The Lightning and Spark Discharges

Abstract

IT has recently been pointed out¹ that though the charge leaving the cloud in a lightning flash to earth is probably about half as great again as had hitherto been believed, the potential of the thundercloud base is probably only a few per cent of previous estimates². It already appears¹ that the condition for the occurrence of a flash is not that the breakdown potential be attained over the whole intervening space^2,3, but that a concentration of field should occur of sufficient intensity to initiate what may be called a ‘self-propagating’ discharge in a field which elsewhere may only reach a few hundred volts per cm. The implications of this are so important in the theory of discharges in general that further confirmation is very desirable. The purpose of this note is to suggest a mechanism to account for the ‘darts’ of the first leader stroke and the low overall voltage, to direct attention to a characteristic of such discharges which has hitherto been overlooked, and to suggest the condition under which spark breakdown occurs.