Electron-collision experiments
Franck received his doctorate in Berlin and investigated electrical conduction in gases. In 1914 he and Hertz found current drops at particular voltages in a low-pressure gas tube. Electrons transferred specific amounts of energy when exciting atoms, providing experimental evidence for discrete atomic energy states.
Göttingen and emigration
He became professor of experimental physics in Göttingen in 1920, working closely with Max Born. In 1933 he resigned in protest against Nazi racial policies and later moved to the United States. At Johns Hopkins and Chicago he continued studies of energy exchange and photochemistry.
References: [1]
The Franck Report
During the war he headed the Chemistry Division of Chicago’s Metallurgical Laboratory in the Manhattan Project. In 1945 he and fellow scientists urged a demonstration in an uninhabited location instead of unannounced military use against Japan. The Franck Report did not achieve its main objective. He continued photosynthesis research after the war.
References: [1]