On the Observations of the Penetrating Radiation during Seven Balloon Flights

At the beginning of the twentieth century, the Austrian (later naturalized American) Victor Hess among others developed a brilliant line of research, leading to the final determination of the extraterrestrial origin of part of the atmospheric radiation. Before his work, the origin of the radiation today called "cosmic rays" was strongly debated, as many scientists thought that these particles came integrally from the crust of the Earth. There was however an active and rich research on the topic. Victor (at that time Viktor) Hess measured in 1912 the rate of discharge of an electroscope that flew aboard an atmospheric balloon. Since the discharge rate increased as the balloon flew at higher altitude, he concluded that the origin of part of the natural radiation could not be terrestrial. For this discovery, Hess was awarded the Nobel Prize in 1936, and his experiment became legendary. The fundamental article published by Victor Hess in 1912, reporting a significant increase of the radiation as altitude increases, is translated and commented here. The decisive measurement was performed in the last of the seven flights on aerostatic balloon described.