use," replied Jonas, "there was not air enough."

"There was air in the stump," said Rollo.

"Yes," replied Jonas, "but all the life of it was consumed by the first
piece of birch bark which you put in."

"The life of it?" said Rollo.

"Yes," replied Jonas; "what do you suppose it is, that makes anything
burn?"

"Why, it burns itself," said Rollo.

"No," answered Jonas; "the air makes it burn: it must have good air
around it, or else it won't burn. There is something in the air which I
call the life of it; this makes the fire burn. But when this is all
gone, then that air will not make fire burn any longer. It will only
burn in good fresh air, which has got the life in it."

"I thought fire would burn in any kind of air," said Rollo.

"No," replied Jonas; "you can see if you stop up the hole I made here."

Jonas then took a piece of turf from the field, and put it before the
hole, and crowded it in hard with the heel of his boot. Rollo observed
that the fire was almost immediately deadened.

"Now," continued Jonas, "light a small piece of birch bark, and put it
in."

Jonas helped Rollo fasten a small piece of bark upon the end of a stick,
and then Rollo set it on fire, and held it down a little way into the
stump. It burned very feebly.

"See," said Jonas, "how quick it is stifled."

"Yes," replied Rollo, "it goes out almost directly."

"You see," said Jonas, "that the fire already in the stump consumes all
the goodness of the air; and I stopped up the hole, so that no fresh air
can come in."

"Why doesn't it go in at the top?" said Rollo.

"It does a little," said Jonas, "but not much, because the hollow of the
stump is already full of bad air, and there is nothing to make a
current. When there is an opening below, then there is a current up
through."

"Yes," said Rollo, "it is just like a chimney."

"Yes," replied Jonas, "the stump is the chimney, and the hole is the
fireplace."

"And the air in the stump," said Rollo, "gets hot, and so the cold air
all around is heavier, and so it crowds down under it, and buoys the hot
air up out of the stump. My father explained it all to Nathan and me."

Rollo then wanted to open the hole again, to see if the effect would be
as he had described.

Then Jonas pulled away the turf from the hole at the bottom of the
stump, and Rollo observed that the fire brightened up immediately.

He then held a smoking brand near the hole, and he saw that the smoke
was