﻿Absorption of X- Rays and Fluorescent X-Ray Spectra. 991 



distance between the two lines on the spectrum is so great 

 compared with the distance of one from the end, the scale of 

 abscissae has been made different in the two halves of the 

 diagram separated by the broken line. The scale on the 

 right-hand side has been reduced to about -^ that on the left. 

 From many substances only the spectral line of series K has 

 been observed, from others only that of series L, and from 

 many light elements neither line, but there is strong evidence 

 of the existence of both lines and indeed lines of other series 

 not yet observed in the fluorescent spectra of many elements. 

 There is no evidence that these lines do not exist in 

 the fluorescent spectra of all elements. The curve shown 

 above the characteristic spectrum of an element R, say, 

 represents by its ordinates the relative absorptions in 

 that particular element of the radiations w r hose absorba- 

 bility in Al is represented by abscissa). The ordinates to 

 the right of the vertical broken line have been reduced in 

 something like the same ratio as the abscissa), though not 

 accurately so, as from no single element has the complete 

 absorption curve been obtained ; consequently the true 

 relative values of the ordinates in the two halves of the 

 diagram have not been determined. In the case of some 

 substances, the curve has been obtained in the region of the 

 spectral line K only, in others in the region of line L, and in 

 still others in regions far removed from the two. 



We thus have, as far as is at present known, cue fluorescent 

 spectrum characteristic of all elements, the only difference 

 between the various elements being that the scale of ab- 

 sorbability varies from element to element. Corresponding 

 to this spectrum there is one absorption curve characteristic 

 of all elements, the scale of absorptions (ordinates) varying 

 with the element. 



The character of this absorption curve for an element R, 

 say, may be expressed as follows : — Commencing with rays 

 of more absorbable type than the L line in the spectrum of 

 R, the absorption in R is proportional to the absorption in 

 the standard substance S. This is represented by the straight 

 line AB, which being produced passes through the origin. 

 As the radiation becomes more penetrating in type than the 

 L line the absorption in R ceases to diminish at the same 

 rate as in S, and then increases rapidly along CD. It then 

 slowly approximates to proportionality with absorption in S, 

 as shown by the line EF. Before the penetrating power of 

 the K line is reached, the absorption in R becomes pro- 

 portional to the absorption in S, as shown by the line GH. 

 Again, when more penetrating rays than those of the K line 



