Cathode and Lenard Rays. 



227 



" Cathode and Lenard Kays." By J. A. McClelland, M. A., 

 Junior Fellow R.U.I. Communicated by Professor J. J. 

 Thomson, F.R.S. Received March 15 —Read April 8, 1897. 



(From the Cavendish Laboratory.) 



The close connexion between the cathode rays and the more 

 recently discovered Rontgen rays gives a new interest to the study of 

 the properties of the former, although, indeed, the two widely different 

 views that are held as to the nature of these rays render such an 

 impetus unnecessary. 



One theory holds that the cathode rays are a stream of material 

 particles shot off from the negative electrode, and carrying with them 

 a negative charge, while the other theory ascribes the rays to a 

 phenomenon in the ether. Both theories have received a large amount 

 of support. 



Hertz* found that thin films of gold-leaf, when placed in the path 

 of the rays were sufficiently transparent to allow a slight phosphor- 

 escence to be produced behind the films. 



This at first sight does not appear consistent with the view that 

 the cathode rays consist of a stream of charged particles, and that 

 the phosphorescence is produced by the rapid approach of these 

 particles up to the surface of the phosphorescing substance. Even 

 the thinnest films of gold-leaf could not allow the passage through 

 them of such material particles. 



But it has been suggested by Professor J. J. Thomsonf that under 

 the action of the cathode rays the thin film of gold-leaf itself acts as 

 a cathode, and thus from its further surface we have rays given off 

 similar to those given off by the primary cathode. 



If this be the true explanation of the phenomenon we would expect 

 these secondary cathode rays to be identical in their properties with 

 the primary cathode rays which produce them. 



Recently Lenard, % in a very valuable series of experiments, has 

 studied the secondary rays which are produced, and which are usually 

 called by his name, when the cathode rays fall upon thin films of 

 aluminium, and the results he obtains appear to be explicable by 

 the above-mentioned suggestion of Professor J. J. Thomson. 



The experiments described in this paper have to do, partly with 

 these Lenard rays, and partly with the cathode rays themselves. Iu 

 the first place experiments were devised to test whether the rays 

 produced by the incidence of the cathode rays on thin films carried 

 a negative charge as the cathode rays do. 



* 'Wied. Ann.,' 45, p. 28, 1892. 



t 1 Recent Researches,' p. 126. 



% ' Wied. Ann.,' 51, p. 225 ; also 52, p. 23. 



