450 Dr. C. A. Sadler on Homogeneous 



The ratio of the total ionization per sec. due to the cor- 

 puscular radiation to that produced by the exciting homo- 

 geneous Rontgen radiation per sec. in 1 cm. of air 



(7) 



=^T=^S-^x7) = R ^- • • • (8) 



where E is written for ~ — , 



C 47T 



and therefore 



A = !(A + *i)(^-l), . . • • (9) 



No information is at present available for a determination 

 of either C or D. 



In the former paper a method, by which the determination 

 of R could be obtained, v>as described. It was pointed out 

 that a correction was necessary to allow for the ionization 

 produced by the tertiary Rontgen radiation from R 3 (that 

 from the aluminium window being small in comparison). 



The ratio determined was that of the total ionization pro- 

 duced by the corpuscular radiation from R 3 to that produced 

 by the secondary incident radiation and the tertiary radiation 

 from R 3 = R' say. If, then, we find the ratio of the ioniza- 

 tion produced by the secondary and tertiary radiation to 

 that produced by the secondary alone =R", and multiply 

 these ratios together, we obtain the value of It of 

 equation (8). 



Let k 1 be a quantity such that the fraction of the incident 

 energy of the secondary beam passing normally through a 

 thin layer of the tertiary radiator of thickness &e which is 

 transformed into tertiary radiation is Jc' Lv~ Then if o»' be 

 the mean solid angle subtended by the ionization-chamber at 

 any point of the tertiary radiator, X 3 the absorption coefficient 

 of the tertiary radiation in the material of which the radiator 

 is composed, and X 4 the absorption coefficient in air, it can 

 be shown that the ratio R 2 ' 



A.TT A : + \2 (eK — 1) £ X i ' 



To determine the ratio R/' plates of pure iron and copper 

 of equal size and shape were alternately placed in the position 

 R 2 shown in fig. 1. This position could be reproduced with 

 great accuracy. A plate of pure iron served as the tertiary 

 radiator. The ratio of the ionizations produced in the 

 chamber I and in the electroscope E 2 were noted with the 



