﻿988 



Prof. C. G. Barkla and Mr. V. Collier on the 



the characteristics o£ the relation were seen to be the same 

 whatever the element R employed. At that time, however, 

 the series of spectral lines * had not been observed, nor had 

 sufficient experiments been made to accurately test the 

 generality of the curves over a large range of penetrating 

 power, especially in the region of the spectral lines. 



In further experiments f we have therefore examined the 

 absorption of X-rays by Br and Ag, the latter of whose 

 spectral lines of series K is about 35'5 times as penetrating 

 as that characteristic of Fe. If we plot, as previously, 

 absorption in Br or in Ag as ordinates, and absorption in Al 

 of the corresponding homogeneous radiations as abscissae, we 

 get a curve possessing similar characteristics to those 

 previously published for the absorbing elements Fe, Ni, Cu, 

 and Zn. This was, of course, expected. If, however, we 

 arrange the scales of ordinates and abscissae for each 



^ * 



AqFe 



Spectral line of element i? 



/Ibsorptioh ih Aluminium 



Showing relation between absorption in element R and in standard 

 substance (Aluminium) in region of spectral line of R. One curve 

 K is common to all elements R if spectral line is of series K. 

 Curve L shows similar relation when spectral line is of series L. 



absorbing substance such that the absorption of Fe radiation j 

 in Fe, Ni radiation in Ni, Cu radiation in Cu, &c, are all 

 indicated by the one point A (fig. 1), it appears that there is 



* Barkla, Phil. Mag. Sept. 1911, pp. 39G-412. 



t In this paper, as in the paper by Barkla and Sadler, the absorption 

 coefficient X is defined by the equation I = I e -;u in the usual notation. 

 It should be noticed, however, that I represents the intensity of radiation 

 of the same penetrating power as the incident radiation transmitted in 

 the same direction as that of the incident radiation. It does not include 

 the scattered or transformed radiations. 



t (Series K.) 



