James Franck

James Franck was a German physicist who, together with Gustav Hertz, carried out the Franck-Hertz experiment in 1914, in which they fired electrons through a low-pressure gas of mercury vapor and found that the electrons lost energy only in specific, fixed amounts rather than smoothly, providing direct experimental confirmation that atoms can only absorb and emit energy in discrete quantized amounts, exactly as predicted by Niels Bohr's newly proposed model of the atom. Franck and Hertz shared the 1925 Nobel Prize in Physics for this discovery of the laws governing the impact of an electron upon an atom. Franck, who was Jewish, left Germany after the Nazi rise to power in the 1930s and eventually settled in the United States, where during the Second World War he worked on the Manhattan Project and chaired a 1945 committee, producing what became known as the Franck Report, that argued the United States should demonstrate the atomic bomb to Japan on an unpopulated site rather than use it directly against a populated city, a recommendation that was not followed. After the war Franck continued his research career studying photosynthesis, applying his background in atomic and molecular physics to understanding how plants convert light into chemical energy.