274 



Prof. Barkla and Miss White on the 



absorptions were too nearly alike to show clearly on the same 

 scale. The interesting features of these curves are described 

 below. 



Fig. 1. 

 Showing absorption curves in the neighbourhood of J spectral lines. 



Absorption in Capper ("/p). 



Characteristic Radiations of J Series. 



The simplicity of the form of each curve is broken by a 

 feature which indicates the existence of an X-radiation 

 characteristic of each substance. Similar curves were first 

 shown by Barkla and Sadler* in association with the 

 K-radiations, and by Barkla and Collier f in association with 

 the L-radiations. No such irregularity has ever been observed 

 except in association with a characteristic X-radiation. 



The three " discontinuities," as we shall call them, being 

 due to the elements aluminium, oxygen (in both water and 

 paper), and carbon (in paraffin- wax) , we see that the higher 

 the atomic weight the more penetrating is the radiation at 

 which the discontinuity occurs ; in other words, the higher 

 the atomic weight of the element the higher is the frequency 

 of its characteristic radiation. This is in harmony with the 

 results obtained for K and L radiations. 



[Any discontinuity in the absorption curve for hydrogen 

 would be inappreciable and could not be detected in the 

 curves for paper, water, and paraffin-wax, of which it is a 

 constituent. That due to carbon is clearly marked in the 



* Phil. Mag. May 1909. 

 t Phil. Mag. June 1912. 



