Prof. J. J. Thomson on Cathode Rays. 311 



its neighbourhood ; moving the hotly involves the production 

 of a varying electric field, and, therefore, of a certain amount 

 of energy which is proportional to the square of the velocity. 

 This causes the charged body to behave as if its mass were 

 increased by a quantity, which for a charged sphere is | e 2 /fia 

 (' Recent Researches in Electricity and Magnetism'), where 

 e is the charge and a the radius of the sphere. If we assume 

 that it is this mass which we are concerned with in the 

 cathode rays, since m/e would vary as e/a, it affords no clue 

 to the explanation of either of the properties (1 and 2) of 

 these rays. This is not by any means the only objection to 

 this hypothesis, which I only mention to show that it has not 

 been overlooked. 



The explanation which seems to me to account in the most 

 simple and straightforward manner for the facts is founded on 

 a view of the constitution of the chemical elements which has 

 been favourably entertained by many chemists : this view is 

 that the atoms of the different chemical elements are different 

 aggregations of atoms of the same kind. In the form in which 

 this hypothesis was enunciated by Prout, the atoms of the 

 different elements were hydrogen atoms ; in this precise form 

 the hype thesis is not tenable, but if we substitute for hydrogen 

 some unknown primordial substance X, there is nothing known 

 which is inconsistent with this hypothesis, which is one that 

 has been recently supported by JSlr Norman Lockyer for 

 reasons derived from the study of the stellar spectra. 



If, in the very intense electric field in the neighbourhood 

 of the cathode, the molecules of the gas are dissociated and are 

 split up, not into the ordinary chemical atoms, but into these 

 primordial atoms, which we shall for brevity call corpuscles ; 

 and if these corpuscles are charged with electricity and pro- 

 jected from the cathode by the electric field, they would behave 

 exactly like the cathode rays. They would evidently give a 

 value of m/e which is independent of the nature of the gas 

 and its pressure, for the carriers are the same whatever the 

 gas may be ; again, the mean free paths of these corpuscles 

 would depend solely upon the density of the medium through 

 which they pass. For the molecules of the medium are com- 

 posed of a number of such corpuscles separated by considerable 

 spaces; now the collision between a single corpuscle and the 

 molecule will not be between the corpuscles and the molecule 

 as a whole, but between this corpuscle and the individual 

 corpuscles which form the molecule ; thus the number of 

 collisions the particle makes as it moves through a crowd of 

 these molecules will be proportional, not to the number of the 



Z2 



