674 Secondary Rontgen Radiation from Gases and Vapours, 



proportionality between the amounts o£ ionization produced 

 in a gas by Rontgen rays and the secondary radiation from 

 it. The figures are given, for the sake of comparison, in 

 Table V. The first column gives the relative ionization due 

 to soft rays *, the second column the relative ionization for 

 hard rays f, and the third the relative amount of secondary 

 radiation. 



Table V. 



Gas. 



Relative Ionization. 



Secondary 

 Radiation. 



Soft Rays. 



Hard Rays. 



Air 



1-00 

 •11 

 1-1 

 1-60 

 1-47 

 7-97 

 45-3 

 720 



1-00 

 •42 



2 : 3 



4-9 

 135 



1-00 

 •12 

 112 

 153 

 1-53 

 2-80 

 93 

 415 



H 



o 



C0 2 



N 2 



S0 o 



CC1, 



CH,I 





It will be noticed, however, on comparing the first two 

 columns of the table, that the relative amounts of ionization 

 for such gases as sulphur dioxide and methyl iodide diminish 

 rapidly as the hardness of the rays is increased, while the 

 relative amount of secondary radiation given off was inde- 

 pendent of the hardness of the primary beam, except in the 

 case of methyl iodide and stannic chloride, in which an increase 

 m the hardness of the primary rays produced an increase in 

 the amount of secondary radiation. It seems probable, there- 

 fore, that some further effect is also involved. 



The variation .of the properties of a substance for Rontgen 

 rays with the nature of the rays is so marked, that it is 

 extremely difficult to compare results obtained at different 

 times and by different observers. Experiments are in 

 progress in which simultaneous observations are being made 

 on the amounts of secondary radiation given off by a gas, and 

 the ionization in it. It is hoped that in this way some further 

 light may be thrown upon this, at present, rather obscure 

 problem. 



Summary. 



Experiments were made on seventeen different gases and 

 vapours with the following results : — 



(i.) All gases and vapours when subjected to X-rays are a 

 source of secondary radiation. 



* Strutt, Proc. Koy. Soc. lxxii. p. 209 (1903). 

 t Eve, Phil. Mag. viii. p. 610 (1904). 



