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LESSON XLVII.

Learning to Think.-Part I.

[graphic][subsumed]

at-ten'-tive-ly, carefully. grad'-u-al-ly, bit by bit. e-las-tic'-i-ty, springiness.

in-ter-fered', meddled, hindered. spring'-i-ness, elasticity.

fric'-tion, rubbing. "Now, Charles, let me give you an instance of the value of learning to think. It will explain all your questions about your hoop, and why it runs so.

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"It is a law of nature that matter, or every substance around us, will always remain in the same state in which it is, unless forced into another state. A stone lying on the ground would lie for ever, if nothing moved it; and a bullet, fired out of a gun, would fly forward for ever, if nothing stopped it."

"Would it really?"

"Yes; and, in like manner, your hoop, when once set in motion, would run on for ever, if nothing prevented it."

"But what does prevent it? There is nothing stops it, unless it happens to run

a post."

against a wall or

“There you are wrong. Every pebble it meets with, however small, prevents it, in some degree, from running on as it otherwise would do. When you drive it through mud or water, it will not go far without stopping, because the mud and the water stop its progress. When you drive it over grass, it is the same; the grass stops it."

'Yes, I know that; but when I drive it on broad flagstones, it runs along smoothly, and nothing stops it then.”

"In this case, as you say, it runs on faster; but still, to say nothing of the wind which it may have to push through, it rubs against the ground, and this rubbing, or friction, as it is called, makes it, if you do not strike it again, gradually go slower and slower till it stops.

"The reason, then, why your hoop, when once set in motion, runs on so famously, is because it has so little friction, so small a part of it rubs against the ground. And the reason why a pocket handkerchief will not run along at all, is because it has so much friction, or rubs so much against the ground."

"Well, I am glad I know at last; but why does my narrow iron hoop run along better than my broad wooden one ?"

"For this simple reason: it is heavier, according to its bulk, and has less friction. Your broad hoop has two or three times as much wind to push through, when it meets the wind; and, being two or three times broader, it must of necessity rub more against the ground than the other."

"I understand, then, that when I have once knocked my hoop along with my stick, it runs on, according to the law you spoke of, until the rubbing or friction stops it by degrees?"

"Exactly so; and it is just the same with the peg-top. The string by being wrapped round it, forces it to spin when you dash it on the ground, and there it would spin for ever, or until it wore itself away, if the rubbing or friction against the air and the ground did not stop it."

"That is just like the hoop. I understand it now thoroughly; so please to explain why a ball bounces."

"Do you remember what elasticity is?"

"Oh yes! That is one of the qualities that you told me of it is springiness."

"What do you mean by springiness?"

I mean the quality of springing back again when a thing is pushed out of its place."

"Very good! Now here is a bit of Indiarubber. If I stretch it out, the moment I loose it, it springs into its place again; and if I push it hard with my finger, and dent it in, the instant I take away my finger, the dented part springs up to its former position. Thus it is with the ball, which is elastic. The blow against the ground dents it in; and its elasticity, or sudden effort to force itself into its former round form makes it spring into the air.”

'Capital! I shall never forget why my ball bounces now."

QUESTIONS:-1. What is this lesson about? 2. Who do you think speaks to Charles, a teacher or a scholar like himself? 3. What does he say? 4. What instance did he give him? 5. What was the first question Charles asked? 6. What are you told about the laws of nature? 7. Was Charles told the same? 8. What is the law of nature here stated in regard to water? 9. How did the teacher make Charles understand that? 10. Did Charles understand it. 11. What did he say? 12. Do you understand it? 13. What was the law of nature said to be in regard to a stone? 14. Why does a hoop run so well? 15. Why will a handkerchief not run at all? 16. Why does a narrow iron hoop run better than a broad wooden one? 17. Explain this. 18. How does a peg-top spin? 19. What makes it stop? 20. Tell me why a ball bounces. 21. What is the meaning of springiness? 22. When you stretch out India-rubber, and then let it go, what happens? 23. Is every ball elastic? 24. Will an iron ball bounce if you throw it on the ground? 25. Will a wooden one? 26. Why not? 27. Does your elastic ball bounce? 28. Explain why.

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LESSON XLVIII.

Learning to Think.-Part II.

ac-cus'-tom-ed, was in the

habit of.

clear'-ly, rightly, cleverly. con-clude', find out, reason.

di-vīd'-ed, separated.

gain'-ing, getting, acquiring.

in-hab'-i-ted, lived in.

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"I DO want to be able to think, for thinking seems to tell one about everything."

Thinking clearly and properly, Charles, is a great help in gaining knowledge. Think, for a moment, what a number of trees and flowers there must be in the world. Now, all these have been divided into classes, so that the moment a flower or tree, with a blossom upon it, is seen, it is known to what class it belongs."

"Indeed!"

Yes; and the same with the living creatures of the earth. You would be surprised if you knew how much knowledge a little thinking gives a person. Now, then, listen a moment. Suppose a strange creature was found, that nobody had ever seen before; a thinking person would find out a

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