670 



Mr. J. A. Crowther on the Secondary 



The two sets of values show a very satisfactory agreement, 

 the maximum divergence being only about 2 per cent. ; and 

 we may therefore assume that the secondary radiation from a 

 compound is equal to the sum of the radiations from the atoms 

 composing it. 



We can thus employ the results given in Table I. to calculate 

 the relative amounts of secondary radiation given off per 

 atom for the dozen different elements concerned. As air was 

 chosen as the standard gas for the experiment, and for the 

 sake of convenience, I have takeu oxygen as the standard 

 atom, and calculated the secondary radiation per atom of the 

 other elements, on the assumption that that from oxygen is 

 equal to 16. The results are given in Table III. 



Table III. 



Element. 



Atomic weight. 



Secondary radiation 

 per atom (0 = 16). 



Secondary radiation 



Atomic weight. ' 



Hydrogen 



Helium 



1-0 

 40 

 120 

 14-0 

 16-0 

 320 

 35-4 

 59 

 75 

 80 



118 



127 



1-7 



4-5 

 12-0 

 14-0 

 160 

 451 

 58-6 

 120 



5860 



6280 



1830 



1170 



1-7 



1-1 



1-0 



1.0 



10 



1-4 



1-6 



2-0 



7 51 



v 85 



1 5-5 



94 



Carbon 



Nitrogen 



Sulphur.. 



Chlorine 



Nickel 



Arsenic 



Bromine .... 

 Tin 



Iodine 





Glancing through this table, the most striking point is the 

 relatively huge amounts of secondary radiation given off by 

 the atoms of arsenic and bromine, and in a lesser degree by 

 ihose of tin and iodine. With regard to the latter, it must be 

 noted that the amount of secondary radiation given off by 

 them increases with the hardness of the rays, and although 

 the measurements given were made with the bulb as hard 

 as the coil would work it, it is probable that if it had been 

 possible to use still harder rays, values for tin and iodine 



