Rollo's Philosophy. [Air]

g, as his father was sitting by the fire, with a book in his ha

busy now,-think

aid his

are not, I want to read you so

his lap, and Nathan opened his littl

the water, and w

ground, I could

t funny?"

nny," said

ad wings,"

said hi

en I cou

culties which prevent boys from flying. One is, they have no

d use them; I am pretty strong.

"but I do not think that you would be stron

I am stronger than

th than a bird, but not more in proportion to your s

mean by that?

r, 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

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 supp

st commenced the conversation with Nathan, but who had been listening for a few minutes past to

I can. I have done

ould you go?"

er, the rounds are too far up. I can't reach up very well. I

nds 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 i

at their father was saying, but they both admitted

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

the strokes; and those of humming-birds, which are smaller

he began to imitate the flapping of the wings of a bi

e same motions. "That is as fast as cr

hereas you only move hands and arms. If you had great wings, as lo

ould they be

haps as big as the to

s big as that. The crow's wings are not longer than hi

rger 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 woul

mselves up by the air," said Nathan. "I di

omething real,"

ithout moving their wi

ather, "and so ha

!" repea

one fly?" s

ou never see a stone fly through

Rollo, "when so

one in motion, it will continue in motion for so

w birds," said Nathan; and he

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 u

d seen the swallows sailing swiftly round and round in the

ay of a boy's flying, is not the want of wings, but the want

t?" said

n 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 appl

rong enough to paddle themselves along

pon it. But air cannot support them; and, of course, a great part of the effort which they would make, would be required to

water is sometimes in rapid motion.

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 f

h," said Rollo, "to float in

n it was calm," replied his fathe

ght enough to float i

I don't think of any vis

by visible subst

here are some other kinds of air, which are lighter than

louds. They float, and th

vier 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 woul

rom the top of the c

ises; 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 horizont

r a little time, they wou

e gradually dissolved, and disappear, and thus never reach the earth. I should think they would descend

ill float in the

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 tha

ther?" s

the earth, and float upwards, till they got up where the air

Rollo, "we sh

rm 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

air, they sink in it, like stones or iron in water. Only those that are very

by expanded, fat

ittle different way. A feather is expanded, that is, it is spread out in fine filaments, which extend, in every direction, into the air,

anded in a soap b

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 ca

it?" sa

r 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

ollo, as they were playing in the yard,

there is one

said Nathan; "a

, what is the same thi

t the same?"

only a large umbrella; and father has got a large umbrella in the

t got any ballo

r for that,"

ing to get up into t

hed, and jump off that, and h

about the parachute. After describing to him the construction of it, and its use by men who go up in

igh place, and jump off, and hold the parachute over my

James, "I don't

ngs down a great deal of air with it, and this makes it come very slowly.

towards him, thinking tha

ned 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

e but that he could jump off the house with it; and, at any rate, he could jump off the shed, he knew. He accordin

, as he had to put out both his hands, to save himself, when he reached the ground. As it was, he came down

yourself, Roll

d Rollo,

the umbrella di

bbing his elbows, "it didn't, and

st as hard as you

t broke his back; I don't believe

ttle. 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 mean

STI

n 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 str

the earth's surface were light enough? What are clouds composed of? What difficulty did Rollo's father point o

to co