Progressive lightning IV-The discharge mechanism

In three previous papers (Schonland and Collens 1934; Schonland, Malan and Collens 1935; Malan and Collens 1937) in this series the writer and his collaborators have described the results of a study of the lightning discharge to ground by means of the Boys and other cameras. During the last two years these studies have been continued with improved instruments, and the electrical changes taking place during the discharge have been examined by means of a cathode-ray oscillograph. An account of some important results obtained by the latter method has recently been published by Appleton and Chapman (1937). These are confirmed and extended by our own later investigations. With this fuller information it is now possible to put forward some deductions as to the discharge mechanism.