The Mechanism of the Negative Point Corona at Atmospheric Pressure in Relation to the First Townsend Coefficient

On the basis of recent work by P. L. Morton and G. W. Johnson on ionization by electrons in divergent electrical fields, it is shown that at atmospheric pressure it is permissible to compute the ionization in electron avalanches by means of the Townsend expression $\int e^{}\alpha \mathrm{dx}$ down to points of the order of 1×${10}^{-3\mathrm{}}$ cm radius. The phenomena resembling a glow discharge, observed at atmospheric pressure with the negative points normally used, must be ascribed to ionization of the Morton type which can only be produced in the positive space charge fields built up at the point later in the course of pulse formation. The ionization at both positive and negative points must initially be of the Townsend type. This conclusion clarifies difficulties, and is consistent with the pulse build-up time of 0.4 microsecond just observed by W. N. English with a Synchroscope. An explanation is also given for the equality of starting potentials of pulses from positive and negative points in air, while in pure ${\mathrm{N}}_2$ and ${\mathrm{H}}_2$, the negative pulses start at much lower potentials.