164 PROGRESS OF SCIENCE IN THE CENTURY. 



this outside the tube, affecting photographic plates 

 and electrified bodies. The rays are also affected 

 by a magnet, and Lenard regarded them as prolonga- 

 tions of the cathode rays. 



In 1895, Rontgen found that rays issue from the 

 tube which affect a photographic plate after passing 

 through plates, e.g., of aluminium, opaque to ordi- 

 nary light, which pass from one substance to another 

 without refraction and with little regular reflection. 

 These are apparently not affected by a magnet. 

 They are also remarkable in the way in which they 

 alter the properties (especially the electrical proper- 

 ties) of the substances through which they pass. 



Thus, as Professor J. J. Thomson says,* " we may 

 conveniently divide the rays occurring in or near a 

 vacuum tube traversed by an electric current into 

 three classes ; without thereby implying that they are 

 necessarily distinctly different in physical character. 

 We have (1) the cathode rays inside the tube, which 

 are deflected by a magnet; (2) the Lenard rays out- 

 side the tube, which are also deflected by a magnet; 

 and (3) the Rontgen rays which are not, as far as is 

 known, deflected by a magnet." 



Two views are held as to the cathode rays: (a) 

 that " they are particles of gas carrying charges of 

 negative electricity, and moving with great velocities 

 acquired as they travelled through the intense electric 

 field which exists in the neighbourhood of the nega- 

 tive electrode"; or (&) that they are waves in the 

 ether. 



If the nature of the cathode rays is uncertain, so 

 much the more is that of Rontgen's. They differ 

 from light in the absence of refraction, but that 

 may be interpreted as due to the exceeding smallness 



* Address to Section A, Rep, Brit, Ass, for 1896, p. 701. 



