Robert Millikan

Robert Andrews Millikan was born on March 22, 1868, in Morrison, Illinois, the second son of Silas Franklin Millikan, a Congregationalist minister, and Mary Jane Andrews Millikan, a former dean at a small Michigan college. When Robert was seven the family moved west to Maquoketa, Iowa, where he grew up in a household that prized education but had little money to spare ^[1].

His boyhood was rural and physically active. He worked summer jobs on farms and in a barrel factory, swam in local rivers, and later credited that outdoor upbringing with the stamina he brought to long laboratory campaigns. The local high school offered almost no science; by his own account the physics instruction he received there was poor, and nothing in his early schooling suggested a future in research ^[1].

In 1886 Millikan entered Oberlin College in Ohio, where his parents had studied. He concentrated on Greek and mathematics, and his path into physics began almost by accident: at the end of his second year his Greek professor asked him to teach the introductory physics course, reasoning that anyone who could handle Greek could learn physics from a textbook. Millikan spent the summer working through the subject and discovered he enjoyed both the material and the teaching. He took his bachelor's degree in 1891 and stayed on as a tutor while completing a master's degree ^[2].

Millikan received a fellowship to Columbia University and in 1895 became the first person to earn a doctorate in physics there, with a thesis on the polarization of light emitted by incandescent surfaces ^[2]. On the advice of the physicist Michael Pupin he then borrowed money for a year of postgraduate study in Europe, attending lectures by Max Planck in Berlin and working in Walther Nernst's laboratory in Göttingen at the very moment X rays and radioactivity were being announced ^[1].

In 1896 Albert A. Michelson offered him an assistantship at the new Ryerson Physical Laboratory of the University of Chicago. Millikan accepted and remained at Chicago for twenty five years, rising to full professor in 1910. During his first decade he published comparatively little research, pouring his energy instead into teaching and into a series of physics textbooks, several written with colleagues, that were used in American classrooms for generations ^[3].

Around 1907, conscious that his scientific reputation lagged behind his standing as an educator, Millikan turned decisively toward research. He chose a problem many physicists considered fundamental and unresolved: whether electric charge came in discrete, identical units, and if so, what the value of that elementary charge was. Earlier cloud based measurements by J. J. Thomson's group in Cambridge had given only rough averages, and some respected scientists still doubted that individual electrons were real physical objects rather than convenient fictions ^[4].

The work at the heart of any Robert Millikan biography is the oil drop experiment. Beginning with water droplets and then, from 1909, using tiny drops of watch oil that did not evaporate, Millikan and his graduate student Harvey Fletcher observed single charged droplets suspended between charged metal plates. By balancing gravity against the electric force and timing each drop's rise and fall, Millikan could calculate the charge it carried. Every measured charge proved to be a whole number multiple of one smallest value. In 1913 he published the elementary charge as 4.774 times ten to the minus tenth electrostatic units, a figure within about one percent of the modern value, and the result settled the argument over the electron's reality ^[4].

His second landmark was a decade long test of Albert Einstein's 1905 photoelectric equation. Millikan doubted Einstein's light quantum hypothesis and expected to refute it. Instead, in meticulous experiments completed by 1916 using freshly cut alkali metal surfaces in vacuum, he confirmed the equation in every detail and used it to make the first direct photoelectric measurement of Planck's constant ^[5]. The irony was real: a skeptic of quantum ideas supplied some of their strongest experimental support. For the elementary charge and photoelectric work together, Millikan received the 1923 Nobel Prize in Physics, the second American to win the physics prize ^[2].

Asking who was Robert Millikan beyond these two experiments leads to his later research on high altitude radiation. In the 1920s he and his students at Caltech sent instruments up on balloons and sank detectors in mountain lakes, demonstrating that the penetrating radiation came from above the atmosphere rather than from the Earth. In 1925 he named the phenomenon cosmic rays, the term still in use, although his own theory that the rays were photons produced by atom building in space was eventually disproved by his former student Carl Anderson and others ^[6].

A later controversy deserves honest mention among Robert Millikan facts. Harvey Fletcher contributed substantially to the early oil drop work, yet the key 1910 and 1913 papers appeared under Millikan's name alone, under an arrangement the two men agreed to at the time; Fletcher described the episode in a memoir published after both had died. Historians have also examined Millikan's laboratory notebooks and debated his selection of which drops to publish, with most concluding that his exclusions rested on stated experimental grounds rather than fraud ^[7].

In 1902 Millikan married Greta Erwin Blanchard, a graduate of the University of Chicago whom he had met through the university community. The couple spent part of their honeymoon in Europe, where Millikan combined travel with scientific visits. They had three sons: Clark, who became a distinguished aeronautical engineer at Caltech; Glenn; and Max, who later directed an international studies center at the Massachusetts Institute of Technology ^[1].

Millikan was a lifelong and public Christian who wrote and lectured frequently on the relationship between science and religion. In books such as Evolution in Science and Religion, published in 1927, he argued that scientific inquiry and religious faith addressed different questions and could coexist without conflict, a message that made him a sought after speaker in interwar America ^[3]. He was also, by every account, formidably energetic: colleagues joked about the Millikan unit of publicity, and his face appeared on the cover of Time magazine in 1927, when he was among the most recognizable scientists in the country ^[6].

During the First World War Millikan served as a vice chairman of the National Research Council and directed research on submarine detection and meteorological instruments for the Army Signal Corps, work that convinced him of the value of organized cooperation between scientists and government ^[3].

In 1921 the astronomer George Ellery Hale persuaded him to leave Chicago for Pasadena, where the small Throop College of Technology had just been renamed the California Institute of Technology. Millikan became director of the Norman Bridge Laboratory of Physics and chairman of the Executive Council, in practice the institute's president, though he never took that title. Over the next twenty four years he recruited faculty, courted donors, and built Caltech from a modest regional school into one of the world's leading scientific institutions, attracting visitors including Einstein and nurturing students such as Carl Anderson, who discovered the positron there in 1932 ^[6].

Millikan retired from his administrative post in 1945 at the age of seventy seven but kept an office on campus and continued writing; his autobiography appeared in 1950. He died of a heart attack at his home in San Marino, California, on December 19, 1953, at eighty five ^[2].

Millikan's measured value of the elementary charge became one of the anchor constants of twentieth century physics, feeding into calculations of Avogadro's number, the mass of the electron, and much else. The oil drop experiment itself is still taught and reproduced in university laboratories as a model of how ingenuity and patience can extract a fundamental number from tabletop equipment ^[4]. Among the lasting Robert Millikan achievements, his photoelectric measurements gave early quantum theory an empirical foundation it badly needed, and the field of cosmic ray physics he named grew into a major branch of astrophysics and particle physics ^[5].

His institutional legacy is equally concrete. Caltech's rise under his leadership reshaped American science, and buildings, awards, and a crater on the Moon carried his name. That legacy has also been reassessed. In 2021 Caltech removed Millikan's name from its central library and other campus honors after a committee documented his service as a trustee of the Human Betterment Foundation, a Pasadena organization that promoted eugenic sterilization ^[8].

The result is a complicated but instructive portrait: a minister's son from small town Iowa who became a Nobel laureate, an institution builder whose university outgrew him, and a public figure whose views on human heredity now draw sharp criticism. For students first encountering Robert Millikan facts through the oil drop experiment, his career remains a case study in both the power of careful measurement and the way reputations are weighed anew by later generations ^[8].