"Yes," said his father, "crows move their wings as fast as that, whereas you only move hands and arms. If you had great wings, as long, in proportion, as the crows, you could not move them so fast."
"How large would they be?" said Rollo.
"O, I don't know,—perhaps as big as the top of the dining-table."
"O father," said Rollo, "I don't think they would be as big as that. The crow's wings are not longer than his body, and so mine would not be longer than my body."
"Perhaps you never saw a crow's body," said his father. "His feathers and his tail, which are very light, swell out his body, and make it appear much larger than it really is. I presume his wings, when they are spread, are twice or three times as long as his body. If you had wings in proportion, it would be with the utmost difficulty that you could use them at all. You certainly could not strike the air with them fast enough to pull yourself up by them."
"I did not think that the birds pulled themselves up by the air," said Nathan. "I did not know that the air was anything real."
"O yes; it is something real," said his father.
"I've seen birds fly without moving their wings at all," said Rollo.
"Yes," said his father, "and so have I seen a stone."
"A stone!" repeated Rollo.
"What, a stone fly?" said Nathan.
"Yes," replied his father; "did you never see a stone fly through the air, without any wings at all?"
"Why, yes," said Rollo, "when somebody threw it."
"Very well," said his father. "If you set the stone in motion, it will continue in motion for some time, without any wings; and so will a bird."
"But, father, they don't throw birds," said Nathan; and he laughed aloud at such an idea.
"Birds throw themselves," said his father; "that is, they strike their wings upon the air, hard and quick, and thus get into very quick motion, and then they can keep their wings still for a time, and go on, as long as the impulse they have given them lasts. This shows what prodigious strength they have in their wings. They can not only strike the air hard and frequently enough to raise themselves up, and move along, but they can do it so easily, as to get such a velocity, that they can rest their wings for some time, and sail away through the air, only expending the impulse they had accumulated."
Rollo and Nathan were silent. Rollo was thinking how he had seen the swallows sailing swiftly round and round in the air, with their wings spread out motionless by their side.
"So, you see," continued his father, "the difficulty in the way of a boy's flying, is not the want of wings, but the want of strength to use them. It would be very easy to make wings."
"Would it?" said Nathan.
"Yes," said his father. "At least it would not be very difficult. Ingenious mechanics would soon find out modes of making something to answer the purpose of wings, to strike upon the air, if there was the necessary power to work them. The great difficulty in almost all cases in mechanics is, in getting the power; there is very little difficulty in applying it to any purpose it is wanted for. So, you see, next time, Nathan, when you want to fly, you must wish, not that you had wings, but that you were strong enough to use them."
"Well, father," said Rollo, "men are strong enough to paddle themselves along in the water; why can't they in the air?"
"Because," said his father, "water supports them by its buoyancy, and they have nothing to do but to move themselves along upon it. But air cannot support them; and, of course, a great part of the effort which they would make, would be required to keep them up. And then, besides, the water is generally nearly at rest, but the air is generally in a state of rapid motion."
"Why, father," said Rollo, "I'm sure water is sometimes in rapid motion. The rivers run very swiftly, often."
"Yes," replied his father; "but then, when they do, men cannot paddle, or row boats upon them. A current that should run at the rate of four or five miles an hour, would be very hard to row against. But the air is seldom in a state of less motion than that. It is very often moving at the rate of fifteen or twenty miles an hour; sometimes sixty. So, you see, there is a double reason why men cannot fly in the air, as well as paddle on the water."
"If we were only light enough," said Rollo, "to float in the air, then we could fly."
"We could paddle about in it, when it was calm," replied his father, "but that would not be flying."
"Is there anything light enough to float in the air?" said Rollo.
"No," said his father, "I don't think of any visible substance that is."
"What do you mean by visible substance?" said Nathan.
"Why, anything that you can see," replied his father. "There are some other kinds of air, which are lighter than common air, but there is nothing else, so far as I know."
"Why, father, there are clouds. They float, and they are visible, I am sure."
"Yes," said his father. "There is some mystery about the floating of clouds. I don't fully understand it. Clouds are formed of small globules or little balls of water; and water, I should think, whatever the size of the little drops might be, would be heavier than air. And yet they seem to float. If they are large, like rain drops, they fall quickly to the ground. If they are small, like mist, they fall slowly. That I should expect. If they are finer still, like vapor or fog, I should think that they would fall still more slowly; but still I should suppose that they would descend. But they do not appear to descend; they seem to float, nearly at rest; though perhaps all the clouds we see, may be slowly descending all the time, while we do not perceive it."
"The smoke goes up from the top of the chimney," said Rollo.
"Yes," said his father, "there is no difficulty about that. The vapor from a fire is carried up by the warm air, no doubt. Air swells when it is heated, and so becomes lighter, and rises; and the hot air from the top of the chimney carries the vapor up with it, no doubt. After it rises a little way, and becomes cool, it ceases to ascend, but floats away horizontally. Perhaps it begins to descend when it gets cool, though very slowly; and perhaps all clouds are really descending all the time, though too slowly for us to perceive the motion."
"Only," said Rollo, "after a little time, they would get down to the ground."
"Perhaps not," said his father; "for, when they get down nearer the earth, where it is warm, they may be gradually dissolved, and disappear, and thus never reach the earth. I should think they would descend, being composed of globules of water, which, however small, must, I should think, be heavier than air."
"A soap bubble will float in the air," said Rollo.
"I never saw one that would," said his father, "unless it got into a current, which carried it up. A soap bubble—make it ever so thin—shows a tendency to descend, unless you put it out in the open air, where there are currents to carry it up. It descends very slowly, but still it descends. It is heavier than the air. I am not absolutely certain, but I believe there is no visible substance that is lighter than the air; and it is very well for us there is not."
"Why, father?" said Rollo.
"Because, if there were any, they would immediately rise from the earth, and float upwards, till they got up where the air was so light and thin, that they could not go up any higher."
"And so," said Rollo, "we should lose them."
"That would not be all," said his father. "They would float about, above us, and, if there were enough of them, they would form a perpetual cloud over our heads, to keep out the sun, and to make the world dark and gloomy. There seems to have been no way to keep all the solid and visible substances of the earth down upon its surface, but to make them all heavier than the air.
"And thus," continued his father, "all solid substances being heavier than the air, they sink in it, like stones or iron in water. Only those that are very much expanded in surface, sink very slowly, and sometimes almost seem to float."
"What do you mean by expanded, father?" said Nathan.
"Spread out," said his father. "An umbrella, for example, when it is spread out, is said to be expanded; other things are expanded in a little different way. A feather is expanded, that is, it is spread out in fine filaments, which extend, in every direction, into the air, all around the stem of it. Things that are expanded take a great deal of air with them when they descend, and so can only descend slowly."
"And water is expanded in a soap bubble," said Rollo.
"Yes," replied his father, "and there is a great deal of air included in it, which all has to be brought down when the bubble itself descends. And thus, you see, the bubble must descend slowly. Water is expanded, too, in clouds; for, in that case, it is divided into millions of small particles, by which it is spread out over a great deal of air, and cannot descend without bringing a large portion of the air with it. Men have contrived, on this principle, to make an apparatus to prevent being hurt by falling from great heights."
"What is it?" said Rollo.
"Why, it is called a parachute. It is a sort of umbrella; in fact, it is an umbrella, only made very large. It is folded up, and fastened under a balloon, just over the car, which the man is in. Then, if the balloon bursts, or any other accident happens to it, and the man begins to fall, the parachute opens and spreads, and then the man falls very slowly. The reason is, that the parachute takes hold of a large mass of air, and brings it down with it; and so it cannot descend very fast."
A few days after this, Nathan said to Rollo, as they were playing in the yard, that he wished that he had a parachute.
"I know where there is one," said Rollo.
"A parachute," said Nathan; "a real parachute?"
"Yes," said Rollo, "or, what is the same thing, a great umbrella."
"Is that just the same?" said Nathan.
"Yes," said Rollo; "for father said that a parachute was in fact only a large umbrella; and father has got a large umbrella in the closet, and I have a great mind to go and get it for a parachute."
"But you haven't got any balloon," said Nathan.
"O, no matter for that," said Rollo.
"Then how are you going to get up into the air?" asked Nathan.
"Why, I can climb up on the shed, and jump off that, and hold the umbrella over my head."
Just at this moment, Rollo's cousin James came into the yard, and Rollo ran to him, to explain to him about the parachute. After describing to him the construction of it, and its use by men who go up in balloons, he said he was going to get his father's umbrella, which would make an excellent parachute.
"And then," continued he, "I am going to get upon some high place, and jump off, and hold the parachute over my head, and then I shall come down as light as a feather."
"O Rollo," said James, "I don't believe you will."
"Yes I shall," said Rollo: "you see the parachute is expanded, and so brings down a great deal of air with it, and this makes it come very slowly. Air is a real thing, James, and it keeps the parachute back a great deal."
"James and Nathan both ran towards him, thinking that he must be hurt."—Page 37.
So Rollo ran off after the umbrella, very much interested in proving to James, by actual experiment, that the air was a real thing. When he came with it, he was himself inclined to make the first experiment from the low side of the shed. He could climb up, by means of a fence at the corner. James advised him, however, to try it first from the end of a woodpile, which was pretty high, but yet not so high as the shed. James was not quite sure that the experiment would succeed, and he was afraid that Rollo might get hurt.
Rollo said that he was not afraid to jump off the shed. He knew the parachute would bear him up. He did not believe but that he could jump off the house with it; and, at any rate, he could jump off the shed, he knew. He accordingly clambered up, and, taking his station upon the eaves, he spread the umbrella over his head, and then jumped off.
Down he came with great violence; his cap flew off in one direction, and his umbrella rolled away in another, as he had to put out both his hands, to save himself, when he reached the ground. As it was, he came down upon all fours, and in such a way, that James and Nathan both ran towards him, thinking that he must be hurt.
"Did you hurt yourself, Rollo?" said James.
"No," said Rollo, "not much."
"I don't think the umbrella did you much good."
"No," said Rollo, as he got up rubbing his elbows, "it didn't, and I don't see what the reason is."
"You came down just as hard as you would without it."
"Yes," said Nathan, "and he almost broke his back; I don't believe the air is any real thing at all."
The fact was, that the umbrella did do some good. Rollo did not come down quite so hard as he would have done without it. It retarded his descent a little. But it was not large enough to enable him to descend in safety. When his father said that a parachute was in fact only a large umbrella, he meant a great deal larger than Rollo had supposed. A parachute, such as is used with balloons, is a great deal larger than any umbrella that ever was made.
QUESTIONS
What was Nathan's wish, after he had read his father something out of his book? Did he think that he could fly if he had wings? Did his father think so? What deficiency did his father think was even more important than that of wings? Did Nathan think that a boy was stronger than a bird? Is a boy absolutely stronger than a bird? Is he relatively stronger? What is the meaning of relatively stronger? Would a man be strong enough to work wings that were sufficiently large to bear him up into the air? Would there be any great difficulty in constructing wings for him if he were strong enough?
Is any visible substance lighter than air? What would be the consequence if any of the loose substances about the earth's surface were light enough? What are clouds composed of? What difficulty did Rollo's father point out, in regard to their floating in the air? What is a parachute? Describe Rollo's experiment with the umbrella.
CHAPTER III.
VALVE MAKING
One morning, when Rollo awaked, he heard a sharp clicking against the window.
"Nathan," said he, "Nathan, I believe there is a snow-storm."
But Nathan was too sleepy to hear or understand.
Rollo looked up, but there was a curtain against the window, and he could not see very well. He listened. He heard a low, moaning sound made by the wind, and a continuance of the sharp clicking which he had heard at first.
When he had got up, and dressed himself, he found that there was a violent snow-storm. At first he was glad of it, for he liked snow-storms. But then, pretty soon, he was sorry, for it had been winter a long time, and he was impatient for the spring.
After breakfast, he and Nathan read and studied for two hours, under their mother's direction. When they were released from these duties, Rollo proposed to Nathan that they should go out into the shed, and see how the storm came on. There was a large door in the shed, opening towards the street, where they could stand, protected from the wind, and see the drifts of snow.
They accordingly put on their caps, and went. They found that the snow was pretty deep. It was heaped up upon the fence and against the windows; and there was a curious-shaped drift, with the top curled over in a singular manner, running along from the corner of the shed towards the garden gate.
"Ah," says Rollo, "when it clears up, I mean to go and wade through it."
"And I too," said Nathan.
"O Nathan," said Rollo, "it is over your head."
"Hark!" said Nathan; "who is that pounding in the barn?"
"It is Jonas, I suppose," said Rollo. "I mean to go out and see what he is doing."
"How are you going to get there?" said Nathan.
"O, I can put on my boots," said Rollo, "and go right out through the snow."