Part 12 (1/2)
_Mr Barlow._--To-morrow you shall hear it; at present we have read and conversed enough; it is better that you should go out and amuse yourselves.
The little boys then went out, and returned to a diversion they had been amusing themselves with for several days, the making a prodigious s...o...b..ll. They had begun by making a small globe of snow with their hands, which they turned over and over, till, by continually collecting fresh matter, it grew so large that they were unable to roll it any farther. Here Tommy observed that their labours must end, ”for it was impossible to turn it any longer.” ”No,” said Harry, ”I know a remedy for that.” So he ran and fetched a couple of thick sticks about five feet long, and giving one of them to Tommy, he took the other himself.
He then desired Tommy to put the end of his stick under the ma.s.s, while he did the same on his side, and then, lifting at the other end, they rolled the heap forward with the greatest ease.
Tommy was extremely surprised at this, and said, ”How can this be? We are not a bit stronger than we were before; and yet now we are able to roll this s...o...b..ll along with ease, which we could not even stir before.” ”That is very true,” answered Harry, ”but it is owing to these sticks. This is the way that the labourers move the largest trees, which, without this contrivance, they would not be able to stir.” ”I am very much surprised at this,” said Tommy; ”I never should have imagined that the sticks would have given us more strength than we had before.”
Just as he had said this, through a violent effort, both their sticks broke short in the middle. ”This is no great loss,” observed Tommy, ”for the ends will do just as well as the whole sticks.”
They then tried to shove the ball again with the truncheons which remained in their hands; but, to the new surprise of Tommy, they found they were unable to stir it. ”That is very curious indeed,” said Tommy; ”I find that only long sticks are of any use.” ”That,” said Harry, ”I could have told you before, but I had a mind you should find it out yourself. The longer the stick is, provided it is sufficiently strong, and you can manage it, the more easily will you succeed.” ”This is really very curious,” replied Tommy; ”but I see some of Mr Barlow's labourers at work a little way off, let us go to them, and desire them to cut us two longer sticks, that we may try their effect.”
They then went up to the men who were at work, but here a new subject of admiration presented itself to Tommy's mind. There was a root of a prodigious oak tree, so large and heavy, that half-a-dozen horses would scarcely have been able to draw it along; besides, it was so tough and knotty, that the sharpest axe could hardly make any impression upon it.
This a couple of old men were attempting to cleave in pieces, in order to make billets for Mr Barlow's fire.
Tommy, who thought their strength totally disproportionate to such an undertaking, could not help pitying them; and observing, that certainly Mr Barlow ”did not know what they were about, or he would have prevented such poor weak old men from fatiguing themselves about what they never could perform.” ”Do you think so?” replied Harry; ”what would you then say, if you were to see me, little as I am, perform this wonderful task, with the a.s.sistance of one of these good people?” So he took up a wooden mallet--an instrument which, although much larger, resembles a hammer--and began beating the root, which he did for some time, without making the least impression. Tommy, who imagined that, for this time, his friend Harry was caught, began to smile, and told him, ”that he would break a hundred mallets to pieces before he made the least impression upon the wood.”
”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 ma.s.s 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 s.h.i.+fting 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 c.h.i.n.k. 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.”
”One thing more,” added Mr Barlow, ”as we are upon this subject, I will show you.” So he led them into the yard, to the bottom of his granary, where stood a heavy sack of corn. ”Now,” said Mr Barlow, ”if you are so stout a fellow as you imagine, take up this sack of corn, and carry it up the ladder into the granary.” ”That,” replied Tommy, laughing, ”is impossible; and I doubt, sir, whether you could do it yourself.”
”Well,” said Mr Barlow, ”we will, at least try what is to be done.” He then led them up into the granary, and, showing them a middle-sized wheel, with a handle fixed upon it, desired the little boys to turn it round. They began to turn it with some little difficulty, and Tommy could hardly believe his eyes, when, presently after, he saw the sack of corn, which he had despaired of moving, mounted up into the granary, and safely landed upon the floor. ”You see,” said Mr Barlow, ”here is another ingenious contrivance, by which the weakest person may perform the work of the strongest. This is called the _wheel_ and _axle_. You see this wheel, which is not very large, turns round an axle which goes into it, and is much smaller; and at every turn, the rope to which the weight is fixed that you want to move, is twisted round the axle. Now, just as much as the breadth of the whole wheel is greater than that of the axle which it turns round, so much greater is the weight that the person who turns it can move, than he could do without it.” ”Well,” said Tommy, ”I see it is a fine thing indeed to acquire knowledge, for by these means one not only increases one's understanding, but one's bodily strength. But are there no more, sir, of these ingenious contrivances, for I should like to understand them all?” ”Yes,” answered Mr Barlow, ”there are more, and all of them you shall be perfectly acquainted with in time; but for this purpose you should be able to write, and comprehend something of arithmetic.”
_Tommy._--What is arithmetic, sir?
_Mr Barlow._--That is not so easy to make you understand at once; I will, however, try to explain it. Do you see the grains of wheat which he scattered in the window?
_Tommy._--Yes, sir.
_Mr Barlow._--Can you count how many there are?
_Tommy._--There are just five-and-twenty of them.
_Mr Barlow._--Very well. Here is another parcel; how many grains are there?
_Tommy._--Just fourteen.
_Mr Barlow._--If there are fourteen grains in one heap, and twenty-five in the other, how many grains are there in all? or, how many do fourteen and twenty-five make?
Tommy was unable to answer, and Mr Barlow proposed the same question to Harry, who answered, that, together, they made thirty-nine. ”Again,”
said Mr Barlow, ”I will put the two heaps together, and then how many will there be?”