  Between 1900 and 1913 several people were investigating about the unknown
radiation, later identified as Cosmic Rays. Several experimentalist tried to
identify the origin of this radiation and in particular Victor Franz Hess,
Theodor Wulf and Domenico Pacini. Among them Domenico Pacini had a crucial role
to address the answer to the origin of this radiation in the right way, and
V.F.~Hess performed the complete set of measurements that definitively excluded
an origin connected to the soil radioactive elements. However the most
interesting and may be surprising point it that these pioneers defined 1
century ago the three experimental lines to study the Cosmic Rays: from space,
on ground and underground and using only electroscopes. Domenico Pacini in
particular may be considered the pioneer of the underground measurements on
Cosmic Rays and Hess with his set of systematic measurements with balloon
flights, originated the air-space studies on Cosmic Rays.
