Jim, the humble fireman in the Cortlandt Street factory, told me once: “This country, my lad, is a monument to the lives of men of brains and character and action who made it.” From that day on the name “United States of America” recalled to my mind Washington, Hamilton, Franklin, Lincoln, and the other great men who are universally regarded as the fathers of this country; and when I learned to know and to appreciate them I felt that I was qualified to consider myself a part of this country. Maxwell and La Grange had taught me that Archimedes, Galileo, Newton, Carnot, Helmholtz, and other great investigators had made the dynamical sciences; and from that time on these sciences like monuments recalled to my mind the names of the men who made them. I never saw a man handling a crowbar without remembering that it was the historic lever which in the philosophy of Archimedes served as the earliest foundation for the science of statics. The word _force_ always recalled the picture of Galileo dropping heavy bodies from the Leaning Tower of Pisa, and watching their uniformly accelerated motions, produced by the force which was impelling the falling body to the earth. The picture reminded me that by these ideally simple experiments Galileo had banished forever the mediæval superstition that bodies fall because they are afraid of the vacuum above, and had substituted in its place the simple law of accelerating force, which prepared the foundation for the science of dynamics. I never saw a moving train being brought to a standstill by the frictional reactions of the brakes without seeing in my imagination the image of Newton formulating his great law of equality between physical actions and physical reactions, the crowning point of modern dynamics. These pictures illustrated what Maxwell meant when he spoke of the material things to which the labors of Archimedes, Galileo, and Newton gave a meaning, and when I caught that meaning I felt that I was no longer a stranger in the land of science. Their highest meaning, I knew, was the recognition that the truth which they conveyed was a part only of what my mother called the “Eternal Truth.” My work in Cambridge, guided principally by Maxwell and La Grange, reminded me, therefore, continually of the fathers of the sciences which I was studying and of the material things to which their labors gave a meaning. These thoughts gave me a satisfactory interpretation of my mother’s words: “Cambridge is a great temple consecrated to the eternal truth; it is filled with icons of the great saints of science. The contemplation of their saintly work will enable you to communicate with the spirit of eternal truth.” My description of the scientific activity of Cambridge had produced this image in her mind, which was dominated by a spirit of piety and of reverence. This spirit, I always thought, is needed in science just as much as it is in religion. It was the spirit of Maxwell and of La Grange.