158 



Transactions of the Canadian Institute. 



[vol. IX 



Table II. 

 Air in apparatus. 



Brass electrode B. 



Voltage on polonium = 77 volts. 



The first column states the time between any reading and the ini- 

 tial 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 ionisation current through the gas. This 

 decrease could be attributed to a farther withdrav/al of air from the ap- 

 paratus by the pump after the pressure had been reduced to less than 

 l/iooo of a mm. of mercury. If this were the case this decrease in ioni- 

 sation 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 Then the air withdrawn by the pump would be equal 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 con- 

 stant 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 ionisation current through the hydrogen. But on account of the 

 different nature of the two gases this final ionisation current would be 

 different in the two cases and hence the final rate of charging of the elec- 

 trode would also be different in the two cases. 



In order to find out whether this was true the apparatus was filled 



