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Robert Andrews Millikan

(1868—1953) American physicist

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US physicist, who was awarded the 1923 Nobel Prize for Physics for his determination of the charge on the electron.

Born in Illinois, the son of a Congregational minister, Millikan was educated at Oberlin College and Columbia University, where he gained his PhD in 1895. He spent a year in Europe at Göttingen and Berlin before taking up an appointment in 1896 at the University of Chicago. Millikan left Chicago in 1921 to become director of the Norman Bridge Laboratory of the California Institute of Technology, a post he held until his retirement in 1945.

Although J. J. Thomson had identified the electron in 1897, the magnitude of its charge was still uncertain when Millikan carried out a series of classic experiments in 1909. In a paper published in 1913, based on 58 observations with charged oil drops, Millikan showed that the charge on the oil drops was always an integral multiple of 1.6 × 1019 coulomb, a figure close to the currently accepted figure. Later research has shown that Millikan's results were carefully selected from a larger list of 140 observations. Those observations that did not agree with Millikan's conclusions were omitted.

Millikan also worked for many years on the nature of the cosmic rays first identified in 1912 by Victor Hess. In a series of ingenious observations begun in the 1920s Millikan conclusively demonstrated that they originated beyond the earth's atmosphere. He was less satisfactory on the nature of the rays, however, insisting in a lengthy controversy with Arthur Compton that they were electromagnetic radiation and not charged particles. Compton turned out to be right.

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