1912] 



Secondary Rays Excited by the Alpha Rays. 



'59 



with pure and dry hydrogen and left standing over night at atmospheric 

 pressure. Previously the apparatus had been depleted as much as pos- 

 sible 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 i/ioooof a 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. 



Brass electrode 



Table III. 



Hydrogen in Apparatus. 



Voltage on polonium = 77 volts; 



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 v/ith 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 difference in the final ionisation currents through 

 air and through hydrogen. The experimental results, go to show that 

 the final ionisation currents were the same. This seemed hardly pos- 

 sible on account of the difference in density of the two gases. Another 

 explanation of the reason why these two final 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 no ioni- 

 sation current was possible. 



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 ionisation 

 current through the air and through the hydrogen. In order to answer 

 this question the following 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 



