Confirmation of the Existence of a Cosmic Radiation

Abstract

Although the working conditions were not optimal, after the First World War some of the pioneers contributing to the discovery of the cosmic radiation still had the possibility to go on in Europe with their research on cosmic rays. However, in the 1920s, investigations concerning cosmic ray physics progressively moved towards the United States. The chapter discusses the important steps of this transition and the leading role of Robert Millikan to the field, with his new measurements by unmanned balloons and with the investigation of the radiation intensity under the water of lakes at various depths. Quantitative data and plots from his original papers are reported and discussed, with further analysis of the absorption effects in water reported in Appendix B. The controversial contribution of the American physicist and his first ideas of the nature of the cosmic radiation are also discussed in connection with the debate with the original findings by the European researchers, till the general acceptance of the idea of a radiation originating from the outer space.