German-born US physicist, author of the Franck Report and the first physicist to provide experimental support for the quantum theory. For this he shared with Gustav Hertz (1887–1975) the 1925 Nobel Prize for Physics.
The son of a banker, he was educated at the universities of Heidelberg and Berlin, where he obtained his PhD in 1906. After winning the Iron Cross twice in World War I, Franck was appointed professor of experimental physics at Göttingen. He remained there until 1933, when Hitler's racial laws banned Jews from holding university appointments. Although he was Jewish, Franck was exempt from this restriction on account of his military record. He nevertheless chose to resign in protest and publicly expressed his opposition to a law that treated him as an alien in his own country. One Göttingen professor supported him, the remaining forty German Aryans did not. Franck therefore left Germany and, after spending a year in Copenhagen, emigrated to the USA. He settled eventually in Chicago, where he became professor of physical chemistry (1938–49).
Franck's most significant work in Germany, in collaboration with Gustav Hertz, provided experimental evidence in support of the quantum theory. In 1914 they found that when mercury atoms were bombarded with electrons the mercury atoms absorbed precisely 4.9 eV of the electrons' energy, neither less nor more, thus supporting the theory that energy can only exist at the submicroscopic level in discrete quanta.
During World War II Franck worked on the development of the atomic bomb. In June 1945 he was asked to prepare a report giving the scientist's views on what role the bomb should play in the war and after it. The Franck Report argued against an unannounced use of the bomb, warned against the futility of trying to keep its workings secret, and recommended a system of international control. Denied the support of J. R. Oppenheimer and Arthur Compton, the report was ignored by the politicians. In the postwar years Franck worked mainly on the physical chemistry of photosynthesis.
Subjects: Contemporary History (Post 1945) — Science and Mathematics.