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