GG6 Dr. Sadler and Mr. Steven on an Apparent Softening 



It will be seen from column IV. that the iron specially 

 cuts down the secondary radiation from iron as predicted, 

 i. e., the iron selectively absorbs those constituents of the 

 primary capable of exciting radiations in itself. It will be 

 seen also that the softer radiations, too soft to excite iron 

 radiation but capable of producing considerable radiation 

 from Ti and Cr, are cut down by the iron to a lesser extent 

 than the average. These latter, on the other hand, are cut 

 down more readily by the aluminium than those which 

 specially excite on iron (see column III.). 



It is interesting in this connexion to show the subsequent 

 absorption by aluminium of the primary beam after being 

 cut down by iron and aluminium respectively to the same 

 extent (63 per cent.). 



Of the initial beam aluminium -00305 absorbs 28*9 % 



„ „ „ cut down by Fe „ „ „ 41*4 % 



» j> » >« ^* >» j? v Zz'Z [ 



The softening of the primary beam when cut down by 

 various substances and tested by a thin sheet of a substance 

 other than aluminium, has also been observed. The following 

 two examples indicate, however, that the occurrence of the 

 effect depends on certain relations existing between the 

 radiations characteristic of the absorber and of the test 

 substance. 



I. Cutting down the primary beam 60*3 per cent, by iron: 



Per cent, absorbed by test substance : Per cent, of 

 Before cutting After cutting- secondary from 



Test Substance. down by Iron. down by Iron. test substance cut 



down by Iron. 



m 49 56-6 54-9 



Fe 60 52-6 65 



II. Cutting down the primary beam 50*7 per cent, by 

 nickel : 



Per cent, absorbed by test substance : Per cent, of 

 Before cutting After cutting- secondary from 



Test Substance, down by Nickel, down by Nickel." test substance cut 



down by Nickel 



Ni 47-7 46-2 62 : 7 



Fe 60*3 67-9 52 



From what has been said in a previous portion of the 



