ROLLO'S

PHILOSOPHY.

[AIR.]

THE ROLLO SERIES IS COMPOSED OF FOURTEEN VOLUMES, VIZ

Rollo Learning to Talk. Rollo Learning to Read. Rollo at Work. Rollo at Play. Rollo at School. Rollo's Vacation. Rollo's Experiments. Rollo's Museum. Rollo's Travels. Rollo's Correspondence. Rollo's Philosophy—Water Rollo's Philosophy—Air. Rollo's Philosophy—Fire. Rollo's Philosophy—Sky.

A NEW EDITION, REVISED BY THE AUTHOR.

BOSTON: PHILLIPS, SAMPSON, AND COMPANY

Entered, according to Act of Congress, in the Year 1855, by PHILLIPS, SAMPSON, & CO., In the Clerk's Office of the District Court of the District of Massachusetts.



PREFACE.

The main design in view, in the discussions which are offered to the juvenile world, under the title of THE ROLLO PHILOSOPHY, relates rather to their effect upon the little reader's habits of thinking, reasoning, and observation, than to the additions they may make to his stock of knowledge. The benefit which the author intends that the reader shall derive from them, is an influence on the cast of his intellectual character, which is receiving its permanent form during the years to which these writings are adapted.

The acquisition of knowledge, however, though in this case a secondary, is by no means an unimportant object; and the discussion of the several topics proceeds accordingly, with regularity, upon a certain system of classification. This classification is based upon the more obvious external properties and relations of matter, and less upon those which, though they are more extensive and general in their nature, and, therefore, more suitable, in a strictly-scientific point of view, for the foundations of a system, are less apparent, and require higher powers of generalization and abstraction; and are, therefore, less in accordance with the genius and spirit of the Rollo philosophy.

As teachers have, in some cases, done the author the honor to introduce some of the preceding works of this class into their schools, as reading books, &c., considerable reference has been had to this, in the form and manner of the discussion, and questions have been added to facilitate the use of the books in cases where parents or teachers may make the reading of them a regular exercise of instruction.



CONTENTS.

CHAPTER I. Page. LOST IN THE SNOW, 9

CHAPTER II. FLYING, 19

CHAPTER III. VALVE MAKING, 40

CHAPTER IV. EXPERIMENTS, 51

CHAPTER V. PRESSURE, 64

CHAPTER VI BALLOONING, 79

CHAPTER VII. PHILOSOPHICAL DISCUSSION, 94

CHAPTER VIII. TASKS, 108

CHAPTER IX. BURNING, 121

CHAPTER X. GRAVITATION, 143

CHAPTER XI. AIR IN MOTION, 158

CHAPTER XII. AIR AT REST, 178



CHAPTER I.

LOST IN THE SNOW.

One pleasant morning, very early in the spring, Rollo's cousin Lucy came to call for Rollo to go on an expedition, which they had planned the day before. It was near the end of March, and the snow had become so consolidated by the warm sun in the days, and the hard frosts at night, that it would bear the children to walk upon it. The children called it the crust; but it was not, strictly speaking, a crust, for the snow was compact and solid, not merely upon the top, but nearly throughout the whole mass, down to the ground.

Rollo and Lucy were going to have an expedition upon the crust. Rollo had a sled, and they were going to put upon the sled such things as they should need, and Rollo was to draw it, while Lucy and Nathan, Rollo's little brother, were to walk along by his side.

Rollo's sled was ready at the back door, when Lucy came. Lucy brought with her some provisions for a luncheon, in a basket. This was her part of the preparation. Rollo got his axe, and one or two boards a little longer than the sled, which he said were to make seats. He also had a tinder-box, and some matches, to enable him to make a fire. When all things were ready, the three children set out together.

Rollo drew the sled, with the boards, the basket, and some other things upon it, all bound together securely with a cord. The load appeared to be considerable in bulk, but it was not heavy, and Rollo drew it along very easily. They were not obliged to confine themselves to the roads and paths, for the snow was hard in every direction, and they could go over the fields wherever they pleased. In one place, where the snow was very deep on the side of a hill, they went right over the top of a stone wall.

It was a cloudy day, but calm. This was favorable. The sky being overcast, kept the sun from thawing the snow; but yet their father told them that probably it would begin to grow soft before they came home, and, if so, they would have to come home in a certain sled road, which Jonas had made that winter by hauling wood. He advised them not to encamp at any great distance from the sled road.

They came at last to a pleasant spot on the margin of a wood, near where there was a spring. The rocks around the spring were all covered with snow, and the little stream, which in summer flowed from the spring, was frozen and buried up entirely out of sight. But the spring itself was open, which Rollo said was very fortunate, as they might want some water to drink.

Here they encamped. Rollo cut some stakes, which he drove down into the snow, and contrived to make a rude sort of table with his boards. He also cut a large number of hemlock branches, which Lucy and Nathan dragged out and spread around the table for them to sit upon. Then Rollo built a fire of sticks, which he gathered in the wood. The ground was covered with snow, so that it would have been very difficult for him to have found any sticks, were it not that some kinds of trees, in the woods, have a great many small branches near the bottom, which are dead and dry. These Rollo cut off, and Lucy and Nathan dragged them out, and put them on the fire when he had kindled it. The fire was a little way from the table, with the carpet of hemlock boughs between.

There was a high hill covered with snow at a little distance, and, after they had eaten their luncheon, Rollo said,—

"O Lucy, we will play go up the mountains. There is a hill for us. That shall be Chimborazo."

"Well," said Lucy, "if you will cut us some long staves."

Accordingly Rollo went into the wood, and selected some tall and slender young trees, about an inch in diameter, and cut two for Lucy, two for Nathan, and two for himself. These he trimmed up smoothly, and each of the children took one in each hand. They played that Rollo was the guide, and Lucy was the philosopher. Nathan was the philosopher's servant. Rollo conducted them safely to the summit; but just after they got there, it began to snow.

The snow descended in large flakes, and Rollo was delighted to see it; but Lucy seemed a little anxious. She said that, if there should be much snow, it would make it hard for Nathan to get home, and she thought that they had better go down the mountain immediately, and set out for home. Rollo was rather unwilling to go, but he allowed himself to be persuaded, and so they all came down the mountain together.

They packed up their things as quick as they could, leaving the fire to burn itself out, only Rollo first piled on all the hemlock branches,—which made a great crackling. The snow began to fall faster. The air was full of the large flakes, which floated slowly down, and lodged gently upon the old snow.

The children went along very successfully for some time, but at length Rollo lost his way. The air was so full of snow-flakes, that he could see only a very little way before him; and the old snow covered the ground, so as to hide all the old marks, and to alter the general aspect of the fields so much, that Rollo was completely lost. He, however, did not say anything about it, but wandered on, Lucy and Nathan wondering all the while why they did not get home; until at length they came across a track in the snow.

"O! see this track," said Rollo. "Here is a track, where somebody else has been along with a sled."

"Yes," said Lucy, "some boys, who have gone out to slide, perhaps."

The track was partly obliterated by the snow which had fallen upon it since the boys that made it had gone along. Rollo wondered whose track it could be. He said that he thought it very probable it was Henry's. Lucy thought that it might be the track of some children, that had gone out to find them.

"At any rate," said Rollo, "we will follow the track a little way, and see what it leads to. Perhaps we shall overtake the boys."

Accordingly Rollo turned along in the track, but Lucy stopped.

"No, Rollo," said she, "we must go the other way if we want to find the boys;—the track is going the other way. But never mind," she added, "I don't want to find the boys; I want to go home; so we will go this way."

Rollo went on, secretly pleased to find the track, for he supposed that by retracing it, as he was doing, it would lead him back home. He had, however, a great curiosity to know who could have made it; and in fact the mystery was soon unraveled.

For, after following the track a short distance, they saw before them a large, dark spot upon the snow, and, on drawing near to it, to see what it was, they found it was the place of their own encampment; and the track which they were following was their own track, leading them back to the mouldering remains of their own fire. They had gone round in a great circle, and come back upon their own course. Rollo looked exceedingly blank and confused at this unexpected termination of the clew, which he had hoped was to have led him out of his difficulty. What he was to do now, he did not know.

The fact, however, that they were lost, was no longer to be concealed; and Lucy proposed that they should go into the woods, where the tops of the trees would act as a sort of umbrella, to keep the snow from falling upon them, and wait there until it stopped snowing; and then the air would be clear, and they could find their way out.

"O," said Rollo, "I can easily make a hut of hemlock branches, and we can go into that for shelter."

"But, Rollo," said Nathan, "how do you know but that it will snow all day? We can't stay in the woods all day."

"No," said Rollo; "when it snows in great flakes, it is not going to snow long. Jonas told me so."

So the children went into the woods, and Rollo began to make his hut; but he was soon interrupted, and the attention of all the children was called off by a little bird, which they saw there, hopping about, and appearing benumbed with cold. After some effort, Rollo succeeded in catching her in his cap.

"We'll carry her home," said Nathan; "we'll carry her home, and show her to mother."

"Yes," said Rollo, "I'll carry her in my cap."

"No," said Lucy, "you must have your cap on your head, or you will take cold. Let me carry her in my hands."

"No," said Rollo, "you will have to lead Nathan. I'll tell you what we will do. We will put her into the basket, for a cage."

Lucy, on the whole, liked this plan, and they accordingly put the bird in the basket, and Rollo contrived to make a cover of boughs, to keep her from getting away.

By the time that this was all arranged, the children found, to their great satisfaction, that it had ceased snowing; and they immediately set out for home. Rollo drew the sled, with the basket and bird upon it, secured as before with the cord; and Lucy led Nathan. They now had no difficulty in finding their way, and soon reached home in safety.

They kept the bird until the next day, and then, as it was mild and pleasant, they let her fly away.

QUESTIONS.

By what process had the snow become hardened at this time? Did Rollo's father expect that it would continue hard till noon? Why not? Did it continue hard? What prevented its melting? How did Rollo get sticks for his fire? What name did he give to the hill which they ascended? What occasioned the difficulty in the way of Rollo's finding his way home? What conversation took place when he found the track? Was this track in the new snow, or in the old snow? How had it become partly obliterated? How did they carry the bird home?



CHAPTER II.

FLYING.

Nathan became very much interested in the bird, and that evening, as his father was sitting by the fire, with a book in his hand, which he had been reading, Nathan came up to him, and said,—

"Father, are you busy now,—thinking, or anything?"

"No," said his father.

"Because," said Nathan, "if you are not, I want to read you something out of my little book."

So Nathan's father took him up into his lap, and Nathan opened his little book, and began to read as follows:—

"'With fins for the water, and wings for the air, And feet for the ground, I could go everywhere.'

"Isn't that funny?" said Nathan.

"Rather funny," said his father.

"I wish I had wings," said Nathan.

"Why?" said his father.

"Why, then I could fly."

"That is not certain," said his father. "There are two difficulties which prevent boys from flying. One is, they have no wings; and the other is, they have not strength to use them."

"O father," said Nathan, "I could use them; I am pretty strong. I can wheel Rollo's wheelbarrow."

His father smiled. "Very possibly," said he; "but I do not think that you would be strong enough to use wings, even if you had them."

"Why, at any rate, I am stronger than a bird," said Nathan.

"Yes," said his father, "you have more actual strength than a bird, but not more in proportion to your size. You are absolutely stronger, but not relatively."

"What do you mean by that?" said Nathan.

"Why, you have actually more strength than a bird,—a robin, for instance; you could hold him so that he could not get away; and you could lift more than he could too. But then you are a great deal larger, and you are not as much stronger than he is, as you are larger. If you are a hundred times as heavy as he, you are not a hundred times as strong. That's what I mean by saying that you are absolutely stronger, but not relatively. That is, you are not as many times stronger, as you are larger and heavier. You are absolutely stronger, but not relatively; that is, in proportion to your size and weight.

"Now I can prove to you," continued his father, "that you would not be strong enough to fly with wings, even if you had them. Suppose there was a pole fastened across the room, and another pole just above it; could you pull yourself up, from one pole to the other, by your hands alone, without touching your feet?—Or a ladder," continued his father,—"it will be better to suppose a ladder. Now, if there was a ladder leaning up against a building, could you climb up on the under side by your hands, drawing yourself up, hand over hand, without touching your feet?"

Here Rollo, who was reading in a little chair at the back part of the room, when his father first commenced the conversation with Nathan, but who had been listening for a few minutes past to what his father had been saying, jumped up, and came across the room to his father, and said,—

"Yes, sir, yes, sir; I can. I have done it often in the barn."

"How high up could you go?" said his father.

"O, almost up to the loft," said Rollo. "Only, you see, father, the rounds are too far up. I can't reach up very well. If they were nearer together, I could climb up so, very well."

"Well," said his father, "a bird, when flying, has to climb up in much the same way. He has to pull himself up by the air, with his wings, just as you do with your hands and arms, by the rounds of the ladder; only the air is not fixed, like the ladder, but constantly gives way under his wing; and so, to make the case the same, you must suppose that the ladder is not firm, but is floating in the air, and sinks down with your weight, so that you have to climb up faster than you pull the ladder down. Do you think you would have strength enough in your arms to do that?"

Rollo and Nathan looked very much interested in what their father was saying, but they both admitted that they could not climb up such ladders as those.

"The air," added their father, "gives way continually under the bird's wing; and yet they have to pull themselves up by it. And this is very hard. They must either have very large wings, and prodigious strength to use them, so as to pull upon the air with very hard and heavy strokes, or else, if they have small wings, they must have strength to strike very quick and often with them.

"The wings of sparrows move so quick, that you cannot count the strokes; and those of humming-birds, which are smaller still, so fast that you cannot see them. They make a hum."

"I could make my wings go so fast," said Nathan; and he began to imitate the flapping of the wings of a bird, with his arms, as rapidly and forcibly as he could.

"So can I," said Rollo; and he made the same motions. "That is as fast as crows' wings move, when they are flying."

"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."



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."

"I wish I could go," said Nathan.

"Well," said Rollo, "I can carry you on my back."

Nathan clapped his hands at this proposal, being doubly pleased at the prospect of both getting into the barn to see what Jonas was doing, and also of having a ride, on the way.

So Rollo put on his boots, while Nathan went and got Rollo his straps, to fasten his pantaloons around them. When all was ready, Rollo sat down upon the step of the door, in order that Nathan might get on easily.

"We'll play that I am a camel," said Rollo, "and that I'm kneeling down for you to get on."

"Do camels kneel down," said Nathan, "when the men want to ride?"

"Yes," said Rollo; and so saying, he rose laboriously, with his heavy burden upon his shoulders. He staggered along with some difficulty, but yet safely, until he came to the great drift; and, after wallowing into the midst of it, he lost his balance, and both camel and driver rolled over together into the snow. The snow got up under Nathan's sleeve, and he began to cry.

"O Nathan," said Rollo, "don't cry. I'll run and get Jonas to come and carry you in."

So Rollo ran into the barn, and called to Jonas to come quick. Jonas laid down his hammer upon the bench, and followed Rollo. He found Nathan in the snow, and took him up in his arms, and carried him into the barn.

As soon as he got him under cover, he brushed the snow off, and told him not to cry. "I've got a fire in the shop," said he, "and you shall see me do my work. I'm mending the bellows."

So he led Nathan through the barn, and thence along under a shed to a sort of shop-room, where there was a large fireplace and a fire. Rollo put on some sticks, which made a great blaze; and so Nathan soon got warm and dry, and forgot all his troubles. Then Jonas sat him up, upon a high stool, near the bench, where he could see him work. He was just drawing out some of the nails, by which the leather of the bellows was nailed to the sides.

"What is the matter with the bellows?" said Nathan.

"The valve is out of order," replied Jonas.

"The valve," repeated Nathan; "what is the valve?"

"The valve is a kind of clapper," said Jonas. "I will show it to you in a few minutes."

So Jonas proceeded to take off the leather from one of the sides of the bellows. There was a hole in one of the sides, but no hole in the other. Nathan had often noticed the hole, but he did not know what it was for.

"What is the hole for?" said Nathan.

"That is to let the air in," said Jonas.

"What do they want the air to come in for?" said Nathan.

"To make wind of," said Jonas.

"Do they make wind out of air?" said Nathan.

"Yes," said Jonas, "they get the bellows full of air, and then blow it out through the nose, and that makes wind."

"Wind is air, put in motion," said Rollo. "I read it in a book."

By this time, Jonas had taken off the leather so far that Nathan could see into the bellows. He saw that there was a little clapper over the hole, in one of the sides of the bellows.

"Is that the valve?" said he to Jonas.

"Yes," said Jonas.

"What is it for?" said Nathan.

"It is to keep the wind from coming out of that hole."

"Why don't they want the wind to go out of that hole?" said Nathan.

"Because," said Jonas, "they want it to go to the fire,—to blow the fire."

"You see," said Rollo, "it can't go out of the hole, and so it has to go out of the long nose, which is pointed towards the fire."

"What makes it go out at all?" said Nathan.

"Why, when we blow the bellows, we press the two sides together, and that presses the wind out. It can't go out of the hole whence it came in, because the clapper stops it up, and so it goes out the long nose, right into the fire, and makes the fire burn."

By this time, Jonas had got the leather off so far, that he could get at the clapper to mend it. He told the boys that it was old and worn out, and he must make a new one.

"How are you going to make it?" said Rollo.

"You'll see," said Jonas, "if you watch me closely."

So Jonas took some leather, and cut out a piece, of an oblong shape, a little wider than the hole, and about twice as long. Then he laid this down over the hole. It covered it entirely. Then he took some small carpet nails, and nailed one of the ends of the leather down to the board. Then Jonas put his hand down under the board, and run one of his fingers up through the hole, and pushed the leather up a little way.

"There," said he to the boys, "you see I have nailed the leather, so that, when it lies down in its place, it covers the hole completely; and yet I can push it up a little with my fingers, so that there will be an opening."

Then Jonas cut a small leather strap, and nailed one end of it down upon one side of the clapper, and the other end upon the other side of the clapper. He put one little carpet nail into each end of the strap. The strap, when it was nailed, passed directly across the clapper or valve. It was not drawn tight across, but it lay upon the clapper loosely. The ends were nailed tight, but the middle rested loosely upon the clapper.

"Now," said Jonas, "I can push the clapper up a little way, but I can't push it far. The strap keeps it from coming up far."

"But why," said Nathan, "do you want it to go up at all?"

"To let the air in," said Jonas. "When I get the leather all nailed on again, I'll show you the whole operation of it."

"And you can be telling us about it in the mean time," said Rollo.

"Well, then," said Jonas, "when I lift up the upper side of the bellows by the handle, to blow, the air comes in by the hole. The clapper lifts up a little way, and lets it in. Then, when I press down the handle again, it presses the air out through the nose, because it can't go back through the valve hole."

"Why not?" said Nathan.

"Because," said Jonas, "the valve falls down over the hole, and stops it up. It is made so as to lift up easily, and then to fall down and cover the hole exactly, and prevent the air going out the same way it came in. So, as it cannot get out by the valve, it has all to go out through the nose. If the nose were stopped up, it could not get out at all."

"And what then?" said Rollo.

"Why, then," replied Jonas, "you could not bring the two sides of the bellows together again. The air between would keep them apart."

"I should like to try," said Rollo.

"Well," said Jonas; "and there are some other experiments you may perform with it too."

At length, Jonas said that he had got the leather all nailed on, and they might try the experiment. He took hold of the nose of the bellows, and held his thumb near the end of it, ready to stop up the hole.

"Now, Nathan, you may take hold of the handles, and pull them apart as if you were going to blow."

Nathan did so. He pulled the handles apart, and held them open.

"Now," said Jonas, "I will stop up the nose, and the valve will close itself; and then you will find that you cannot bring the sides together again."

So Jonas put his thumb over the hole, and told Nathan to blow.

Nathan pressed hard, and the sides came together again, about as easily as usual.

"What!" exclaimed Jonas with surprise. He did not know what to make of the failure of his experiment.

"There must be a leak somewhere," said he. And he took the bellows out of Nathan's hand to look for it.

He found there was a corner, on the side opposite to the one where he had been working, where the leather was open, he having forgotten to nail it down.

"Ah!" said he, "here is the difficulty. When I have nailed this down, we will try again."

"Is that a leak?" said Nathan.

"Yes," said Jonas. "When you worked the bellows, you pressed the air all out through there. I did not know that that was open. Let me nail this down, and then we will begin our experiment regularly."

QUESTIONS.

What was Jonas doing in the shop, when Rollo and Nathan went out to find him? What part of the bellows was out of order? How did he make a new valve? How did he fasten it to its place? Did he nail down only one edge, or both edges? Why did he want the other edge to be left at liberty? How did he prevent its lifting up too far? What was the first experiment which he performed with the bellows, after he had finished the mending? Did it succeed at first? Why not? In working a pair of bellows, where does the air come in? Where does it go out? Why cannot the air escape through the valve where it comes in?



CHAPTER IV.

EXPERIMENTS.

When Jonas had finished nailing down the corner, he said, "Now there are several experiments, which we can perform with the bellows. I will be the professor, and you two shall be my class in philosophy, and I will direct you how to make the experiments.

"First," said Jonas, "you, Rollo, may take hold of the nose of the bellows with your hand, in such a way as to put your thumb over the end of it, to stop it up, and then let Nathan try to blow."

Rollo did so, and Nathan tried to blow. He found that he could open the bellows very easily; but when he attempted to press the sides together again, he could not. He crowded the handle belonging to the upper side down, as hard as he could, but it would not move.

"What makes it do so?" said Nathan.

"The air inside," said Jonas. "We have stopped up all the places, where it could get out. The valve stops itself. Rollo stops the nose with his thumb, and I have nailed the leather down close, about all the sides. And so the air can't get out, and that keeps you from bringing the sides together again."

Nathan tried again with all his strength. The sides came together very slowly.

"They're coming," said he.

"Yes," said Jonas. "They come a little, just as fast as the air can leak out through the little leaks all around."

"I thought you stopped all the leaks," said Nathan.

"Yes," replied Jonas, "I stopped all the real leaks, but still I can't make it perfectly tight. Some air can escape between the leather and the nails all around, and just as fast as it can get out, so fast you can press the sides together, and no faster."

Here Nathan tried again with all his strength; but he could only bring the sides together very slowly.

"Now comes the second experiment," said Jonas. "While Nathan is trying to press the two handles together, you, Rollo, may run your finger into the hole, and push up the valve a little."

Rollo did so. He pushed up the valve a little with his finger, and that allowed the air to escape through the opening. The consequence was, that the bellows collapsed at once under the pressure which Nathan was exerting upon them.

"There," said Jonas, "you see that when the air is kept in, you cannot bring the sides together; but when I let the air out, then they come together easily."

"Yes," said Nathan; "do it again, Rollo."

So they performed the experiment again. Nathan pulled the handles apart wide, while Rollo kept his thumb over the nose, to keep the air from issuing through. Then Nathan tried to press them together; but he could not, until Rollo put his finger under, and pushed up the valve a little, and then they came together again very easily.

"The air is a real thing, I verily believe," said Nathan.

"Yes," said Rollo, "I know it is. And now for the third experiment, Jonas."

"The third experiment," said Jonas, "is this. Turn the bellows bottom upwards, and try to blow."

Nathan did so. He found that he could work the bellows easily—too easily, in fact; but they did not blow.

"Hold your hand opposite the nose, and see if any wind comes," said Jonas.

They did so; there was no wind, or rather scarcely any.

"The reason is," said Jonas, "that, when the bellows are bottom upwards, the valve hangs down off from the hole all the time, and lets the air all out through the hole in the side; and it can come out more easily there than through the nose, and so it don't blow well."

"Well, Jonas," said Rollo, "that's a pretty good experiment; but what is the next? Let me try the next. Nathan, it is my turn."

"The next experiment, which is the fifth,——"

"No, the fourth," said Nathan.

"The fourth, then," said Jonas, "is to prove what I said to you—that the air, which is blown out at the nose of the bellows, really comes in through the valve. Let me see,—I want something to make a smoke."

"Will not paper do?" said Rollo.

"Yes," said Jonas, "here is some brown paper, which will do." So Jonas rolled it up, and told Rollo to set it on fire, and then, when it was well burning, to step on it with his foot, and put the flame out.

Rollo did so, and the paper lay in a heap, making a great smoke upon the hearth, just before the fire.

"Now," said Jonas, "put the bellows upon its edge, by the side of the paper, so as to have the valve near the smoke, and then hold still a minute, until the smoke comes up steadily by the valve."

When this was done, Jonas told Nathan to take hold of the nose of the bellows, to steady it, so that Rollo could blow. He then directed Rollo to lean the bellows over a little towards the smoke, so that the moving side should not rub upon the hearth, when he began to blow.

"Now," he continued, "if you work the bellows, you will see that the smoke will be drawn in through the valve, and then will come out through the nose."

This experiment succeeded perfectly well, only just in the midst of the interest that they felt, in seeing the smoke come pouring out through the nose, they heard a bell ring at the house. They knew at once that this bell was for Rollo and Nathan; and so the two boys jumped up from the hearth, and ran out to see what was wanted. They went through the shed into the barn, and thence on till they came to the great barn door, where they had come in. There Rollo stopped,—for he did not like to go out into the snow,—and asked Dorothy, who was ringing the bell, what she wanted.

"Where's Nathan?" said Dorothy.

"He's here with me," said Rollo. Nathan was coming along, as fast as he could, through the barn.

"Do you want us?" said Rollo.

"No," said Dorothy, "only we did not know where you were. You may stay half an hour more, and then it will be nearly dinner time."

Dorothy then went in, leaving the boys at the great barn door. The door opened in such a direction, that the wind did not blow in; and Rollo and Nathan looked out for some time, watching the falling snow, and listening to the wind, as it roared through the tops of the trees. At last, when they began to think of returning to the shop, Rollo said,—

"O Nathan, let us go and hide, and then Jonas will not know where we are."

"Well," said Nathan, "we will."

The boys accordingly began to look about the barn for a place to hide. It was a large barn, with stalls for oxen and cows, and cribs for horses, and one or two calf-pens. Then there was a granary in one corner, and a tool-room near it, and lofts and scaffolds above. The boys found plenty of places to hide in, and it took them some time to decide which to choose. At last, they found a good warm place, by some bundles of wheat straw, up in the barn chamber; and they amused themselves by choosing out large straws, and making tubes of them to blow through. They called them their bellows.

They entirely forgot that they were hid from Jonas, for nearly half an hour; and then Rollo proposed that they should creep softly down, and see what Jonas was about. So they went down stairs on tiptoe; Rollo first, and Nathan following. They crept softly along to the door leading out into the shed, through which they had to pass in order to get to the shop; and Rollo was going to open this softly, when, to his surprise, he found it fastened.

"Why, Nathan," said he, "this door is fastened."

"How came it fastened?" said Nathan.

"I don't know," said Rollo, "unless Jonas fastened it. I think he must have finished his work, and gone into the house; and so he has fastened this door."

"And now he won't come and find us," said Nathan.

"No," said Rollo, "and we must go out the front door. And I don't care much," he continued, "for it is pretty near dinner time."

The boys then went back to the front door of the barn, and, to their surprise and alarm, found that fastened too.

"What shall we do?" said Rollo; "Jonas has fastened us in." As Rollo said this, his face assumed an expression of great solicitude, and Nathan began to cry.

"Don't cry, Nathan," said he; "we can find some way to get out. But I don't see, I confess, what made Jonas lock us in."

The truth was, that Jonas did not know that the boys were in the barn when he fastened it up. As they did not come back after they had gone to answer the bell, he supposed that they had gone into the house; and when he was ready to come in himself, he shut and fastened the back doors of the barn, as he usually did when he left the shop. He then came around to the front barn door, and although that was on the sheltered side, so that the wind did not blow in, he thought it possible that the wind might change, and so drive the snow in upon the barn floor; and therefore, to make all safe, he thought that he would shut them, too. He accordingly shut the great doors, and put the fid into the staple. The fid is a wooden pin, to be passed through the staple when the doors are shut, to fasten them. The doors cannot be opened again until the fid is taken out.

Rollo went all around the barn, trying to find some place where he could get out; but he could not find any place at all.

"Let us go up stairs," said he, at length, to Nathan.

"O, it will not do any good to go up stairs," said Nathan. "It would kill us to jump out the window."

"I know we can't jump out the window," said Rollo, "but perhaps we can find out some way to get down. O, there is a ladder; I remember now, Nathan, there is a ladder. We can get down from the window by the ladder."

"I shall be afraid to go down the ladder," said Nathan.

"O no," said Rollo, "I will go first, and see if it is safe."

By this time they had reached the barn chamber. There was a window in it, with glass, over the great barn door; but Rollo could not get it open. He told Nathan that, if he could only get it open, and could find a long pole, he could reach it down, and knock the fid out, and so open the great doors. But, with all his efforts, he could not raise the window.

There was another window, which had no glass, but was closed by a wooden shutter, which opened upon hinges like a door. Rollo said he meant to open this window. Now, it happened that this window was upon that side of the barn which was exposed to the wind and storm; and, the moment that Rollo had pushed open the shutter a little way, the wind forced it instantly from his hand, and slammed it back against the side of the barn, with great violence. It almost pulled Rollo himself out of the window.

Nathan looked frightened. Rollo himself looked somewhat astonished at such an unexpected effect; but presently said,—

"Well, Nathan, I rather think that, if you had had hold of that shutter, you would have thought that air was a real thing."

"O, that was the wind, Rollo; that was the wind," said Nathan.

Rollo did not answer, but went to the ladder, which was standing up against the hay-loft. It was a pretty long, but yet a very light ladder; and Rollo and Nathan succeeded, after some difficulty, in getting it down, and in running the end out of the window. When the lower end reached the ground, the upper end was two or three feet above the bottom of the window; so that Rollo could easily get upon it to descend. The wind and storm, which raged with great violence, were somewhat terrifying; but he knew that the ladder was secure, the upper part being confined in the window; and so he resolutely descended. When he had fairly reached the ground, he looked up, with an expression of great satisfaction upon his countenance, and said,—

"There! now, Nathan, for your turn."

But Nathan was afraid to venture; and Rollo himself was half afraid to have him make the attempt. While they were standing in this perplexity, Rollo heard a voice behind him, calling out,—

"Rollo."

Rollo turned, and saw Dorothy standing by the door.

"What are you doing, Rollo?" said Dorothy.

"I am trying to get Nathan out of the barn," said Rollo.

"How came he in the barn?" said Dorothy.

"Why, Jonas locked us in, and I had to come down the ladder; but Nathan is afraid, and I can't get him out."

"Why don't you go to the door, and let him right out?"

"O," said Rollo, laughing, "I never thought of that. Go down, Nathan," he continued, "to the door, and I will go round and knock out the fid."

So Nathan went down, and Rollo, meeting him there, knocked out the fid, and released him from his imprisonment.

QUESTIONS.

What was the first experiment with the bellows, described in this chapter? Why could not Nathan press the two sides of the bellows together, while the nose was stopped? What was the second experiment? What was the effect produced by turning the bellows bottom upwards, as in the third experiment? What was the fourth experiment? What was the use of the smoke of the paper? How were the experiments interrupted? What evidence did Rollo and Nathan have that the air was a real substance, when in the barn chamber?



CHAPTER V.

PRESSURE.

One evening, just after tea, Rollo came to his father, who was sitting by the side of the fire, and said,—

"Father, I wish we could see the air, as we can the water, and then perhaps we could try experiments with it."

"O, we can try experiments with the air as it is," said his father.

"Can we?" said Rollo; "I don't see how."

"We cannot see the air, it is true; but then we can see its effects, and so we can experiment upon it."

"Well, at any rate," said Rollo, "we can't build a dam, and make it spout through a hole, like water."

"No," said his father, "not exactly. In your dam, for instance, when it was full, you had water on one side of the board, and no water on the other; and then, by opening a hole in the board, the water spouted through; but we cannot very well get air on one side of a partition, and no air on the other; if we could, it would spout through very much as the water did."

"Why can't we do that, sir?" said Rollo.

"Because," replied his father, "we are all surrounded and enveloped with air. It spreads in every direction all around us, and rises many miles above us. Whereas, in respect to water, you had one little stream before you, which you could manage just as you pleased. If you were down at the bottom of the sea, then the water would be all around you and above you; and there, even if you could live there, you could not have a dam."

"No, sir," said Rollo, "the water would be everywhere."

"Yes," replied his father, "and the air is everywhere. If, however, we could get it away from any place, as, for instance, from this room, then bore a hole through the wall, the weight of the air outside would crowd a portion of it through the hole, exactly as the weight of the water above the board in your dam crowded a part through the hole in the board."

"I wish we could try it," said Rollo.

"We can try it, in substance," said his father, "in this room; or—no, the china closet will be better."

There was a china closet, which had two doors in it. One door opened into the parlor, where Rollo and his father were sitting. The other door opened into the back part of the entry. Rollo's father explained how he was going to perform the experiment, thus:—

"If we could, by any means, get all the air out of the closet for a moment, then the pressure of the air outside would force a jet of it in through the key-holes of the doors, and the crevices."

"And how can we get the air out?" said Rollo.

"We can't," said his father, "get it all out; but we can get a part of it out by shutting the door quick. The door will carry with it a part of the air that was in the closet, and then the outside air will be spouted in, through the key-hole of the other door. Only we can't see it, as we can the water."

"No," said Rollo; "but I can put my hand there, and feel it."

"A better way," said his father, "would be to hold a lamp opposite to the key-hole, and see if it blows the flame."

Rollo tried the experiment, in the way his father had described. He went into the closet with the lamp. He held the lamp opposite to the key-hole, and pretty near to it, and then he asked Nathan to shut the other door suddenly. Nathan, who was standing all ready by the other door, which was about half open, put his two hands against it, and pushed it to, with all his strength, producing a great concussion.

"O Nathan," said his father, "you need not be quite so violent as that."

"It succeeded, father, it succeeded," said Rollo.

"I'm glad it succeeded," said his father; "but Nathan need not have shut the door with so much force."

"I wanted to drive out all the air," said Nathan.

"I'll show you how to do it," said his father.

Rollo's father accordingly arose, and came to the closet door. He opened the door wide, and then explained to the boys, that the beginning of the movement of the door, when it was wide open, did not drive out any air.

"For," said he, "there is so large a space between the edge of the door and the wall, that the air that is put in motion by the movement of the door, can pass directly round the edge, back into the closet again. It is only when the door is almost shut, when the edge of it comes close to the casing all around, that the movement of the door drives the air out."

Then he took hold of the latch of the door, and put it almost to, very gently. He turned the latch so as to prevent its snapping against the catch, and then pushed it suddenly into its place three or four times, opening the door only a very little way every time.

"Now," said he, "hold the lamp at the key-hole, and watch the flame, while I shut the door two or three times in this way."

Rollo did so, Nathan standing all the time by his side. They observed that the flame of the lamp was driven into the room every time the door was shut; proving that, every time a little of the air was driven out by the door, a little puff rushed in at the key-hole.

"Let us stop up the key-hole," said Rollo, "and then it can't get in."

"Yes," said his father, "there are a great many little crevices all around the closet, where the air can come in."

"Couldn't we stop those up too?" said Rollo.

"No," said his father, "not so as to make the closet air-tight. For, if the crevices could all be stopped exactly, the air would come in through the very wood itself."

"How?" said Rollo.

"Why, there are little pores in wood, that is, little channels that the sap flowed in when the wood was growing, and the air can pass through these."

Here Rollo's father observed that Rollo was looking very intently at the table; and he asked him what he was doing: he said he was trying to find some of the pores.

"You can't see them there," said his father. "St. Domingo mahogany is a very hard and close-grained kind of wood. If it was summer, and you could dig down and get a small piece of the root of the great elm-tree in the yard, you could see the pores and channels there."

After some more conversation on this subject, Rollo asked his father if he could not think of some other experiments for them to try. His father said that he did not just then think of any experiment, but that, if Rollo and Nathan would come and sit down by the fire, he would give them some information on the subject. Rollo's mother said that she should like to hear too. They accordingly waited until she was ready, and then, when all were seated, Mr. Holiday began thus:—

"Air is in many respects much like water."

"Yes," interrupted Rollo, "just like water, only thinner, because, you see——"

"You must not interrupt me," said his father, "unless to ask some question, which is necessary to understand what I say. It is entirely irregular for a pupil, instead of listening to his teacher, to interrupt, in order to tell something that he knows himself."

Rollo's father smiled, as he said this, but Rollo looked rather ashamed. Then his father proceeded:—

"There is one very remarkable difference between them. Water is not compressible by force; but air is."

"What is the meaning of compressible?" said Nathan.

"Compressible things," said his father, "are those that can be compressed, that is, pressed together, so as to take up less room than they did before. Sponge is compressible. A pillow is compressible. But iron is not compressible, and water is not compressible."

"I should think it was," said Nathan; "it is very soft."

"It is very yielding," replied his father, "when you press it, but it is not pressed into any smaller space. It only moves away. If you have a tumbler half full of water, and press a ball down into it, you could not crowd the water into any smaller space than it occupied at first; but, as fast as the ball went down, the water would come up around the sides of the ball."

"But suppose," said Rollo, "that the ball was just big enough to fit the tumbler all around; then the water could not come up."

"And then," said his father, "you could not crowd the ball down."

"Could not a very strong man?" said Nathan.

"No," replied his father, "the water cannot be sensibly compressed. But now, if the tumbler contained only air, and if a ball were to be put in at the top, just large enough to fit the tumbler exactly, and if a strong man were to crowd it down with all his strength, he would, perhaps, compress the air into half the space which it occupied before."

"Perhaps the tumbler would break," said Nathan.

"Yes," replied his father, "and the tumbler will answer only for a supposition; but for a real experiment it would be best to have a cylinder of iron."

"What is a cylinder?" said Nathan.

"An iron vessel, shaped like a tumbler, only as large at the bottom as it is at the top, would be a cylinder. Now, if there was a cylinder of iron, with the inside turned perfectly true, and a brass piston fitted to it——"

"What is a piston?" said Nathan.

"A piston," said his father, "is a sort of stopper, exactly fitted to the inside of a cylinder, so as to slide up and down. It is made to fit perfectly, and then it is oiled, so as to go up and down without much friction, that is, hard rubbing. There is a sort of stem coming up from the middle of the piston, called the piston rod, which is to draw up the piston, and to press it down by.

"Now," continued his father, "if a strong man had a cylinder like this, with a piston fitted to it, and a strong handle across the top of the piston rod, perhaps he might press the air into one half the space which it occupied before. That is, if the cylinder was full of air when he put the piston in, perhaps he could get the piston down half way to the bottom. Then the air would be twice as dense as it was before; that is, there would be twice as much of it in the same space as there was before. It would be twice as compact and heavy. This is called condensing air. The philosophers have ingenious instruments for condensing air.

"If, however, a man condenses air in this way, by crowding down a piston, he does not begin the condensation when the piston begins to descend. The air is condensed a great deal before he begins. All the air around us is condensed."

"How comes it condensed?" said Rollo.

"Why, you recollect that, when you bored a hole through the board in the bottom of your dam, the water spouted out."

"No, father," said Rollo, "we pulled the plug out; Jonas bored the hole."

"Well," said his father, "the water spouted out."

"Yes," said Rollo.

"What made it?" said his father.

"Why, the water above it was heavy, and pressed down upon it, and crowded it out through the hole."

"Yes," said his father, "and the deeper the water, the more heavily it was pressed."

"Yes, sir," said Rollo, "and the farther it spouted."

"Because it was pressed down by the load of such a high column of water."

"Yes, sir," said Rollo.

"Well," replied his father, "it is just so with the air. The air all around us is pressed down by the load of all that is above us. We are, in fact, down at the bottom of a great ocean of air, and the air here is loaded down very heavy."

"How heavy?" said Rollo.

"O, very heavy indeed," said his father.

"Why, air is pretty light," said Rollo.

"Yes," replied his father, "but then the column of it is very high."

"How high?" said Rollo.

"Why, between thirty and forty miles. But it grows thinner and thinner towards the top; so it is not as heavy, by any means, as a column of air would be, thirty miles high, and as dense all the way up as it is here."

"What makes it grow thinner and thinner towards the top?" said Rollo.

"Because," said his father, "that which is near the top, has not as much load of air above it, to press it down."

"And that which is at the top," said Rollo, "has none above it, to press it down."

"No," replied his father.

"And how thin is it there?"

"Nobody knows," said his father.

"What, nobody at all?" said Nathan.

"No, I believe not; at least I do not; and I don't know that any body does."

"How do they know, then, how high it is?" said Rollo.

"The philosophers have calculated in some way or other, though I don't exactly know how. I believe they have ascertained how great the pressure of the air is here at the surface of the earth, and have calculated in some way, from that, how high the air must be to produce such a pressure."

"And how high must it be?" said Nathan.

"Why, between thirty and forty miles," said Rollo; "father told us once."

"And yet," continued his father, "water, thirty or forty feet deep, would produce as great a pressure as a column of air of thirty or forty miles. That is, the air around presses about as heavily, and would force a jet of air through a hole with about as much force, as water would, coming out at the bottom of a dam, as high as a common three-story house."

These explanations were all very interesting to Rollo and to his mother; but Nathan found it rather hard to understand them all, and he began to be somewhat restless and uneasy. At length he said,—

"And now, father, haven't you almost done telling about the air?"

"Why, yes," said his father; "I have told you enough for this time; only you must remember it all."

"I don't think I can remember it quite all," said Nathan.

"Well, then, remember the general principle, at any rate," said his father, "which is this—that we live at the bottom of a vast ocean of air, and that the lower portions of this air are pressed down by the load of all the air above; that, being so pressed, the lower air is condensed,—so that we live in the midst of air that is pressed down, and condensed, by the load of all that is above it; and that, consequently, whenever the air is taken away, even in part, from any place, as you removed some of it from the china closet, the pressure upon the air outside forces the air in through every opening it can find."

"I think that is a little too much for me to remember," said Nathan.

Nathan's father and mother laughed on hearing this, though Nathan did not know what they were laughing at. His father told him that he could not expect him to remember all; and that, to pay him for his particular attention, he would tell him a story.

So he took Nathan up in his lap, and told him a very curious story of a boy, who went about the yard with a little dog upon one of his shoulders, a cat upon the other, and a squirrel on his head. The squirrel was tame.

QUESTIONS.

Why cannot experiments be performed upon the pressure of air, as conveniently as upon the pressure of water? How did Rollo's father contrive to remove a part of the air from the china closet? Where did they expect that the air would be forced into the closet? How were they to make this effect visible? Did the experiment succeed? Suppose the key-hole had been stopped up; where would the air have been forced in? Suppose all the crevices had been closed. Is water compressible? Is air compressible? What is the shape of a cylinder? What is a piston? How might air be compressed by means of a cylinder and piston? What was the general principle which Rollo's father stated, in conclusion?



CHAPTER VI.

BALLOONING.

The next evening, Rollo and Nathan had another conversation with their father, respecting air. When they were all seated, he commenced as follows:—

"I told you yesterday, that air may be compressed by force, while water cannot be. It has another property, which is in some respects the reverse of this. It springs back into its original bulk, when the pressure is removed."

"How?" said Nathan; "I don't exactly understand you."

"Why, you remember what I said about the experiment with the iron cylinder and a piston to fit it."

"Yes, sir," said Rollo.

"What was the experiment?" said his father.

"Why, if a man were to press the piston down hard, he could crowd the air all into the lower half of the cylinder."

"Yes," replied his father. "Now, the property I am going to tell you about this evening is this—that, if the man lets go of the piston rod, the air that is condensed into the bottom of the cylinder, will spring up, and force the piston up again. This property is called elasticity. It is sometimes called the expansive force of the air. For it is a force tending to expand the air, that is, to swell it out into its original dimensions. This is another great difference between air and water.

"Now, as all the air around us," continued Rollo's father, "is pressed down very heavily, and is condensed a great deal, it is all the time endeavoring to expand; and it would expand, were it not that the great burden of the air above it keeps it condensed. But water is not compressed, and has no tendency to expand. The water of Rollo's dam, for instance, had all the weight of the atmosphere resting upon it, but it did not compress it at all, and so it did not tend to expand.

"And now," said his father, "I cannot perform any experiment, to show you that air tends strongly to expand or swell out into a great space, while water does not; but I can make a supposition, which will illustrate it. Suppose we had a large, but very thin, glass bottle, filled with water, and put down upon the floor in the middle of this room. Suppose, also, that we had another bottle, of the same size and shape, filled with air, and we put that down upon the floor by the side of the other; both bottles being stopped very tight. Now, if we could by any means suddenly take away all the air from the room, so that there should be nothing around the bottles, then the bottle of water would remain just as it is, for the glass would have nothing to support but the weight of the water, and it would be strong enough for that. But the bottle of air would fly all to pieces; for that would not rest quietly, like the water, satisfied with the space which it already has, and only pressing with its own weight upon the sides of the glass; but it would immediately expand with so much force as to break the thin glass all to pieces."

"Would it!" exclaimed Rollo and Nathan together. "And would it make a loud noise?"

"Yes," replied their father, "I presume it would make a loud explosion; that is, if the air in the room around it could by any means be all at once and suddenly removed.

"And so you must remember," he continued, "that there are two very remarkable differences between air and water. Air may be condensed by pressure, and, as it exists all around us, is greatly condensed by the pressure of the air above, and it may be compressed more. And air is expansive, while water is not. Whenever the pressure upon it is removed, it suddenly expands, or spreads out in all directions."

"O dear me!" said Nathan, with a sigh.

"What is the matter?" said his father.

"Why, I can't understand it very well."

"Can't you?" said his father. "Well, I must admit that you are rather too young to study pneumatics."

"Pneumatics?" repeated Rollo.

"Yes," said his father; "that is the name of this science."



"What, the science of air?" said Rollo.

"Yes," said his father, "the science which treats of air, and of all other compressible and expansive fluids. But let me think. I must try to tell you something which Nathan can understand and be interested in. If I had a very light feather, I could let him perform an experiment."

"Would a little down do?" said Rollo's mother.

"Yes," replied his father, "that would be better than a feather."

Mrs. Holiday then went and brought a little down, and handed it to Rollo's father. Now, there was a lamp upon the table, of a peculiar kind, called a study lamp. It had a glass tube, called a chimney, around the wick, and consequently around the flame itself, being round, like a ring.

Rollo's father told Nathan to hold the down over the top of this glass chimney, and then to let it go.

Nathan did so. The little tuft of down was wafted up into the air, quite high above the lamp, and then it sailed slowly away, and fell down upon the table.

"I know what makes it rise," said Rollo. "It is the heat. The heat makes it rise."

"Do you think so?" said his father. "Then take the down, and lay it gently upon the hearth, before the fire, as near as you can."

Rollo did so. He had to take his hand away very quick, for it was quite hot there. The little tuft remained quietly upon the hearth where he placed it.

"There," said his father, "is not that a hotter place than it was over the lamp?"

"Yes, sir," said Rollo.

"Then, if it was heat that made it rise, why does not it rise now?"

Rollo could not tell.

"I will tell you how it was," said his father. "Heat makes air more expansive. When air is heated, it swells; when it is cool, it shrinks again. Now, if it swells, it becomes lighter, and so it is buoyed up by the heavier air around it; just as wood at the bottom of the sea would be buoyed up, and would rise to the surface of the water. Now, the heat of the lamp heats the air that is in the glass chimney, and swells it. This makes it lighter; and so the air around it, which is heavier, buoys it up, and it carries up the feather with it."

"No, the down, father," said Nathan.

"Yes, the down," said his father.

"Then it seems to me, after all," said Rollo, "that it is the heat which makes it rise."

"Yes," said his father, "it does, indirectly. It expands the air; that makes it lighter; then the heavy air around it buoys it up, and, when it goes up, it carries up the down. So that it is not strictly correct to say, that the heat carries it up. The heat sets in operation a train of causes and effects, the last of which results in carrying up the feather.

"Now," continued his father, "there is always a stream of air going up, wherever there is a lamp, or a fire, or heat, which heats the air in any way. The expanded air from a fire goes up chimney. The cool and heavy air in the room and out of doors crowds it up."

"The air out of doors?" said Rollo. "How can that crowd it up?"

"Why, it presses in through all the crevices and openings all around the room, and crowds the light air up the chimney. All the smoke is carried up too with it, and it comes pouring out at the top of the chimney all the time."

"You can see that the air presses in at all these crevices," continued Rollo's father, "by experiment."

"What experiment is it?" said Rollo; "let us try it."

"I will let Nathan try it," said his father, "and you may go with him and see the effect. First," he continued, "you see by the smoke, that the air really goes up the chimney; and I will show you that other air really crowds into the space, from other parts of the room."

So he took a lamp from the table,—not the study lamp; it was a common lamp,—and held it at various places in the opening of the fireplace, by the jambs and near the upper part; and Rollo and Nathan saw that the flame, in all cases, was turned in towards the chimney.

"Yes," said Rollo, "I see it is drawn in."

"No," said his father; "strictly speaking, it is not drawn in; it is pressed in, by the cool and heavy air of the room."

"I thought," said Rollo's mother, "that the chimney drew the air from the room into it."

"That is what is generally said," replied Mr. Holiday, "but it is not strictly true. The common idea is, that the hot air rises in the chimney, and so draws the air from the room to supply its place; but this is not so. In the first place, nothing can rise unless it is forced up. The lightest things have some weight, and would, if left to themselves, fall. The hottest and lightest air in a chimney would fall to the earth, if there was no cooler and heavier air around it, to force it to rise;—just as the lightest cork, which would rise very quick from the bottom of the sea, would fall back again very quick, if the water was not there.

"Remember, then, Nathan and Rollo, that, when a fire is built in a fireplace, so as to warm the air in the chimney, it makes this air not so heavy; and then the cool air all around it in the room and out of doors, presses in, and crowds under the light air, and makes it ascend."

"But, father," said Nathan, "you said I might perform an experiment."

"Very well, I am ready now. Take the lamp, and carry it around the room, and hold it opposite any little opening you can find."

"I can't find any little openings," said Nathan.

"O yes," said his father; "the key-hole of the door is a little opening, and there is a narrow crevice all around the door; and you will find little crevices around the windows. Now, hold the lamp opposite any of these, and you will see that the air presses in."

So Nathan went with the lamp, Rollo following him, and held the lamp opposite to the key-hole, and the crevices around the door and windows; only, when he came to the window, his father told him to be very careful not to set the curtain on fire.

Rollo wanted Nathan to let him try it once; and so Nathan gave him the lamp. He said he meant to make a crevice; and so he pushed up the window a very little way, and held the lamp opposite to the opening. The air pressed the flame in towards the room, in all cases.

"People commonly say, that it is drawn in," said his father, "but that is not strictly correct; it is really pressed in. There is no power of attraction, in the air that is in the room, to draw in the air that is out of doors, through the crevices; but the air that is out of doors, is so heavy, that it presses in, and crowds the warm and light air up the chimney.

"And now," said his father, "I cannot tell you anything more this evening; but, if you remember this, I will give you some further instruction another time."

"Well, sir," said Nathan, "only I wish you would tell me a little story, as you did last evening. Have not I been still?"

His father had noticed, that he had been very still and attentive, but did not think before, that it was in expectation of being rewarded with a story.

"Well," said his father, "I will tell you a story, or give you a little advice. How should you like a little advice?"

"Well, father, a little advice; just which you please."

"I advise you, then,—let me see,—what shall I advise you?—No, on the whole, I will tell you a story. Once there was a man, and he was a philosopher. He understood all that I have been explaining to you about the air being light when it was hot. So he got some very thin paper, and made a large paper bag. He cut the paper very curiously, and pasted it together at the edges in such a way, that the bag, when it was done, was round, like a ball; and it had a round opening at the bottom of it. In fact, it was a large paper ball."

"How large was it?" said Nathan.

"It was so large, that, when it was swelled out full, it would have been higher than your head."

"O, what a large ball!" said Nathan. "But what was it for?"

"Why, the man thought, as hot air is lighter than cool air, and floats up, that perhaps, if he could fill his paper ball with hot air, it would go up too."

"And did it?" said Nathan.

"Yes," said his father. "He filled it with hot air; and the hot air was so light, that it rose up and carried the paper ball with it."

"How did he get the hot air into it?" said Rollo.

"Why, he held it over a little fire, with the mouth down. Then the hot air from the fire went up into the ball, and swelled it out full."

"How high did it go?" said Nathan.

"O, it soared away," said his father, "away up into the air, very high; until at length it got cool, and then it came down."

"I should like to see such a ball as that," said Nathan.

"Such a ball as that is called a balloon," said his father.

"I wish I could see a balloon," said Nathan.

QUESTIONS.

What is the important difference between air and water, which was explained in the last chapter, and mentioned in this? Does the air tend to expand again after it is compressed? What is this property of the air called? Is the air around us already condensed, or is it in its natural state? What causes it to be condensed? Suppose a thin glass vessel were to be filled with air, and another with water, and the air suddenly removed from the room around them; what would be the effects? What effect does heat have upon the expansibility of air? How may this effect be made to appear over a lamp? In a chimney? What was the story which Rollo's father told Nathan?



CHAPTER VII.

PHILOSOPHICAL DISCUSSION.

Some time after this, Rollo, and Nathan, and James, were playing in the shed, one pleasant morning in the spring. They were building with sticks of wood, which they piled in various ways, so as to make houses. They took care not to pile the wood, in any case, higher than their shoulders, for Jonas had told them that, if they piled the wood higher than that, there would be danger of its falling down upon them.

After some time, Rollo went into the house a few minutes, and James and Nathan went to the open part of the shed, and began to look out of doors. The sun was shining pleasantly, but the ground was wet, being covered with streams and pools of water, and melting snow-banks.

"What a pleasant day!" said James. "I wish it was dry, so that we could go out better."

"I wish we could fly," said Nathan, "for it is very pleasant up in the air."

"I wish we had a balloon," said James. "If we had a balloon, we could go up in the air, easier than to fly."

"O James," said Nathan, "you could not get into a balloon if you had one."

"Why not?" said James.

"Because," said Nathan, "it would not be big enough."

"Why, Nathan," said James, "a balloon is bigger than this house."

"O James, it is not higher than my head."

"It is," said James, "I know it is. I have read about balloons bigger than a house."

"And my father," said Nathan, putting down his foot in a very positive air, "my father told me himself, that a balloon was about as high as my head."

The boys disputed some time longer upon the subject, and finally, when Rollo came out of the house, they both appealed to him very eagerly to settle the dispute.

"Isn't a balloon higher than Nathan's head?" said James.

"Is it as high as a house?" said Nathan.

"Why, I know," said Rollo, "that a man made a balloon once about as high as Nathan's head, because my father said so; but perhaps it was a little one."

"Yes," said James, "I know it must be a little one; for balloons are big enough for men to go up in them."

"O James," said Nathan, "I don't believe it. Besides, the fire would burn 'em."

"What fire?" said James.

"The fire they burn under the balloons, to make the air hot," said Nathan.

"I don't believe they have any fire," said James.

Just then Nathan, happening to look around, saw Jonas standing behind them; he had just come out of the house, and was going out to his work. Hearing the boys engaged in this dispute, he stopped to listen. The boys both appealed to Jonas.

Jonas heard all that they had to say, and then replied,—

"I cannot tell you much about going up in a balloon, but I can tell you something about getting along pleasantly down here upon the earth, which I think may be of service to you."

"What is it?" said James.

"Why, that you will neither of you get along very pleasantly until you can bear to have any body else mistaken, without contradicting them. James, you think Nathan is mistaken about the size of a balloon, do you?"

"Yes, I know he is," said James.

"Well," said Jonas, "now why not let him remain mistaken?"

"Why,—I don't know," said James.

"He isn't willing to be convinced, is he, that a balloon is as big as a house?"

"No," said James, "he is not."

"Then why don't you let him remain unconvinced? Why should you insist on setting him right, when he don't want to be set right?"

"And you, Nathan, suppose that James is mistaken, in thinking that the balloon is so big."

"Yes," said Nathan, "and that men can get into it, and go up in the air."

"Well, now, if he wants to believe that balloons are so big, why are you not willing that he should? Why should you insist upon it that he should know that they are smaller?"

"Because I know," said Nathan, very positively, "that they are small; and, besides, the paper would not be strong enough to bear a man."

"I did not ask you," said Jonas, "why you believed that men could not go up in balloons, but why you were so anxious to make James believe so. Why not let him be mistaken?"

"Why—because," said Nathan.

"You see, Nathan," continued Jonas, "the world is full of people that are continually mistaken; and if you go about trying to set them all right by disputing them, you'll have a hard row to hoe."

"A hard what?" said Nathan.

"A hard row to hoe," repeated Jonas. "It's never of any service to attempt to convince people that don't want to be convinced; especially if they are wrong."