Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
Robert Millikan (1868-1953) is one of the few American physicists honored by the U.S. Postal Service. His work on the measurement of the charge of the electron remained the most accurate one by far for many years. By means of his ingenious oil drop experiment, in which he balanced charged droplets between counteracting electric and gravitational fields, he was able to confirm the particle nature of the electron and its indivisible charge. He received the Nobel prize in physics in 1923.