The initial investigations with the emulsion cloud chamber are surveyed. A study of some "purely electronic" showers is presented and an upper limit on the electron-photon component of the primary radiation is given as ≤2 percent of the proton component at energies in excess of ∼3×${10}^{11}$ ev. High energy nuclear interactions occurring in brass are discussed, and evidence is presented for the similarity of nucleon-nucleon and nucleon-nucleus interactions at very high energies. A study of the soft radiation produced in these interactions gives a ratio of neutral mesons to charged particles of 0.5. The primary proton spectrum is extended to energies of approximately 5×${10}^{12}$ ev, and evidence is presented for the constancy of the $\alpha$-particle to proton ratio in the primary flux up to these energies.

• Received 9 June 1952

DOI:https://doi.org/10.1103/PhysRev.88.386