NATURE 



[March 6, 1913 



that is, of positive charges endowed with a mass 

 (electromagnetic) of the same older of magnitude 

 as that of the negative electrons, all such efforts 

 have ended in failure. It is, therefore, natural 

 to consider only the negative electrons, from which 

 one may eliminate the adjective, and admit that 

 in the positive ions each valence is due, not to 

 the addition of a positive electron, but to the sub- 

 traction of a negative electron or electron strictly 

 so called. This naturally led Thomson to attribute 

 to positive electricity certain special characters 

 within the atoms, and to assume for these a special 

 structure in which the negative electrons have a 

 preponderating influence ; which view is in con- 

 formity with known facts, and, in particular, with 

 the Zeeman effect, from which is deduced, as is 

 well known, that the emission of light has its 

 origin in the vibration of negative electrons. 



Taking, as point of departure, an idea suggested 

 by Lord Kelvin's " Aepinus Atomised " (according 

 to the picturesque expression employed by him), 

 Thomson assumed that a neutral atom is composed 

 of a sphere of positive electricity in which are 

 immersed negative electrons, the total charge of 

 which is equal in absolute value to that of the 

 sphere. The electrical force which acts on each 

 of these throughout the positive sphere is pro- 

 portional to the distance from the centre, and 

 maintains them in closed orbits, the stability of 

 which needs a special distribution of the electrons 

 themselves. 



Some concrete idea of such a species of solar 

 systems was opportunely found in the old experi- 

 ment of floating magnets, due to the physicist 

 Mayer, which was thus rescued from the unmerited 

 oblivion in which it had been left. 



This hypothesis of the structure of the atoms, 

 although most daring, seems to respond to all 

 exigencies. It may be modified with the progress 

 of time, and certainly needs completion ; but it 

 is probable that its essential features will be 

 retained by the science of the future. 



A necessary complement of the present-day 

 theory of the kathode rays is found in the theory 

 elaborated in much detail by J. J. Thomson to 

 explain the production and nature of the rays 

 discovered by Rontgen. It presents such a 

 character of evidence, and, in short, is so intuitive, 

 that everyone feels that he could have conceived 

 it himself, which idea, however, is only one of 

 many similar illusions of amour propre. Indeed, 

 how can one avoid admitting the production of 

 sudden electromagnetic perturbations in the sether, 

 at the spot where the electrons are entirely 

 arrested or retarded, as occurs when the kathode 

 NO. 2262, VOL. Oil 



rays encounter an obstacle? It will naturally 

 follow, I believe, that the X-rays will be considered 

 as the manifestation of those perturbations, in 

 spite of there having been proposed recently a 

 new hypothesis, according to which these rays 

 are of a corpuscular nature and composed of the 

 motion of neutral couples (one negative electron 

 and one positive). It will be necessary at least 

 to bring proof on proof for this new hypothesis 

 before Thomson's theory is abandoned. And in 

 such a case it will be necessary to establish what 

 happens to the perturbations due to the variations 

 of velocity of the electrons constituting the kathode 

 rays, which undoubtedly are produced. 



In creating the actual current of ideas relative 

 to the nature of matter and the common prime 

 cause of phenomena of light and electromagnetism, 

 in addition to the experimental work of Thomson 

 other discoveries of recent years have contributed, 

 above all, that of Zeeman (1897), to which I have 

 already alluded, and that of radio-activity — the 

 latter thanks to the very simple and ingenious 

 explanation given by Rutherford and Soddy. If 

 from the measurements carried out on the kathode 

 rays was demonstrated the existence of the 

 electrons as integral parts of the atoms, the facts 

 of radio-activity lead us further — to the view that 

 the atom is a complex structure of negative 

 electrons and positive ions, or at least that at 

 a given moment, perhaps in consequence of the 

 continuous irradiation of part of its energy, there 

 can separate electrons and positive ions, the latter 

 being, at any rate in the cases studied as yet, 

 not other than bivalent ions of helium. This inter- 

 pretation of radio-active phenomena seems so 

 natural as to give rise easily to the illusion 

 that the phenomena themselves could have 

 been foreseen. On the other hand, they may 

 make the importance of Thomson's work appear 

 to some less than it undoubtedly is ; but it is 

 necessary to go back in mind to the period at 

 which it was carried out and take account of 

 the mode of thought prevailing at the time, to 

 appreciate the acuteness and originality of mind 

 which were necessary in order to dare to snatch 

 from the atom its dogmatic prerogatives of 

 indivisibility and invariability. 



There are other examples in the history of 

 physical science of discoveries made at short 

 intervals of time converging to a truth which the 

 discovery of a final fact put into a clear light. 

 It is usual then to say that that truth was "in 

 the air," as if any person in favourable circum- 

 stances would have been able to discover it. I 

 do not believe, in any case, that the same can be 



