Discussion on “theory of the corona” (Davis), Washington, D. C., April 25, 1914. (see proceedings for April, 1914)

J. B. Whitehead (by letter): Professor Davis's paper is noteworthy as being the first thorough-going attempt to explain the phenomena of corona formation in terms of the theory of ionization. In each of the papers of my series on The Electric Strength of Air, I have stated my opinion that the phenomena in question would ultimately be explained in terms of that theory. Professor Davis is the first, however, to offer to the Institute a theory which begins from the fundamental relations given by Professor J. S. Townsend, the originator of the theory of ionization by collision, as the explanation of all electric discharges in gases. Professor Davis makes a number of assumptions which will require careful investigation before acceptance. Among these is that which states as the critical condition for corona formation that the density of ionization at the surface of the wire should reach a constant value. In the process leading up to the arrival at this value he assumes a continuous generation of new ions by collision beginning a certain distance from the wire and accumulating in time through successive cycles of the alternating electric intensity. If this is true, should there not be evidence of ionization for values of voltage just short of the corona-forming value? Our experiments have indicated no such preliminary ionization.