3ome Experiments with Cathode Rays. 



rapidly to and from the focus. With com- 

 paratively flat, long focus cathodes the 

 coces do not show any signs of being 

 hollow, and produce a uniformly lumin- 

 escent spot upon the carbon of larger or 

 smaller diameter, according to the condi- 

 tions of vacuum and the position of the 

 screen. 



For instance, while cathodes 1*125 inches 

 diameter and 0"708 inch radius of curvature 

 gave in the manner described distinctly 

 hollow convergent and divergent cones, a 

 cathode 1 inch diameter and 1*5 inches 

 radius of curvature gave convergent and 

 divergent cones that appeared to be uni- 

 formly solid under all conditions. 



The Rays cross at the Focus with no Rotation. 



In order to investigate the cathode rays 

 in a focus tube still further, and more 

 especially in order to discover whether the 

 various rays from the cathode cross one, 

 another at the focus, or diverge again with- 

 out crossing, and also in order to discover 

 whether there is any twist or rotation of 

 the rays, similar to what has been ob- 

 served in the case of rays focussed by mag- 

 netism,* a tube was constructed similar to 

 that used in the previous experiments, with 

 a carbon anti-cathode which was also the 

 anode, fixed at the opposite side of the 

 focus from the cathode, with the focus 

 about equally distant between it and the 

 cathode. The peculiarity of this tube con- 

 sisted in the fact that a sector of the alumi- 

 nium cathode, equal to one-eighth of the 

 total area of the cathode, had been entirely 

 removed, as shown at C, fig. 9. It was 

 expected that on using this tube, with the 

 proper degree of vacuum to form a well- 

 defined ring on the anti-cathode screen, that 

 a portion of the ring, corresponding with 



* See experiments by K. Birkeland, 'Electrical 

 Eeview,' June 12, 1896. 



