different Metals by Rontgen Bays. 299 



portional to I e-^dx. If ~k' be the coefficient of absorption of 

 the corpuscular rays in the metal, the number which emerge 

 from this layer will be proportional to I e- ? ^e-k'xdx, and if we 

 call the total number of corpuscles emerging from the metal 

 N', we have that 



If we let the total number of corpuscles generated in the metal 

 be N, then 



f<x>-Xx 

 NxT / e ax 



Therefore 



or 



a 

 A 



Since the corpuscular rays are much more easily absorbed than 

 the Rontgen rays producing them, the quantity y will be very 

 large compared to unity, and we can say 



A 



1ST is not, however, directly proportional to the intensity of the 

 ionization measured in the ionization chamber. To find what 

 relation the ionization measured bears to N' we must take into 

 consideration the absorption of the corpuscles in air, and the 

 number of ions produced by a corpuscle per cm. of path for 

 different velocities. For the range of velocities encountered 

 in these experiments, however, I think we are justified in 

 assuming that the corpuscles from all the metals produce the 

 same specific ionization, for the following reason. 



Durack * has measured the specific ionization produced by 

 Lenard rays having velocities of about 4-xlO 9 cms./sec, and that 

 produced by the deflectible Becquerel rays having velocities of 

 from 2 - 4-xl0'° to 2 - 8xl0 10 cms./sec. In the first case he finds 

 the specific ionization equal to about 0*4 and, in the second, to 

 about 047 ions per corpuscle per cm. of path; a fall of about 



*Phil. Mag. (6) iv, 29, 1902 ; and v, 550, 1903. 



