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