where e is the charge on an ion,
n = number of ions per c.c.,
p = their partial pressure,
and u is the velocity due to the electric force X in the direction of the axis of x. When a steady state is reached,
dp nXeK
---- = 0 and u = ---- ,
dx p
Let N be the number of molecules in a cubic centimetre of gas at the pressure P and at the temperature 15° C., for which the values of u and K have been determined. Then N/P may be substituted for n/p, and, since P at atmospheric pressure is 106,
then
3 × 108u1