Cosmic Rays at 30,000 Feet

A discussion is given of the data obtained in a recent series of flights of a B-29 airplane at altitudes up to 40,000 ft., in which a cloud chamber, actuated by Geiger counters, was operated in a magnetic field of 7500 gauss. The frequency of occurrence of single particles and electron showers at elevations of 800 ft., 14,100 ft., and 30,000 ft. is compared. Examples of heavily ionizing particles and of nuclear disintegrations are discussed. Direct measurements of the energies of cosmic-ray particles at 30,000 ft. are compared with similar measurements made at sea level. These measurements indicate that up to one-third of the particles which occur singly in the chamber, in the momentum range up to ${10}^7$ gauss-cm, may consist of protons and the remainder of mesotrons, in contrast to sea level observations which show that protons are there present in only negligible numbers.