"What is it?" said Rollo.
"A squall," said Jonas,-"and coming down directly upon us."
"What shall we do?" asked Rollo.
"Put the boat before the wind," replied Jonas, "and let her run: we must go where the squall carries us."
Jonas immediately began to pull the stern of the boat around with his paddle, so as to turn the head of it away from the quarter which the wind was blowing from; and then the wind drove the boat along very rapidly over the waves, which curled and foamed on each side, driving onward with great fury. When they looked around behind them, they saw that the pond, which was of a very dark color, though spotted with the white tips of the waves all over its surface, was almost black for a large space in the direction from which the squall was coming. It advanced with great rapidity, and at last struck the boat with a noise like thunder. The froth and foam flew over the surface of the water like tufts of cotton, and the boat seemed to fly along the water with almost as much speed as they; and the roaring of the winds and waves was so loud that Rollo had great difficulty in making Jonas hear what he had to say. After a few minutes, the violence of the wind somewhat abated; but it still blew a steady and furious gale, so that Jonas had to keep his boat directly before it. Thus they were driven on, wherever the wind chose to carry them, for more than half an hour.
Then they began to draw near the land, far, however, very far from the place where they had intended to go. Rollo observed that Jonas was looking out very eagerly towards the shore, and he asked him what he was looking for.
"Why, here we are," said Jonas, "on a lee shore, and I am looking out for a place to land."
Rollo looked, and saw that the waves were tumbling with great violence upon the rocks and gravelly beaches which lined the shore, and he was afraid that the boat would get dashed to pieces upon them. Jonas, however, observed a large tree, which originally stood upon the bank, but which had fallen over, and now lay with its top partly submerged. He thought that this might afford him some shelter, and so he made great exertions to guide the boat so as to bring it in to the shore around behind this tree. By means of great efforts he succeeded; and so he and Rollo both escaped safe to land.
The boys did not get home until late that night, for they were thrown upon the shore nearly two miles from the Mill village, and of course they had that distance to walk. Jonas was detained a little there, too, in making arrangements to send a boy for the boat after the storm had subsided. When they got home, Rollo's father said that he was sorry for their fatigues and exposures, but he was very glad that Jonas had persevered and found the carpenter; for the high wind had blown down the back chimney and broken the roof over the kitchen, and it was very necessary to have it repaired immediately.
QUESTIONS.
What is momentum? Has air momentum, when it is in motion, as
well as water? At what time in the spring of the year does the
sun rise at six o'clock? What did Rollo think was the prospect
in respect to the weather? What did Jonas think? What is meant
by being under the lee of a shore? What is a squall ? What
indications did Jonas observe of the approach of the squall?
What course did he pursue in order to avoid the danger of it?
CHAPTER XII. AIR AT REST.
A few days after the adventure described in the preceding chapter, Rollo heard his father proposing to his mother that they should take a walk the next morning before breakfast. Rollo wanted to go too. His father said that they should be very glad to have his company; and he promised to wake him in season.
Rollo felt rather sleepy, when his father called him the next morning; but he jumped up and dressed himself, and was ready first of all. It was a cool, but a very pleasant morning. The sun was just coming up. The ground in the path before the door was frozen a little, and the air seemed very still.
When Rollo's mother came out to the door, she said,-
"Well, husband, which way shall we go?"
"Up on the rocks," said Rollo; "let's go up on the rocks, mother. It will be beautiful there this morning."
"Well," replied his mother; "we'll go up on the rocks."
The place which Rollo called the rocks, was the summit of a rocky hill, which had a grassy slope upon one side, by which they could ascend, and a precipice of ragged rocks upon the other. There was a very pleasant prospect from the top of the rocks.
As they walked along, Rollo said that it was very different weather that still morning, from what it was the day that he and Jonas were out upon the pond.
"Yes," said his father, "you had an opportunity to see the effects of air in motion then."
"And now air at rest," replied Rollo.
"Pretty nearly," said his father.
"Yes, sir, entirely," said Rollo; "there is no wind at all, this morning: hold up your hand, and you can feel."
So Rollo stopped a moment upon the grass, and held up his hand to see whether there was any wind.
"I know there is not any wind that you can perceive in that way," said his father.
"How can we perceive it, then?" said Rollo.
"I'll tell you," replied his father, "when we get to the top of the hill."
They reached the top of the hill soon after this, and sat down upon a smooth stone. There was a very wide prospect spread out before them,-fields, forests, hamlets, streams,-and here and there, scattered over the landscape, a little patch of snow. The sun was just up, and the whole scene was very bright and beautiful.
"Now, father," said Rollo, "tell me how you know that there is any wind at all."
"I did not say that there was any wind. I said motion of the air."
"Why, father," replied Rollo, "I thought that wind was motion of the air."
"So it is," said his father; "but all motion of the air is not wind. Wind is a current of air, that is, a progressive motion;-and in fact, there is, this morning, a slight current from the westward."
"How can you tell, father?" asked Rollo.
"By the smokes from the chimneys; don't you see that they all lean a little from the west towards the east?"
"Not but a little, father;-and there's one, from that red house, which goes up exactly straight."
"Yes," said his father, "there is one; but, in general, the columns of smoke lean; which is proof that there is a gentle current of air to the eastward."
"Westward, you said, father," rejoined Rollo.
"Yes, from the westward, but to the eastward.
"That is what is called a progressive motion," continued Rollo's father; "that is, the whole body of air makes progress; it advances from west to east. But there is another kind of motion, called a vibratory motion."
"What kind of a motion is that, father?" asked Rollo.
"It is a very hard kind to describe, at any rate," said his father. "It is a kind of quivering, which begins in one place and spreads in every direction. Don't you hear a kind of a thumping sound?"
"Yes," said Rollo, "a great way off; what is it?"
"Look over across the pond there," said his father; "don't you see that man cutting wood?"
"Yes," said Rollo; "that's what makes the noise.-No, father," he continued, after a moment's pause, "that's not it. Look, father, and you'll see that the thumping sound comes when his axe is lifted up."
They all looked, and found that it was as Rollo had said. The strokes of the axe kept time, pretty well, with the sound of blows, which they heard, only the sounds did not correspond with the descent of the axe. When the axe appeared to strike the wood, they did not hear any sound, but they did hear one every time the axe was lifted up.
"So, you see," said Rollo, "it is not that man that we hear. There must be some other man cutting wood."