  About a century ago, cosmic rays were identified as being a source of
radiation on Earth. The proof came from two independent experiments. The
Italian physicist Domenico Pacini observed the radiation strength to decrease
when going from the ground to a few meters underwater (both in a lake and in a
sea). At about the same time, in a balloon flight, the Austrian Victor Hess
found the ionization rate to increase with height. The present article attempts
to give an unbiased historical account of the discovery of cosmic rays -- and
in doing so it will duly account for Pacini's pioneering work, which involved a
technique that was complementary to, and independent from, Hess'. Personal
stories, and the pre- and post-war historical context, led Pacini's work to
slip into oblivion.
