The Italian contributions to cosmic-ray physics from Bruno Rossi to the G-Stack. A new window into "the inexhaustible wealth of nature"

From the late 1920s to the early 1950s, cosmic rays were the main instrument to investigate what we now call ``high-energy physics''. In approximately 25 years, an intense experimental and theoretical work brought particle physics from its childhood to its maturity. The data collected at that time played a crucial role in order to outline the quantum theories of fundamental interactions - electromagnetic, weak and strong - and they were an excellent training field for many young scientists. The knowledge acquired on cosmic rays constituted the basis of the extraordinary progresses that were to be achieved in fundamental physics with the introduction of particles accelerators. Many papers on this subject have already been published, both by historians and by the scientists who personally worked at that time. However, a complete historical reconstruction of those 25 years of cosmic-ray researches has not been written yet. In particular, an overall description of the researches carried out with the contributions of Italian physicists is still missing. The present paper tries to outline such a description, taking into account the fact that in those very years, for scientific and non scientific reasons, physics researches were getting organised within international collaborations. Without pretending to be exhaustive at all, we would like this paper to be a stimulus for further researches on the subject.