  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.
