illustrated "by the Behaviour of Electric Vacuum Valves. 5 



1. With the tap closed, so that nothing could pass by the 

 supplementary path. A was made negative and B positive. 



Cathode rays are then given off strongly from the end of 

 the rod A and make the glass glow up to about where the 

 tube above widens. They excite phosphorescence also up 

 at the top near B. There are practically no cathode rays 

 from any other part of the rod A, and there are none in the 

 small bulb round it. Hardly any positive glow is visible, 

 and the resistance of the tube, thus connected, is very high. 



2. The connexions were reversed, so that A was positive 

 and B negative ; the tap being still shut. 



Strong cathode rays now emanate from the bottom end of 

 the spiral, heating the glass there vigorously and threatening 

 to destroy it ; but there are no cathode rays in the bulb 

 above, outside the spiral, showing that they do not start in 

 all directions without regard to where positive charges can 

 be found. It is well known' that they do not pay any 

 attention to the position of the anode, but they do to the 

 position of the positive carriers. 



There was little or no luminous glow, apart from the 

 phosphorescence of the glas^, in either of these two first 

 cases, i. e. with the tube shut. 



