1894.] On some Phenomena in Vaeuumrtubes. 235 



will be observed that the bands approach towards the centre, but 

 still do not fill the tube ; sometimes one or two new bands appear. It 

 is difficult at present to say why this should be the case, for, apart 

 from other views which may be taken, the following two conditions 

 might exist : 



1. If the apparent repulsion of the bands is due to the electrifica- 

 tion of the glass of the tube, then an effect is produced somewhat 

 similar to that in the gold leaf electroscope, and by placing the hand 

 upon the tube, a discharge being produced, the bands will approach 

 in the same way as in the case of the leaves of an electroscope when 

 discharged, but the glass being a bad conductor, the discharge is 

 partial only. 



2. The view might be taken that when the hand is placed on the 

 tube a condenser is formed, and the surface of the glass within the 

 tube becomes more highly electrified, and the approach of the bands 

 is due to this cause. If this explanation is true, the ocular effect of 

 repulsion is not really due to repulsion. 



The condenser action appears to be con firmed by my experiments, 

 and is very prettily shown in the following manner : 



Adjust the current in any vacuum tube until the discharge is just 

 visible. Now carefully reduce the current until the tube is dark, i.e., 

 when there is no visible discharge. If the hand is now placed on the 

 tube the latter will light up brightly. If the adjustment is made 

 with sufficient care, the very fact of placing the hand within an inch 

 or so of the tube will cause it to light up as if by magic. The re- 

 pulsion effect may also be true, although it appears to me evident 

 that more current flowing into the tube, when the outside is 

 earthed, is in no way caused by any discharge from the interior of 

 the tube. 



A tube is now taken of much smaller diameter, 25 mm., the bands 

 will now be formed the whole length of the tube ; other phenomena 

 are the same as with the large tube. (See fig. IA.) 



Experiment 2. 



A similar tube was employed, but it contained in the centre of its 

 length a very slight glass rod, attached to the side, supporting a 

 short thick glass rod lying along the axis of the tube (see fig. 2, where 

 dimensions are given, as in the case of other figs.). The object of 

 this experiment is to see whether the repulsive effect would be in- 

 creased ; or, if not increased, whether the phenomenon could be made 

 more clear. The latter proved to be the case. In passing the current 

 in the same manner as in the previous experiment, bands were formed 

 throughout the length of the tube, one appearing at the centre of the 

 little rod and one at each end or near the ends of the rod. Ou in- 



