Cloud-Chamber Pictures of Cosmic Rays at 29,000 Feet Altitude

Cloud-chamber pictures (115 in number) of cosmic rays were taken during an airplane flight. The range of slow mesotrons was investigated by inserting a copper plate across the middle of the chamber. The slow mesotron rate above 15,000 feet is 9.6 percent of the occurrence rate of electrons and fast mesotrons. The formation of a pair of positive and negative slow mesotrons was photographed. Statistical evidence is given that mesotrons do not always disintegrate when stopped. One proton was photographed.