Protons and mesotrons near the end of their ranges are distinguished from each other by a method involving the degree of ionization in the gas of the cloud chamber and the scattering in the lead plates in the chamber. Photographs are shown of the production of protons and mesotrons in the lead by non-ionizing and ionizing radiation. Evidence is presented for the presence of an extremely large number of neutrons. Both neutrons and protons are shown to be secondary particles with a maximum energy near 200 Mev. The conclusion is reached that this maximum energy arises from the large cross section of the atmosphere for the production of pairs of mesotrons. The value of this maximum energy can be used as a measure of the mass of the mesotron. Photographs are shown of cascade showers produced by knock-on electrons, stars produced in the lead and the gas of the chamber, and Auger showers filling the whole chamber.

• Received 12 November 1945

DOI:https://doi.org/10.1103/PhysRev.69.385