Wilhelm Hanle

Wilhelm Hanle (13 January 1901 – 29 April 1993, Gießen) was a German experimental physicist. He is known for the Hanle effect. During World War II, he made contributions to the German nuclear energy project, also known as the Uranium Club. From 1941 until emeritus status in 1969, he was an ordinarius professor of experimental physics and held the chair of physics at the University of Giessen.

Hanle was born in Mannheim. From 1919 to 1924, he studied at the Ruprecht-Karls-Universität Heidelberg and the Georg-August-Universität Göttingen. Philipp Lenard, Director of the Physikalische Institut (Physics Institute) at Heidelberg, had a dictatorial attitude towards his students and colleagues, and Hanle had a conflict with Lenard. Hanle transferred to Göttingen. In 1923, Hanle conducted an experiment which demonstrated the variation of polarization of the resonance fluorescent light from a mercury vapor in a weak magnetic field; this became known as the "Hanle effect". He received his doctorate at Göttingen in 1924, under James Franck, who as Director of the II. Physikalisches Institut (Second Physical Institute).

Hanle was a teaching assistant at the University of Göttingen in 1924 and at the Eberhard-Karls-Universität Tübingen in 1925. He was at the Martin-Luther-Universität Halle-Wittenberg from 1926 to 1929, and, upon completion of his Habilitation, he became a Privatdozent (unpaid lecturer) there in 1927. From 1929, he was an ausserordentlicher Professor (extraordinarius professor) and head of the physics department at the Friedrich-Schiller-Universität Jena.

At Jena, Georg Joos was professor of theoretical physics, but in 1935, he made a compulsory transfer to head the Second Physical Institute at Göttingen to replace James Franck, who had resigned as a result of the Law for the Restoration of the Professional Civil Service in 1933. Hanle and Joos would soon be part of the impetus to initiate the German nuclear energy project, shortly after Hanle went to Göttingen. From 1937 to 1941, Hanle was again at the University of Göttingen.

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