56 C. D. Coohsey — Secondary Cathode Rays. 



been measured with the object of finding the dependence of 

 the ratio on the penetrating power of the exciting rays. 



The fluorescent secondary X-rays from tin, zinc, iron, and 

 chromium were used as exciting rays, representing an increase 

 in absorbability as measured in aluminium of about 8000 per 

 cent between tin and chromium. 



After allowing for the absorption of the exciting rajs in the 

 layer of the metal from which the cathode rays come and in 

 the air of the ionization chamber, it was found that there was 

 no definite variation in the ratio of emergence to incidence 

 effect. 



In closing I wish to express my thanks to Professor H. A. 

 Bumstead for the interest he has taken in the work. 



Sheffield Scientific School, Yale University, 

 New Haven, Conn., March, 1912. 



