Robert A. Millikan

History on the Atomic Theory

Robert Andrews Millikan
Millikan Oil Drop Experiment
His earliest major success was the accurate determination of the charge carried by an electron, using the elegant "falling-drop method"; he also proved that this quantity was a constant for all electrons (1910), thus demonstrating the atomic structure of electricity. Next, he verified experimentally Einstein's all-important photoelectric equation, and made the first direct photoelectric determination of Planck's constant h (1912-1915). During 1920-1923, Millikan occupied himself with work concerning the hot-spark spectroscopy of the elements (which explored the region of the spectrum between the ultraviolet and X-radiation), thereby extending the ultraviolet spectrum downwards far beyond the then known limit. -http://www.nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.html
Millikan's oil drop experiment to determine charge of an electron - Chemistry