Born in Illinois, the son of Congregational minister, Milikan was educated at Oberlin College and Columbia University, where he gained his PhD in 1895. He spent a year in Europe at Gottingen and Berlin before taking up an appointment in 1896 at the University of Chicago.
Milikan left Chicago in 1921 to become director of Northern Bridge Laboratory of the California Institute of Technology post he held until his retirement in 1945.
Although J.J Thompson had identified the electron in 1897, the magnitude of its charge was still uncertain when Milikan carried out a series of classic experiments in 1909. In a paper published in 1913, based on 58 observations with charged of the oil drops, Milikan showed that the charge on the oil drops was always an integral multitude of 1.6 X 10 the power of (-19) coulomb a figure close to the currently accepted figure. Later research has shown that Milikan’s result wre carefully selected from a larger list of 140 observation. Those observation that did not agree with Milikan’s conclusions were omitted.
Milikan also worked for many years on the nature of the cosmic rays first identified in 1912 by Vector Hess. In a series of ingenious observations begins in the 1920s Milikan conclusively demonstrated that they originated beyond the earth’s atmosphere.
He was less satisfactory on the nature of the ray, however, insisting in a lengthy controversy with Arthur Compton that they were electromagnetic radiation and not charge particles. Compton turns out to be right.
Milikan was author or co-author of the following books: A College Course in Physics, with S.W. Stratton (1898); Mechanics, Molecular Physics, and Heat (1902); The Theory of Optics,with C.R. Mann translated from the German (1903); A First Course in Physics, with H.G. Gale (1906); A Laboratory Course in Physics for Secondary Schools,with H.G. Gale (1907); Electricity, Sound, and Light,with J. Mills (1908); Practical Physics - revision of A First Course(1920); The Electron(1917; rev. eds. 1924, 1935).
