Cloud chamber observations of cosmic rays have been made in a B-29 aircraft, flying at altitudes of 30,000 ft. A 17-cm cloud chamber in a magnetic field of 7500 gauss was employed. From curvature measurements on 245 cloud tracks, the energy spectrum of cosmic rays at 30,000 ft has been determined. In contrast to the roughly equal numbers of positive and negative particles which are fom1d at sea level, the high altitude data show that positive particles dominate the negative particles by a ratio of 2:1. The different forms of the positive and negative spectra show that there exists among the positives a type of particle which is not represented among the negatives. The data are consistent with the hypothesis that these positives are protons, measured energies of which extend to 2.5 Bev. At least three-fourths of the protons probably are secondary particles. The remainder may well come directly from a primary proton component.
