42 Dr. C. D. Oooksey on Asymmetry in the Distribution 



in the air of the ionization-chamber and to some extent in 

 the layer of the metal from which the cathode rays come. 

 The ratio of the number of emergence cathode rays coming 

 from a layer of the metal so thin that the exciting rays 

 suffer no absorption in it to the number of incidence cathode 

 rays coming from the same layer is the true value sought. 

 Let this be designated by R. Let ft be the coefficient of 

 absorption of the cathode rays in the metal from which they 

 come, X { the coefficient of the exciting X-rays in the same 

 metal, and A2 their coefficient in air. The number of 

 emergence cathode rays produced in a layer of thicknes- da 

 at a depth x of the metal by X-rays of intensity I is equal to 



K I (U; 



where K is some constant. If the intensity of the X-rays 

 on entering the metal is I , and the thickness of the plate /. 

 the number of the emergence cathode ray- which get out of 

 this layer into the ionization-chamber is equal to 



and the total number getting out of the whole plate is 



_ Klpe"^ Q8-\,X , 



The X-rays after being absorbed in the plate on the front of 

 A are absorbed by the air in A and by the plate on the back 

 of A. Therefore the intensity of these ray- alter reaching a 

 depth ,v of the second plate will be 



T —\.t -X.Y' -\..r 



where /' La the length of the ionization-chamber. Therefore 

 the number of incidence cathode rays setting into the 

 ionization-chamber from the second plate oi thickness t 

 will bo equal to 



; _KI (> 6 - ri-tP+W. 



Et(£ + Xl) L J ' 



The ratio of the Dumber of emergence cathode ray- entering 



A to tin 1 cumber of incidence cathode rays is therefore 



,.,_ 1 ,^x,^v + x/p'' , - v '-n 



