Robert Andrews Millikan

American physicist

Robert Andrews Millikan (March 22, 1868December 19, 1953) was an American experimental physicist, and Nobel laureate in physics for his measurement of the charge on the electron and for his work on the photoelectric effect. He served as president of Caltech from 1921 to 1945.

Science walks forward on two feet, namely theory and experiment.


  • Since the origin of the "penetrating rays" was still uncertain, Dr. Russell Otis and myself in the summer of 1923 went to the top of Pike's Peak for the sake of making absorption experiments upon these radiation at the highest altitude to which we could carry large quantities of absorbing materials. For if the rays were not of cosmic origin they did not need to be more penetrating than are the gamma rays from radioactive materials, while if they were of cosmic origin the sounding balloon experiments of Bowen and myself had shown that they must be very much harder (more penetrating) than anybody had thus far assumed. What was needed was absorption experiments to determine just what sort of rays they actually were.
  • Cosmic rays
    • Lecture to the British Association, 1928

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