje, Leyden, 1879-1901. 9. Ibn AM Usaybi a. (Uyun al-anba', ed. A. Muller, Cairo, 1882, 2 vols. 10. Ibn Yunus, Le Livre de la Grande Table Hakemite, translated C. Caussin, Paris, 1804. 11. Al-Birum, The Chronology of Ancient Nations, trans, and ed. Edward Sachau, London, 1879.

Donald R. Hill 75 12. These are the first four letters of the Arabic alphabet. 13. H. Suter, Die Mathematiker und Astronomen der Araber und ihre Werke, Leipzig, 1900. From a scholarly point of view Suter is more reliable than Sarton, but he gives no general summary. 14. See also Suter, op. cit., 20-1. 15. This should probably read Menelaos. See Hauser 13. 16. Ibn Khaldun, Muqaddimah, trans. F. Rosenthal, Routledge and Kegan Paul, London, 2nd Edition, 1967. 17. Al-Jazarl, The book of knowledge of Ingenious Mechanical Devices, trans, and ed. Donald R. Hill, Reidel, Dordrecht, 1974. 18. E. Wiedemann and F. Hauser, 'Uber Trinkgefasse und Tafelaufsatze nach alGazari und den Banu Musa', Der Islam 8, (1918), pp. 268-91. 19. F. Hauser, 'Uber das 'Kifab al-IJiyaV — das Werk uber die sinnreichen Anordungen der Banu Musa.' Abhandlungen zur Gesch. der Naturwissenschaften und der Medizin, Erlangen, 1922. (Annotated translation of complete work by Donald R. Hill forthcoming.) 20. Donald R. Hill, Construction of a Water-Clock attributed to Archimedes, Turner and Devereux, London, 1976. 21. Abu Abd Allah al-Khuwarizmf, Liber Matatih al-Otum. Arabic text with Latin critical apparatus, ed G. Van Vloten, Leyden, 1895. 22. The Pneumatica of Philo exists in latin MSS., fragments of Greek Mss, an Italian Ms, an Arabic Ms, and there are fragments preserved in another Arabic Ms. The references for the last two are A.S. 3713, Aya Sophia, Istanbul and Eastern Manuscript 954, Bodleian Library, Oxford, respectively. The work has been dealt with by several modern writers, as follows: (a) Carra de Vaux, 'Le Livre des Appareils Pneumatiques et des Machines Hydrauliques par Philon de Byzance,' Paris Academie des Inscriptions et Belles Lettres, 38 (1903), Pt. 1. (b) W. Schmidt, 'Physikalisches und Technisches bei Philon von Byzanz', in Bibliotheca Mathematica 3, Series II, (1901). (c) W. Schmidt, 'Aus der antiken Mechanik' in Neue Jahrbucherfur das klassische Altertum, 1904, pp. 329-51. (d) A. G. Drachmann, 'Ktesibios, Philon and Heron; a study in Ancient Pneumatics', Acta Historica Scientiarum et Medicinalium, (ed. Bibliotheca Universitatis Hauniensis, Copenhagen), 4, (1948), 1-197. (e) F. D. Prager, Philo of Byzantium-Pneumatica, Ludwig Reichert, Wiesbaden, 1974. Carra de Vaux's work includes the full Arabic text of A.S. 3713 with a French translation. The translation is good although in places it strays from the literal meaning, with no indication that this has occurred. The illustrations are reconstructions by Carra de Vaux — the original drawings from the manuscript are not reproduced. This important omission aside, the work can be used with some confidence. Prager's work has serious defects. His historical analysis of the Philo traditions, his presentation of the Western side of that tradition, and his attempt to isolate Philo's own contributions, all show sound scholarship. His high regard for theoretical science, however, is accompanied by apparent distaste for engineering applications that leads him to undervalue and even deprecate the work of the Arabic writers, such as Arimad bin Musa, al-Jazan and al-Kindf, who 'show an almost exclusive interest in the demonstration of assorted contraptions' (p. 54). This attitude leaves out of account the value of the technical innovations made by the Arab engineers and the fact that al-Jazarf in particular described his constructional techniques in scrupulous detail. Moreover, Prager makes heavy weather of interpreting certain devices. For instance, A.S. 3713 includes one of al-Jazarf s devices, a slave girl who emerges from a cupboard (Category II, Ch. 10 in al-JazarT; Ch. 30, A.S. 3713). Prager comments (p. 177, note 520) that the description in both texts is so vague that a 'graphic reconstruction of the mechanism is impossible'. This is nonsense: the construction and operation of the device, one of al-Jazari's simplest, is made perfectly clear by his text and illustrations. By far the most serious defect in Prager's work, however, lies in his treatment of the photographs reproduced from A.S. 3713. He says (pp. 125-6) that the reference letters and legends are explained beneath the reproductions of thefirstforty-three illustrations, but from then on the explanation is omitted, 'in general because we found the legends undecipherable, as in Chapter 58 (Fig. 58) or because we found them difficult and the reference letters obvious'. This is bad enough, since in fact the legends can almost everywhere be read with

76 The Banu Musa and their 'Book of Ingenious Devices' comparative ease, including those in Fig. 58. But the reader is led to expect that the legends on the earlier reproductions are translated fully and accurately, and this is not the case. They are often either inaccurate or completely wrong, and are in many cases omitted. To cite only two instances: Fig. 12, p. 134 is upside down and the English legends, all incorrect and incomplete, do not therefore tally with the Arabic ones; Fig. 43, p. 197 has eight legends, all legible, but only one of these is translated, incompletely. The evidential value of the photographs to a non-Arabist is therefore minimal or rather, if he is unaware of these defects, negative. 23. Hero, 'Les Mecaniques ou L'Elevateur de Heron d'Alexandrie sur la Version Arabe de Qosta ibn Luqa'. Translated and edited by Carra de Vaux in Journal Asiatique, 9e Serie (1898), Tome I, pp. 386-472; Tome II, pp. 152-92, 193-269, 420-514. 24. The Pneumatics of Hero of Alexandria. A facsimile of the 1851 edition by B. Woodcroft. Introduced by Marie Boas Hall, London and New York, 1971. 25. See note 20. 26.H.Diels,'Uberdie von Prokop beschriebene Kuntsuhr von Gaza', Ablaudlungen d. preuss. Akad. Wiss., Berlin, (Phil.-Hist. Klasse), No. 7, 1917. 27. Derek de Solla Price, Gears from the Greeks, Science History Publications, New York, pp. 51 f. 28. Vitruvius, On Architecture, ed. and translated F. Granger, Loeb Classical Library, London and New York, 1931 (reprinted 1970). 29. Thorkild Schiller, Roman and Islamic Water-Lifting Wheels, Odense University Press, 1973, p. 169. 30. Donald R. Hill, 'Trebuchets', Viator 4, (1973), 101-2. 31. Article, 'Gondeshapur', in Encyclopaedia of Islam. 32. Bar. Hebraeus, op. cit., 266. 33. Two MSS of Ridwan's work are known: Gotha, Arab 1348; MS Istanbul, Koprulu I. 949. The reference is in 1348, Folio 4, recto. An abbreviated translation was supplied by E. Wiedemann and F. Hauser in 'Uber die Uhren in Bereich der Islamischen Kultur', Nova Acta, Abh. der Kaiserl. Leop. Carol Deutsch. Akad. der Naturforscher 100, (Halle, 1915), 176-272. The reference is on pp. 179-80. 34. Hans E. Wulff, The Traditional Crafts of Persia, M.I.T. Press Cambridge, Mass., 1966, passim. 35. Suter. op. cit. pp. 40-2. 36. E. Wiedmann, Aufsatze zur Arabischen Wissenschaftgeschichte, ed. W. Fischer, Vol. I, Olms, Hildesheim, 1970, pp. 69-70. (This al-Kindr should not of course be confused with the famous philosopher.) This work of Wiedemann's is a collection in two volumes of his Beitrage for the Erlangen Society. The index to Vol. II should be consulted for other references to Hero, and other writers, Greek and Islamic. 37. Derek de Solla Price, 'Automata in History', Symposium on Automata and Simulated Life as a Central Theme in the History of Science, University of California Los Angeles, 1963, pp. 13-16. 38. Suter, p. 117. 39. The first description of this casting technique in Europe is in Biringuccio's Pirotechnica written in A.D. 1540. It was probably adopted in the west at the end of the fifteenth century. See Cyril Stanley Smith. 'The Early History of Casting, Moulds, and the Science of Solidification' in Metal Transformations, ed. Mullins and Shaw, New York, 1968, p. 23. 40. Price, 'Automata', (see note 37), p. 17. 41. I am indebted to Dr David A. King, of the Smithsonian Institution Project in Medieval Islamic Astronomy, in Cairo, for passing on to me information about this important work. The machine section in fols. IV-48V is part of a larger work entitled Kitab al-asrar ft nafa'ij al-afkar, MS Biblioteca Medicea laurenziana Or. 152, No. 282 in Assemani's catalogue. See the article 'al-Jayyani' in the Dictionary of Scientific Biography. Working from a microfilm of this MS, which is unfortunately in very poor condition, I have been able to publish a preliminary evaluation of this work. See Donald R. Hill 'A Treatise on Machines by Ibn Mutadh Abu fAbd Allah al-Jayyanfin Journal for the History of Arabic Science, Aleppo University, I, 1977. In general, Ibn Mufad/z's water-clocks and other machines are large and robust, with advanced gearing and mechanical transmissions. His applications of hydrostatics and aerostatics are, however, less sophisticated than those of Banu Musa and al-Jazari.

A R o m a n

N o t e M e t a l

o n T u r n i n g

J. F . C A V E T h e publication in 1972 of Alfred M u t z ' s monograph, Die Kunst des Metalldrehens bei den Romern,1 drew attention to an important but hitherto largely neglected aspect of R o m a n metalworking t e c h n i q u e : lathe t u r n i n g . Prior to the publication of this pioneering study, furnishing as it does overwhelming evidence of metal turning practices, very little seems to have passed into print on the subject. 2 Even the late H e r b e r t M a r y o n , a formidable authority on ancient metalworking technique, remained virtually silent on turning, acknowledging only on rare occasions in his published papers that some ancient metal artefacts bear signs of lathe working. 3 T h i s is all the more extraordinary when one considers the likelihood of finding one or more turned metal objects on open display in provincial museums possessing only the most modest Roman collections. And if this is true of smaller collections then, as one might expect, the quantity and diversity of turned metalwork in a major collection such as that of the British M u s e u m certainly confirms the impression given by M u t z ' s study that the turning of metals was a very c o m m o n craft practice in the R o m a n world. Precisely why the whole question of lathe turning in Greek and R o m a n antiquity should not have attracted wider scholarly attention is rather puzzling. Although very early evidence of lathe work is exceedingly t h i n a n d wholly i n a d e q u a t e for t h e construction of anything like a coherent chronology or possible patterns of diffusion, later Greek and R o m a n turned artefacts do survive in sufficient n u m b e r s to make these issues seem worth an extensive investigation. F u r t h e r m o r e , even a cursory examination of some of the metal artefacts reveals varying degrees of accuracy, of technical sophistication, and in some cases of sheer b r u t e metal deformation which make it difficult to accept that any one p a r t i c u l a r t y p e of p r i m i t i v e lathe was involved in t h e i r manufacture. Until very recently it appears to have been a matter of orthodoxy to regard m o d e r n primitive lathe types (i.e., windingcord, bow- and pole-lathes) 4 as essentially the same as those a G r e e k or R o m a n craftsman m i g h t have e m p l o y e d . T h i s assumption is hardly surprising, perhaps, if one considers among other factors the many examples of primitive mechanical devices

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A Note on Roman Metal

Turning

surviving in use from antiquity. A l t h o u g h the slender iconographic evidence, such as it is, supports this view, on closer inspection it is far from clear that all known examples of turned metalwork — especially later Roman work — can easily be explained, or indeed explained at all, in terms of these simple reciprocating types of lathe. And considering just how little is actually known of turning metals on such lathes the assumption must appear loosely founded; in spite of the fact that metalturning by these primitive means is still practised in some parts of the world, very little appears to be widely known of the methods and skills involved or of the full potential of the primitive lathe as a metalworking tool. A search through the key bibliographical index to this subject 5 reveals, as might be expected, that very little documentary detail is available either. Even otherwise important and comprehensive treatises on lathe turning, such as those of Plumier and Moxon, 6 leave much to the imagination when it comes to metal-turning. Before going on to consider in detail some of the evidence for Roman metal-turning and to examine the mechanical requirements, it may be useful to rehearse a few more or less well established facts about the lathe and its origins. T h e Oxford English Dictionary defines a 'lathe' as: A machine for turning wood etc. in which the article to be turned is held in a horizontal position by means of adjustable centres and rotated against cutting tools. Allowing that 'adjustable centres' may also include a spindlemounted chuck or faceplate, these criteria are sufficient to characterise a lathe — although for some time vertical axis machines have also qualified for the description. By these criteria, it is obvious that even the most unsophisticated arrangement may be regarded as a true lathe. For simple cylindrical turning it is necessary only to be able to rotate the workpiece between two firmly fixed points using — say — a piece of partially wound cord pulled back and forth, and to present a steadied cutting tool. What is not so obvious, and this will be dealt with more fully below, is that such a simple arrangement can in fact be adapted for more complex turning and manipulated to give continuous rotary motion. On the basis of the fragmentary and somewhat doubtful earlier evidence, Woodbury has suggested that the lathe originated some three thousand years ago. 7 Insufficient is known to pinpoint its place or places of origin, though in very general terms the practice of lathe turning seems to have diffused outwards from the eastern Mediterranean area to northern Europe. T h e lathe was certainly familiar enough to the Greeks by the fifth century B.C. for Euripides to employ it in a simile, and later the references become

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far more frequent in Greek literature. T h e earliest representation of a lathe is considerably later and appears on an Egyptian wall painting of the third century B.C. This illustration simply depicts two operators kneeling beside a rectangular frame fitted with two centres between which is suspended a cylindrical workpiece. One of the operators is shown manipulating a winding cord while the other performs a shaping operation. 8 Like many of the earlier turned artefacts, the workpiece in this painting is probably wood but at least as early as the fourth century B.C.9 the lathe was certainly employed for turning a variety of other materials and large numbers of surviving objects from this period attest to Greek skill in turning stone and metal. A number of stone toilet vessels, particularly a fine marble pixys of the fourth century B.C. in the British Museum, 1 0 bear all the hallmarks of turning: concentricity, small indentations to facilitate centering and an overall complexity of profile inconsistent with 'hand-working'. Many bronze mirror-cases also survive from the same period which appear either to have been turned in some degree from castings or at least finished on the lathe. These are characteristically decorated on the inside with concentric rings of quite deep relief, each often being of quite random profile in cross section (Fig. id). And in virtually all cases, at the centre of the base is to be found the small indentation that was almost certainly the point of accommodation for a lathe centre. A shallow Greek silver vase 11 in the British Museum of the second or third century B.C. bears more obvious signs of having been turned; not only is the overall decorative treatment and dimensional accuracy consistent with turning, the quite well preserved surface also exhibits clear circular striations. Considered together with the sharpness of all the circular detailing, these appear to result from a positive cutting action rather than an abrasive finishing operation. In addition, a small gilt plug is carefully positioned where one would expect the centering mark to be. As with the transmission of so many other Greek ideas in mechanical and civil engineering, it is tempting and altogether plausible to think that Roman metal-turning techniques derive largely from Greek practice. Considering the high esteem in which Greek craftsmanship was held and especially the fact that this led to the direct employment of increasingly large numbers of Greek craftsmen, it would be surprising if such an important technique failed to become established in the Roman world. Certainly, where comparisons can be made between earlier Greek and later Roman turned works, suggestive technical as well as purely stylistic similarities are apparent. Precisely the type of ring decoration described above, for instance, reappears much later on the bases of countless numbers of Roman paterae12 and other vessels (Fig. ic).

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Turning

Figure ia. Part cross section through a Roman Silverflangedbowl of the type illustrated by Mutz. A single thin sheet is folded — almost certainly spun — to form both the body and the flange. Figure ib. Part cross section of a similarflangedbowl but featuring two 1800 folds. Figure ic. Part cross section of a typical Roman patera (handle omitted). The randomly profiled high relief rings have the appearance of having been incised into the bronze base after casting. Figure id. Part cross section through a Greek bronze mirror case featuring similar ring decoration on the inside of the heavy cast body. Whatever the difficulties may be of sorting out the problem of diffusion, the fact remains that Roman craftsmen did indeed capitalize very extensively on turning techniques for metalworking. T h e range of wholly or partially turned metalwork, especially of the later period, is surprisingly wide and includes such items as bowls, jugs, vases, plates, paterae, mirrors, inkwells and almost certainly piston-pump component parts. 13 More likely than not, most of these surviving turned works have never been examined expressly from the point of view of their fabrication. And scattered around different collections as they now are, the task of producing something like a comprehensive classification must appear a daunting one. Unfortunately, this gap in primary research is bound to be felt all the more acutely by the historian of technology since collectively these artefacts represent the most important clue

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we have about the metal-turning lathe itself. Of course, any kind of cataloguing would be impossible without a clear idea of what counts as turned work and so from a close examination of miscellaneous pieces the study must begin. There are several possible criteria for determining whether or not an artefact has been turned, and these may be grouped under the broad headings: visual, dimensional and metallurgical. It must not be imagined, of course, that any single test is capable of establishing unequivocally that an artefact has been turned; all the available evidence — and this varies considerably from piece to piece — has to be carefully weighed and evaluated. T o begin with, there may well be an element of intuition in selecting what qualifies for closer inspection, but even to the non-experienced eye many of the visual clues are obvious. Circular grooves cut into a plate, for example, must suggest either the work of a compass sweeping around on the stationary plate or else the work of a fixed tool cutting into the rotating workpiece as on the lathe. 14 T o the experienced eye, various other decorative features and technical accomplishments invite immediate attention. Unfortunately, as is well known, and certainly evident in most museum exhibitions, the state of preservation of ancient metal artefacts varies greatly, and an otherwise suggestive but badly corroded or heavily deformed piece may well frustrate attempts at closer analysis. This is especially true of bronze though very often, thanks to 'plating', 15 tinning or just simply propitious circumstances of preservation, the original surfaces survive intact in their entirety or in patches. Where a metal surface retaining some or all of its integrity is available for inspection, much can be deduced from superficial markings resulting from methods and tools employed in fabrication. T h e lid of a Greek bronze mirror case, 16 for example, of a date possibly as early as the sixth century B.C., is decorated on the inside with a figure lightly incised in outline which had originally been tinned or plated. This surface treatment has had the effect of preferentially preserving the figure against the rest of the highly corroded bronze so that on the figure alone, clear circular polishing marks may still be seen radiating out from the centre of the lid — strongly suggesting that the whole thing had been mounted, turned and lapped. Luckily, many Greek and Roman artefacts were never finished to a perfect degree of brilliance or smoothness; by modern standards, many were left with a surprisingly rough finish, often showing sure signs of the turner's work left unerased. This is true of precious as well as of base metal objects as a fine Roman gold vase of the second century A.D. in the British Museum adequately testifies. T h e vase, after having been beaten and raised into shape, was evidently mounted between centres to be finally trued up and

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A Note on Roman Metal

Turning

finished (Fig. 6). Although most of the surface is now finely pitted, the one or two remaining patches of original surface bear clear striations running around the body, suggesting at least that it was turned and finished off with • a coarse abrasive. Further con| firmation of turning appears on the base, where there is a prominent centering mark enclosed by two concentrically cut grooves. Of the countless other examples it would be possible to mention, it is worth pausing to dwell on several unobtrusive marks to be found on parts of the British Museum's two Bolsena pumps 1 7 since these may well be 022, unique among mechanical devices in evincing signs of lathe-work. These double-acting bronze piston pumps of the Roman Imperial period are both modelled on the Ctesibian arrangement with two vertical cylinders standing either Figure 2. Enlarged view of side of a rising central outlet pipe. mushroom valve from the second Though similar in principle, the Bolsena pump against a part actual pumps differ in several section of the valve seating. respects: the bronze body castings Circular striations — apparently turning marks — are visible on a are quite dissimilar, the valve relatively uncorroded part of the mechanisms are entirely different stem and valve head. and one of the two is in fragments. From the fragmented pump it is possible to withdraw one of the several original mushroom valves which, incidentally, both in appearance and operation are virtually identical to our modern equivalents. And clearly visible at the top of the stem on this loose valve is a series of striations, highly characteristic of rough turning, which extend halfway around the stem until they are obscured by a more corroded patch (Fig. 2). These are of considerable interest because unless one assumes that lathe work was involved in truing up the original casting or even turning the valve from the solid, it is difficult if not impossible to account for them. Only two other possibilities come quickly to mind; either the marks were caused by hand lapping or they are the product of occasional contact with the valve seat causing wear (the valves are free to revolve). But neither of these alternatives really stands up to closer inspection since, in the first case, only the base of the stem has to be lapped for a sliding fit in the socket insert and in the second it is clear from working the valve up and down in its original socket that the top of

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Figure 3. Detached bronze piston and connecting rod socket of the type used in thefirstBolsena pump. The socket casting is slightly misshapen resulting in the turned decorative grooves penetrating deeper on one side. A high degree of unevenness in the thickness of the piston walls together with the dimensional accuracy of the exterior suggest that this too has been turned or finished between centres. the stem can never come into contact with another part. Indeed, the lathe hypothesis is all the more compelling when one considers that the use of mushroom valves — as alternatives to the technically less demanding 'flap' valves on the other pump — depends upon the technical possibility of ensuring accuracy and good fits, both of which requirements can most easily be satisfied with a simple lathe operation. This seems all the more plausible when it is remembered that there are several scattered literary references to turning pistons for pumps of this variety. 18 If this was in fact a conventional practice, it seems quite reasonable to suppose that other appropriate parts, such as these valves, would have been similarly treated.

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A Note on Roman Metal

Turning

Interestingly enough, an odd detached piston of the same provenance and identical to those partially corroded into the complete pump does lend credibility to the literary passages. This hollow cast piston is complete with its articulated cast-bronze connecting-rod socket, which in all probability once accommodated a wooden rod (Fig. 3). T h e socket can best be described as slightly banana-shaped and it is this chance feature of the casting that adds interest to the decorative ' V grooves cut into its surface, for both of these are correspondingly deeper on the bowed-out side of the socket •— just as one would expect if the grooves were produced by turning the casting between centres. Unfortunately, no significant markings remain on the surface of the lightly corroded piston itself but its dimensional accuracy, along its length as well as diametrically, certainly suggests something more than hand lapping. Dimensional evidence generally is an important indicator of lathe-working and where corrosion or deformation are not seriously inhibiting factors, the circularity of decorative detailing or even clear surface markings may be determined to within fine limits. Of course, circularity itself is not sufficient evidence of turning but it is, nevertheless, a necessary feature of all carefully turned work prior to the introduction of geometric chucks. And this dimensional evidence can be crucial in deciding whether or not a piece has been 'worked' entirely by hand since given skill and time, it is possible to produce results in any material deceptively like those of lathe work. Pye 1 9 speaks of 'shape determining systems' to characterize tools of varying degrees of complexity whose mode of operation guarantees the constancy of at least one factor in the work they do. Like the wood plane, which produces a constant thickness of cut, the lathe obviously falls into this category for even the crudest type, if carefully used, guarantees an otherwise unobtainable standard of circularity. In the case of cast metal artefacts, it is by no means clear that circular or concentric detailing must result from a cutting operation. It might, for instance, be objected that the kind of apparently incised ring decoration to be seen on Roman paterae are possibly just cast that way. Judging from the evidence of brittle fractures on numerous bronze fragments it seems quite certain that large numbers of thin-walled bronze vessels were cast, though due to subsequent working it is usually impossible to be sure precisely how. Durable solid moulds are one possibility, and Mutz 2 0 illustrates fragments of a Roman stone mould which is very accurately bored out and also calcified on the inside where molten metal has evidently been in contact with the walls. But the use of solid moulds such as this one fails to account for the undercutting which is almost invariably a feature of these high relief rings and

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therefore, if cast from a solid mould, the decoration must either have been finished on the lathe or cut entirely from the solid cast base. An alternative method of casting, one which avoids this problem altogether, is the cire perdu process which involves 'investing' a prepared wax pattern in a refractory mould material such as clay, baking it to melt out the wax, and then pouring metal into the resulting cavity. With this technique, the original wax pattern can be reproduced in metal with a high degree of fidelity and it is therefore naturally tempting to believe that where possible cutting a wax pattern would have found favour over removing solid metal. In a sense, this explanation only pushes back the problem to the making of the wax pattern but this would be quite easily accomplished on a lathe or even a potter's wheel. This question, among others, may eventually be answered by the more extensive application of metallographic techniques. With few exceptions, relatively little research appears to have been attempted in this area expressly to provide evidence of latheworking, though it has to be said that this is due largely to the unacceptable degree of damage that would result in otherwise well preserved pieces. But this is not so true of fragments or incomplete artefacts and where it is possible to take a section, polish and suitably etch it, and then observe microscopic detail, much can be deduced about its metallurgical history. Once again, it is not necessarily possible to establish unequivocal answers in this way; metallographic analysis may reveal characteristic effects of cold working, including cutting but rarely, with a high degree of certainty, precise causes. Since cutting will result in local strain hardening of the underlying layer of metal, it has been suggested that surface hardness — or rather, the pattern of micro-hardness variations across a surface — might be a useful indicator of lathe turning, especially since the analysis is not destructive. 21 However, as hardness may also be increased by burnishing or even abrasive polishing, such a technique would not be without its problems. Before considering the mechanical requirements of lathe turning, it must be added that another and altogether more spectacular achievement of Roman metal-turning is slowly achieving recognition, and this is the process known as spinning. This technique, widely held to be of comparatively recent early nineteenth-century origin, involves turning sheet metal at high speed on a suitable lathe and then causing the desired deformation by literally pushing it into shape with a blunt-nosed tool. Normally the disc of metal would be wedged against a wooden former or pattern of the desired profile — to be ultimately pressed over it — but in some instances the metal can be pushed into shape without this support. There are several scattered indications of metal-spinning

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A Note on Roman Metal 22

Turning

practices in antiquity but the evidence for Roman metal spinning — inexplicably long overlooked — seems to be both extensive and, more importantly, quite conclusive. At the beginning of his study, for example, Mutz pays attention to a Roman flanged silver dish of the first century A.D. now in the Rijksmuseum which exhibits the classical signs of having been spun. As his illustration shows, the flange surface is not smooth but is covered with regularly spaced concentric ripples or corrugations. 23 These markings can only be interpreted as the result of a blunt-nosed tool pressing into the turning metal surface; that they cannot simply be explained away as the result of burnishing, following hand beating, is partly evident from Mutz's cross-sectional drawing of the bowl (Fig. ia). It would be enormously difficult to produce anything like this complex profile other than by spinning it and impossible to produce the hollow rim at the top where the metal is folded over 180 degrees — or indeed, obtain the uniformity of spacing between the two outer walls (within ± 1 mm) all around. Nor is this particular example by any means unique; a secondcentury A.D. example, part of the British Museum's Chaourse Treasure, 24 is even more sophisticated from a technical point of view with the top of the flange folding in underneath to meet the side of the bowl (Fig. ib). In addition, a surprisingly large variety of other Roman metal work, in particular the later silverware, bears similar signs of having been spun and would certainly seem to deserve very close attention, if not an independent study, in the future. Confronted with all the evidence of metal-turning and even metal-spinning during the later Roman period, the problem naturally arises of being able to account for it all in terms of a suitable lathe. T h e iconographic evidence, such as it is, helps very little and the literary sources, 25 numerous as they are, indicate only what was turned and never how. In support of any particular thesis, it therefore remains to fall back upon general mechanical considerations, clues from the artefacts themselves, and whatever else we know about Roman mechanical technology — which, of course, is precious little. T h e most widely held view appears to be that the lathe of antiquity was in all probability a simple reciprocating type such as the pole-lathe. For wood-turning, there can be little objection; the reciprocating lathe itself can be of astonishing simplicity or crudity yet be capable of impressive work, and the power requirements are not excessive even for the single operator who simultaneously works a bow- or pole-sprung cord and manipulates the cutting tool. In the case of metal-cutting, on the other hand, the power required for a correspondingly heavy cut is far more substantial and the eflFort necessary to execute it is also greater, both of which factors, on the face of it anyway, suggest that the reciprocating

Figure 4. The general arrangement of Mutz's (speculative) reconstruction of a Roman lathe. The spindle mounted faceplate is driven by a cord belt powered by means of the large hand-cranked pulley wheel at the rear. At the opposite end one of the three heavy wooden upright stocks houses afixedcentre which is adjustable by means of pegs and wedges. All the major components of the lathe are of wood.

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Turning

lathe is not especially suited to metal-turning. This is the view expressed by Woodbury 26 who draws attention to the adoption — probably in the mid-sixteenth century — of the alternative continuously-driven belt lathe for the turning of metal artefacts. Evidently in agreement, Mutz has gone to the length of actually constructing what he considers to be a plausible unidirectional lathe which, however, considering the period, a more cautious observer might be inclined to treat with some scepticism (Fig. 4). While careful to maintain that this interpretation of a Roman metalworking lathe is very much a hypothesis rather than a positive solution, Mutz has in fact proposed a device not unlike a typical seventeenth-century 'great wheel' lathe complete with a cord belt drive and cranked driving wheel. T h e entire lathe is constructed of wood, apart from small metal parts such as bearing strips, and consists of a heavy frame serving as the bed into which are wedged three upright stocks or 'poppets'. T h e headstock assembly comprises two of these three stocks bored out to house a large diameter spindle connected via a cord belt to the large cranked wheel at the rear. T h e spindle terminates with a rigid faceplate and the workpiece can be secured to this by pressure from the tail-stock centre. This is mounted on a single stock and is fully adjustable by inserting pegs in the line of holes along its length and wedging these against the stock. On the face of it, there seems to be a lot to recommend Mutz's 'reconstruction'. It avoids the supposed difficulties of turning metals on a form of reciprocating lathe and easily accommodates non-cylindrical work; it also functions successfully and without the need for mechanical sophistication. However, of the technical features, modest as they may appear, there is no evidence for the use of the continuous belt drive in antiquity and no positive evidence for the use of the crank.27 In spite of these objections, it is easy to see why Mutz has arrived at this particular form of lathe yet the question must arise of whether, in principle, it is the most likely explanation for the turned work we have. It is indeed arguable not only that a plausible alternative still exists in the form of the less advanced lathe of the reciprocating type, but that this latter must remain the more plausible alternative until proven otherwise. A contention that the reciprocating type of lathe will not serve for turning most of the metalware under discussion is open to serious doubts, since too little is known of the possibilities of primitive lathe working to draw firm conclusions. On the contrary, it may be the case that reciprocating lathes have simply been misunderstood to a large extent and that one ought to attach great significance to the fact that pole-lathes remained in use for metal-turning into the nineteenth century. In all reciprocating lathes the work is driven by means of a cord

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or leather thong normally wrapped several times around the workpiece itself. Both ends of this winding cord may be hand-held (by one or more operators) to be pulled back and forth or the cord may be stretched between the two ends of a bow stick. Alternatively, both ends may be attached to treadles or one end only attached to the treadle and the other to a springy pole. Although in western Europe the pole-lathe is the most common form, a number of interesting variations on all these themes is possible of which some indication is to be found in Holtzapffel's classic Turning and Mechanical Manipulation.28 Irrespective of national or regional variation, the modus operandi of the reciprocating lathe is usually thought of as follows: first, the cord is pulled to rotate the workpiece towards the operator thus enabling him to take a cut; this is the positive half of the cycle or the power stroke. Secondly, after the workpiece has finally ceased revolving, the winding cord is pulled back and the workpiece also turns back with it until it is at rest again; this is the negative half or return part of the cycle. These two movements add up to what may be called the ideal reciprocating lathe cycle and this is the stereotype many writers appear to have in mind when describing its operation. It can be represented graphically as a square wave (Fig. 5a). Like all ideal cycles, this one fails to correspond to reality. If one allows for acceleration at the beginning of the power and return strokes and retardation due either to the cutting action or braking effect of the cord, a more realistic picture begins to emerge (Fig. 5b). It would obviously be difficult if not impossible to arrive at a typical representation of the cycle since there are likely to be so many variables as a result of the operator's style in relation to a particular piece of work, but it is clear that the two halves of the cycle are unlikely to appear symmetrical on the graph. What might not readily be appreciated is that this lack of symmetry may well depend to a greater or lesser extent on the inertia of the workpiece. If, for example, the treadle of a pole-lathe is released before a moderately heavy workpiece has stopped turning forwards, there is bound to be considerable slippage before — using Moxon's terminology — the cord commands the workpiece and starts it revolving backwards. If the treadle is released very suddenly and the cord becomes very slack around the workpiece, it may fail to exert any effect whatsoever, even allowing the work to continue turning forward until the subsequent positive half cycle begins. Because, in practice, a considerable amount of energy would be lost in totally reversing the motion of the workpiece during the negative half cycle, it seems reasonable to think that deliberate slipping of the winding cord would become an integral part of the turner's skill when dealing with especially heavy work. Furthermore, a few simple experiments 29 confirm that it is possible to convert the reciprocating action of the winding cord to

+ve

(

R.P.M.

)

O

MAX.

DURATION OF CYCLE

Figure 5a. Graphic representation of the 'ideal' reciprocating lathe cycle. Acceleration and retardation in both directions is assumed to be instantaneous and the speed of the workpiece uniform during the useful working phase (dotted line). The negative half of the cycle is shown as symmetrical though arguably, in the ideal case, it would not be. Figure 5b. A more realistic working cycle would consist of an acceleration phase (almost certainly not uniform) followed by retardation duefirstto the cutting operation and then to the braking effect of the winding cord. The precise shape of an actual cycle would obviously depend upon a number of factors including the personal style of the operator. Figure 5c. Turning either a heavy piece of work or a relatively light piece in conjunction with aflywheelusing only the reciprocating winding cord can be made to yield continuous rotary motion. The inertial effect can thus be exploited to build up speed before taking a heavy cut.

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continuous rotary motion of the workpiece by the exercise of this simple procedure which is especially easy — it seems the 'natural' thing to do — when the hand-held winding cord is used. Providing that the work or its mounting is of sufficient mass, it is quite possible to build up and maintain a modest speed which allows heavy intermittent cuts to be made in soft metal such as brass. Removing a lot of metal is therefore just a question of time. It seems far from fanciful to imagine that in antiquity the flywheel principle of the heavy potter's wheel might have been applied to lathe turning 30 and if this hypothesis is accepted, the problem only remains of explaining how the work could have been mounted. Cylindrical work can obviously be turned between centres, and this includes various types of hollow vessel which it is possible to plug at the open end (Fig. 6). For flat plates or shallow dishes all that is required is a mounting-block part of which is made cylindrical to accommodate the cord. The workpiece could be firmly bonded to this with a hot pitch or wax and resin compound and the whole assembly again mounted between centres — which avoids, incidentally, the problem of tolerably accurate bearings required for the spindle-mounted faceplate (Fig. 7). Even the most awkward shapes can in fact be mounted between centres in this way including, for instance, a spherical bronze bottle illustrated by Mutz 3 1 which has several sets of concentric rings cut into the spherical surface. All that is required in this case are two temporarily bonded wooden blocks fastened either side of the vessel for location of the centres and for driving with the cord. This is equally true for an almost identical Roman glass bottle to be seen in the Royal Museum at Canterbury. 32 This small vessel is decorated with a similar configuration of deeply cut ' V grooves which, however the glass was actually removed, certainly suggest that the bottle was turned against the tool. Admittedly, some turned metalwork is not at all easy to explain in this way. If, for example, we take Vitruvius' report 33 of turning the inner and outer 'cones' of bronze stop-cocks at face value, it would obviously be impossible to remove metal from the female half by turning between centres. This would appear to require the headstock of something like Mutz's arrangement, even though it would not necessitate the continuous drive. On a small scale, it is not out of the question to perform spinning operations using the method suggested above but the spinning of work such as the Roman flanged bowls has to be regarded as an entirely different proposition. An animate or inanimate powered arrangement using gears is one answer, and a plausible one considering that gears were extensively used for power transmission in corn-milling. But this is pure speculation and so, for the time being anyway, Roman metal-spinning must remain a most intriguing problem.

WOODEN

PLUG

t Figure 6. Hollow-ware such as the vase illustrated can be 'plugged' and turned between centres.

WINDING

CORD

MOUNTING BLOCK DISH CENTER

Figure 7. What would normally be considered faceplate work can be turned between centres employing a suitable mounting block. A shallow dish or flat plate can be turned by this means using the winding cord as shown.

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Any study at this early stage in the investigation is bound to generate more questions than answers but it certainly seems worth publicising some of the issues involved if only to elicit fresh points of view. The problem of accounting for Roman metal-turning is only one of several involving ancient lathe-work, but it is this problem in particular that seems likely to be of continuing interest to historians of technology. 34 ACKNOWLEDGEMENT The author would like to thank members of the Department of Greek and Roman Antiquities and of the Research Laboratory of the British Museum for their help, advice and permission to inspect various artefacts. Notes i. A. Mutz, Die Kunst des Metalldrehens bei den Romern, Birkhauser Verlag, Basel und Stuttgart, 1972. 2. See for example, R. S. Woodbury, History of the Lathe to 18so, Society for the History of Technology, Cleveland 6, Ohio, 1961. 3. For example, H. Maryon, 'Metalworking in the Ancient World', American Journal of Archaeology, Vol. 53, No. 2, 1949. 4. For a detailed description of some of these see C. Holtzapffel & J. J. Holtzapffel, Turning and Mechanical Manipulation, Vol. 4, London: Holtzapffel & Co., 1897. 5. Abell, Leggat & Ogden, A Bibliography of the Art of Turning and Lathe and Machine Tool History, The Society of Ornamental Turners, 1956. 6. See for example, J. Moxon, Mechanick Exercises; or the Doctrine of Handy-Works, No. 12, London, 1677-96, p. 212. 7. R. S. Woodbury, 'The Origins of the Lathe', Scientific American, 208, No. 4, 1963, P- 133. 8. An engraving on a later Roman gravestone illustrates the use of the bow rather than a winding-cord for turning a horizontal lapidary spindle. 9. A number of suggestive artefacts earlier than this seem to have escaped attention. The terminals of a seventh century B.C. Irish gorget, for example, now in the Victoria & Albert Museum, are decorated with perfectly concentric corrugations, possibly impressed into the thin gold sheet whilst it was turning. 10. British Museum Registration No. 1906. 3-10. 2. 11. British Museum Registration No. 1897. 7-26. 1. 12. It has been suggested that here they have the functional purpose of promoting more efficient heat exchange. 13. Examples of most of these are to be found on display in the rooms of the Department of Greek and Roman Antiquities at the British Museum. 14. A suitably modified form of compass can be used to make light cuts in metal and one therefore has to be very cautious. Moxon {op. cit., p. 215) describes a kind of beam compass ('sweep') with which he claims to have worked brass as successfully as he might with the lathe. 15. Pliny speaks of coating copper vessels with stagnum, an alloy of lead and silver, Natural History, Bk. XXXIV. XLVIII. 160. 16. British Museum Registration No. 73. 1-11. 3. 17. British Museum Registration Nos. 1892. 5-17. 1. (Complete.) 1892. 5-17. 2. (Fragmented.) 18. See for example, Vitruvius, De Architectura, Bk. X. VII. 3. 'Pistons are now inserted from above rounded on the lathe, (tournus) and well oiled . . .' 19. D. Pye, The Nature of Design, Studio Vista, London, 196420. Mutz, op. cit., p. 38.

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21. The suggestion of Mrs J. Laing of the British Museum Research Laboratory. 22. Strong sees evidence of spinning in Hellenistic footless bowls: D. E. Strong, Greek and Roman Gold and Silver Plate, Methuen, 1966, p. 108. For evidence of spinning in two Belgic bowls of about the beginning of the Christian era see R. F. Tylecote, Metallurgy in Archaeology, E. Arnold, London, 1962, p. 149. 23. Mutz, op. cit., p. 34. 24. British Museum Registration No. 1890. 9-23. 3. 25. The most prolific sources are Vitruvius and Pliny. Those for Vitruvius are: De Architectural Bk. IX. 1. 2. Bk. IX. VIII. 6. Bk. X. I. 6. Bk. X. III. 2. Bk. X. VII. 3. Bk. X. VIII. 1. Bk. X. XIII. 6. Bk. X. XV. 4. 26. Woodbury, as Note 2, p. 44. 27. Drachmann, it should be noted, has found some slender literary evidence for the use of the crank. See, A. G. Drachmann, 'The Crank in Graeco-Roman Antiquity', in Teich & Young (ed.), Changing Perspectives in the History of Science, Heinemann, London, 1973. 28. Holtzapffel, op. cit. 29. The experiments in question were actually carried out on a modern centre lathe by making use only of the two centres and using the tool post as a hand tool rest. Employing the type of mounting shown in Fig. 7. it was found possible to take intermittent deep cuts or continuous light cuts in a sheet of brass continuously rotated only by a reciprocating plastic cord. Also, it was possible to turn the workpiece either with both ends of the cord hand held or with one end fastened to a large tension spring to simulate pole lathe working. The whole issue of turning metals in this way clearly warrants further investigation. 30. No inertial effect is in fact necessary for the turning of small objects on the reciprocating lathe. 31. Mutz, op. cit., p. 136. 32. Accession No. Royal Museum 6433. 33. Vitruvius, De Architectura, Bk. IX. VIII. 34. Markings on the backs of numerous turned pieces suggest that a more convenient method of mounting was commonly adopted in which the workpiece was pushed against three spikes protruding from the face of the driving component of the lathe. But it has to be pointed out that the use of this mounting technique does not necessarily presuppose the spindle mounted faceplate of something like Mutz's reconstruction; the spikes could usefully be set into the face of the mounting block shown infig.7 where they would avoid the necessity for a semi-permanent bond to be made.

O l d

D a m s JOSE

A.

i n

E x t r e m a d u r a

GARCIA-DIEGO

Spanish D a m s Spain occupies a distinguished place in the history of hydraulic technology. Besides her very important aqueducts and canals, she also possesses a series of historic dams whose interest and importance are unequalled in any other country. T h e importance of irrigation and the need to develop hydroelectric energy to the m a x i m u m — as the country is completely lacking in oil and its coal mines are of little importance — has led to the construction of many more dams in m o d e r n times: Spain occupies a leading place in the world's catalogue of large dams. W e will summarize the historical development of Spanish dams u p to the eighteenth century; for a more detailed picture of the subject we recommend N o r m a n A. F . Smith's excellent book ^4 History of Dams.1 ROMAN EPOCH T h e two most important dams preserved anywhere in the whole of the R o m a n Empire's territory and which continue to function normally today are those of Cornalvo and Proserpina in Merida (and therefore also in Extremadura, although I shall not refer to t h e m in my study). Another interesting one is the Alcantarilla d a m which was the origin of Toledo's water-supply and which suffered a partial collapse at some unknown date. Since the publication of Smith's book an interesting paper by Raul Celestino has appeared which describes Alcantarilla in detail 2 and there has also been published the first study of the buttress dam of Esparragalejo, in the Merida area. 3 Another Roman dam, in Consuegra, province of Toledo, has recently been discovered. 4 MIDDLE AGES Some Arab dams have survived although in general later additions and modifications have obscured their original form. Examples are Albalate de la Cuba and Mestalla. Plenty of information also exists about Arab irrigation systems. 5 N o remains of Christian works of this period have been located, though they certainly existed. RENAISSANCE T h i s is the epoch in which Spanish hydraulic technology reached its peak, both in inventiveness and in the volume of work carried out. A series of storage dams for irrigation was constructed some of which attained dimensions that were not to be surpassed until the n i n e t e e n t h c e n t u r y . M o s t of t h e m are situated near t h e

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Old Dams in Extremadura

Mediterranean shores, where irrigation had a long tradition reaching back before the period of Arab domination. There certainly exists too, though they have not been studied, a series of weirs from this period which to some extent feature new technical solutions. This is evident from one of the chapters of the codex attributed to Juanelo Turriano which is preserved in the National Library in Madrid. 6 THE ENLIGHTENMENT In this period of prosperity, during which the decline of the country was to some extent checked, hydraulic works were once more prosecuted. We shall quote only two examples. In the north of Spain D o n Pedro Bernardo Villarreal de Berriz, a Basque nobleman who pursued a variety of technological interests and was also a keen amateur scientist, planned and built five dams, one of the arch type and four of the multiple-arch type; the latter are the oldest known specimens of their kind. They exist today and are in a good state of repair. D o n Pedro also published a book largely devoted to descriptions of his new ideas and techniques. Here we have, I believe for the first time, a printed work on dam design and construction by an engineer who was anxious to communicate his thoughts and experiences to other practitioners. 7 Lastly, and with it I reach the theme of my work, in 1747 there was built in Extremadura the dam of Albuera de Feria, which Smith calls Almendralejo. Discovered and described by Juan Lazaro in 19363s it has since come to be regarded as the first buttress dam of the modern age. But it is an isolated example; the only previous ones (Roman) were of much smaller size and a good deal less important. It must be remembered that the use of buttresses to give strength to retaining walls and as structural elements in the Romanesque and Gothic styles was already well known; the novelty of Albuera de Feria is the use of buttresses in a hydraulic structure. According to the usual hypothesis, the second buttress dam would be that of Lampy on the Canal du Midi (1777-81). And one author goes so far as to state that its designer, M. Garripuy, knew the unique example in Extremadura and was inspired by it. 9 Our objective will be to show that this hypothesis is not accurate. In reality Albuera de Feria was but one example, although admittedly a very important one, of a whole sequence of buttress dams built in Extremadura over a long period. The introduction of the buttress dam in the modern age does not date from the eighteenth century but from the sixteenth (or perhaps before) and their basic characteristics were preserved practically unaltered until a period comparatively close to our own.

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Garcia-Diego

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Extremadura Notwithstanding the fact that most of the land is dry and arid, it was here that the Romans created the city of Merida, the capital of the province of Lusitania. Merida prospered in such a way that the Gallic poet Ausonius, in the fourth century, considered it to be the ninth city in the E m p i r e ; it appeared in the list after R o m e , Constantinople and Alexandria, b u t before Athens. 1 0 T h e greatness of the city influenced the surrounding territory. But its splendour ended with the Romans, and since then the region has had a very moderate development, always below the average for the country. It has produced neither important businessmen nor politicians who, with the development of the M o d e r n State, might have secured substantial economic aid for the region. T h r o u g h o u t history, the fundamental features of the economic and social systems of Extremadura have been two. T h e l a t i f u n d i a . W e know that these great estates already existed in the thirteenth century and that a basic feature of the system was the supply of labour by peasants who had no land, though some of them owned oxen. T h i s pattern of social organization and land distribution has continued until the present day: it has even been stated that the map of the great properties in the fifteenth century would not differ much from the present one. 1 1 O n these great estates — in which Extremadura's dams are nearly all situated — the principal occupation was, and still is, the breeding of livestock, advantage being taken of the fact that there are usually good winter pastures. T h e wool of the merino sheep was the type most appreciated in the sixteenth century and it was exported, t h r o u g h the port of Seville, to the whole world. T h e second most important activity is agriculture. Cereals and timber are grown and an especially important product is cork. T h e m i g r a t i o n o f h e r d s a n d flocks. Until comparatively recent times, when spring arrived the shepherds moved their animals to regions further north, so as to be able to ensure a supply of food. It has been supposed that this nomadic way of life influenced the spirit and attitudes of Extremaduran peoples, predisposing t h e m to travel and adventure rather then engendering in them the practical attitudes necessary to achieve a pre-capitalist state. Such a theory would explain Extremadura 5 s great contribution to the conquest of America; in fact, many of the most famous leaders were born there. But in my view, this explanation is oversimplified. I n the sixteenth century there was, with the return of the conquistadores, a certain period of splendour, albeit rather

98

Old Dams in Extremadura

superficial. It was an age of beautiful architectural achievements, outstanding among which are the old part of the city of Caceres and the village of Trujillo, and there are other very interesting examples as well, but the traditional social scheme was preserved and the region did not adopt the capitalism which was already growing in other parts of Spain. Afterwards we have only decadence. During the eighteenth century the population went up from 400,000 to only 425,000 inhabitants, whereas it doubled in most other parts of Spain. And yet the fact is that this epoch — the Enlightenment — was the only one in which the State tried to intervene in order to bring about agrarian reform. T h e attempt failed due not only to the opposition of great landowners but also to the peasants' lack of capital. The course of later events I shall not pursue since they are outside the time limits I have chosen for my study. The D a m s The criterion for including a dam in this study is that it was built, so far as is known, before 1800 and on this basis the list comprises twenty-three structures. In Table I are given their names and basic characteristics. TABLE 1

Name BUTTRESS DAMS 1 Arce de Aba jo 2 Arce de Arriba 3 Arroyo de la Luz 4 Barroso 5 Barrueco de Aba jo 6 Barrueco de Arriba 7 Casillas I 8 Casillas II 9 Cueto 10 El Lugar 11 Feria 12 Garcia 13 Grena 14 La Generala 15 Lancho 16 Trujillo 17 Vegas Altas 18 Zalamea GRAVITY DAMS 19 Casabaya 20 Castellar 21 Zamores LOOSE MATERIAL DAMS 22 Mata de Alcantara 23 Molino de Cabra

Height (m)

Length (m)

4 7 6 6 7 9 10 9 8 4 24 7 9 9 7 11 6 17

120 262 250 130 120 90 182 80 220 206 170 219 240 200 142 175 178 113

4 8 8 2 7 6 3 1 6 2 7 5 3 2 1 3 2 2

15 19 9

120 100 107

1 3 2

4 4

130 75

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Figure I It will be useful to make some remarks about the names that appear in the Table. Officially (Ministry of Public Works), some of them are preceded by the words Albuera de . . , 12 or else Charca de .. . 13 The word albuera, of Moorish origin, (written albuhera in the old days), means reservoir. T h e meaning of charca (literally 'pond') is the same in Extremadura, though it generally refers to lesser volumes of water; the same name is also given to lagoons and even to pools. If one is looking for the site of one of these old dams, the best thing is to ask the peasants where la charca is. However, in order to simplify and unify the nomenclature in this paper both terms have been dispensed with. Furthermore in the case of dam N o . 16 the name Trujillo dam has been adopted simply because the structure is located almost within the village of that name; up to now it has always been known as the Albuera dam, which of course does not make sense if taken literally. T h e dams are marked on the map in Fig. i. As may be seen, they are grouped in four zones. i. Most of them are between Alcantara and the region south of

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Caceres. At the first named place stands what is perhaps the most beautiful and important of extant Roman bridges and nearby is a m o d e r n dam and a hydro-electric power station that is among the most powerful in Europe. Alcantara was the headquarters of the military and religious Order of that name and it was this group which was perhaps responsible for the construction of some of the dams. I n fact, the Knights of Alcantara formed a group that was very powerful both economically and politically, not only in itself but also through its close connection with the aristocracy. T h e Crown installed them in the region in the thirteenth century soon after the area had been reconquered from the Arabs and was still relatively insecure. Moreover there was a certain lack of enthusiasm on the part of the inhabitants of Castile to move to more southerly parts. 2. T h e village of Trujillo, of R o m a n origin and important in different ages of Spanish history, and its immediate surroundings. 3. A zone to the south of Badajoz (capital of the province of that name), the centre of which we may consider to be Zafra. 4. T h e beautiful dam of Zalamea, isolated from the rest. I n Figs. 2 to 12 are shown sections and ground plans of most of the dams and from these, in conjunction with the statistics shown in T a b l e 1, a few broad conclusions relating to dimensions and sizes can be drawn. H e i g h t s . T h e highest dam is Feria at 24 m. It is followed by the recently disappeared — as we shall mention later — dam of Castellar (19 m) and then Zalamea, 17 m high and architecturally the finest of them all. It is interesting that, if one had to choose the five most representative dams, three of them have just been mentioned; the other two are those of Trujillo and Grefia. T h e average height of all twenty-three dams is 9.2 m. L e n g t h s . T h e longest is Arce de Arriba at 262 m. T h e average length of the twenty-three is 153 m. Seven of the dams have a length equal to or greater than 200 m ; and only three are less than 100 m in length. V o l u m e s o f t h e r e s e r v o i r s . T h e volumes range from 0.8 x i o 6 m 3 to 0.1 x i o 6 m 3 and the average is 0.36 x i o 6 m 3 . Such capacities are undoubtedly small and yet every reservoir was intended for water storage and each was evidently sufficient for its intended purpose. It m u s t be remembered that the rivers on which they are situated are so small that if a certain annual regulation were not achieved they could not be useful for more than a few months in each year. STRUCTURAL TYPES T a b l e I shows that the twenty-three dams studied can be classified

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into three structural types. By far the biggest and most significant group are the buttress dams, eighteen of them. B u t t r e s s d a m s . T h e preponderance of this structural type suggests that the use of buttress dams is the fundamental characteristic of Extremaduran dam-building. Of course these buttress dams were not designed on the basis of any analysis using the strength of materials; this branch of engineering science did not evolve until the second half of the eighteenth century in a theoretical form or until the nineteenth century in a practical one. T h e thickness of the water-supporting decks is, in general, less than that necessary to resist the water's pressure — at least theoretically — by self-weight alone. T h a t is to say that most are true buttress dams and they are not gravity dams to which buttresses were added as a device to ensure greater stability; similarly arch dams have been designed and sometimes built, even in the twentieth century, with such a thick section as to make the arched shape superfluous. If we call the m a x i m u m thickness of the decks W and the m a x i m u m height H , the ratio W / H is in general little more than 0.40. But we find values as low as 0.15 in three of t h e m (Barroso, Cueto and Grena) and there is only one very high figure, 0.88 at Arroyo de la L u z . Moreover in this case we do not strictly speaking have a buttress dam at all; only one buttress appears clearly defined, while the section in other parts is increased with blocks that are wider than they are high and distributed at random (Fig. 5). Of course all of this does not mean that the design of these works is structurally daring (we should remember that the dimensions either were fixed intuitively or were based on tradition). 1 4 F o r in a good many cases the lightness of the deck is more than compensated for by the buttresses being wide and closely spaced. Also, the adjoining mill often occupies a large part of the central area of the dam and the buttresses only act fully in the abutments. G r a v i t y d a m s . Of the three we know about, that of Castellar is outstanding for several reasons. I n the first place, in the 'Inventory of Spanish D a m s I973' 1 5 t h e date of its construction is given as 1500, although I have found it impossible to find the basis for this statement. T h e work is clearly very old and if the dating were accurate it would mean that Castellar occupies a very important place in the history of d a m s ; few examples from such an early date have survived. Unfortunately it will never be possible to study Castellar in detail. A short time ago a higher dam for irrigation was constructed immediately d o w n - s t r e a m . W h e n t h e new d a m h a d b e e n

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