SECTION III., 1911. [7] Trans. R.S. C. 
On the Mobilities of Ions in Gases at High Pressures. 
By A. J. Dempster, M.A. * 
Presented by Prof. J. C. McLennan. 
(Read May 17, 1911.) 
Although several theories bearing on the velocity of ions through 
gases have been given, notably by Langevin,’ Wellisch? and Sutherland,’ 
yet none of the results calculated from these theories agree very satis- 
factorily with the values obtained by experiment. As the mobility of 
ions is so fundamental in the conduction of electricity through gases 
it was thought that the determination of the velocities through gases 
at pressures much above those hitherto used might be of interest and 
perhaps throw further light on the mechanism of the conduction of the 
ions through gases and the connection of the mobility with various 
constants of the gas. 
A diagram of the apparatus used is given in Fig 1. A is a steel 
cylinder about 30 ems. long and 10 ems. external diameter with walls 
2 cms. thick, having a pressure gauge Dat one end. Through the other 
end passes the air valve and three wires insulated by ebonite rods. One 
of these X leads to a sensitive electrometer of the Dolazalek type, the 
others Y and Z lead to the ends of a battery B,, Z being made alternately 
positive and negative by means of two batteries B, and B, and a com- 
mutator C. 
Langevin Thèses présenties à la Faculté des Sciences, 1902. 
Wellisch Phil. Trans. (A) 209-249, 1909. 
Sutherland Phil. Mag., (6), 18, 1909. 
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