TRAVERSED BY CATHODE RAYS. 
55 
very little effect on the motion of these carriers. On the other hand, the velocity of 
the ions in Rontgenised air has been found by Rutherford* to be about 1 ‘6 centims. 
per second, under a field of a volt a centimetre, and consequently of the order of that 
of the blast. In the experiment described, the effect of the blast, therefore, was to 
decrease the conduction away from the electrode by removing the ionized gas; and as 
no change was made in the intensity of the rays impinging on the disc, this con¬ 
sequently produced an increase in the residual charge. This increase, however, did 
not go on indefinitely, but ceased when the field it set up was sufficient to neutralise 
the effect of the blast; hence the second stationary value for the charge. 
Another means of increasing this limiting charge was afforded by the removal of 
the air surrounding the electrode. To show this the gauze cap was removed from 
the apparatus in fig. 2, and the metal tube surrounding the wire was brought forward 
and sealed to the anode of the discharge tube. The arrangement is shown in fig. 3. 
With this apparatus it was found that, as the exhaustion proceeded in the chamber 
B, the negative charge received by the electrode A gradually increased, until finally, 
at a very high vacuum, a momentary discharge of the rays was sufficient to raise its 
potential beyond the range of the electrometer. This result, therefore, confirms the 
explanation already given of the discharging action of the rays. In a recent paper 
by LenardI this charging action of the cathode rays in a high vacuum was described, 
but its connection with the ionized air surrounding the electrode was not brought 
out. From the experiments just described it is clear that, while this action is directly 
due to the fact that the cathode rays carry a negative charge, the extent of the effect 
obtained in all cases depends to a very great degree upon the opposing influence 
exerted by the ionized air surrounding the electrode upon which the rays fall. 
4. Ionization not due to Rontgen Rays. 
It has been thought by some that the ionization produced by cathode rays was due 
to Rontgen rays, which might possibly be sent out from the window at the same 
time. The results of experiment are, however, entirely opposed to this view. 
* ‘Phil. Mag.,’ November, 1897, p. 436. t ‘ Wied. Ann.,’ vol. 63, p. 253. 
