220 



THE ROYAL SOCIETY OF CANADA 



ever, be admitted into the evacuated chamber containing the metals, 

 a great increase takes place in the contact difference of potential be- 

 tween the metals. 



In view of all these experiments it was thought well to investi- 

 gate what the effect would be on the intensity of the delta radiation 

 from zinc under bombardment by alpha rays when care was taken to 

 remove as far as possible all gases from the surface of the zinc bombard- 

 ed. The following paper contains an account of this investigation 

 and from what follows it will be seen that with freshly prepared zinc 

 surfaces the delta ray effect is exceedingly small ; but that when air 

 is permitted to be occluded in such surfaces a very great increase 

 takes place in the magnitude of the effect. 



II. Apparatus. 

 The apparatus used in conducting the experiments is similar 

 to that used by Hughes^ in his investigations on the photo-electric 

 effect and is shown in Fig. 1. It consisted of a glass tube about 3 



EtftttoMcrr 



Fig. 1. 



1 Hughes. Phil. Trans. A. CCXH, p. 205, 1912. 



