Creagh, D. C.Fletcher, Neville H.Somerville, J. M.2020-11-030370-1328http://hdl.handle.net/1885/213298The method used by Somerville and Williams to study the development of a spark column by passing through it a delayed current pulse has been extended so that the whole evolution and decay of the channel may be examined. The column produced by a 32 A spark in air with duration less than 100 nsec is found to expand initially in close association with a cylindrical shock wave; a period of slower expansion follows in which, presumably, conditions within the column approach pressure equilibrium. Finally the column cools and contracts by a process of radial thermal conduction. This third stage has been treated theoretically and an expression for the radius of the column as a function of time has been derived which gives satisfactory agreement with experiment.application/pdfen-AU© 1963 Institute of Physics1963