670 THE POPULAR SCIENCE MONTHLY. 



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 after- 

 ward, to understand what I mean. I shall use, doubtless, uncon- 

 sciously, 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 t\e 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 illustra- 

 tion. 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 lan- 

 guage, 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 



