feo: 
XXXV. The Relative Amount of Ionization produced in Gases 
by Réntgen Rays of Different Types. By R. K. McCuuna, 
M.A., Trinity College, Cambridge ; 1851 Exhibition Science 
Scholar”. | 
Introduction. 
tae question of the relative amount of ionization pro- 
duced in different gases by the action of Réntgen rays 
is one which has been investigated by several experimenters. 
Being a fundamental question in connexion with ionization 
in gases, it was investigated quite early in the history of 
Réntgen rays. Perrint and Rutherford{t about the same 
time, but quite independently, tested the ionization in several 
gases and found the relative values for these gases. Later 
J.J. Thomson§ made a very comprehensive set of experi- 
ments which included a large number of gases. The values 
obtained by these different observers for the various gases 
are in most cases in fair agreement with one another, but 
in a few instances there is considerable disagreement. This 
disagreement is especially noticeable in the case of hydrogen. 
It has been suggested by Prof. J. J. Thomson, in speaking 
of this point in his recent book on the ‘ Conduction of Elec- 
tricity through Gases,’ that this discrepancy might be ex- 
plained by the fact that the different experimenters used 
rays of different degrees of hardness, and that probably the 
relative amount of ionization in different gases depends upon 
the type of rays used. The experiments described in this 
paper were undertaken, therefore, to see if some explanation 
could be found for this discrepancy in previous results, 
especially in the case of hydrogen. 
For the purpose of these experiments it is very necessary, 
in order to obtain perfectly definite results, that, in com- 
paring the ionization in two gases, rays of exactly the same 
sort and the same intensity should be used to ionize each 
gas. A balance method was therefore adopted by which the 
two gases under investigation in any given instance were 
ionized simultaneously by the rays. Any change in the 
ionizing power of the rays would thus affect both gases at 
the same time. Another reason for adopting this method 
* Communicated by Prof. J. J. Thomson, F.R.S. <A preliminary 
account of some of these experiments was published in the Proceedings 
of the Cambridge Philosophical Society, vol. xii. pt. v. February 1904, 
and also in a short article in ‘ Nature,’ March 10th, 1904. 
+ Perrin, Annales de Physique et de Chimie, xi. p. 496 (1897). 
t Rutherford, Phil. Mag. vol. xliii. p. 241 (1897). | 
§ J. J. Thomson, Proc. Camb. Phil. Soc. x. p. 10 (1900). ; 
Phil. Mag. 8. 6. Vol. 8. No. 45. Scpi. 1904. | 2B 
