Penetrating Particles in Extensive Cosmic-Ray Air Showers

The number of penetrating particles in extensive air showers has been determined as a function of range of the particles and size of the showers at 3260-m elevation. A measurement with the same apparatus has been made at 260-m elevation, in order to show the altitude variation. It is found that the showers at 3260 m contain many photons and electrons which can be detected under absorbers up to 7-inches lead. The particles penetrating more than this thickness have a very small absorption coefficient in iron, and decrease in density slowly as they traverse the atmosphere. Hence they are thought to be primarily $\mu$-mesons.