NATURE 



[March 6, 19 13 



far back as 1894 succeeded in outlining an 

 electrical theory of matter. But, however seduc- 

 tive these theoretical investigations appeared, and 

 in their comprehensiveness they represented a 

 considerable advance on earlier theories, the real 

 existence of electrons could not be accepted by 

 physicists until a satisfactory experimental demon- 

 stration of their existence was forthcoming. 



To succeed in such a demonstration undoubtedly 

 appeared to everyone a sufficiently difficult matter ; 

 yet such has actually been achieved, thanks to 

 the study of the kathode rays, that is, of certain 

 peculiarities presented by electrical discharge and 

 already known for some considerable time. 



The phenomena of discharge have always at- 

 tracted the attention of physicists, and innumerable 

 studies have been made in this field. The peculiari- 

 ties which they present, varied as they are almost 

 indefinitely, and certain brilliant aspects which 

 they possess, even though not always of the 

 highest scientific interest, have rendered these 

 studies so attractive, that it is difficult for anyone 

 who has once pursued them to free himself from 

 their seductiveness and pursue other researches. 

 A rich material of facts thus went on accumulating, 

 between which, however, in the majority of cases 

 there was no intimate connecting link ; this 

 material was later to be coordinated by the 

 electronic theory, which in turn gained many 

 indirect confirmations from it. Finally, when, 

 with the perfecting of technique, it became an 

 ' easy matter to produce the greatest rarefaction 

 of gases, the phenomena of the kathode rays 

 assumed their due importance in the eyes of 

 physicists ; and all those who, by natural dis- 

 position or as a result of long experience in 

 physical researches, possessed that fine intuition 

 which in certain cases appears almost as a true 

 divination, presaged that from the study of the 

 kathode rays would accrue results of capital im- 

 portance, capable of throwing light on the nature 

 of electricity. 



The very brilliant and ingenious experiments 

 described by Crookes, and the theory of " radiant 

 matter " proposed by him to explain them, gave 

 a great impulse in the direction which has led to 

 the actual views of to-day. It is true that thai- 

 theory was combated, unfortunately, even by 

 physicists of such high reputation as Hertz ; but 

 there were some, at least, who at once welcomed 

 it with enthusiasm. 



The present writer can boast that he was one 

 of this small band, and that he drew from the 

 theory the inspiration of numerous experiments, 

 NO. 2262, VOL. 9l] 



demonstrating the existence of electrified particles 

 (ions) in gases under atmospheric pressure trans- 

 mitting the discharge, and capable of producing 

 with their movements regulated by electrical forces 

 phenomena of " electrical shadows " similar to 

 those produced by the kathode rays. 



Meanwhile, shortly afterwards and independ- 

 ently of the explanation given of the kathode rays, 

 various physicists sought to explain by the 

 presence of mobile charges the conducting pro- 

 perties possessed by gases in certain circum- 

 stances, and it then appeared that they could not 

 do better than apply to gases the mechanism ima- 

 gined in the case of electrolytes. Schuster, 

 Arrhenius, Elster, Geitel and others obtained note- 

 worthy results in this field, bringing forward 

 numerous proofs of the existence of ions in gases, 

 and basing on the facts observed the explanation 

 of divers phenomena. 



It was not easy, however, to apply directly to 

 gases the electrolytic theory. In the first place, 

 an enormous difference exists between the two 

 orders of phenomena as regards the difference of 

 potential required to bring about a transmission 

 of electricity, this difference being exceedingly 

 small in the case of liquids and relatively great 

 in the case of gases. Another formidable difficulty 

 also presented itself in the fact that, whilst it 

 1-. a most natural thing for atoms of different 

 chemical nature to carry charges of different sign, 

 so that, for example, there are negative ions of 

 oxvgen and positive ions of hydrogen, it was not 

 easy to conceive that, in a given simple gas, there 

 could exist ions of the same chemical nature but 

 some charged positively and some negatively. 



But this difficulty disappeared when, by the 

 classical experiments of J. J. Thomson, it was 

 rendered probable, and demonstrated, so far as 

 this is humanly possible, that negative electrons 

 or "corpuscles" exist and form an integral part 

 of the structure of the atoms. 



The suggestive fact having been observed by 

 l'errin, and then by Thomson, of the effective 

 transport of negative charges by the kathode 

 rays, a fact which suggested the hypothesis 

 that such rays consisted of the movement of 

 particles expelled from the kathode, Thomson com- 

 menced in 1S97 those famous experimental 

 researches in which he succeeded in measuring, at 

 the same time, the ratio e/m between charge and 

 mass of the said particles and their velocity v. 

 Having obtained for v a value clearly inferior to 

 the velocity of light, and, above all, a value for 

 e'/tn nearly two thousand times that corresponding 



