Later in his career, Millikan became increasingly involved in the broader aspects of science, acting as an advisor for various foundations and corporations, raising money for Caltech, and contributing to the formation of national science policies. Subsequent experiments carried out by Millikan were also important for providing evidence that Albert Einstein’s formula mathematically explaining the photoelectric effect, which he proposed in 1905, was correct. Millikan’s oil-drop experiment helped firmly establish that electrons are discrete particles, a claim that was under significant dispute at the time, and gave credence to Niels Bohr's quantum theory of the atom. The difference in the values has been commonly attributed to Millikan's utilization of an inaccurate value for the viscosity of air.
By repeating his experiment numerous times, Millikan demonstrated that the charge on a single electron was a constant, 1.592 × 10 − 19 coulomb, a number slightly smaller than the contemporary value of the elementary charge (1.602 × 10 −19 coulomb). This was primarily because other physicists had tried to determine the charge of an electron through observations of a cloud of water droplets exposed to an electric field, while Millikan refined the process by observing single drops of a liquid, first water and then oil, which did not pose the same evaporation problems as water. The Millikan experiment was designed to determine the charge of an electron, an objective that had already been attempted by several other scientists, but never with such a high level of success. However, it appears that his famous Millikan oil-drop experiment had a greater influence on his academic career, since the publication describing the experiment and Millikan’s results was released shortly before he received his professorship. Early in his career he developed several physics textbooks that were widely used for many years. Millikan eventually began teaching at the University of Chicago, where he became a full professor in 1910. Millikan returned to the United States in 1896 when he was offered a position as assistant to Albert Michelson at the University of Chicago’s Ryerson Laboratory. He subsequently spent a year abroad, as was customary for postgraduates at the time, where he carried out research at the Universities of Berlin and Göttingen in Germany. Millikan’s interest in physics led him to pursue graduate degrees in the field, which he received in 1893 (MS) and 1895 (Ph.D.). Later, in his autobiography, Millikan said that his first experience teaching physics was probably the best teaching he had ever done due to his enthusiasm for the topic, which he was carefully trying to master one step ahead of his students.
In fact, his eventual interest in physics is often attributed to his Greek professor, who reportedly urged him to teach an elementary physics course despite his unfamiliarity with the field, claiming that if Millikan could do well in learning Greek, then he was capable of teaching physics. As an undergraduate, Millikan began the typical Classics curriculum and particularly enjoyed mathematics and Greek. He soon enrolled at Oberlin College in Ohio, the alma mater of his mother, Mary Jane Andrews. Millikan was born on March 22, 1868, in Morrison, Illinois and took a job as a court reporter after he graduated from high school.