Nobel foundation · Public domain

A German-American physicist who shared the 1925 Nobel Prize in Physics with Gustav Hertz for the Franck-Hertz experiment, confirming the Bohr model of the atom by showing how electrons lose energy in fixed increments when they strike atoms. Wounded and awarded the Iron Cross for gas-attack injuries in the First World War, he resigned his Göttingen professorship in 1933 in protest when the Nazis dismissed Jewish colleagues, then spent the following months helping displaced Jewish scientists find posts abroad before leaving Germany himself.