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."
[Illustration: "James and Nathan both ran towards him, thinking that he
must be hurt."--Page 37.]
So Rollo ran off after the umbrella, very much interested in proving to
James, by actual experiment, that the air was a real thing. When he came
with it, he was himself inclined to make the first experiment from the
low side of the shed. He could climb up, by means of a fence at the
corner. James advised him, however, to try it first from the end of a
woodpile, which was pretty high, but yet not so high as the shed. James
was not quite sure that the experiment would succeed, and he was afraid
that Rollo might get hurt.
Rollo said that he was not afraid to jump off the shed. He knew the
parachute would bear him up. He did not believe but that he could jump
off the house with it; and, at any rate, he could jump off the shed, he
knew. He accordingly clambered up, and, taking his station upon the
eaves, he spread the umbrella over his head, and then jumped off.
Down he came with great violence; his cap flew off in one direction, and
his umbrella rolled away in another, as he had to put out both his
hands, to save himself, when he reached the ground. As it was, he came
down upon all fours, and in such a way, that James and Nathan both ran
towards him, thinking that he must be hurt.
"Did you hurt yourself, Rollo?" said James.
"No," said Rollo, "not much."
"I don't think the umbrella did you much good."
"No," said Rollo, as he got up rubbing his elbows, "it didn't, and I
don't see what the reason is."
"You came down just as hard as you would without it."
"Yes," said Nathan, "and he almost broke his back; I don't believe the
air is any real thing at all."
The fact was, that the umbrella did do _some_ good. Rollo did not come
down quite so hard as he would have done without it. It retarded his
descent a little. But it was not large enough to enable him to descend
in safety. When his father said that a parachute was in fact only a
large umbrella, he meant a great deal larger than Rollo had supposed. A
parachute, such as is used with balloons, is a great deal larger than
any umbrella that ever was made.
QUESTIONS.
What was Nathan's wish, after he had read his father something
out of his book? Did he think that he could fly if he had
wings? Did his father think so? What deficiency did his father
think was even more important than that of wings? Did Nathan
think that a boy was stronger than a bird? Is a boy _absolutely_
stronger than a bird? Is he _relatively_ stronger? What is the
meaning of _relatively_ stronger? Would a man be strong enough
to work wings that were sufficiently large to bear him up into
the air? Would there be any great difficulty in constructing
wings for him if he were strong enough?
Is any visible substance lighter than air? What would be the
consequence if any of the loose substances about the earth's
surface were light enough? What are clouds composed of? What
difficulty did Rollo's father point out, in regard to their
floating in the air? What is a _parachute_? Describe Rollo's
experiment with the umbrella.