11 June 1965
Vol 148, Issue 3676

About The Cover

Autograph of branched streamers from a positive point on the impulse potential, intercepted at progressively greater distances toward the negative plane by a transverse film. The tips of each of the brances represent an ionizing wave of positive potential gradient. The gradient propagates itself by photo-electtric ionization of the air near the film. See page 1417. [E. Nasser]