On the nature of corona loss

If a high voltage is applied between two electrodes, experience shows that in any given case there is a limiting voltage below which no loss occurs, a permanent current flows only if the voltage is an alternating one and is then a purely charging current. Above this voltage loss appears, accompanied by the familiar phenomenon of corona; a permanent current flows even in the case of continuous potential, showing that the air space between the electrodes becomes a conducting part of the circuit.