so 



ROYAL SOCIETY OF CANADA 



7. The gradual changes in the character of the emergent cor- 

 puscular secondary radiation were observed when the exciting rays 

 were varied from a very hard to a very soft type (figs. 3, 5). 



8, When reversals of plates are made, as described, the four 

 readings obtained are nearly in proportion. (Table IV.) 



Addendum. i 



"^'HSince completing this work I have obtained a copy of F. E. 

 Hackett's paper in the Transactions of the Royal Dublin Society 

 (Jan. 1909) entitled " The Secondary Radiations excited by y rays". 



Fig. 6. 



His method differed from mine, for his apparatus was so arranged 

 that the emergent secondary rays passed obliquely to a testing 

 vessel which was not itself traversed by the exciting j rays. 

 rv , His results are shown graphically by me in figure 6. As the 

 primary j rays were screened by only 2 mm. of lead it is evident 



