J.J. Thompson And The Discovery Of The Electron

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<ul><li><p>J.J.Thomson and the Discovery of the Electron</p></li><li><p>Thomson in the 1920s </p></li><li><p>Page of cathode ray manuscript in Thomsons own hand</p><p>iii</p></li><li><p>J.J.Thomson and the Discovery of theElectron</p><p>E.A.DAVIS and I.J.FALCONER</p></li><li><p>UK Taylor &amp; Francis Ltd., 1 Gunpowder Square, London EC4A 3DEUSA Taylor &amp; Francis Inc., 1900 Frost Road, Suite 101, Bristol, PA 19007</p><p>This edition published in the Taylor &amp; Francis e-Library, 2005.</p><p>To purchase your own copy of this or any of Taylor &amp; Francis or Routledges collection of thousands of eBooks please go towww.eBookstore.tandf.co.uk.</p><p>Copyright Taylor &amp; Francis Ltd 1997</p><p>All rights reserved. No part of this publication may be reproduced, stored in aretrieval system, or transmitted, in any form or by any means, electronic,</p><p>electrostatic, magnetic tape, mechanical, photocopying, recording or otherwise,without the prior permission of the copyright owner.</p><p>British Library Cataloguing in Publication DataA catalogue record for this book is available from the British Library</p><p>ISBN 0-203-48409-6 Master e-book ISBN</p><p>ISBN 0-203-79233-5 (Adobe eReader Format)ISBN 0-7484-0696-4 cased</p><p>0-7484-0720-0 paper</p><p>Library of Congress Cataloging Publication Data are available</p><p>Cover design by Youngs Design in Production</p></li><li><p>To Christine and Kenneth</p></li><li><p>Contents</p><p> Foreword ix</p><p> Preface xxi</p><p>1 Formative Years 1</p><p> Education at Owens College 1</p><p> Cambridge and the Mathematics Tripos 6</p><p>2 Early Research 9</p><p> Analytical Dynamics 9</p><p> Electromagnetic Mass 12</p><p> College LectureshipVortex Atoms 12</p><p> The Cavendish Laboratory 14</p><p> Facsimiles: J.J.Thomson, On the Electric and Magnetic Effects Produced by the Motion ofElectrified Bodies, Philosophical Magazine, 11 (1881), 22934.</p><p> 20</p><p> J.J.Thomson, Treatise on the Motion of Vortex Rings, 1882, pp. 12 and 11424. 25</p><p>3 Cavendish Professorship: First Years 35</p><p> Appointment as Cavendish Professor 35</p><p> Gaseous Discharge 36</p><p> The Changing Nature of the Cavendish 41</p><p> Facsimiles: J.J.Thomson, On the Theory of the Electric Discharge in Gases, PhilosophicalMagazine, 15 (1883) 42734.</p><p> 47</p><p> J.J.Thomson, Some Experiments on the Electric Discharge in a Uniform Electric Field, with someTheoretical Considerations about the Passage of Electricity Through Gases, Proceedings of theCambridge Philosophical Society, 5 (1886) 3919.</p><p> 52</p><p>4 Gaseous Discharges: Further Developments (18911895) 60</p><p> Grotthus Chains and Faraday Tubes of Force 60</p><p> Electrodeless Discharges 65</p></li><li><p> Electrolysis of Steam and Condensation 67</p><p> Electricity of Drops 69</p><p> The Gyroscopic Atom and Chemical Combinations 70</p><p> Summary 72</p><p> Facsimile: J.J.Thomson, The Relation between the Atom and the Charge of Electricity Carried byit, Philosophical Magazine, 40 (1895) 51127.</p><p> 74</p><p>5 X-rays and Cathode Rays (18951900) 87</p><p> Research Students 87</p><p> X-rays 89</p><p> The Cathode Ray Controversy 96</p><p> Resolution of the Cathode Ray Problem 97</p><p> Measurement of the Charge 101</p><p> Corpuscles versus Electrons 105</p><p> Acceptance of Subatomic Particles 106</p><p> Facsimiles: J.J.Thomson, Cathode Rays, Proceedings of the Royal Institution (1897), pp. 114. 110</p><p> J.J.Thomson, Cathode Rays, Philosophical Magazine, 44 (1897) 296314. 121</p><p> J.J.Thomson, On the Masses of the Ions in Gases at Low Pressures, Philosophical Magazine, 48(1899) 54767.</p><p> 135</p><p>6 Later Years 151</p><p> The Electromagnetic View of Matter and the Thomson Atom 151</p><p> Positive Rays 157</p><p> The Structure of Light 161</p><p> Views on Physical Theories 165</p><p> Last 20 Years 166</p><p> Facsimile: J.J.Thomson, The Structure of the Atom, Proceedings of the Royal Institution, 18 (1905)115.</p><p> 171</p><p>7 Subsequent Developments 185</p><p> Elementary Particle Physics 185</p><p> The Electronics Revolution 188</p><p> Index 191</p><p>viii</p></li><li><p>ForewordDavid Thomson</p><p>The Masters Lodge at Trinity College in Cambridge faces onto the Great Court of grand and pleasingproportions and is backed by its walled garden leading down to the River Cam. It has been the serene homefor more than three hundred years of great academic figures. Sir Joseph Thomson, my grandfather and thelast Master to hold the position for life, died there in August 1940 at the age of 83. He and his wife Rosehad lived in the Lodge, together with their daughter Joan, for 22 years, presiding over the grandest ofCambridge Colleges with a simple wisdom, tact and humour that complemented his achievements as aphysicist of super-eminence, as Lloyd George once described him.</p><p>1940 was a bleak moment for the nation and scarcely an appropriate time to assess the place in science ofJ.J. Thomson, the initials by which he was invariably known rather than the title Sir Joseph. The mainperiod of his creativity lay roughly between the years 1890 and 1910; the high point, which gave him fame,was his work with cathode rays leading in 1897 to his theory about corpuscles smaller than atoms, later tobe called electrons, and subsequent confirmation of these theoretical ideas with proof of the particlesexistence, which many had doubted, by a series of brilliant experiments.</p><p>The setting for these discoveries was the Cavendish Laboratory of which J.J. was professor for the longspan of 35 years. Apart from his own ground-breaking work which took the first steps into the subatomicphysics of the twentieth century, he directed, recruited and inspired a succession of brilliant young menround him at the Cavendish who were to share this work and later to create whole new fields of science. It isprobable that there has never been such a successful and sustained record of new scientific discovery in onelaboratory across such a broad field as that which happened under J.J.s leadership of the Cavendishlaboratory from 1884 to 1919. It can claim to be the first real School of Physics in the modern sense, and inhis time it was generally regarded as the leading experimental laboratory of physics in the scientific world.</p><p>In 1997 we are celebrating the centenary of J.J.s first exposition of his thesis that a cathode ray particleis more than 1000 times lighter than the lightest chemical atom and a universal constituent of matter. It isalso an opportunity, now long overdue, to re-assess J.J.s own reputation and place in the history of science,judged against the developments throughout the twentieth century both in pure and applied science whichbuilt on the foundations of his work and that of the group round him at the Cavendish.</p><p>At J.J.s death his great period of work had ceased a whole generation earlier. He was certainly not a manwith only one discovery to his name, as his subsequent work on positive rays leading to the discovery withAston of non-radioactive isotopes, and the constant ferment of his intellectual energy amply proved. However,by the time the First World War started in 1914, when he was nearing sixty, his main work had beenachieved.</p><p>The effect of that war on the laboratory practically brought original research to an end. The youngerscientists, including J.J.s son, soon found themselves in France, fighting at the Front. J.J. himself was</p></li><li><p>drawn into War Committee work and also became President of the Royal Society. Shortly before the end ofthe war Montagu Butler, then Master of Trinity, died and J.J. was appointed to succeed. He did not thereforetake up an active research role when peace time conditions returned and he retired officially from theCavendish in 1919, though retaining an honorary professorship and space for his own research. His mostfamous pupil and collaborator, Ernest Rutherford, succeeded him and J.J. became increasingly a seniorspokesman of Science. He did however continue to produce new work, much of it based round universaltheories of the ether, harking back to some of his earliest concepts.</p><p>In 1940 then, the formal honours were paid at his death. He was a national figure. In the popular mindthe man who split the atom, he was the senior member of the Order of Merit, the epitome of Cambridgescience and something of a legend, in Cambridge at least, as a much admired, if sometimes absent-minded,genius.</p><p>His ashes were buried in Westminster Abbey and the stone above them lies in the shadow of IsaacNewtons memorial and next to that of Rutherford, who had predeceased him, sadly early, three yearsbefore.</p><p>Trinity did not lack for great names to succeed him. After science, it was the turn of history. Theappointment at Trinity is a royal one on the Prime Ministers recommendation, and the choice most aptlywas George Trevelyan. To quote Trevelyan, a mans reputation with the world at large is usually at itslowest exactly a hundred years after his birth, especially in the realm of letters. It was to be true ofTrevelyan himself, and in the realm of science equally true of his predecessor at Trinity. In both cases thetide is turning. </p><p>J.J.s background was Manchester; liberal, mercantile Manchester, where his family had lived for threegenerations. His great-grandfather came from Scotlandhence the Scottish spelling of Thomsonandstarted a small business selling antiquarian books, occasionally acting as a publisher too. It must haveprospered sufficiently to give a reasonable living and a house with servants in the middle-class suburb ofCheetham. Socially this would have put the family in the merchant middle class, somewhat below thedoctors, solicitors and clergy of the professional classes.</p><p>J.J.s father, also Joseph, died aged 38 when the boy was only 16, and the only other child, Frederick,four years younger. Though not much seems to be remembered of the father, it is recalled that he was proudto be acquainted with some of the scientific and literary people of Manchester, many of whom wouldprobably have known his bookshop. Indeed it was in this way that he came to hear of Owens College and itsgrowing reputation for good teaching. The father seems to have decided that his sons aptitude formathematics suggested that engineering was a more suitable choice than bookselling, perhaps hoping thatthe younger son would follow in the family line. As the engineering apprenticeship to a Manchester firm ofengine-makers could not be started until 16, and J.J. had precociously outgrown his school by 14, OwensCollege would fill the gap.</p><p>J.J. in later days regarded this as the lucky chance that shaped his life. When his father died unexpectedlyafter two years at Owens, there was no money to pay for the apprenticeship; the business was sold, hismother, Emma, moved to a smaller terraced house nearer the College and found enough money to keep J.J.there.</p><p>Manchester had of course a great tradition of science. Its Literary and Philosophical Society founded in1781 was older than the corresponding Royal Institution in London. John Dalton, the great chemist andauthor of the atomic theory, had his laboratory in the Society and was its servant as Secretary and thenPresident from 1800 to 1844. He was succeeded by James Joule who, at the early age of 22, had discoveredthe law named after him and, at 25, had published the paper which led to the acceptance of the principle ofthe Conservation of Energy. J.J. was to write in his autobiographical Recollections and Reflections that this</p><p>x</p></li><li><p>discovery was a striking instance of how great generalisations may be reached by patient work, a phrasethat might be used of his own work on the electron. When J.J. was a boy he had been introduced to Joule byhis father who had said afterwards some day you will be proud to say you have met that gentleman.</p><p>It was this sort of influence and background that shaped the schoolboys thoughts to science. He was ashy boy but determined and knew which way he was pointing. It was at about this time that when asked bya cousin what he wanted to do when he grew up, he replied that he intended to go in for original researcha rare ambition in 1870and his cousin remembered my brother-in-law tapped him on his head and saiddont be such a little prig, Joe. </p><p>Owens College, called after the merchant who left his money to found it in 1851, had a shaky start buttwenty years later when J.J. arrived it had started to prosper. There was probably no other college outsideOxford and Cambridge that could match it in England, though Glasgow was perhaps its equal in Scotland.Later, in his Recollections, J.J. was to write though Owens College was badly housed, no university in thecountry had a more brilliant staff of Professors. The range of lectures in engineering, mathematics andnatural philosophy, as physics was then called, was impressive. In effect he had been through universitycourses in three subjects while still a schoolboy, and thrived on it.</p><p>He needed to proceed by scholarships; there was no money otherwise to go forward academically, andhis virtuosity had made it clear to his teachers that Cambridge, with its great reputation for mathematics,was the place to aim for. The route had to be mathematics; there were no entry scholarships for engineeringor physics. He succeeded at his second try at Trinity, the College with the highest reputation and the hardestto get into by scholarship. There were by then a number of reasons pointing to Trinity. The first was his ownself-confidence in his ability; he knew he was in the top division and did not hesitate to test himself. Thesecond was that a number of his teachers had been Trinity men, particularly Thomas Barker, the professorof Mathematics, who had also been Senior Wranglerthat sonorous intellectual title of Victorian academia.And a young member of staff, John Poynting, arriving at Owens shortly before J.J. left and one of his closestfriends in later years, was also from Trinity. Not long before, John Hopkinson, a future Professor ofEngineering at Cambridge, had left Owens for the same destination and won distinction as Senior Wrangler.It all seemed to point in the same direction.</p><p>Perhaps a final reason for a young man with his eyes on original research, and who had published hisfirst short paper in the Proceedings of the Royal Society when aged 19, before leaving Owens, was thatTrinity had famously been the home of Sir Isaac Newton and was currently the College of James ClerkMaxwell, the first Cavendish Professor of Experimental Physics, whose famous Treatise on Electricity andMagnetism was a starting point for much of J.J.s early thoughts about research.</p><p>J.J.s personal life divides quite simply; his family background and education in Manchester, and hissubsequent life in Cambridge. In his long life he never lived anywhere else but those two places. To roundoff the Manchester period, it would be appropriate to say something of the family he was about to leavebehind. His relations with his mother had always been close. She was a sweet-natured person, proud of herson without, I suspect, understanding anything at all of his work. He spent part of his summers with herregularly, after his marriage as well, up to her death in 1901, either in Manchester or at some seaside resort.His younger brother, Fred, a bachelor all his life, was from my fathers account a man of selfless decencyand kindness. He seems to have accepted his brothers success with admiration, and felt no rancour that hehad not had the education...</p></li></ul>

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