422 Prof. J. C. McLennan and Mr. C. L. Treleaven on 



electrometer was the same as it would have been if the radia- 

 tion had been emitted from a portion of the walls of the 

 instrument. In taking the readings with alpha rays the 



A very small 



arrangement used is that shown in fig. 4. 



Fiff. 3. 



Fiar. 4. 



piece of copper coated with polonium was placed on the end 

 of a brass rod, which was attached to a brass plate and in- 

 serted in the drying-chamber mentioned above in a manner 

 shown by the diagram. In this case, as m the experiments 

 with the beta radiation, the readings were taken with the 

 gases first under natural conditions and afterwards with 

 them traversed by the alpha radiation. 



In the experiments with gamma radiation a small quantity 

 of radium bromide was sealed up in a glass tube. This tube 

 was then placed in a cylinder of zinc with walls about 

 2 cm. thick, which was held in position (figs. 5 and 6) 



Fig. 5. 



Fiar. 6. 



\ 





1 



LbJ- 





m 



' 





. . 



against one of the plane sides of the ionization-chaniber of 

 the electrometer. In this set of experiments the natural 

 ionization was again measured with each of the gases and 

 then the ionization when the gases were traversed by the 

 gamma rays from the source just mentioned. 



