﻿Absorption of X- Bays and Fluorescent X-Raij Spectra. 995 

 fraction of the total less. By experimenting on the ab- 



sorption of radiations of high penetrating power by elements 



of low atomic weight, this may be tested. In Table II., 



column 2, are given the ratios of absorption in carbon to 



absorption in aluminium of various homogeneous X-radia- 



tions. The value rises from '1 to "4. If, however, the 



s 

 scattering coefficient - be subtracted from each absorption 



coefficient, as given in Table I., we find that the ratio of 

 absorptions is again constant, as shown in column 3. 



g 



[- has been previously shown to be *2.] 



Thus to obtain perfect generality in the absorption laws it 

 is necessary to neglect (or subtract from the total absorption 

 as defined above) the absorption due to scattering. This 

 becomes the most important term in the absorption of 

 penetrating radiations by light elements, something like 

 80 per cent, of Ba radiation (series K), for instance, being- 

 scattered by carbon. A larger proportion is, of course, 

 scattered by elements of still lower atomic weight. 



Table II. 



Radiation : the fiiiores- 

 centX-radiation, series 

 K, from elements below'i 



Ratio of absorption in 

 carbon to absorption 

 in aluminium [absorp- 

 tion includes radiation 

 scattered]. 



(Vp) c 



(Vp) a1 



Ratio of absorption in 

 carbon to absorption 

 in aluminium [absorp- 

 tion does not include 

 radiation scattered]. 



\ pjc \ P / A1 



Cr 



•112 



'114 



•111 



•111 



•109 



•108 



•111 



•108 



•164 



•223 



•3151 



.305 approxi- 



. 4l3 f mate. 



•111 



•112 



•108 



•108 



•105 



•104 



•103 



•99 



•104 



•109 



"125 ^ 



. 10 [approxi- 



, | male. 



Fe 



Co 



Ni 



Cu 



Zn 



As 



Se 



Ag 



Sn 



T 



Ba 



Ce 





Absorption in Gases and Vapours. 



No systematic experiments have previously been made on 



the absorption of homogeneous beams of X-rays by gases. 



There appears, however, to be no doubt as to the generality 



of the absorption laws, whether applied to solids, liquids, or 



3T 2 



