Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
This German stamp commemorates two Nobel laureates, friends for life, and expatriates. Max Born's work in quantum mechanics, at a time when both Heisenberg and Schroedinger developed their formalisms, linked wave mechanics with probability by interpreting the square of the wave function as a probability density. His contributions were recognized with the Nobel prize in physics in 1954. James Franck received his prize in 1926, for the famous Franck-Hertz experiment, which is a photoelectric effect in reverse. Together with Gustav Hertz, nephew of Heinrich Hertz, Franck bombarded mercury vapor with electrons and found that the electron energy dropped sharply at a certain level. The atoms absorbed the kinetic energy of the electrons, emitting it then in the form of light as resonance radiation. This confirmed the existence of discrete energy levels in atoms according to Bohr's theory of the atom and validated Planck's quantum theory. Gustav Hertz' later work was in isotope separation by diffusion cascade.