On the passage of Electricity through Gases exposed to Röntgen Rays, in The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, Vol. XLII, 5th Series, November Issue, 1896, pp. 392-407 [EXTRACT]

Thomson, J. J. and Rutherford, E.

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FIRST EDITION EXTRACT (complete July issue) of Thomson and Rutherford's 1896 "epoch-making investigation on the ions produced in gases exposed to X-rays" (Science in the Making, Volume 2: 1850-1900, 312). Thomson and Rutherford's collaborative investigation "made important progress in understanding the conduction of electricity through gases by using X-rays to create charged species in various gases. The experiments confirmed Thomson's developing view that conduction in gaseous discharges occurred via charged portions of the molecules and served to show that the process was analogous to that occurring in dilute solutions of electrolytes" (ibid). Röntgen's 1895 discovery of X-rays stimulated global interest not only in the use of X-rays for medical purposes, but for inducing electrical conductivity in gases exposed to them. Thomson had already established that â??Röntgenised' gases showed unexpected conductivity, thus "it was only natural that [Thomson] assisted this time by Rutherford, would undertake similar experimental studies to the ones he had done for over a decade, this time using X-rays, in order to get new ideas for building a definitive theory of electric conduction in gases. The radical novelty was that Thomson and Rutherford managed to put forward a quantitative theory of conduction, as opposed to the only qualitative suggestions of previous theories. With this, they could calculate, for instance, the number of particles into which the molecules of a gas would dissociate or the rate at which a â??Röntgenised' gas would leak (i. e., would cease to be a conductor). "Following Thomson's understanding of the passage of electricity through gases as involving electrified particles, and with the new quantitative methods, Rutherford and Thomson inferred that â??the charged particles in the gas exposed to the Röntgen rays are the centres of an aggregation of a considerable number of [neutral] molecules' (Thomson & Rutherford, 1896, 402). In other words, Thomson [and Rutherford] thought that conduction was due to the movement of aggregations, the size of which seemed to be much larger than the ordinary structure of the gas molecules" (Navarro, History of the Electron, 77). Thomson's next step, of course - and one that would have unexpected consequences, "was to see if his new theory of electric currents in gases was also valid, as he had hoped, for cathode rays, thinking that they might also be aggregates of molecules around a charged atom and, therefore, bigger than atoms" (ibid). Building on his 1896 research with Rutherford, Thomson designed a series of experiments specifically to study the nature of electric discharge in a high-vacuum cathode-ray tube - and in so doing would, in 1897, discover the electron. "Even with today's knowledge, detailed interpretation of the results of this paper is not easy. The charged species were likely to have been atoms and molecules; free electrons (not discovered until later) were probably also present and these would have had a much higher mobility (velocity per unit field) than the value give above. No doubt the gases used were not pure and associations with foreign molecules might have occurred. The important features of the paper, however, reside in the clear demonstration of gaseous ionization by X-rays, the theoretical analysis of the current-voltage characteristics, and the estimates of the degree of ionization and of the velocity of the ions" (Science in the Making, 316). Perhaps most importantly, however, and as Falconer pointed out, the lessons Thomson and Rutherford learned from these experiments were critical to their later work, namely Thomson's discovery of the electron just [a year] later and to nearly all aspects of Rutherford's work. Falconer wrote: "J. J. learnt that a less fundamental approach may be more productive than a fundamental one; and he acquired the basis of a mathematical formulation of ionization theory which he built on extensively. Rutherford gained pract.

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Bibliographic Details

• Title: On the passage of Electricity through Gases exposed to Röntgen Rays, in The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, Vol. XLII, 5th Series, November Issue, 1896, pp. 392-407 [EXTRACT]
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