396 Conduction in Solutions and Gases , 



The alternative to the molecular-torrent theory is to suppose 

 that the cathode radiation is a disturbance of the aether. This 

 view was maintained by several physicists,* and notably by 

 Hertz,f who rejected Varley's hypothesis when he found 

 experimentally that the rays did not appear to produce any 

 external electric or magnetic force, and were apparently not 

 affected by an electrostatic field. It was, however, pointed 

 out by Fitz Gerald* that external space is probably screened 

 from the effects of the rays by other electric actions which 

 take place in the discharge tube. 



It was further urged against the charged-particle theory 

 that cathode rays are capable of passing through films of metal 

 which are so thick as to be quite opaque to ordinary light ; 

 it seemed inconceivable that particles of matter should not be 

 stopped by even the thinnest gold-leaf. At the time of Hertz's 

 experiments on the subject, an attempt to obviate this difficulty 

 was made by J.-J. Thomson,! | who suggested that the metallic 

 film when bombarded by the rays might itself acquire the 

 property of emitting charged particles, so that the rays which 

 were observed on the further side need not have passed through 

 the film. It was Thomson who ultimately found the true 

 explanation ; but this depended in part on another order of 

 ideas, whose introduction and development must now be 

 traced. 



The tendency, which was now general, to abandon the 

 electron-theory of Weber in favour of Maxwell's theory 

 involved certain changes in the conceptions of electric charge. 



* E.g. E. Wiedemann, Ann. d. Phys. x (1880), p. 202; translated, Phil. Mag. 

 x (1880), p. 357. E. Goldstein, Ann. d. Phys. xii (1881), p. 249. 



t Ann. d. Phys. xix (1883), p. 782. 



J Nature, November 5, 1896 ; Fitz Gerald's Scientific Writings, p. 433. 



The penetrating power of the rays had been noticed by Hittorf, and by 

 E. "Wiedemann and Ebert, Sitzber. d. phys.-med. Soc. zu Erlangen, llth December, 

 1891. It was investigated more thoroughly by Hertz, Ann. d. Phys. xlv (1892), 

 p. 28, and by Philipp Lenard, of Bonn, Ann. d. Phys. li (1894), p. 225 ; lii (1894), 

 p. 23, who conducted a series of experiments on cathode rays which had passed out 

 of the discharge tube through a thin window of aluminium. 



|| J. J. Thomson, Recent Researches, p. 126. 



