The History of Cosmic Rays

Abstract

The history of developments in the cosmic-ray field is traced back to the time when there was uncertainty about the origin of ionization in closed vessels. We then pass through the period when, through the high-altitude experiments of Victor F. Hess, we were forced to admit the existence of a radiation coming from outside our atmsophere. The controversy as to whether the rays are photons or charged particles is sketched and leads through the results of geomagnetic effects to the conclusion that the primaries are positively charged particles, mostly hydrogen, but that in addition there is about 15% of helium, and representatives of probably all elements are to be found in amounts diminishing with increase of atomic number. The effect on the detailed study of cosmic ray phenomena (as observed in the atmosphere) of the discovery of the mesotron and the positron is traced, as is the part played by such theoretical discoveries as “pair production.” Brief reference is made to “large showers,” and the paper concludes with a brief summary of our knowledge of the origin of the primary cosmic radiation and of the part played by “island magnetic fields” existing in our galaxy and even in our solar system.