﻿e.vcited by the Alpha Rays from Polonium, 



821 



In order to find out whether this was true the apparatus 

 was filled with pure and dry hydrogen and left standing over 

 night at atmospheric pressure. Previously, the apparatus 

 had been depleted as much as possible of air by keeping it 

 at low pressure and pumping out the air which came from 

 the walls. The polonium was charged to a positive potential 

 of 77 volts, the hydrogen was pumped out to less than 

 1/1000 of mm. of mercury, and then readings were taken as 

 with the air of the rate of charging of the brass electrode, 

 and are given in the following Table : — 



Table III. 



Hydrogen in Apparatus. 



Brass electrode B. Voltage on polonium = 77 volts. 



Time. 



Current to electrode. 



minutes 



86-6 



6 „ 



73-1 



16 „ 



651 



31 „ 



62-6 



91 „ 



59-5 



95 „ 



59-5 



121 „ 



59-0 



It will be seen on looking at the Table that there was a 

 decrease in the rate of charging of the electrode with the 

 time, as with the air. On comparing Table II. and Table III. 

 it will also be seen that the initial rates of charging of the 

 electrode were different with the two gases, but the final 

 rates were the same. The experimental results, therefore, 

 did not agree with the predicted results, for it was predicted 

 that the final rates of charging of the electrode would be 

 different using two different gases on account of the dif- 

 ference in the final ionization currents through air and 

 through hydrogen. The experimental results go to show 

 that the final ionization currents were the same. This 

 seemed hardly possible on account of the difference in density 

 of the two gases. Another explanation of the reason why 

 these two finnl rates of charging were the same was therefore 

 looked for. The simplest one that suggested itself was that 

 when the final rates of charging were the same there was 

 such a small quantity of either air or hydrogen in the 

 apparatus that practically no ionization current existed. 



The next question that naturally arose was whether all of 

 the drop in the rate of charging of the electrode was due to 

 a drop in the ionization current through the air and through 

 the hydrogen. In order to answer this question the following 



