22S Prof. Barkla and Miss J. Gr. Dunlop on the 



to appear in the results obtained by two different methods,, 

 each giving only approximate valnes. The difference 

 between the results of the two methods was usually less than 

 10 per cent., although in experiments from copper a variation 

 as large as 40 per cent, was obtained. Subsequent exami- 

 nation of the observations taken suggests that the discrepancy 

 was possibly due to the fluorescent radiation from the copper 

 not having been completely absorbed in the experiments 

 the results of which are shown by an asterisk. However 

 that may be, the conclusions stated below hold equally well,, 

 consequently the experiments were not repeated. 



Absorbability of 

 X-radiation. 



\pJ Al. 



Relative Scattering. 



(S/p)cu 

 (S/P)A1 ' 

 (a) (b) 



(S/p)Sn 



( S /P)A1 



(a) (b) 



(S/P)p b 



(S/p)cu 



(a) (b) 



•33 

 •345 

 •35 

 •4 



•56 



•75 



1-41 



2-18 



*l-44 T06 



*1'79 l-25 c 

 *l-85 1-35 6 ' 

 *2-44 2-0 

 2-35 2-2 



1-6 1-47 



1-72 1-79 

 2-1 2-3 



The only results obtained by the first method (a) are given 

 above along with the corresponding results by method (b), to- 

 show the order of agreement. 



The final results of the measurements are given in Table LL 

 The numbers given in columns 3, 4, 5 and 6 indicate the 

 intensity of radiation scattered from copper, silver, tin, and 

 lead relative to that scattered from aluminium ; the wave- 

 length and absorbability of the radiation are given approxi- 

 mately in columns 1 and 2. The absorbability of each 

 radiation was measured by finding the thickness of aluminium 

 necessary to diminish the ionization in the measuring electro- 

 scope by about half and applying the equation for homo- 

 geneous radiation J = T £ _Az . This of course gives only an 

 approximate measure of the absorbability of a radiation not 

 strictly homogeneous. The approximate wave-lengths were 

 then obtained by plotting Barkla's absorbabilities against 



