The electric strength of air at high frequencies

The paper describes a series of experiments on the electrical breakdown strength of air under sinusoidal voltage conditions over a frequency range from 50 to 900 kc./sec. It is shown that with frequencies of the order of 200¿1000 kc./sec. there is a noticeable reduction in the breakdown voltage between spherical electrodes one of which is insulated and the other earthed, the reduction becoming more marked as the frequency is increased. A modification of Townsend´s theory, based on a consideration of the ionization conditions prior to breakdown, is suggested, which explains the reduction in the electric strength of a sphere-gap at the higher frequencies.