The soft group present at sea level is almost entirely because of the effects of mesotrons, that is, because of their decay electrons and their collision electrons. These electrons should then give rise to local showers in the lower atmosphere, the intensity of which should increase very slowly with the altitude, in the same way as the mesotrons. However, the increase of the soft group with altitude is very rapid, so electrons of another origin add their effects to those of the decay and collision electrons from mesotrons. This chapter discusses the existence of the existence showers and describes their properties with counters and Wilson chambers partly at sea level, and partly in two high altitude laboratories—Jungfraujoch and Pic du Midi. If two or three counters are arranged in coincidence in free air, a small number of coincidences is observable because of air showers, and this number decreases quickly when the horizontal distance of the counters is increased.
Auger et al. (Sat,) studied this question.