“I will put a stick in, and keep the crack open, while you drive the wedge in, in another place.”

“O, that won’t do,” said the boy; “a stick would not keep it open.”

“Why not?” said Rollo.

“Because it is not solid enough; the sides of the cleft draw together very hard. They would crush the stick.”

Here Rollo put his hand into his pocket, and drew out a walnut, and he asked the boy if it would crack a walnut.

“Try it,” said the boy.

So Rollo put the walnut into the crack. He slipped it along until he got it to a place where the crack was just wide enough to receive it, and hold it steady. He left it there, and then the boy began to knock out the wedge.

He struck it first upon one side, and then upon the other, and thus gradually worked it out. The walnut was crushed all to pieces. The boy then drove in the wedge again, so as to open the log as it was before. He then went to the place where he had got the beetle and wedge at first, and brought a large wooden wedge which he had made before, and began to put that into the crack, not very far from the iron wedge.

“This will keep it open,” said he.

“Yes, I think it will,” said Rollo. “But put it up close to the iron wedge.”

“No,” said the boy; “for then I can’t knock the iron wedge out.”

So the boy put the large wooden wedge in, at a little distance from the iron one, and drove it in rather gently with the beetle. This opened the cleft a little more, so that the iron wedge came out pretty easily.

“I don’t see what makes the sides of the logs draw together so hard,” said Rollo.

“O, they can’t help it,” said the boy.

“That is no reason,” rejoined Rollo. “I should think that, after the log is once split open, it would stay so. If I split a piece of wood in two with my knife, the pieces don’t try to come together again.”

So Rollo began to examine the log, and to look into the cracks, to see if he could find out what it was that made the parts draw together so hard as to crush the walnut. Presently, he observed that the log was not split open from end to end. The crack commenced at one end, and extended nearly towards the other, but not quite; so that at this other end the log was solid and whole, just as it always had been. So Rollo perceived that the two halves being joined and held together firmly here, they could only be separated at the other end by the wedge springing them open, and, of course, by their elasticity they tended to spring together again. Then besides, he saw, by looking into the crack, a great number of splinters, large and small, which extended obliquely from one side to the other, and bound the two sides strongly towards each other.

By this time the boy had got the wedge knocked out.

“It is strange,” said Rollo, “that such a small wedge will split such a tough and solid log.”

“O, not very strange,” said the boy. “You see,” he continued, taking up the wedge, and pointing to the several parts as he explained them, “you see here at this part, where it enters the wood it is sharp, and the sides spread out each way, so that, when I drive it in, they force the wood apart.”

“Why don’t they have the back of the wedge wider still? and then it would force the wood open farther; and then you would not have to put in a wooden wedge afterwards,—so,” he added, making a sign with his fingers. He put the tips of his fingers together, and then separated his hands, so as to represent a very blunt-shaped wedge.

“Then it would not drive in so easily,” answered the boy. “Perhaps I could not drive it in at all, if it was so blunt.”

“They might have the wedge longer then,” said Rollo, “and then it would be just as tapering, and yet it would be a great deal broader at the back, because the back would be farther off.”

“That would make the wedge a great deal too heavy. It would not drive.”

“Why, yes, it would,” said Rollo.

“No, it would not,” said the boy. “It would be just like a shoemaker’s lap-stone; pounding it would hardly move it.”

Rollo did not understand what the boy meant by what he said about the shoemaker’s lap-stone; so he paused a moment, and presently he said,

“I don’t think it would make any difference, if it was heavy. And, besides, it might be made of wood, and that wouldn’t be heavy.”

“O, wood wouldn’t do,” said the boy.

Now it happened that while they had been talking, the boy had gone on driving in his wooden wedge into the cleft that the iron one had made, and it had been gradually splitting the log open more and more. So that just as the boy was saying that “a wooden wedge wouldn’t do,” Rollo was actually seeing with his own eyes that it would do; for at that moment the boy gave the last blow, and the halves of the log came apart and fell over, one to one side, and the other to the other.

“Why, there,” said Rollo, “you have split the log open with a wooden wedge.”

“O, that is because I had an iron one in first,” said the boy.

“What difference does that make?” said Rollo.

“A great deal of difference,” said the boy.

“But what difference?” persisted Rollo.

“I don’t know exactly what difference,” said the boy; “only I know you can’t do any thing with a wooden wedge until you have first opened a seam with an iron one.”

Rollo was confident that it could not possibly make any difference whether a wooden wedge was used first or last. The boy was sure that it did, though he could not tell why. Finally, they determined to try it; so the boy struck his axe into the end of the next log, and then attempted to drive in his wooden wedge. But he did not succeed at all. The wedge would not stay. Rollo told him that he did not strike hard enough. Then he struck harder, but it did no good. The wedge dropped out the moment he let go of it, and on taking it up, they found that the edge of it was bruised and battered; so that even Rollo gave up all hopes of making it enter.

“Ah!” said the boy, taking up the wedge, and looking at it, “now I know what the reason is. It is the edge.”

“Where?” said Rollo. “Let me see.”

“Why, when there is no crack,” said the boy, “you see the edge of the wedge comes against the solid wood, and when I drive, it only bruises and batters it; but the iron is hard, and goes in. But then, when a crack is made, the wedge can go in easily; for the edge does not touch; then only the sides rub against the wood.”

“How?” said Rollo. “I don’t understand.”

“I’ll show you in a minute,” said the boy. So he took the iron wedge, and went to work driving it into the log. It soon began to make a crack, which ran along the log, and opened wider and wider. When, at length, it was pretty wide, he put the wooden wedge in, and he showed Rollo that the edge of the wedge did not now have to force its way, but went easily into the crack, and only the sides came in contact with the two parts of the log which it was separating.

“That’s curious,” said Rollo.

“Yes,” said the boy.

“I wish I had a little beetle and wedge,” said Rollo. “I have got a hammer. That would do for a beetle, if I only had a wedge.”

“O, a hammer won’t do,” said the boy.

“Why not? Would not an axe do as well as a beetle?”

“No,” said the boy, “it would spoil the axe and the wedge too.”