the charged electrode A , and the conductivity of the gas tested immediately afterwards at an electrode B , which was placed close to A . The insulated electrodes A and B were fixed centrally in the metal tube L , which was connected with earth.
For convenience of calculation, it is assumed that the electric field between the cylinders is the same as if the cylinders were infinitely long.
Let a and b be the radii of the electrode A, and of the tube L respectively, and let V = potential of A.
The electromotive intensity X (without regard to sign) at a distance r from the centre of the tube is given by
Let u1 and u2 be the velocities of the positive and negative ions for a potential gradient of 1 volt per cm. If the velocity is proportional to the electric force at any point, the distance dr traversed by the negative ion in the time dt is given by
dr = Xu2 dt,
or
Let r2 be the greatest distance measured from the axis of the tube from which the negative ion can just reach the