Point‐discharge currents and the earth's electric field

An account is given of measurements of the current flowing to earth through a point set up at a height of 12 m, together with the electric field near the ground. Point‐discharge current of either sign may be represented approximately as increasing with the square of the field, as found by Whipple and Scrase. In the light of recent work on corona discharges between a point and a plane in air at atmospheric pressure it is suggested that for high fields the point‐discharge current will vary directly as the field. Irregularities in the curves relating averages of discharge current and field are attributed to space charge arising from local point discharge at or near the raised apparatus used for measuring the field. An advancement of field changes ahead of the corresponding point‐current changes is considered to be an example of the reversal, by space charges, of the sign of field between the level of a raised point and the ground, described by Lutz.