March 6, 1913] 



NATURE 



with the ion of hydrogen, and, moreover, as it 

 could be shown that the same identical particles 

 always resulted on changing the substances dealt 

 with in the experiments (electrodes, gases, &c), 

 it was revealed that those particles were neither 

 atoms nor molecules, but the electrons themselves, 

 contained in and expelled from the atoms. Others 

 had previously employed the action of a magnetic 

 field on the kathode rays to obtain the foregoing 

 determinations, and Thomson himself had made a 

 similar attempt, but without attaining immediately 

 the results indicated. 



If is here clearly seen how a theoretical concept 

 or a happy hypothesis devised to guide the 

 experimenter can be of the greatest assistance 

 in obtaining far-reaching results. In fact, it is 

 difficult to decide which most to admire in 

 Thomson — the ability of the proved experimenter 

 or the felicitous intuition of the keen thinker 

 which leads him to foresee and anticipate the final 

 interpretation of the facts observed. Even to-day 

 it would require most prolonged and difficult 

 experimental work to show in a rigorous manner 

 that the ratio ejm is really (save the influence 

 of v on the value of m) constant on all occasions, 

 whatever be the circumstances in which the 

 kathode rays originate (the nature of the electrodes, 

 of the rarefied gas, the pressure of the latter, &c). 

 But with inspired generalisation, Thomson, con- 

 scious of the accuracy of his own measurements, 

 and with great faith in the conceptions that were 

 becoming matured in his mind, did not hesitate 

 to proclaim that his experiments furnished the 

 proof of the existence of particles negatively 

 electrified and having a mass not greater than 

 one two-thousandth part of the mass of the atom 

 of hydrogen. 



With this was assumed that the charge of 

 each was equal to that corresponding with one 

 atomic valence; but in strictness the results 

 obtained could have been interpreted alternatively 

 by attributing to the said particles somewhat large 

 charges and a mass of atomic magnitude. How- 

 ever probable the first interpretation seemed, there 

 still remained a gap to fill in. Thomson suc- 

 ceeded in this by utilising the studies carried out 

 in his laboratory by C. T. R. Wilson, who had 

 recognised that electrified particles, and more 

 particularly the negative ones, acted as nuclei of 

 condensation for water vapour. The experimental 

 method adopted by Thomson, which enabled him 

 to evaluate the charge of each single corpuscle, 

 is a true model of ingenuity. The numerical 

 result obtained was perfectly favourable to the 

 interpretation adopted in the earlier experiments; 

 mo. 2262. vol. ail 



and if not at first very exact, was soon corrected 

 by the later experiments of H. A. Wilson and of 

 Thomson himself. 



When the results were first communicated to 

 the British Association in 1S99, they were so 

 favourably received that it may be said that from 

 that date the new ideas on the nature of the 

 kathode rays were accepted by the majority of 

 physicists. 



Meanwhile other discoveries of considerable 

 importance were made, which brought unexpected 

 confirmation to these hypotheses. The pheno- 

 menon discovered by Zeeman, which was at once 

 explained by the electronic theory of Lorentz, and 

 the discovery of radio-activity by Becquerel, came 

 at the most opportune moment in support of the 

 electrical theory of matter, which now became 

 almost irresistible and had its basis in the experi- 

 ments of Thomson which have been recorded. 



It was not, in fact, possible to conceive how the 

 kathode rays could be composed of corpuscles 

 always identical whatever the nature of the bodies 

 present, or taking part in their formation, without 

 supposing that such corpuscles pre-existed in the 

 atoms of every substance, and were thus identical 

 with the electrons already assumed to be con- 

 stituent parts of the atoms. From this to the 

 hypothesis that the atoms consist only of electrons 

 is a short step. And, in truth, the mass of the 

 corpuscles may be entirely electromagnetic, that 

 is, due solely to the motion with which the elec- 

 trical charges are possessed. The well-known 

 experiments of Kaufmann also came at an oppor- 

 tune moment in support of this opinion, demonstra- 

 ting as they did that the mass of the electrons 

 emitted by radio-active bodies appears so much the 

 greater the greater their velocity. Thus, from 

 experiments on the kathode rays a theory was 

 evolved the philosophical import of which is evi- 

 dently of the highest, inasmuch as it enables one to 

 eliminate one of the fundamental or primitive 

 entities (matter) which have been invoked to give 

 an explanation of the phenomena of the physical 

 world. 



One can conceive, in fact, the possibilitv of 

 building up a system of philosophy with only aether 

 and electrons as a basis ; a system all the more 

 seductive on account of the simplification that it 

 carries with it. 



The known dualism of electricity of two signs, 

 which causes differences more or less considerable 

 in every fact, becomes accentuated when the single 

 electrons are considered. In fact, in spite of the 

 numerous and varied attempts that have been made 

 to demonstrate the existence of positive electrons. 



