1 91 2] Secondary Rays Excited by the Alpha Rays. 171 



2. This secondary radiation has been proved to be in part due to 

 the presence of gas occluded in or at the surface of the brass or carbon. 



3. When this gas is being removed from the brass or carbon it is 

 found that the secondary radiation decreases and gives rise to an effect 

 similar to a "fatigue" of the secondary rays. 



4. This fatigue effect is found to be greater for carbon than for brass. 

 This last result was to be expected when the fatigue effect was traced to 

 the presence of occluded gases since carbon is known to possess a greater 

 capacity for occluding gases than a metal such as brass. 



5. From the experiments which have been described it will be seen 

 that the secondary radiation emitted by a substance like carbon under 

 bombardment by « rays furnishes a new means of investigating the 

 process by which gases are occluded in carbon and probably also in other 

 substances. 



In conclusion I wish to express my gratitude to Professor McLennan 

 for his suggestions and help throughout the course of this investigation. 



Physical Laboratory, 



University of Toronto. 



