PROCEEDINGS 



OF THE 



Cantkitrg^ |PPas0p]^ka:I Scrmtg. 



The Laws of Mobility and Diffusion of the Ions formed in 

 Gaseous Media. By E. M. Wellisch, Emmanuel College. 

 [Communicated by Sir J. J. Thomson.] 



[Head 9 November 1908.] 



The information we possess with regard to the size and 

 structure of the ions formed in gases by the action of Kontgen 

 *rays is almost entirely derived from a knowledge of their rates 

 of diffusion and their velocities under given electric forces*. In 

 order to obtain this information theoretical expressions are 

 necessary for the coefficient of diffusion (D) of an ion through 

 a gas and for its velocity (k) under unit electric intensity. From 

 considerations based on the kinetic theory of gases Langevinf 

 has shown that k and D are expressible in the forms: 



MV 3 ' 



where e denotes the charge associated with the ion, M the mass 

 of the ion, L its mean free path through the gas, and V its mean 

 velocity of thermal agitation. From these forms however no 

 very exact information can be deduced inasmuch as the values 

 of the quantities involved cannot be directly determined from 

 experiment. In the present paper expressions are given for 

 k and D which involve only known physical constants of the gas 

 and from which, therefore, we may expect to derive reliable 

 information with regard to the constitution of the ion. 



A molecule is regarded for the present purpose as a nucleus 

 surrounded by a " sphere of force " of radius |s. 



* J. J. Thomson, Conduction of Electricity through Gases, 2nd edit. Art. 38. 

 t Ann. de Chim. et de Phijs. vn. 28, p. 324, 1903. 



VOL. XV. PT. I. 1 



