Optical and electrical techniques have been used to investigate the way in which an electric discharge propagates across the surface of a liquid electrolyte. Field measurements have been carried out both in the column of the discharge, and beneath the liquid surface, by means of small metal probes. Schlieren photography has revealed a complex discharge structure and the presence of a strong liquid wave disturbance accompanying propagation. A significant difference in behaviour between positive and negative point discharges has been found. High speed cine-photography has shown that the speed of propagation of the discharge increases with voltage and with distance travelled and that this speed is influenced by resistive gradients in the electrolyte.