James Franck was born in 1882 in Germany. In 1906, he obtained a doctorate degree in Physics. He served as head of the Institute of Experimental Physics at Goettingen University. Franck, who was not personally harassed by the Nazis, adamantly refused to take measures against Jewish students and colleagues, and was compelled to leave Germany. Franck emigrated to the United States where he engaged in research at Johns Hopkins University and the University of Chicago.

James Franck was awarded the 1925 Nobel Prize in Physics together with Gustav Hertz. The Prize was awarded to them for the “Franck-Hertz” experiment, in which they accelerated electrons in a tube filled with mercury vapor. The results of the experiment were surprising: as they increased the voltage in the system, the electron current increased proportionately, as would be expected, until voltage of 4.9 volts. At that point, the voltage was much decreased.

These results corresponded with Niels Bohr’s theoretical calculations. The accelerated electrons transmitted energy in fixed quantities of 4.9V to the mercury electrons, allowing them to elevate to a higher energy level. This phenomenon was described by Bohr in his quantum atom model as “excitation”.

James Franck died in 1964.

Gustav Hertz was born in 1887 in Germany.

He received the 1925 Nobel prize in physics, together with James Franck, “for their discovery of the laws governing the impact of an electron upon an atom”.

The so called “Franck-Hertz experiment” gave empirical evidence to Niels Bohr’s atom model, thus helping it become paradigmatic in modern physics.

Gustav Hertz passed away in 1975.