86 



Mr. A. A. C. Swinton. 



the amount of the cathode cut away, woald be found wanting ; and 

 that by the position of this gap in the ring it would be possible to 

 ascertain whether the rays crossed at the focus, and whether there was 

 any rotation. What actually was observed is shown for three different 

 conditions of vacuum in fig. 9, B being for the highest, and B" for 

 the lowest vacuum. As will be seen, the expected gap in the ring 

 was obtained, but with the unexpected addition that the dimensions 

 of this gap, instead of being only one-eighth of the circumference of 

 the ring, was seven -eighths of the circumference. In fact, the 

 amount of ring shown corresponded not with the seven-eighths of 

 the remaining cathode surface, but with the one-eighth of the cathode 

 that had been removed. The portion of ring that did appear was of 

 a length corresponding exactly to the arc of the removed sector of 

 the cathode, according to its greater or lesser nearness to the centre 

 with different conditions of vacuum ; and as the portion of ring was 

 in each case exactly in line with the portion of cathode that had been 

 cut away, it would appear *that there is no rotation of the cathode 

 beam as a whole, that the rays do cross at the focus ; and, further, 

 that when the hollow convergent cone is, as it were, «plit in this 

 manner, some unexplained action, similar in effect to the existence of 

 a circular surface tension, causes the gap to widen out and the 



