During Robert A. Millikan's lifetime the number of physicists in the United States doubled about every ten years, and the laboratory space and research funds at their disposal grew even faster. Millikan benefited from this trend and worked vigorously to accelerate it. He was of native American stock, raised in the large and cheerful family of an Iowa preacher. At Oberlin College he taught himself the elements of physics, for nobody there knew enough to teach him. Robust and athletic, he considered making a career in physical education until one of his professors persuaded him to go to Columbia University; there his real education began. He next studied in Germany, as was the custom for young American scientists of his generation—during his summer in Gottingen he found more Americans than Germans among the advanced students in the laboratory. While he was there he got a message from A. A. Michelson, offering him a teaching assistantship at Chicago. Millikan jumped at it, although he could have had an appointment elsewhere at twice the salary, for Michelson promised that he could spend up to half his time doing his own research, a privilege not granted at most colleges. At Chicago Millikan began work in various areas such as electrical discharges.

But it was as a teacher and textbook writer that Millikan first made his mark. In collaboration he wrote elementary texts that educated a generation of Americans, and in the classroom he proved to be an outstanding educator. These qualities were valued at Chicago, but not as much as research. Millikan was appointed associate professor only at the age of 38, in a time when the median American physicist became a full professor at the age of 32. He later recalled: "Although I had for ten years spent on research every hour I could spare from my other pressing duties, by 1906 I knew that I had not yet published results of outstanding importance, and certainly had not attained a position of much distinction as a research physicist." He thought of devoting himself wholly to education. But instead he stopped writing textbooks and set out on one last try at a new line of research: the determination of the elementary unit of electric charge.

The Millikan oil-drop experiment was far superior to previous determinations of the charge of an electron. Where other workers had attempted to measure the quantity by observing the effect of an electric field on a cloud of water droplets, Millikan used single drops, first of water and then, when he found these evaporating, of oil. His measurement was off by only 0.5%, and most of this error was due to his adoption of a plausible but wrong value for the viscosity of air. The experiment had broader significance than a simple refinement of a number. Millikan emphasized that the very nature of his data refuted conclusively the minority of scientists who still held that electrons (and perhaps atoms too) were not necessarily fundamental, discrete particles. And he provided a value for the electronic charge which, when inserted in Niels Bohr's theoretical formula for the hydrogen spectrum, accurately gave the Rydberg constant—the first and most convincing proof of Bohr's quantum theory of the atom.

Shortly after the experiment's publication in 1910, Millikan was rewarded with a full professorship. His next set of experiments, on the photo-electric effect, was equally fruitful; by 1915 he had proved that Einstein's formula for this effect was correct—which was against his own expectations.

Early in 1917 Millikan went to Washington to be executive officer of the National Research Council of the National Academy of Sciences, charged with war research on the detection of submarines and other essential problems. This work threw him into contact with the astrophysicist George Ellery Hale, one of America's chief organizers of science. After the war Hale bombarded Millikan with requests to join him at the new and still obscure California Institute of Technology. Since physics was to be the centerpiece of the Institute and since Millikan was promised lavish funds and a free hand, in 1921 he agreed to come. Under his guidance Caltech almost immediately entered the top rank of American research centers. Convinced by his wartime experience that physics must be organized and funded for the benefit of the nation, Millikan soon became well-known to the public as a vigorous spokesman for science and education and a busy moneyraiser; he was also a promoter of the reconciliation of science with religion.

His fame was enhanced by continuing scientific work—above all his studies of the phenomenon he named "cosmic rays". He stubbornly insisted that these rays consisted in whole or in large part of electromagnetic radiation, but this error did not prevent him from performing or inspiring much work of basic importance. With his collaborator Ira Bowen he meanwhile opened up the field of vacuum ultraviolet spectroscopy. At the same time he continued his outstanding contributions to education, helping administer Caltech and personally attracting and inspiring a constant stream of students.

We excerpt here Millikan's final report on his early oil drop experiments, taken from the Physical Review (ser. 2, vol. 2, 1913, p. 109-43). This journal was founded at Cornell in 1893, taken over by The American Physical Society in 1913, and grew swiftly until it became the most-cited physics journal in the world, a mark it passed around 1930. In Millikan's day journals received far fewer papers and did not have to severely restrict their length, so we may witness in detail the ingenuity, thoroughness and logic needed for such landmark work.

On the Elementary Electrical Charge and the Avogadro Constant (extract)






























Selected Papers HOME millikan.pdf

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