For many years the theory of the mechanism of spark discharge as derived by Townsend 1 has been more or less widely accepted as essentially describing the phenomenon. This theory in essence ascribes the spark as being due to conditions set up in the gas between the electrodes such that there is a continuous supply of electrons from the neighborhood of the cathode produced by the interactions of the rapidly moving positive ions with other gas molecules or with the electrodes.
In the mechanism of the spark at atmospheric pressure between plane parallel electrodes however a serious discrepancy arose in past years which has caused some workers to abandon this elegant theory3 ,3 The difficulty lay in the fact that with the fields of the order of 30,000 volts/cm, usually causing spark discharge at this pressure the positive ions could not possibly in sufficiently large numbers get the energy to produce the phenomena required. It was particularly emphasized by the writer 4,5 in recent years that the theory could still be applied if a gratuitous assumption as to the fields at breakdown, acting on positive ions near the cathode, be abandoned. This gratuitous assumption was that the fields at the instant of breakdown were uniform. If actually as a result of the dark current preceding breakdown there are space charges formed which produce fields near the cathode 1