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IONIZATION OF OASES AND THE ABSOEPTION OF 
EONTOEN EATS. 
By Lewis Simons, B.Sc. (Lond. and Cape), Lecturer in Physics, 
Victoria College, S telle nbosch, South Africa. 
There are promising indications that the study of the influence of 
Eontgen rays on matter generally can be very much simplified by keeping 
in mind the processes which occur during the passage of the rays through 
gases. The processes involved are so essentially concerned with the atom 
and not with the molecule, except perhaps in one case which will be con- 
sidered later, that we are bound to conclude that the physical condition of 
the substance through which the rays are passed does not affect the energy 
transformations at their source. 
In gases we are concerned with a comparatively open structure ; the 
ionization within the gas can be measured. Such a measurement cannot be 
made in the case of solids or liquids, for in these the total absorption of the 
incident energy, the emission of characteristic rays and of corpuscles from 
the surface are the effects observed. In working with gases there is the 
difficulty that there are so few gaseous elements that it is impossible to 
obtain a set of results over a large range of atomic weights. In experi- 
menting on vapours containing heavy atoms, it is impossible to perform 
control experiments eliminating the effects of the other atoms present. 
When the first experimental investigations were made of the relative 
ionizations produced in gases or vapours when these were under the influence 
of homogeneous beams of X-rays, the notions of Bohr and Einstein were 
not applied in studying the energetics of ionization. The searching test to 
which Millikan has recently subjected Einstein's photo-electric equation and 
the similarity of the processes involved naturally lead one to apply the 
same test to X-rays. 
It has been shown that the major part of the ionization produced in the 
gases Hg, Oo, COo, Air, SHo, SOo, and in the vapours of CgH^Br, and 
CII3I could be accounted for by the emission of rapidly moving corpuscular 
rays which ionized neighbouring atoms by collision.* In a later paj)er the 
* Barkla and Simons, Phil. Mag. (6), xxiii, p. 333. 
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