Gaseous Mixtures hy Rontg en and Corpuscular Radiations. 841 



only two, C0 2 and C 2 H 5 Br, were published at the time, 

 as these two were typical of all the others. The relation 

 between the ionization of a gas and its characteristic spectrum 

 was then shown, and a considerable portion of the ionization 

 in ethyl bromide was seen to be due to the secondary corpus- 

 cular radiation from bromine. The results of experiments 

 by Sadler were made use of in estimating the ionization due 

 to the corpuscular radiation. From later work by Beatty 

 and Bragg it appears that some of these results of Sadler's 

 were somewhat small. Accepting Beatty's experimental 

 results instead, the calculated percentage of ionization in 

 C 2 H 5 Br and air due to corpuscular radiation becomes about 

 80 per cent. Beatty made a careful investigation of the 

 ionization in seleniuretted hydrogen, and concluded that in 

 some cases at least much the greater part of the ionization 

 was due to the secondary corpuscular radiation. By the 

 application of the results already given in this paper to the 

 results of Beatty's experiments, we can show that there is 

 probably very close agreement between the ionization due to 

 secondary corpuscular radiation and the total X-ray ionization. 

 In the absence of more definite information, however, Beatty 

 assumed that the corpuscles ejected from Se in SeH 2 pro- 

 duced the same number of ions in SeH 2 as they would in 

 air. As Se has an atomic weight very close to that of Br, 

 and as H 2 in SeH 2 takes the place of C 2 H 5 in C 2 H 5 Br, we 

 should estimate the number of ions that would be produced 

 in SeH 2 to be about 1*6 times the number in air. If, 

 then, we multiply Beatty's calculated value of the ionization 

 produced by the corpuscular radiation by 1*6, we find in the 

 various cases considered that 120, 87, 84, 86, and 103 per 

 cent, of the ionization was due to the secondary corpuscular 

 radiation. The average of these is 96 per cent. 



Bragg, however, was the first to insist on the interpretation 

 that the whole ionization was due to the secondary action of 

 the ejected corpuscles. All experiments on ionization, how- 

 ever, did no more than merely indicate the possibility of this. 

 The first convincing proof was given by C. T. R. Wilson, 

 who showed by his condensation experiments that all the 

 ions formed in air were to be found along the trails of the 

 secondary corpuscles. 



Turning now to the accurate determination of the relative 

 ionizations produced in various gases and vapours by Rontgen 

 radiation, only the results of experiments on one or two gases 

 have been published. In addition to the work to which 

 reference has been made, E. A. Owen * has recently made 

 careful measurements of the ionizations in C0 2 and S0 2 

 * Proc. Koy. Soc. A. lxxxvi. pp. 426-439 (1912). 



