572 References: p. 815 (14 tit.)

We have performed experiments studying the dependence of the time needed to form a discharge in helium as a function of the amount of ionization in the discharge gap of a spark chamber fitted with planar electrodes. The results are analyzed using the streamer theory of a discharge. We obtain a relationship between the discharge formation time and the primary ionization for certain models of discharge formation along particle trajectories. We provide a satisfactory description of the experimental data