﻿excited by the Alpha Rays from Polonium. 817 



Logeman's Results. 

 Distance between electrodes 5 mm. 



Potential on polonium. 



Reading of current to electrode, i 



volts 



2 „ 

 12 „ 

 14 „ 



1 

 -58-0 



86 



182 



185 



It will be seen, however, from the carve, that as the 

 potential on the polonium was increased beyond 20 volts, 

 the rate ot charging of the electrode gradually decreased. 

 This effect does not appear to have been observed by Logeman. 

 In searching for the explanation of it, further interesting 

 properties of the secondary rays were found by the writer 

 which have not as yet been noted by other experimenters. 



Before seeking for an explanation of the results given in 

 Table I. and shown graphically in fig. 2, it is necessary to 

 enumerate the different currents which would give a charge 

 to the brass electrode B. In the first place there would be a 

 current due to the passage of the a rays from the polonium 

 across the space separating the polonium from the electrode. 

 Since the a rays are positively charged particles this current 

 would charge the electrode positively. Then there would be 

 a current of negatively charged particles from the polonium 

 which would reach the electrode. This current is known as 

 the 8 radiation, and always accompanies a discharge of 

 a particles. The passage of this current would give a 

 negative charge to the electrode. Again, there would be a 

 stream of negatively charged particles emitted by the elec- 

 trode. The researches of Aschkinass and Logeman have 

 proven this stream to exist whenever a substance is bom- 

 barded by a rays, and it has been called the secondary radia- 

 tion. The emission of this stream of negatively charged 

 particles would have the effect of charging the electrode 

 positively. Finally, there would be a current through the 

 air in the chamber, due to the ionization of the air by tlie 

 « rays. The last current would charge the electrode posi- 

 tively, since the polonium was positively charged. This 

 current, which we will call the ionization current, would be, 

 in all probability, very small on account of the small quantity 

 of a'as in the chamber. 



Let us now consider what would be the effect on these 

 different currents of increasing the positive potential on the 



Phil Mag. S. 6. Vol. 23. No. 137. May 1012 . 3 H 



