Notwithstanding a long life devoted to the study of mathematical and experimental physics, during which Kelvin unraveled many a difficult problem in electricity and magnetism and added many a beautiful skein to the texture of our knowledge in electrostatics and electrokinetics, that illustrious man, the acknowledged leader in physical science, made a public admission in 1896 which caused a great stir throughout the scientific world. It was on the occasion of the celebration of the golden jubilee of his professorship of natural philosophy in the University of Glasgow. Delegates had come from all parts of the world; kings and princes had sent their representatives; universities and learned societies of every country of the Old World and the New vied with one another in doing honor to the scientist who had figured so long and so conspicuously in the advances of the age. It was on that solemn occasion and in presence of such a notable assembly that Kelvin made the astonishing admission that, although he had been a diligent student of electricity and magnetism for a period exceeding fifty years, and although he had pondered every day for forty years over the nature of the ether and the constitution of matter, he knew no more about their essence, about what they really are, than he knew at the beginning of his professional work. This confession, remarkable by reason of the man who made it and the circumstances in which it was made, has always appeared to the writer of these lines as having more of the ring of disappointment in it than of blank failure. Kelvin's great analytical mind early and persistently strove to penetrate the closely guarded secrets of nature; and because Dame Nature did not yield to his open sesame, but persisted in her reticence, the philosopher grew pessimistic and disappointed; and, under the sway of such feelings, he summed up the result of his life-quest after the ultimate problems in science and pronounced it a "failure." A "failure" it was not, if science is the discovery and registration of the laws of God as revealed in the universe of mind and matter; for few men of his generation, if any, made more contributions of the first order to the theory of electrostatics, to the doctrine of energy, to hydrodynamics and the thermo-electric properties of matter. This note of disappointment, or wail of despondency, had been sounded before by Faraday, who said that, the more he studied electrical phenomena, the less he seemed to know about electricity itself. Was not Laplace animated by a kindred feeling when he spoke about the infinitude of our ignorance? Lastly, was not this intense feeling of our limited powers precisely that which, after all his discoveries in mathematics, in optics and in celestial mechanics, made Newton compare himself to a child standing on the beach with the vast ocean of truth before him, unfathomed and unexplored?