34 PHYSICAL RESEARCH 



within a discharge tube and that it could apparently 

 pass through thin aluminium foil within the tube. 

 The existence of radiations which could pass through 

 sheets opaque to ordinary light was of great impor- 

 tance if it could be shown to be real, and that was 

 why it was of such singular interest when Lenard 

 succeeded in coaxing the rays to come out into 

 the open. 



Before the time of Herz were the classical 

 experiments of Sir William Crookes who first 

 experimented on a great scale with this strange 

 radiation. He showed what important properties 

 it possessed; how it streamed in straight lines 

 from the negative terminal from the tube; how it 

 made substances phosphoresce, raised bodies to a 

 red heat when it fell upon them, caused little paddle 

 wheels to turn when it struck the blades, could be 

 turned aside by a magnet, and in general possessed 

 properties so unlike in their aggregate the properties 

 of any other radiation then known, that clearly 

 he had crossed the threshold of a treasure chamber 

 new to science. It may help to ease the difficulty 

 of thinking backwards if we realise that these 

 radiations are an important part of the electric 

 discharge of which we have spoken above. They 

 are not the Rontgen rays but the cause of them; 

 the latter have their origin where the former 

 impinge on matter of any kind, and Rontgen could 

 produce the rays which bear his name, because he 

 was actually producing first the rays of Crookes. 



