On the conductivity of a gas, between parallel plate electrodes, when the current approaches the maximum value

The relation connecting the current with the potential difference between parallel plate electrodes when the gas between the plates has been uniformly ionised by Röntgen rays or Becquerel rays has been investigated theoretically by many physicists. In all cases various assumptions are made in order to simplify the calculations, as the problem becomes very complicated when the disturbance of the field due to the separation of the ions is taken into consideration. Perhaps the most complete solution is that given by Mie, in which the only effect that is neglected is that of diffusion. The difference between the velocities of the positive and negative ions is taken into consideration, and the disturbance of the field due to the charge in the gas produced by the excess of ions of one sign in the neighbourhood of the electrodes. The method of analysis, consisting of a series of approximations, is difficult, but the results have been presented in a convenient form, for currents in air at atmospheric pressure that are certain fractions of the saturation current. A curve is given for each current which shows the distribution of force between the plates. The currents investigated ranged between those that were one-fifth and nine-tenths of the saturation current. In the former case the ratio of the electric force at the negative electrode to the minimum force in the filed was found to be 2.7. The ratio diminishes as the force increases, and for the current that is nine-tenths of the saturation current the ratio becomes 1.39.