Rollo's Philosophy Part 2

"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 b.a.l.l.s 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 ma.s.s 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."

[Ill.u.s.tration: "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.