The role of point discharge in the historical development of atmospheric electricity

Abstract. Point discharge, like lightning, is an atmospheric electricity process which has been observed directly and indirectly for centuries. Point discharge occurs when an electric field is enhanced at a point, causing local ionisation of the air and allowing a current to flow between the object and atmosphere. Point discharge sensors are simple instruments which measure the discharge currents caused by enhancements of the atmospheric electric field. In the early 20th Century, several milestone atmospheric electricity investigations were performed which employed the effects of naturally occurring point discharge currents and the measurements made by point discharge sensors. Point discharge was central to some of the arguments made in the proposal of the global atmospheric electric circuit, and the early evidence that was found to support this model. Point discharge sensors continued to be used throughout the 20th and 21st centuries, with understanding of their operations being developed further in this time.