﻿992 Prof. 0. G. Barkla and Mr. V. Collier on tlie 



are used, the absorption in R rises above that of proportion- 

 ality with S, and then rises rapidly as shown by IJ, the 

 character of the rest of the curve being similar to that 

 obtained on the more penetrating side of the L line, the 

 features, however, being more strongly marked. 



The similarity of the absorption curves may be mathe- 

 matically expressed thus : — ■ 



x\r _ j. /x^-s \ 



That is, the coefficient of absorption of any X- radiation in 

 any element R divided by the coefficient of absorption of the 

 radiation characteristic of R in R itself is a function of 

 the coefficient of absorption of that X-radiation in S divided 

 by the coefficient of absorption of the radiation characteristic 

 of R in S, — the characteristic radiations being of the 

 series K. This function is independent — or, at any rate, 

 approximately independent — of the absorbing substance R 

 for all substances hitherto experimented upon. 



The relation between the absorption of a definite homo- 

 geneous X-radiation by various elements and the atomic 

 weight of those absorbing elements has been indicated bv 

 one of us in a paper on " The Phenomena of X-ray Trans- 

 mission '**. 



Observation of the similarity of the behaviour of all sub- 

 stances shows that it is possible to construct more accurately 

 the curves showing the relation between these quantities. 



Thus if we plot absorption f — ) of a certain homogeneous 



X-radiation — say. Ni radiation of series K — by various 

 elements, and the atomic weight of those elements, we have 

 insufficient data to determine the shape of the curve in many 

 regions. But by alteration of the scales of ordinates and 

 abscissse in similar curves got from experiments on homo- 

 geneous X-radiations of neighbouring penetrating power, 

 we can build up a more accurate curve showing the relation. 

 There is a slight variation in form between the curves 

 obtained from experiments on radiations widely different in 

 penetrating power, for the ratio of the atomic weights of the 

 elements giving radiations of the same penetrating power 

 (one in series K, the other in series L) is not a constant for 

 all penetrating powers. 



The curve shown in fig. 3 gives the relation between the 

 absorption of Ni radiation (series Kj by equal, masses of 



* Barkla, Proc. Camb. Phil. Soe. May 1909, pp. 257-268. 



