﻿822 



Mr. V. E. Pound on the Secondary Ila 



7/ naijs 



experiment was performed. It was found that if arc-light 

 carbon was used as the electrode instead of brass, there was 

 a greater drop in its rate of charging than when brass was 

 used under the same conditions. Accordingly, the brass 

 electrode was removed from the apparatus and a similarly 

 shaped piece of carbon was put in. The polonium was 

 charged to a positive potential of 78 volts, and the pump 

 was started exhausting the air, which was initially at atmo- 

 spheric pressure. Seven minutes after the pump was started 

 readings were taken of the pressure of air in the vessel as 

 measured by the McLeod gauge, and the rate of charging of 

 the carbon electrode. Similar readings were made at dif- 

 ferent intervals of time after the initial readings. The pump 

 was kept going continuously throughout all the readings. 

 The results are given in the following Table : — 



Table IV. a. 

 Air in Apparatus. 

 Carbon electrode. Charge on polonium 



78 volts. 



Pressure of air 



Time from initial 



Current to 



in vessel. 



reading. 



electrode. 



•008 mm. 



minntes 



46 



•004 „ 



1 



42 



•002 „ 



5 



38 



^•001 „ 



15 



34-5 



<-001 „ 



30 



31-5 



<-001 „ 



60 



29-0 



<-ooi „ 



120 



29 



The pump was then stopped, and while the pressure 

 gradually increased as the air flowed out from the walls of 

 the apparatus, the series of readings were continued and are 



>iven below 



Table IV. b (continued). 



Pressure of air 



Time from initial 



Current to 



in vessel. 



reading. 



electrode. 



•001 mm. 



123 minutes 



29 



•002 „ 



126 



29 



•005 „ 



129 



30-5 



•009 „ 



134 



30-5 



.012 „ 



139 



31 



•018 „ 



146 



32-5 



•022 „ 



153 



33 



•027 „ 



161 



34 



•035 „ 



171 



35-5 



