Rollo's Museum

nversation with their father, respecting air. Whe

not be. It has another property, which is in some respects the reverse of t

n; "I don't exact

out the experiment with the iron

ir," sa

experiment?" s

n down hard, he could crowd the air al

d 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

d; 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. Th

ther 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 s

and Nathan together. "And

loud explosion; that is, if the air in the room around i

y 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

said Nathan

matter?" sa

understand i

ll, I must admit that you are rat

cs?" repe

her; "that is the n

led slowly a

ience of air?

xpansive fluids. But let me think. I must try to tell you something which Nathan can understa

down do?" said

ther, "that would be

as a lamp upon the table, of a peculiar kind, called a study lamp. It had a glass tube, called

the down over the top of this gla

p into the air, quite high above the lamp, and then

" said Rollo. "It is the he

ake the down, and lay it gently upon the he

ick, for it was quite hot there. The little tuft r

is not that a hotter place

ir," sa

that made it rise, why

ould no

r, 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 la

n, father,"

own," said

ll," said Rollo, "that it is

oys it up, and, when it goes up, it carries up the down. So that it is not strictly correct to say, that the heat carrie

is a lamp, or a fire, or heat, which heats the air in any way. The expanded air from a

?" said Rollo. "How c

om, and crowds the light air up the chimney. All the smoke is carried up to

in at all these crevices," continu

is it?" said Roll

First," he continued, "you see by the smoke, that the air really goes up the chimney; and

at various places in the opening of the fireplace, by the jambs and near the upper part;

llo, "I see it

g, it is not drawn in; it is pressed in,

her, "that the chimney drew t

ot 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,

he air in the chimney, it makes this air not so heavy; and then the cool air all around it in

han, "you said I might

and carry it around the room, and hold it

y little opening

narrow crevice all around the door; and you will find little crevices around the windo

the key-hole, and the crevices around the door and windows; only, when he came to

meant to make a crevice; and so he pushed up the window a very little way, and held the

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 cre

ing more this evening; but, if you remember this, I

ou would tell me a little story, as you

l and attentive, but did not think before, that it

ou a story, or give you a little advice

ittle advice; just

ve 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

was it?"

was swelled out full, it would h

ll!" said Nathan. "

ool air, and floats up, that perhaps, if he could f

it?" sa

ot air; and the hot air was so light, that i

the hot air into

mouth down. Then the hot air from the fire w

id it go?"

ay up into the air, very high; until at l

see such a ball as

t is called a ballo

d see a balloo

STI

s 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

to co