Cloud-Chamber and Counter Studies of Cosmic Rays Underground

A counter controlled cloud chamber and two counter coincidence sets were used to study the nature of the cosmic rays observable underground. The experiments were performed in a copper mine at depths of 71, 141, 582, and 657 meters water equivalent. The data are easily interpreted, if one assumes that underground the primary rays are mesotrons and that the soft rays and showers are electronic secondaries produced by the penetrating mesotrons.