764 Mr. A. L. McAulay on an Electrical Method 



A research was consequently undertaken with the following 

 objects : — 



(1) To develop an electrical method for the measurement 

 of such recoil radiations produced by a rays, so far ex- 

 clusively investigated by the scintillation method. 



(2) To check by ionization measurements the results given 

 by Sir Ernest Rutherford in the paper above referred to, 

 which show that in close collisions between an « particle and 

 a hydrogen atom, the nuclei no longer behave like point 

 charges. 



(3) To see whether any difference could be observed 

 between the curve obtained by ionization showing the ab- 

 sorption of the radiation in aluminium, and that given by the 

 scintillation method, due, for instance, to change in ionizing 

 power with velocity of the hydrogen particle. 



Description of apparatus. 



Three forms of apparatus, all on the same principle, 

 were used in succession. Only the last will be described, 

 It consists of two main parts : the first, figure 1, is a brass 









Fig. 1. 









./ F 























L. ., 





ll 









H 











c 



— ■ — A j 













EJ 



J 



box, 8 cm. long by 2 wide by 6 deep, in which the hydrogen 

 recoil atoms are produced. The source of rays, A generally 

 a brass cylinder about 3 cm. long, coated with active 

 deposit from radium, is carried on a vulcanite plug B, 

 fitting a tube in one end of the box. In the other end, exactly 

 opposite, fits another plug, C, carrying a hollow brass 

 cylinder, D, in which are cut slots with aluminium screens 

 waxed on them for intercepting the a rays. Two slots were 



