10 Prof. Thomson, On Chemical Composition of a Gas [Oct. 31, 



| 6. Final result. 



Substituting in equation (6) the values of J x and J 2 given by 

 equations (12) and (15) we get 



n 



J = (_)i»(n-i) j^-2/n^JM'H^ 



1 



which is the required formula, the inductive proof of which is now 

 complete. 



(2) 1. Metrical Relations between Linear Complexes. 2. 

 Apolar Systems of Quadrics. By J. H. Grace, B.A., Peterhouse. 



(3) Certain Systems of Quadratic Complex Numbers. By 

 A. E. Western, B.A., Trinity College. 



[Printed in the Transactions, Vol. xvil. Part II.] 



(4) On Mittag-Leffler's Theorem. By H. F. Baker, M.A., 

 St John's College. 



(5) On the connection between the Chemical Composition of a 

 gas and the Ionization produced in it by Rontgen rays. By J. J. 

 Thomson, M.A., F.R.S., Cavendish Professor of Physics. 



This paper contains an account of experiments made to 

 determine the ionization produced in a number of different gases 

 when Rontgen rays pass through them. The method used to 

 measure the ionization was as follows. It is well known that 

 the current of electricity passing through Rontgenized gas does 

 not increase proportionately to the electromotive force, the cur- 

 rent approaches a finite limit beyond which it does not increase 

 however large the electromotive force may be. This maximum 

 current which we shall call the saturation current is determined 

 by the condition that the number of ions used up by the current 

 in one second is equal to the number of ions produced in that 

 time by the rays. Thus the value of the saturation current is 

 proportional to the number of ions produced by the rays in one 

 second, so that to compare the ionization in two gases we have 

 only to compare their saturation currents when exposed to rays 

 of the same intensity. The measurement of the saturation current 

 is comparatively easy, the chief difficulty is to ensure that the 

 gases are exposed to radiation of the same intensity. The radiation 

 from the bulbs used in these experiments was not constant enough 

 to allow us to assume that it remained unaltered between successive 

 experiments on different gases, it was therefore necessary to 

 arrange the experiments in some way which would eliminate as 



