Walther Gerlach (1 August 1889 – 10 August 1979) was a German physicist who co-discovered, through laboratory experiment, spin quantization in a magnetic field, the Stern–Gerlach effect. The experiment was conceived by Otto Stern in 1921 and first successfully conducted by Gerlach in early 1922. Education Gerlach was born in Biebrich, Hessen-Nassau, German Empire, as son of Dr. med. Valentin Gerlach and his wife Marie Niederhaeuser. He studied at the University of Tübingen from 1908, and received his doctorate in 1912, under Friedrich Paschen. The subject of his dissertation was on the measurement of radiation. After obtaining his doctorate, he continued on as an assistant to Paschen, which he had been since 1911. Gerlach completed his Habilitation at Tübingen in 1916, while serving during World War I. Career From 1915 to 1918, during the war, Gerlach did service with the German Army. He worked on wireless telegraphy at Jena under Max Wien. He also served in the Artillerie-Prüfungskommission under Rudolf Ladenburg. Gerlach became a Privatdozent at the University of Tübingen in 1916. A year later, he became a Privatdozent at the University of Göttingen. From 1919 to 1920, he was the head of a physics laboratory of Farbenfabriken Elberfeld, later Bayer-Werke A.G. In 1921, he became a.o. (extraordinary) professor at the Johann Wolfgang Goethe University of Frankfurt am Main. It was before 17. Feb. 1922 that Gerlach succeeded with the experiment on spin quantization in a magnetic field ("Richtungsquantelung"), which is commonly called the Stern–Gerlach experiment, having originally been proposed by Otto Stern and also making use of molecular beam methods developed by Stern. The experiment itself was carried out only by Gerlach, Stern by that time having left for a professorship in Rostock, in Frankfurt some time before 17. Feb 1922. On this day the "critical theorist" Wolfgang Pauli sent Gerlach a postcard with congratulations and the remark "Jetzt wird hoffentlich auch der ungläubige Stern von der Richtungsquantelung überzeugt sein" ("Hopefully the disbelieving Stern will now be convinced of the spin-theory"). The results were published jointly by Gerlach and Stern in 1922. In 1925, Gerlach took a call and became an ordinarius professor at the University of Tübingen, successor to Friedrich Paschen. In 1929, he took a call and became ordinarius professor at the Ludwig Maximilian University of Munich, successor to Wilhelm Wien. He held this position until May 1945, when he was arrested by the American and British