"Say you so?" answered Harry, smiling; "then I believe I must try another method;" so he stooped down, and picked up a small piece of rough iron, about six inches long, which Tommy had not before observed, as it lay upon the ground. This iron was broad at the top, but gradually sloped all the way down, till it came to a perfect edge at bottom. Harry then took it up, and with a few blows drove it a little way into the body of the root. The old man and he then struck alternately with their mallets upon the head of the iron, till the root began to gape and crack on every side, and the iron was totally buried in the wood.
"There," said Harry, "this first wedge has done its business very well; two or three more will finish it." He then took up another larger wedge, and, inserting the bottom of it between the wood and the top of the former one, which was now completely buried in the root, began to beat upon it as he had done before. The root now cracked and split on every side of the wedges, till a prodigious cleft appeared quite down to the bottom. Thus did Harry proceed, still continuing his blows, and inserting new and larger wedges as fast as he had driven the former down, till he had completely effected what he had undertaken, and entirely separated the monstrous mass of wood into two unequal parts.
Harry then said, "here is a very large log, but I think you and I can carry it in to mend the fire; and I will show you something else that will surprise you." So he took a pole of about ten feet long,
and hung the log upon it by a piece of cord which he found there; then he asked Tommy which end of the pole he chose to carry. Tommy, who thought it would be most convenient to have the weight near him, chose that end of the pole near which the weight was suspended, and put it upon his shoulder, while Harry took the other end. But when Tommy attempted to move, he found that he could hardly bear the pressure; however, as he saw Harry walk briskly away under his share of the load, he determined not to complain.
As they were walking in this manner, Mr Barlow met them, and seeing poor Tommy labouring under his burthen, asked him who had loaded him in that manner. Tommy said it was Harry. Upon this, Mr Barlow smiled, and said, "Well, Tommy, this is the first time I ever saw your friend Harry attempt to impose upon you; but he is making you carry about three times the weight which he supports
himself." Harry replied, "that Tommy had chosen that himself; and that he should directly have informed him of his mistake, but that he had been so surprised at seeing the common effects of a lever, that he wished to teach him some other facts about it;" then shifting the ends of the pole, so as to support that part which Tommy had done before, he asked him, "if he found his shoulder anything easier than before." "Indeed, I do," replied Tommy, "but I cannot conceive how; for we carry the same weight between us which we did before, and just in the same manner." "Not quite in the same manner," answered Mr Barlow; "for, if you observe, the log is a great deal farther from your
shoulder than from Harry's, by which means he now supports just as much as you did before, and you, on the contrary, as little as he did when I met you." "This is very extraordinary indeed," said Tommy; "I find there are a great many things which I did not know, nor even my mamma, nor any of the fine ladies that come to our house." "Well," replied Mr Barlow, "if you have acquired so much useful knowledge already, what may you expect to do in a few years more?"
Mr Barlow then led Tommy into the house, and showed him a stick of about four feet long, with a scale hung at each end. "Now," said he, "if you place this stick over the back of a chair, so that it may rest exactly upon the middle, you see the two scales will just balance each other. So, if I put into each of them an equal weight, they will still remain suspended. In this method we weigh every thing which is bought, only, for the greater convenience, the beam of the scale, which is the same thing as this stick, is generally hung up to something else by its middle. But let us now move the stick, and see what will be the consequence." Mr Barlow then pushed the stick along in such a manner, that when it rested upon the back of the chair, there were three feet of it on one side, and only one on the other. That side which was longest instantly came to the ground as heaviest. "You see," said Mr Barlow, "if we would now balance them, we must put a greater weight on the shortest side; so he kept adding weights, till Tommy found that one pound on the longest side would exactly balance three on the shortest; for, as much as the longer
side exceeded the shorter in length, so much did the weight which was hung at that end require to exceed that on the longest side."
"This," said Mr Barlow, "is what they call a lever, and all the sticks that you have been using to-day are only levers of a different construction. By these short trials, you may conceive the prodigious advantage which they are of to men; for thus can one man move a weight which half-a-dozen could not be able to do with their hands alone; thus may a little boy, like you, do more than the strongest man could effect who did not know these secrets. As to that instrument by which you were so surprised that Harry could cleave such a vast body of wood, it is called a wedge, and is almost equally useful with the lever. The whole force of it consists in its being gradually narrower and narrower, till at last it ends in a thin edge, capable of penetrating the smallest chink. By this we are enabled to overthrow the largest oaks, to cleave their roots, almost as hard as iron itself, and even to split the solid rocks." "All this," said Tommy, "is wonderful indeed; and I need not ask the use of them, because I see it plainly in the experiments I have made to-day."