as 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,