U. OCT ] l 1897 



LONDON, EDINBURGH, ANJ^UBLm ^~~ 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 

 OCTOBER 1897. 



XL. Cathode Rays. By J. J. Thomson, M.A., F.R.S., 



Cavendish Professor of Experimental Physics, Cambridge *. 



THE experiments f discussed in this paper were undertaken 

 in the hope of gaining some information as to the 

 nature of the Cathode Rays. The most diverse opinions are 

 held as to these rays ; according to the almost unanimous 

 opinion of German physicists they are due to some process 

 in the aether to which — inasmuch as in a uniform magnetic 

 field their course is circular and not rectilinear — no pheno- 

 menon hitherto observed is analogous : another view of these 

 rays is that, so far from being wholly getherial, they are in fact 

 wholly material, and that they mark the paths of particles of 

 matter charged with negative electricity. It would seem at 

 first sight that it ought not to be difficult to discriminate 

 between views so different, yet experience shows that this is 

 not the case, as amongst the physicists who have most deeply 

 studied the subject can be found supporters of either theory. 



The electrified-particle theory has for purposes of research 

 a great advantage over the setherial theory, since it is definite 

 and its consequences can be predicted; with the setherial theory 

 it is impossible to predict what will happen under any given 

 circumstances, as on this theory we are dealing with hitherto 



* Communicated by the Author. 



t Some of these experiments have already been described in a paper read 

 before the Cambridge Philosophical Society (Proceedings, vol. ix. 1897), 

 and in a Friday Evening Discourse at the Royal Institution ('Electrician,' 

 May 21, 1897). 



Phil. Mag. S. 5. Vol. 44. No. 269. Oct. 1897. Y 



