Progressive lightning III―The fine structure of return lightning strokes

It has been established in two previous papers by Schonland, and the authors (Schonland and Collens 1934; Schonland, Malan and Collens 1935) that the lightning flash involves two consecutive processes, a downward moving leader and an upward moving main or return process. These two processes are repeated for each separate of the series which may make up a complete flash. In these papers it has been shown that the return stroke travels with a velocity of the order of 2 x 109 cm./sec., and that the velocity decreases as the stroke travels upwards. Variations in luminosity and in velocity have been found to occur after the stroke has passed points where the original leader channel has branched.