text: When Albert Einstein published his 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 Einsteins 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, published in 1914, confirmed Einsteins predictions in every detail, but Millikan was not convinced of Einsteins interpretation, and as late as 1916 he wrote, "Einsteins 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 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".
  Although Millikans work formed some of the basis for modern particle physics, he was 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 Einsteins 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."
  Millikan is also credited with measuring the value of Planck's constant by using photoelectric emission graphs of various metals.