ROYAL SOCIETY OF CANADA 



The remarkable^dissimilarity in the two cases is at first sight per- 

 plexing, and the object of the present paper is to explain to some ex- 

 tent the cause of the apparent differences. 



In the first place it must^be^pointed out that a comparison of the 

 two tables above given is an unfair one, because the first table really 

 shows secondary radiation of the X ray type, for the kathode rays were 

 mainly absorbed by air before they reached the testing apparatus. 

 But the second table gives the kathode secondary radiation due to y 

 rays, for in this case the kathode rays produce a much greater effect in 

 the electroscope than the secondary ra3^s of the y type. 



A few experiments recently made may be worth recording. The 

 X rays from a very hard tube were employed, such as were used in 

 some previous experiments to compare the ionizations of various gases 

 by y and X rays.' Such hard penetrating rays were then found to 

 ionise gases almost in the same manner as y rays. In the present case 

 the X raj's struck plates of the substances named in Table III., and 

 the incident secondary rays were measured by the electroscope, des- 

 cribed later, used throughout these experiments. The kathode 

 secondary rays were absorbed by the air, between the secondary 

 radiator and the electroscope. The incident secondary radiations 

 from the same plates were also measured, due to 14 mgs. of pure radium 

 bromide placed inside a hollow nickel steeF cylinder, 2.2 cms. thick, 

 having stopped ends. The kathode secondary rays were in this case 

 screened from the electroscope by aluminium 1.63 mms. thick, placed 

 just in front of the very thin face of the electroscope. The results given 

 show that when the kathode rays are in each case removed the orders 

 are not those of atomic weights. Very thick radiators are needed to 

 get the full value of the y rays from the lighter substances. 



TABLE III. 



Secondary rays from X and y rays. 

 Kathode rays removed by absorption. 



» Phil. Mag., Nov. 1904. 

 »5% Nickel. 



