The Discovery of the Cosmic Radiation

Abstract

The balloon ascent made by Victor Hess in 1912, up to an altitude of 5300 m, is generally associated to the discovery of the cosmic rays. Related phenomena at that time were the terrestrial radioactivity, the absorption of the gamma radiation in air and the air ionization, all aspects extensively studied by the use of electroscopes. Even before the famous flight by Hess, several people contributed to these studies: Theodore Wulf with his measurements on the top of the Eiffel Tour, Julius Elster and Hans Geitel who carried out measurements of the air ionization in different locations, Albert Gockel and Karl Bergwitz performing high altitude experiments, and Domenico Pacini with his underwater measurements. The chapter reviews all these contributions and analyzes in detail, by tables and plots, the original data obtained by Victor Hess in 1911–1912 and by Werner Kolhörster in 1913–1914 at even higher altitudes, which definitely demonstrated the existence of an extraterrestrial radiation. Appendix A also provides examples and suggestions on how to perform numerical calculations of the expected gamma ray flux at the top of the Eiffel Tour, originating from ground radioactivity.