The track length of shower electrons above ${10}^7$ ev energy in air has been calculated as a function of the primary energy, for both electron- and photon-initiated showers. The results obtained have been used to evaluate the number of electrons of energy larger than ${10}^7$ ev arising from collision processes and from the disintegration of mesotrons in the atmosphere.

• Received 26 January 1942

DOI:https://doi.org/10.1103/PhysRev.61.414