carried in, in a very strong current, by the cool air, which was
pressing into the hole.

"Yes," said Rollo, "it operates just like a fireplace."

"So you see," continued Jonas, "that whenever you build a fire, you must
see to it, that there is an opening for air to come up from underneath
it. And it must be good fresh air too."

"What is it in the air, which makes the fire burn?" said Rollo.

"I don't know what the name of it is," said Jonas; "it is some part of
the air, which goes into the fire, and is all consumed, and then the
rest of the air is good for nothing."

"Isn't it good for anything at all?" asked Rollo.

"I don't know," said Jonas, "how that is; only I know that it isn't good
for anything for fires. It stifles them."

"I should like to know what the name of that part of the air is, which
is good for fires," said Rollo.

"I knew once," said Jonas, "but it was a hard word, and I have forgotten
it."

"I mean to ask my father," said Rollo.

Jonas then went on with his work, gathering up everything that he could
find around the field, to put upon the fires. Rollo amused himself by
putting large rolls of birch bark around the end of a stick, and then,
after setting them on fire, holding them over the fires, which Jonas was
making, to see how soon the flame was extinguished: then he would draw
them away, and see them revive and blaze up again in the open air. At
last, he called out to Jonas, once more.

"Jonas," said he, "I have found out what makes the blaze go out. It is
the smoke. I don't believe but that it is the smoke."

"No," replied Jonas, "it is not the smoke. I can prove that it is not."

So Jonas came up to the fire where Rollo was standing, and pointed out
to Rollo a place, over a hot part of it, where there was no smoke,
because the fire under it burned clear, being nearly reduced to coals.
He told Rollo to hold his blazing bark there. Rollo did so, and found
that it was extinguished at once, and as completely, as it had been
before, when he had held it in a dense smoke.

"Yes," said Rollo, "it isn't the smoke. But perhaps it is because it is
so hot."

"No," said Jonas, "it isn't that. It is a difference in the air. They
sometimes collect different kinds of air in glass jars, and then let a
candle down in, and see whether it will go out."

"And will it go out?" said Rollo.

"That depends upon what kind of air it is," said Jonas. "They all look
clear, just as if there was nothing