10 



A close parallel thus exists between the scattering of 

 fi rays and that of y and X-rays. 



The shape of the so-called absorption curve may be modi- 

 fied by the shape of the ionization chamber and the position 

 of the screen and active material relatively to the chamber 

 and to each other. 



Absorption of a beam of /3 rays, combined with the 

 effects of scattering and softening, seem sufficient to account 

 for observed effects without the introduction of the idea of 

 a true secondary radiation proceeding from the atoms 

 affected by the primary stream of rays. 



An electron appears to be able to suffer collisions, pro- 

 ducing considerable change in its direction of motion, with- 

 out any great loss of energy. 



In conclusion, I wish to express my best thanks to Pro- 

 fessor Bragg for the suggestions he has kindly given me from 

 time to time during this investigation. 



University of Adelaide, January 5, 1909. 



