e downy tuft?
What experiments did they perform with it? Where did they find
that the air came in which crowded the warm air up the chimney?
What experiments did they perform when the door was opened?
Which way did they find that the current of air was setting at
the lower part of the door-way? Which way did the current set at
the upper part of the door-way? What did Rollo write in his
exercise? What was written in Nathan's exercise?

CHAPTER IX.

BURNING.

After the snow had all gone off, and the ground was dry, Jonas piled up
a heap of stumps, roots, and decayed logs, in a field, not far from the
brook, and one sunny afternoon he and Rollo went down to set the heaps
on fire.

Jonas set one on fire, and then he told Rollo that he might set another
on fire. After this, Jonas employed himself in gathering up sticks,
bushes, roots, and other such things that lay scattered about the field,
and putting them upon the fires, while Rollo amused himself in any way
he pleased.

After a time, Rollo found, on the margin of the field, near the edge of
a wood, an old stump, taller than he was, much decayed. There was a hole
in the top. Rollo climbed up so that he could put a stick in, and run it
down, to see how far down the hole extended. He found that it extended
down very near to the bottom.

Then Rollo called out to Jonas, with a loud voice, saying,--

"Jonas, I have found a hollow stump here. It is hollow away down to the
bottom. May I build a fire in it?"

"Yes," said Jonas, "if you can."

Rollo accordingly went to the nearest fire, and got a quantity of birch
bark, which he had collected there to aid him in kindling his fires. He
lighted one piece, and put it upon the end of a stick, and carried it to
the stump, with the rest of the birch bark in the other hand.

Rollo then spent some time in fruitless attempts to make some lighted
birch bark go down into the stump, and burn there. He succeeded very
well in getting pieces completely on fire; but, after they were dropped
into the hole, they would not burn. Rollo could not think what the
reason could be.

At last he called Jonas to come and help him set the stump on fire.

Jonas said that he did not think that it could be set on fire.

[Illustration: "'Jonas, I have found a hollow stump here,' said Rollo,
calling with a loud voice."--Page 122.]

"Why not?" said Rollo.

"Because," said Jonas, "it is so wet."

"Yes, but, J