On the shapes of the equipotential surfaces in the air near long walls or buildings and on their effect on the measurement of atmospheric potential gradients

Abstract

1. In considering the most suitable arrangements for recording the variations of the atmospheric potential gradient at the East London College, where no large horizontal surface is available, I have had occasion to calculate the distribution of potential in the neighbourhood of walls and buildings of simple shapes. As the results can be applied in practice it seems advisable to put them on record for the use of other observers. Observation shows that during fine weather the potential at a point in the atmosphere over a level portion of the earth's surface in these latitudes increases as the point is raised, at the rate of about 150 volts per metre. This rate of increase diminishes slowly as the point ascends, owing to the slight excess of positive over negative ions in the air near the earth's surface, and at an altitude of a kilometre is reduced to about 25 per cent. of its value at the surface.