﻿excited by the Alpha Rays from Polonium. 835 



polonium was raised above 40 volts in a measure may be 

 attributed, as has been suggested, either to a more profuse 

 reflexion of a rays from the electrode as the potential of the 

 polonium was raised or to a gradual decrease in the ionization 



Fi£. 8. 



*£00 



Vottaai 



+IOOO 



on Polonium 



1000 



current due to a lowering of the pressure of the air in the 

 apparatus. But as a result of the later experiments per- 

 formed with the carbon electrode, it is clear we must add 

 another and more important cause for the fall, namely, the 

 decrease in the secondary radiation throughout the experi- 

 ment as the gas layer on the electrode became less and less 

 dense. 



The experiment just described with the carbon electrode 

 shows that, when the gas-layer was removed, there was no 

 fall in the rate of charging of the carbon electrode as the 

 potential on the polonium was increased, but instead a 

 gradual increase was obtained. 



The question arose, then, whether the brass electrode would 

 act in the same manner as the carbon electrode if the gas- 

 layer was first removed from it. To answer this question 

 the brass electrode was kept in vacuo a long time and the 

 experiment with it was repeated. Contrary to expectation, it 

 was found that there was still a very slight decrease in the 

 rate of charging of the electrode after the potential of the 



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