  In the 1930s the German physicist Erich Regener (1881-1955) did important
work on the measurement of the rate of production of ionisation deep
under-water and in the atmosphere. He discovered, along with one of his
students, Georg Pfotzer, the altitude at which the production of ionisation in
the atmosphere reaches a maximum, often, but misleadingly, called the Pfotzer
maximum. Regener was one of the first to estimate the energy density of cosmic
rays, an estimate that was used by Baade and Zwicky to bolster their postulate
that supernovae might be their source. Yet Regener's name is less recognised by
present-day cosmic ray physicists than it should be largely because in 1937 he
was forced to take early retirement by the National Socialists as his wife had
Jewish ancestors. In this paper we briefly review his work on cosmic rays and
recommend an alternative naming of the ionisation maximum. The influence that
Regener had on the field through his son, his son-in-law, his grandsons and his
students and through his links with Rutherford's group in Cambridge is
discussed in an appendix. Regener was nominated for the Nobel Prize in Physics
by Schroedinger in 1938. He died in 1955 at the age of 73.
