In that first course of public lectures I found it necessary to devote much of my exposition to the correction of erroneous notions lodged in the minds of my audience. When I told that audience that no electrical generator generates electricity, because electricity was made by God and, according to Faraday, its quantity in the universe is constant, and that for every positive charge there is an equal negative one, most members of my audience were inclined to think that I was talking metaphysics. “Then what does it generate?” asked one of my hearers. I answered: “It generates motion of electricity, and by that motion it furnishes us with means of doing useful work like telegraphy, telephony, and electrical lighting.” Then I added: “The electrical science studies the forces which make electricity move against the reactions of the bodies through which it moves; in the overcoming of these reactions the moving electricity does useful work.” Illustrations from dynamics of material bodies did not help very much, because my audience had hardly any knowledge of even the elements of Newton’s great work, although Newton considered these elements obvious truths. All they knew about Newton was that he had “discovered gravitation.” When I told them that Newton had discovered the law of gravitational action and not gravitation itself, they thought that I was splitting hairs. I was never quite sure that those good people had carried away much knowledge from my lectures, but I was quite sure that they had left much knowledge with me. In trying to straighten out their notions I straightened out my own very considerably. Crocker was right when he said: “You have no idea how rapidly a young fellow grows when he tries to teach a new subject to poorly prepared beginners.” That was the real profit from our first course of public lectures.