On the Reflection of Cathode Rays. 



385 



screen the inner cylinder and its connection from all outside influence. 

 The experiments were conducted with the tube connected to the 

 mercury pump, and the ground-glass stopper S being lubricated with a 

 little vaseline was found to maintain the vacuum very well for con- 

 siderable periods, while at the same time permitting of easy rotation of 

 the Faraday cylinder round A into any desired position without the 

 vacuum being impaired. A circular scale of cardboard attached to the 

 tube around the neck near S, allowed of the angles made by the sur- 

 face of A and the axis of the cylinder F with the axis of the cathode 

 stream proceeding from C being accurately determined. The cathode 

 C and the anode B were directly connected, without spark gaps, to a 

 10-inch Ruhmkorff coil with mercury contact breaker, working at about 

 -J full power. The reflector A, as also the terminal G', were joined up 

 to an earth connection which special tests had shown to be efficient, 

 while the inner Faraday cylinder was connected by means of F' also to 

 earth through a D'Arsonval mirror galvanometer, having 250 turns of 

 wire in its coil. The tube was connected with a mercury pump, and 

 also with a McLeod gauge. Even after prolonged exhaustion, it was 

 found that much electrical power could not be applied to the tube for 

 any length of time without largely deteriorating the vacuum, but with 

 less power the latter was more constant. Even then the vacuum was 

 found always to be slightly lower at the end of a series of observations 

 than at the beginning, and in order to avoid this disturbing factor, 

 every series was taken first one way and then again in reverse order, 

 the mean of the two sets giving results from which the influence of 

 the gradual decrease in the degree of exhaustion was very nearly 

 eliminated. 



FIG. 6. 



AXIS 



of Cathode stream. 



60 90 



