﻿820 



Mr. V. E. Pound on the Secondary Rays 



Table II. 



Air in Apparatus. 



Brass electrode B. Voltage on polonium = 77 volts. 



Time. 



Current to electrode. 



minutes 



97 



5 ,. 



81 



10 „ 



76 



15 „ 



67-5 



25 ., 



64 



120 „ 



59 



130 „ 



59 



The first column states the time between any reading and 

 the initial reading, while the second column gives the rate at 

 which the electrode charged up. 



As shown by the Table, the rate at which the electrode 

 gained a charge decreased with the time, and finally came to 

 a constant value. 



In this experiment the polonium was at the same voltage 

 all the time, hence there could be no change in the rate of 

 charging of the electrode, due to a change in voltage. 

 Therefore, according to the theory of the charging of the 

 electrode as outlined in the previous section, the gradual 

 drop in the rate of charging of the electrode as the time 

 passed could only be due to a decrease in the ionization 

 current through the gas. This decrease could be attributed 

 to a further withdrawal of air from the apparatus by the 

 pump after the pressure had been reduced to less than 1/1000 

 of a mm. of mercury. If this were the case this decrease 

 in ionization would continue until the pressure of the air in 

 the vessel reached a constant value. Then the air withdrawn 

 by the pump would be equal to the air which oozed out from 

 the sides of the vessel. The final constant value for the rate 

 of charging of the electrode would denote this equilibrium 

 condition between the air taken away by the pump and the 

 air which oozed out from the walls of the chamber. 



If the above explanation is correct, then, if the apparatus 

 were filled with another gas than air such as hydrogen, and 

 the experiment were repeated as with the air, there would 

 again be a final pressure, and also a final ionization current 

 through the hydrogen. But on account of the different 

 nature of the two gases this final ionization current would 

 be different in the two cases, and hence the final rate of 

 charging of the electrode would also be different in the two 

 cases. 



