I called on Tyndall without much delay, and delivered Barnard’s letter of introduction. One may imagine how I felt when I saw and spoke to the very man whose descriptions of physical phenomena had been the first to disclose to me on the top loft of the Cortlandt Street factory the poetical side of the physical sciences. I expected to find a scientist looking like a poet and a dreamer, but I did not. He looked exactly what he was: a plain and benevolent Irishman. I had seen many an old Irishman, among my New York friends and acquaintances, who looked exactly as Tyndall looked; and when he spoke there was also the fire, the vigor, and the humor of the agile Irish mind. In less than the time it takes to tell this he made me feel that I had always known him, and that he was my old and generous friend. His questions were wonderfully direct, just as direct, I thought, as the questions which he addressed to physical phenomena when in his famous lectures he was deciphering their hidden meaning. He deciphered me very quickly, I thought, as if I were the simplest physical phenomenon which he had ever observed. The fact, however, that I held his attention encouraged me. He apparently attached no very great importance to my lack of early training in experimental physics, but advised me to avoid further delay. He informed me, by way of encouraging me, that he was over thirty when he took his doctor’s degree at the University of Marburg, in Germany. A lack of early advantages, he thought, could always be overcome by redoubling one’s efforts in later years. His own career proved that. He called my attention to a short account of the work of the famous Helmholtz, written for _Nature_ by no less a man, he said, than great Maxwell. This story, he thought, would show me that the great professor at the University of Berlin did not have early advantages in experimental physics, and that he became a professor of physics when he was already fifty years of age. He encouraged me to apply for the new fellowship at Columbia as soon as it became operative, and to make up my mind quickly to migrate to the best physical laboratory that I could find. I asked him what laboratory he would recommend and he again directed my attention to Maxwell’s account of the work of Helmholtz. When I was about to leave, promising, at his request, to call again, he gave me a copy of his lectures on light, which he had delivered in the United States thirteen years before. “Read them,” he said, “and when you come again I shall be glad to discuss with you some of the points of this little book; they will explain to you the full meaning of President Barnard’s letter, and of its historical background. Read also volume VIII of _Nature_.”