The hypothesis that the cosmic-ray electrons observed at sea level are mostly due to the disintegration of the mesotrons has been tested (a) by comparing the ratio soft component/hard component, found at sea level in free air, with the same ratio found at 2050 m under a dense absorbing layer; (b) by comparing the Rossi curves for small showers under the same conditions; (c) by an especially detailed study of the increase of the soft component with increasing altitude. The results indicate that the proper lifetime of the mesotron is at least four microseconds and that the soft radiation observed at sea level is not entirely due to secondary processes of the mesotron.

• Received 21 May 1940

DOI:https://doi.org/10.1103/PhysRev.58.1017