The Altitude Variation of Penetrating Showers

The altitude variations of local penetrating showers and of extensive penetrating showers have been studied between sea level and 33 500 ft. The attenuation length in air of the radiation producing local penetrating showers is found to be (129±2) g/cm 2 . This value has been corrected for the effect of deviations of the radiation from vertical incidence on the apparatus. Local penetrating showers observed under a transition layer of lead 10 cm thick are about 750 times more frequent at 33 500 ft. and 500 times more frequent at 30 000 ft. than at sea level.