Theories of Electricity 145 



ferences now appear to result from a difference in the 

 size of the carriers of the electric discharge, rather than 

 in the electricities themselves. 



At a very low pressure of the gas in the tube there is 

 a very remarkable change in the character of the dis- 

 charge. A type of radiation is emitted from the neg- 

 ative electrode or cathode which travels in straight lines 

 and produces a marked luminosity in the walls of the 

 tube and in a number of phosphorescent substances placed 

 in the path of the rays. These " cathode " rays, appar- 

 ently first observed by Varley in 1857, were investigated 

 in detail by Crookes. Unlike ordinary light, these rays 

 are readily bent from their path by a magnetic field. 

 Crookes supposed that they consisted of negatively 

 charged particles projected at a great speed from the 

 cathode, and, with almost prophetic insight, considered 

 them to be not molecules or atoms of matter but as he 

 expressed it, " a new or fourth state of matter." In sup- 

 port of his views, Crookes showed that the particles ex- 

 erted a mechanical pressure when they impinged on 

 bodies, and were able to fuse a platinum plate exposed 

 to their bombardment. 



For a space of nearly twenty years the true nature of 

 these rays was a subject of much controversy. The 

 English school adopted the material hypothesis advo- 

 cated by Crookes, while the Continental physicists con- 



