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Corpuscles, Electrons and Cathode Rays: J.J. Thomson and the ‘Discovery of the Electron’

Published online by Cambridge University Press:  05 January 2009

Isobel Falconer
Isobel Falconer
Affiliation:
Flat 3, Woodlands, Bridge Road, Leigh Woods, Bristol BS8 3PB, U.K.
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Extract

On 30 April, 1897, J. J. Thomson announced the results of his previous four months' experiments on cathode rays. The rays, he suggested, were negatively charged subatomic particles. He called the particles ‘corpuscles’. They have since been re-named ‘electrons’ and Thomson has been hailed as their ‘discoverer’. Contrary to the accounts of most later writers, I show that this discovery was not the outcome of a concern with the nature of cathode rays which had occupied Thomson since 1881 and had shaped the course of his experiments during the period 1881–1897. An examination of his work shows that he paid scant attention to cathode rays until late 1896.

Type
Research Article
Information
The British Journal for the History of Science , Volume 20 , Issue 3 , July 1987 , pp. 241 - 276
Copyright
Copyright © British Society for the History of Science 1987

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References

This paper is condensed from my Ph.D thesis ‘Theory and experiment in J.J. Thomson's work on gaseous discharge,’ University of Bath, 1985, in which further details may be found. I am grateful to my supervisor,David Gooding for encouragement and helpful criticism and to the University of Bath for financial support. I have enjoyed the hospitality of Oregon State University while writing this paper.

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3 Heilbron points this out in his DSB biography of Thomson. He takes an independent line from other writers [op. cit. (2)] and correctly emphasizes the importance of Thomson's commitment to Maxwell's electromagnetism and the mechanical philosophy in guiding the discharge work. However, he still assigns the cathode ray controversy unwarranted prominence. In particular, he sees the discovery of X-rays as an outcome of controversy rather than vice versa. Heilbron, J. L., ‘Thomson, Joseph John’, Dictionary of Scientific Biography, 13, p. 362.Google Scholar

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24 Kaufmann, W., ‘Die magnetische Ablenkbarkeit der Kathodenstrahlen und ihre Abhängigkeit vom Entladungspotential’, Annalen der Physik und Chemie, (1897), 61, p. 544CrossRefGoogle Scholar; (1897), 62, p. 596; Wiechert, E., ‘Ergebniss einer Messung der Geschwindigkeit der Kathodenstrahlen’, Schriften der physikalischökonomisch Gesellschaft zu Königsberg, (1897), 38, p. 3.Google Scholar

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30 A detailed study of the German ether theories and attitude to the controversy is badly needed. Most accounts are written from the point of view of the winning particle theorists. The best account is Turpin, 's op. cit. (14).Google Scholar

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33 Cambridge University Library MS, Add 7654 NB36.

34 This difference between Schuster and Thomson was probably largely due to the conditions under which they performed their experiments. Neither quotes figures for the pressures they were working at, but Schuster appears to have expended more time in evacuating his apparatus. At the relatively high pressures of Thomson's experiments, cathode rays were not a significant phenomenon, but they probably were in Schuster's experiments. Schuster, A., ‘Experiments on the discharge of electricity through gases: a sketch of a theory’ (Royal Society Bakerian Lecture), Proceedings of the Royal Society, (1884), 37, pp. 317, 495CrossRefGoogle Scholar; ‘Experiments on the discharge of electricity through gases’, Proceedings of the Royal Society, (1887), 42, p. 371Google Scholar; ‘The passage of electricity through gases’, British Association Report, (1889), p. 510Google Scholar; ‘The disruptive discharge of electricity through gases’, Philosophical Magazine, (1890), V, 29, p. 182Google Scholar; op. cit. (20).

35 Thomson, , op. cit. (32), p. 121.Google Scholar

36 The Electrician, (1894), 33, p. 475.Google Scholar

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51 See works referenced in note (2). Heilbron [op. cit. (3)], however, correctly assesses Hertz's experiment as relatively unimportant.

52 FitzGerald, , op. cit. (43).Google Scholar

53 Sharlin, H., The Convergent Century: The Unification of Science in the Nineteenth Century, London, 1966Google Scholar; Wilson, D.B., ‘The thought of late Victorian physicists: Oliver Lodge's ethereal body’, Victorian Studies, (1971), 15, p. 29.Google Scholar

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55 Klein examines the status of the mechanical philosophy and visualisable analogies, particularly Maxwell's use of them: Klein, M. J., ‘Mechanical explanation at the end of the nineteenth century’, Centaurus, (1972), 17, p. 58.CrossRefGoogle Scholar Topper has studied Thomson's commitment to mechanism in general, and to Maxwell in particular, in his thesis and two papers: Topper, D., ‘J. J. Thomson and Maxwell's Electromagnetic Theory’, Ph.D dissertation, Case Western Reserve University, 1970Google Scholar, University Microfilms order No. 71–19065; ‘Commitment to mechanism: J.J.Thomson, the early years’, Archive for the History of Exact Sciences, (1971), 7, p. 393Google Scholar; ‘To reason by means of images: J. J. Thomson and the mechanical picture of nature’, Annals of Science, (1980), 37, p. 31.Google Scholar The last of these is particularly important for containing details of Thomson's vortex analogies and the way he transposed them from one situation to another. However, Topper deals exclusively with Thomson's theoretical work. He does not consider any experimental stimulus for the theory changes he describes, nor the influence of these theoretical commitments on Thomson's experimental work. As Wheaton has pointed out, the mechanical philosophy was implicit in Thomson and Schuster's cathode ray experiments: they assumed that macroscopic mechanical laws carried over into the microscopic realm: Wheaton, B., The Tiger and the Shark, Cambridge, 1983, p. 6.CrossRefGoogle Scholar In my thesis and a forthcoming paper, I discuss other ways in which the mechanical philosophy influenced Thomson's approach to experiment: Falconer, I., ‘J. J. Thomson; an experimental genius?’ (1986)Google Scholar, submitted to Social Studies in Science.

56 Thomson, J.J., ‘On a theory of the electric discharge in gases’, Philosophical Magazine, (1883), V, 15, p. 427.Google Scholar

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63 Thomson, J.J., ‘A theory of the connection between cathode and Röntgen rays’, Philosophical Magazine, (1898), V, 45, p. 172Google Scholar; ‘On the connexion between the chemical composition of a gas and the ionisation produced in it by Röntgen rays’, Proceedings of the Cambridge Philosophical Society, (1898), 10, p. 10Google Scholar; ‘On the charge of electricity carried by the ions produced by Röntgen rays’, Philosophical Magazine, (1899), V, 47, p. 253Google Scholar; ‘The genesis of the ions in the discharge of electricity through gases’, Philosophical Magazine, (1900), V, 50, p. 278.Google Scholar

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70 Rutherford, E., ‘1895–1898’, in A History of the Cavendish Laboratory 1871–1910, London, 1910, p. 159.Google Scholar

71 Cambridge University Library MS, Add 7654 NB39. My thesis contains a much more detailed account of this notebook and the evidence it contains of Rutherford and Thomson's theoretical expectations.

72 Thomson, J.J., ‘The Röntgen rays’, Nature, (1896), 53, p. 391.CrossRefGoogle Scholar

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76 Cambridge University Library MS, Add 7654 NB40. This notebook contains the notes for a series of lectures Thomson gave at Princeton in October 1896. The notes were probably written in August or September 1896, and represent an earlier viewpoint than the Thomson and Rutherford ionization paper, op. cit. (67). The lectures were published in 1898 as The Discharge of Electricity Through Gases, op. cit. (49), by which time Thomson had edited and revised them in the light of his recent cathode ray work.

77 The prevailing theory of magnetization was that suggested by Weber and subsequently developed by Maxwell and by Ewing. It supposed that a magnet consisted of small magnetic particles which were initially randomly oriented but became aligned under a magnetic force. Saturation occurred when all the particles were aligned.

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85 Ibid.

86 This tradition has been interpreted very well by Buchwald, J., From Maxwell to Microphysics, Chicago, 1985.Google Scholar

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89 Here, it may be significant that Napier Shaw, at the Cavendish, was compiling a report on electrolysis for the British Association in 1890: Shaw, W., ‘Report on the present state of our knowledge in electrolysis and electrochemistry’, British Association Report, (1890), p. 185.Google Scholar

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92 Ibid, p. 149.

93 Poynting, J.H., ‘On the transfer of energy in electromagnetic fields’, Philosophical Transactions of the Royal Society, (1884), 175, p. 343.CrossRefGoogle Scholar D. Topper has discussed the Faraday tube theory in great mathematical detail, emphasizing its place in mechanistic philosophy and Thomson's debt to Maxwell, , op. cit. (55).Google Scholar

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98 Ibid. p. 513.

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101 Op. cit. (90).

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107 Ibid.

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129 Zeeman, P., ‘Over den invloed eener magnetische op den aard van het door een stof uitgezonden licht’, Verslagen en Medeelingen der Koninklijke Akademie van Wetenschappen, Amsterdam, (1896), 5, pp. 181, 242Google Scholar; ‘The effect of magnetisation on the nature of light emitted by a substance’, Nature, (1897), 55, p. 347.Google Scholar

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144 Thomson, J.J., ‘Indications relatives à la constitution de la matiere’, Congres International de Physique. Rapports (Paris 1900), (1900), 3, p. 138Google Scholar; ‘The existence of bodies smaller than atoms’, Notices of Proceedings of the Royal Institution, (1901), 16, p. 138.Google Scholar

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146 Ibid.

147 The Electrician, (1897), 39, p. 735.Google Scholar

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150 Two exceptions were Lockyer, [op. cit. (118)]Google Scholar and Elihu Thomson (no relation). Elihu Thomson had apparently been speculating about divisible atoms to explain some X-ray phenomena. He accepted Thomson's theory immediately, writing to The Electrician in 07 1897Google Scholar: ‘Since so eminent a physicist as Prof. J.J. Thomson has, in a recent paper, put forward the hypothesis of the breaking down of what we have been accustomed to call “the elements” and has shown a reasonable basis for such a hypothesis, the writer deems it not improper to state that a similar view had quite independently arisen in his own mind.’ [The Electrician, (1987), 39, p. 317].Google Scholar

151 The Electrician, (1897), 39, p. 299.Google Scholar

152 Milikan, R., The Electron: Its Isolation and Measurement…, Chicago, 1917Google Scholar; Townsend, J., ‘The diffusion of ions into gases’, Philosophical Transactions of the Royal Society, (1900), 193, p. 129CrossRefGoogle Scholar; Wilson, H.A., ‘A determination of the charge on the ions produced in air by Röntgen rays’, Philosophical Magazine, (1903), VI, 5, p. 429.Google Scholar

153 Kaufmann, , op. cit. (24)Google Scholar; Kaufmann, and Aschkinass, , op. cit. (25)Google Scholar; Kaufmann, W., ‘Die magnetische und electrische Ablenbarkeit der Becquerelstrahlen und die scheinbare Masse der Electronen’, Göttingen Nachrichten,(1901), p. 143.Google Scholar

154 Professor of Physics at the University of Moscow.

155 ‘Bien que les travaux de J. J. Thomson soient plus nombreux que ne le sont ceux de W. Kaufmann et embrassent un plus grand nombre de phénomènes, non seulement explorés au point de vue experimentale, mai aussi élucides theoriquement, nos connaissances dan e domaine de physique n'auraient pas atteint en ce moment leur niveau actuel sans les recherches de W. Kaufmann.…’ (Oumoff to the Nobel Foundation 31 January 1904, Nobel Foundation archives).

156 ‘Les résultats de ces expériences ont conduit pour la premiere fois à la notion d'un corpuscle cathodique bien plus petit que l'atome d'hydrogene’, (P. and M. Curie to the Nobel Foundation 26 December 1904, Nobel Foundation archives).

157 ‘Ces conceptions théoriques ont recu diverses confirmations parmi lesquelles nous citerons les recherches recentes de Mr Kaufmann qui sont favorable a l'opinion que la mass des corpuscles négatifs émis par le radium (rayons β), est entierement de nature électromagnétique’, (ibid.).

158 Thomson, , op. cit. (31).Google Scholar

159 Thomson, , op. cit. (135).Google Scholar FitzGerald had in effect suggested this when postulating that cathode rays were ‘free electrons’, as had des Coudres with his ‘weightless convergent lines of force structure’ in the ether.

160 These developments are discussed in McCormach, , op. cit. (7).Google Scholar

161 Hacking, I., Representing and Intervening, Cambridge, 1983.CrossRefGoogle Scholar

162 McCormach points out the significance of this to Lorentz, who recast his theory to treat individual electrons, and was able to determine experimentally the velocity dependence of the electron mass. McCormach, , op. cit. (7), p. 475.Google Scholar