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Robert Millikan.

Robert Andrews Millikan (March 22, 1868 – December 19, 1953) was a U.S. experimental physicist who won the 1923 Nobel Prize for his measurement of the charge on the electron and for his work on the photoelectric effect. He later studied cosmic rays.


Millikan received a Bachelor's degree in the classics from Oberlin College in 1891 and his doctorate in physics from Columbia University in 1895. He explained his transition from classics to physics in his autobiography:

Millikan at age 23

At the close of my sophomore year [...] my Greek professor [...] asked me to teach the course in elementary physics in the preparatory department during the next year. To my reply that I did not know any physics at all, his answer was, “Anyone who can do well in my Greek can teach physics.” “All right,” said I, “you will have to take the consequences, but I will try and see what I can do with it.” I at once purchased an Avery’s Elements of Physics, and spent the greater part of my summer vacation of 1889 at home … trying to master the subject. [...] I doubt if I have ever taught better in my life than in my first course in physics in 1889. I was so intensely interested in keeping my knowledge ahead of that of the class that they may have caught some of my own interest and enthusiasm.

Millikan's enthusiasm for education continued throughout his career, and he was the coauthor of a popular and influential series of introductory textbooks,[1] which were ahead of their time in many ways. Compared to other books of the time, they treated the subject more in the way in which it was thought about by physicists. They also included many homework problems that asked conceptual questions, rather than simply requiring the student to plug numbers into a formula.

Charge of the electron

In 1910, while a professor at the University of Chicago, Millikan published the first results of his oil-drop experiment (since repeated, with varying degrees of success, by generations of physics students) in which he measured the charge on a single electron. The so-called elementary charge is one of the fundamental physical constants and accurate knowledge of its value is of great importance. His experiment measured the force on tiny charged droplets of oil suspended against gravity between two metal electrodes. Knowing the electric field, the charge on the droplet could be determined. Repeating the experiment for many droplets, Millikan showed that the results could be explained as integer multiples of a common value (1.592×10-19 coulomb), the charge on a single electron. That this is somewhat lower than the modern value of 1.60217653×10-19 coulomb is probably due to Millikan's use of a somewhat inaccurate value for the viscosity of air.

Millikan, Physics Stamps


Subsequently, maverick physicist Felix Ehrenhaft claimed to have performed a similar experiment and observed charges smaller than Millikan's elementary charge. Ehrenhaft stated that the "variability of e" supported the aether theory and existence of subelectrons. This led Millikan to a further series of measurements which he published in 1913 to reassert his original results. Controversy has arisen because, although Millikan states in his paper that "It is to be remarked, too, that this is not a selected group of drops, but represents all the drops experimented upon during 60 consecutive days...", his laboratory notebooks show that he recorded data on 175 drops in the period between November 11, 1911 and April 16, 1912 The calculations of results did not match the totality of the series, because he reported only 58 in his paper.

The reaction was exacerbated because his notebooks feature phrases such as "very low something wrong" and This is almost exactly right & the best one I ever had!! Though accusations have been made that Millikan was guilty of fraud and pathological science, some believe that he was using his experimental insight and personal expertise on the subject-matter to reject unreliable observations on sound physical grounds. According to Goodstein, research has shown that an analysis of the totality of his data does not lead to substantially different results.

Photoelectric effect

When Einstein published his seminal 1905 paper on the particle theory of light, Millikan was convinced that it had to be wrong, because of the vast body of evidence that had already shown that light was a wave. He undertook a decade-long experimental program to test Einstein's theory, which required building what he described as "a machine shop in vacuo" in order to prepare the very clean metal surface of the photoelectrode. His results confirmed Einstein's predictions in every detail, but Millikan was not convinced of Einstein's radical interpretation, and as late as 1916 he wrote, "Einstein's photoelectric equation... cannot in my judgment be looked upon at present as resting upon any sort of a satisfactory theoretical foundation," even though "it actually represents very accurately the behavior" of the photoelectric effect. In his 1950 autobiography, however, he simply declared that his work "scarcely permits of any other interpretation than that which Einstein had originally suggested, namely that of the semi-corpuscular or photon theory of light itself."

Since Millikan's work formed some of the basis for modern particle physics, it is ironic that he was rather conservative in his opinions about 20th century developments in physics, as in the case of the photon theory. Another example is that his textbook, as late as the 1927 version, unambiguously states the existence of the ether, and mentions Einstein's theory of relativity only in a noncommittal note at the end of the caption under Einstein's portrait, stating as the last in a list of accomplishments that he was "author of the special theory of relativity in 1905 and of the general theory of relativity in 1914, both of which have had great success in explaining otherwise unexplained phenomena and in predicting new ones."

Later life

In 1917, solar astronomer George Ellery Hale convinced Millikan to begin spending several months each year at the Throop College of Technology, a small academic institution in Pasadena, California that Hale wished to transform into a major center for scientific research and education. A few years later Throop College became the California Institute of Technology (Caltech), and Millikan left the University of Chicago in order to become Caltech's "chairman of the executive council" (effectively its president). Millikan would serve in that position from 1921 to 1945. At Caltech most of his scientific research focused on the study of "cosmic rays" (a term which he coined). In the 1930s he entered into a debate with Arthur Compton over whether cosmic rays were composed of high-energy photons (Millikan's view) or charged particles (Compton's view). Compton would eventually be proven right by the observation that cosmic rays are deflected by the Earth's magnetic field.

In his private life, Millikan was an enthusiastic tennis player. He was married with 3 sons, the eldest of which, Clark B. Millikan, became a prominent aerodynamic engineer.

He died at his home in San Marino, California in 1953 and was interred in the "Court of Honor" at Forest Lawn Memorial Park Cemetery in Glendale, California.

Birth cries of atoms


Further reading

  • Waller, John, "Einstein's Luck: The Truth Behind Some of the Greatest Scientific Discoveries". Oxford University Press, 2003. ISBN 0198607199
  • Physics paper On the Elementary Electrical Charge and the Avogadro Constant (extract) http://www.aip.org/history/gap/


  1. ^ The books, coauthored with Henry Gordon Gale, were A First Course in Physics (1906), Practical Physics (1920), Elements of Physics (1927), and New Elementary Physics (1936).

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