"Now, as much warm air must go out," said she, "as there is cold air coming in; but I don't believe that you and Rollo can find out where it goes out."
Rollo looked all around the room, but he could not see any opening, except the chimney and the door, and the little crevices, which he had observed about the finishing of the room. He said he could not find any place.
His mother then told him to hold his tuft down near the bottom of the door-way. He did so, and found that the current of air was there very strong. The tuft swung into the room very far.
"Now hold it up a little higher," said his mother.
Rollo obeyed, and he found that it was still pressed in, but not so hard.
"Higher," said his mother.
Rollo raised it as high as he could reach. The thread was of such a length, that the tuft hung about opposite to his shoulder. The tuft was still pressed in, but not nearly as far as before.
"So you see," said his mother, "that the air pours in the fastest at the lowest point, where the weight and pressure of the air above it are the greatest; just as, in your dam, the water from the lowest holes spouted out the farthest."
"Yes," said Rollo, "it is very much like that."
"Now," continued his mother, "you see that a great deal of air comes in, and if you look up chimney, you will see that there is scarcely room for so much to go up there;-and yet just as much must go out as comes in.
"Get the step-ladder," said his mother, "and stand up upon it, and so hold your tuft in the upper part of the door-way."
There was in the china closet a small piece of furniture, very convenient about a house, called a step-ladder. It consisted of two wooden steps, and was made and kept there to stand upon, in order to reach the high shelves. Rollo brought out the step-ladder, and placed it in the door-way, and then ascended it. From the top he could reach nearly to the top of the door; but then, as his tuft was at the end of the thread, it hung down, of course, some little distance below his head.
"Why, mother," said Rollo, "it goes out."
"Yes," repeated Nathan, "it goes out."
In fact, Rollo found that the tuft, instead of swinging into the room, was carried out towards the entry.
"You have found out, then," said his mother, "where the hot air of the room goes to, to make room for the cold air, that comes in from the entry."
"Yes, out into the entry," said Rollo.
"Through the upper part of the door," said his mother. "Suppose the entry were full of water, and the parlor full of air, and the door was shut, and the door and the walls were water-tight. Now, if you were to open the door, you see that the water, being heavier, would flow in, through the lower part of the door-way, into the parlor, and the air from the parlor would flow out, through the upper part of the door-way, into the entry. The water would settle down in the entry, until it was level in both rooms, and then the lower parts of both rooms would be filled with water, and the upper parts with air."
"Yes, mother," said Rollo.
"And it is just so with warm and cold air. If the parlor is filled with warm air, made so by the fire, and the entry with cold air, and you open the door, then the cold air, being heavier, will sink down, and spread over the floor of both rooms; and the warm air, being light, will spread around over the upper parts of both rooms; and this will make a current of air, in at the bottom of the door-way, and out at the top.
"Now," continued his mother, "let me recapitulate what I have taught you."
"What do you mean by recapitulating it?" said Nathan.
"Why, tell you the substance of it, so that you can write it down easier."
"O, I can write it now," said Rollo; "I remember it all."
"Can you remember it, Nathan?" said his mother.
"Perhaps I can remember some of it," said Nathan.
So Rollo and Nathan went out into another room, where Rollo kept his desk, and they remained there half an hour. When they returned, they brought their mother two papers.
Their mother opened the largest paper, and read as follows:-
"We took a tuft of down, tied to a thread, and held it in the
cracks and places that the air came in at, to see which way it
went. We held it at the window, and it blew in very strong. At
the bottom of the door, it blew in very strong too; but at the
top, it blew out, into the entry. So, when the entry is full
of cold air, and this room full of warm, the cold air will press
in and drive out some of the warm air, into the entry.
ROLLO."
The other paper was also in Rollo's handwriting, and was as follows:-
"If the entry was full of water, and the parlor full of air, and
the walls were water-tight, and you were to open the door
between the two rooms, the water would flow into the parlor down
below, and the air would flow into the entry up above. We tried
it with a tuft.
NATHAN."
QUESTIONS.
Why were Rollo and Nathan at first glad to see the rain? What
did their mother say to herself on the second day, when she
observed their weary and listless appearance? What did she at
first direct them to do? How did she prepare the 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, Jonas," replied Rollo, "your brush heaps burn, and why should not this stump?"
"Because," said Jonas, "the stump is more solid, and the water soaks into it more in the winter and early in the spring; and it takes it much longer to dry, than it does brush and small roots, which lie open and exposed to the air."