The surface resistance of glass during the initial stages of dew formation on a cooled surface

Measurements of surface resistance and observations of dew formation were made simultaneously as glass and other dielectrics were cooled through the dew point. The surface resistance decreased steadily until it was just possible to detect a dew deposit on the surface. Close to this point the resistance passed through a minimum value, then increased to a maximum before decreasing steadily once more. The limited increase to the resistance maximum was not consistent with a large change in the thickness of the water film and it was concluded that the developing droplets coexisted with the adsorbed film. Coalescence swept the ionic material responsible for conduction into the developing droplets increasing the resistance of the film between the droplets and causing the overall increase in surface resistance.