30 



THE THEORY OF IONIZATION OF GASES 



the centre of the molecule in order that ionization may 

 result from the collision, the distance R being less than 

 <r. For if m is the number of molecules in a cubic 

 centimetre of a gas at 760 millimetres pressure and 

 15 C., then 7rR 2 7/ t =Nx760, and the quantity 7ro- 2 w may 

 be deduced from the coefficients of viscosity. The 

 values of RxlO 8 and o-xlO 8 in centimetres for the 

 different gases are given in the following table, the 

 number m being taken as 3xl0 19 which is the value 

 deduced from the recent investigations by Professor 

 Perrin. 1 The values of o- have been deduced for the 

 same value of m from the expression for the viscosity 

 given by Professor Jeans. 3 



TABLE IX. 



14. Application of the theory to Stoletow's experiments. 



The experiments \vhich have been described were 

 arranged expressly for the purpose of obtaining results 

 from which the values of a could be easily obtained, 

 as no reliable investigations had previously been made 



1 Jean Perrin, Comptes Bendus, Octobre 5, 1908. 



2 Jeans, "Dynamical Theory of Gases," p. 250. The values of 

 10 8 ff given in this treatise on p, 251 correspond to m=4x 10 19 . 



