more compact, or less porous, in one case than in the other. In the first place, I ascertained that steel was made more compact by being hammered and tempered, and that the better it was tempered, the more compact it would become; the size of the pores being made, of course, less in the same proportion. Well, then, I saw the reason I was in search of, at once. For we know a wet sponge is longer in drying than a wet piece of green wood, because the pores of the first are bigger. A seasoned or shrunk piece of wood dries quicker than a green one, for the same reason. Or you might bore a piece of wood with large gimblet holes, and another with small ones, fill them both with water, and let them stand till the water evaporated, and the difference of time it would take to do this, would make the case still more plain. So with the blades; the wet or vapor lingers longest on the worst wrought and tempered one, because the pores, being larger, take in more of the wet particles, and require more time in drying."

"Your theory is at least a very ingenious one," observed Locke, “and I am reminded by it of another of the natural phenomena, of the true explanation of which I have not been able to satisfy myself. It is this: what makes the earth freeze harder and deeper under a trodden path than the untrodden earth around it. All that I have asked, say it is because the trodden earth is more compact. But is that reason a sufficient one?"

"No," said Bunker, "but I will tell you what the reason is; for I thought that out long ago. You know that, in the freezing months, much of the warmth we get is given out by the earth, from which, at intervals, if not constantly, to some extent, ascend the warm vapors to mingle with and moderate the cold atmosphere above. Now those ascending streams of warm air would be almost wholly obstructed by the compactness of a trodden path, and they would naturally divide

at some distance below it, and pass up through the loose earth on each side, leaving the ground along the line of the path, to a great depth beneath it, a cold, dead mass, through which the frost would continue to penetrate, unchecked by the internal heat, which, in its unobstructed ascent on each side, would be continually checking or overcoming the frost in its action on the earth around. That, sir, is the true philosophy of the case, you may depend upon it. But now let me ask you a question and it shall be the last one -a question which, perhaps, you may think a trifling one, but which, for all that, is full of meaning. What is the truest sign by which you can judge of the coming weather?"

"The quantity of dew that has fallen the night before, or that is then falling, if it be evening and the prognostic is required for the next day," replied the other. "At least I

have never noticed any better criterion."

"That is an old rule, and a good one, I grant you," remarked Bunker; "but not so curious and unfailing as another which I, some time ago, began to observe."

"What may that be, sir?"

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you can

Why, this, when you wish to know what the weather is going to be, just go out, and select the smallest cloud see, keep your eye upon it, and if it decreases and disappears, it shows a state of the air which will be sure to be followed by fair weather; but if it increases, you may as well take your great coat with you, if you are going from home, for falling weather will not be far off."

"That is, indeed, a curious and interesting fact in meteorology," responded Locke, "and I can readily see the reason why the indication should generally, at least, hold good."

"And what is that reason?" asked Bunker, with interest. "Why, it is resolvable into electric phenomenon, I suspect," answered the former. "Whenever the air is becoming charged with electricity, you will see every cloud

attracting all less ones towards it, till it gathers into a shower. And, on the contrary, when this fluid is passing off, or diffusing itself, even a large cloud will be seen breaking to pieces and dissolving."

“Right, sir!” cried Bunker; "you are a thinker, and no mistake. And let me tell you, there's more depending on that same electricity than your book philosophers dream of. I am pretty well satisfied, that not only our dry seasons and our wet ones, our cold seasons and our warm ones, are caused by some variation in the state of the electric fluid, but that our epidemical diseases, and a thousand other things that we cannot account for, are to be attributed to the same cause. But we will now drop the discussion of these matters; for I am abundantly satisfied, that you have not only knowledge enough, but that you can think for yourself. And now, sir, all I wish to know further about you is, whether you can teach others to think, which is half the battle with a teacher. But as I have had an eye on this point, while attending to the others, probably one experiment, which I will put upon you to make on one of the boys here, will be all I shall want."

"Proceed, sir," said the other.

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Ay, sir," rejoined Bunker, turning to the open fire-place, in which the burning wood was sending up a column of smoke; "there you see that smoke rising, don't you? Well, you and I know the reason why smoke goes upward, but my youngest boy don't, I rather think. Now take your own way, and see if you can make him clearly understand it."

Locke, after a moment's reflection and a glance round the room for something to serve for apparatus, took from a shelf, where he had espied a number of the articles, the smallest of a set of cast-iron cart-boxes, as is usually termed the round, hollow tubes, in which the axletree of a carriage turns. Then selecting a tin cup, that would just take in the

box, and turning into the cup as much water as he judged, with the box, would fill it, he presented them separately to the boy, and said,

"

"There, my lad, tell me which of these is the heaviest ? "Why, the cart-box, to be sure,” replied the boy, taking the cup half-filled with water in one hand, and the hollow iron in the other.

"Then you think this iron is heavier than as much water as would fill the place of it, do you?" resumed Locke.

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Why, yes, as heavy again, and more too— I know 't is," promptly said the boy.

"Well, sir, now mark what I do," proceeded the former, dropping into the cup the iron box, through the hollow of which the water instantly rose to the brim of the vessel.

"There, you saw that water rise to the top of the cup, did you?"

“Yes, I did.”

"Very well, what caused it to do so ?"

“Why, I know well enough, if I could think; why, it is because the iron is the heaviest, and as it comes all round the water so it can't get away sideways, it is forced up.”

“That is right; and now I want you to tell me what makes that smoke rise up the chimney."

“Why, I guess,” replied the boy, scratching his head, "I guess I guess I don't know."

"Did you ever get up in a chair to look on some high shelf, so that your head was brought near the ceiling of a heated room, in winter? and, if so, did you notice any difference between the air up there and the air near the floor below?"

"Yes, I remember I have, and found the air up there as warm as mustard; and when I got down, and bent my head near the floor to pick up something, I found it as cold as tunket."

"That is ever the case; but I wish you to tell me how the cold air always happens to settle down to the lower part of the room, while the warm air, some how, at the same time, gets above."

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Why, why, heavy things settle down, and the cold airyes, that's it, an't it? the cold air is heaviest, and so settles down, and crowds up the warm air, that is lightest."

"Very good. You then understand that cold air is heavier than the heated air, as that iron is heavier than the water; so we now will go back to the main question. what makes the smoke go upwards?"

"Oh! I see it now as plain as day; the cold air settles down all round, like the iron box, and drives up the hot air, as fast as the fire heats it in the middle, like the water; and so the hot air carries the smoke along up with it, same as feathers and things in a whirlwind. Gorry! I have found out what makes smoke go up-it is curious, though, an't it, you?"

"Done like a philosopher!" cried Bunker. "The thing is settled. I will give up that you are an academician of a thousand. You can not only think for yourself, but can teach others to think; and I therefore pronounce you well qualified for a schoolmaster, in every thing except government, about which we will hope for the best, and run the risk; so you may call it a bargain as quick as you please." "You offer to make it so on your part, I suppose you mean to be understood," said Locke; "for on mine, you remember I told you, some time ago, that I feel unwilling to undertake to govern a school of the character I have discovered yours to be."

"What, back out now?" exclaimed the other, with a disappointed air. "Why, I was beginning to have a first-rate opinion of you, and thought, of course, you would have spunk enough to make a trial, at least. Surely, you an't such a coward as to be afraid to do that, are you?