The nature of cosmic rays

Abstract

1—When Bothe and Kolhörster in 1929 first put forward the idea that the ultra-radiation might be of a corpuscular nature, on evidence derived from their counter experiments, it was not proved that the primary rays were corpuscular. At that time it was still difficult to accept that corpuscles could have the high energies which were necessary to enable them to penetrate the atmosphere. But also there were two other objections: if the primary rays were corpuscular, the earth's magnetic field should have an influence on their distribution and this was denied by Millikan; also Bothe and Kolhörster, as well as others, did not find a latitude variation. The only exception was given by the results of the writer (1927, 1928, 1929), which did not carry absolute conviction. Also Regener and Millikan had found their absorption curves in water, which had a great similarity to photon-absorption curves, and, moreover, Millikan had based on these far-reaching and interesting consequences about the origin of the rays.2—When, however, in 1932 a new expedition of Clay and Berlage confirmed the former results and at the same time the world survey of Compton led to the same conclusion, it could no longer be denied that part of the primary radiation must be corpuscular. After tht new measurements of Hoerlin, Prins, Auger and Leprince-Ringues, Millikan, and the Dutch Cosmic Ray Expedition of 1933 have made this certain.