314 Mr Kleeman, On the Dependence of the Relative Ionisation 
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On the Dependence of the Relative Ionisation in various Gases 
by B Rays on their Velocity, and its bearing on the Lonisation 
produced by y Rays. By R. D. Kieeman, B.A. (Emmanuel 
College), D.Sc. (Adelaide). 
[ Recewwed 9 October 1913. Read 27 October 1913.] 
Experiments which give some information whether the rela- 
tive ionisation by 8 rays in various gases depends on the velocity 
of the rays have already been carried out by the writer*, who 
measured the relative ionisation per c.c. im various gases by the 
8 rays of actinium and uranium. The experiments shewed, as 
far as they went, that the relative ionisation is independent of the 
velocity of the @ ray. Further experiments have been carried 
out on the subject and will be described in this paper. 
A beam of heterogeneous 8 rays was obtained by placing a 
quantity of radium in a thin glass tube at one of the entrances of 
a bore-hole ‘6 cm. in diameter passing through a lead block about 
7cm. square. The beam was allowed to pass into an ionisation 
chamber through an aluminium window ‘16 mm. thick. By 
means of a magnetic field whose lines of force were at right 
angles to the bore-hole the beam of rays could be “hardened” to 
any desired extent by bending some of the slower moving rays 
aside. It was found that the gradual hardening of the beam 
produced no change in the relative ionisation of the gases in the 
chamber. The ionisation of methyl iodide and hydrogen in 
terms of that of air was measured, since these gases differ from 
one another considerably in the nature of the atoms they contain. 
As an illustration of the experiments it may be quoted that in 
one case the ionisation of hydrogen in terms of that of air was 
‘156 without the magnetic field, and ‘151 with the magnetic field. 
The magnetic field in this particular case reduced the ionisation 
in air and hydrogen to about one-half of their previous values. 
In the experiments the ionisation of air and hydrogen were first 
measured without a magnetic field on, putting air into the 
chamber first. Then leaving the hydrogen in the chamber and 
putting the magnetic field on, the ionisation of the hydrogen was 
measured under the new conditions. Lastly, putting air into the 
chamber its ionisation was measured with the same magnetic 
field on. This process was repeated several times and the mean 
of the results taken. When methyl iodide mixed with a certain 
proportion of air was used instead of hydrogen in the experiment 
* Proc. Roy. Society, A, vol. 83, p. 530 (1910). 
