Page:Popular Science Monthly Volume 20.djvu/690

670 language I use; the second is, that you should devote to me your very earnest and best attention, and strive all you can, by thought afterward, to understand what I mean. I shall use, doubtless, unconsciously, a great many words that are new to you, but which are to me just as familiar as household words. I will, however, try to explain them, and endeavor, if I can, to let those words impart to you the very idea that they conjure up in my mind. At the commencement, there are two words in very common use that many of you have heard over and over again, but which convey, in the way I shall use them, perhaps a different conception. These two words are "work "and "energy." I can readily imagine that one of you boys may say, when I call your attention to the words "work" and "energy," "Why, what nonsense to talk to me about work! Have I not been working as hard as ever I can during the past term to gain a prize, and have not I exercised all the energy I possess to distinguish myself in my class?" But the words "work" and "energy" applied in that sense are applied in a mental sense, and not at all in the physical sense in which I shall use them. Now, I dare say many of you live in town; some may live in the country; but, whether you live in town or country, you all know what a garden is, and what a gardener does. Suppose a gardener, with a ton of gravel in front of him, were told to move that gravel to a height of three feet. He would go to work with his spade; he would move shovelful after shovelful from the ground-line up to the three feet height, and after he had moved the whole of it you might readily imagine that he would be a little fatigued. Now, whenever a person does anything which causes fatigue, he does what we call work. The gardener, in lifting the gravel, would perform an amount of work which is capable of being measured. I will give you another illustration. Supposing some of you boys were put beside a pile of cricket balls, and for a wager or prize you were called upon to throw the balls as fast and as far as you could. A good thrower would perhaps throw the first ball eighty yards, he would throw the second ball seventy-five yards, the third seventy yards, the fourth sixty-five yards, and so each ball that he threw would go a less and less distance, until he had no strength left, and he could throw no more balls. Now, that boy would have done work; something would have passed out of him into the balls; he has, as it were, passed something that belonged to him into the cricket-balls, and as a result he feels fatigue through the loss of this something. Take another illustration: Supposing two crews agree to row a race. They start full of life and full of energy; they pull with all their hearts and might, and arrive at the goal, in common language, thoroughly pumped out. Something has gone out of them into the boat. That which has gone out of the crew, and out of the boy who threw the cricket-balls, is what we call energy, and what they have done is to do work upon the boat. Another example is in the case of foot-ball. A boy kicks a foot-ball and makes a splendid goal. To do