Rollo's Philosophy Part 13

Their mother looked at them, and then said to herself, "They have not energy and decision enough to set themselves about something useful, and in fact I ought not to expect that they should have. I must supply the want, by my energy and decision."

Then she said aloud to Rollo and Nathan,--

"I want you, boys, to go up into the garret, and under the sky-light you will see a large box. Open this box, and you will find it filled with feathers. Select from these feathers three or four which are the most downy and soft about the stem, and bring them down to me."

"What are they for?" said Rollo.

"I will tell you," replied his mother, "when you have brought them to me."

So Rollo and Nathan went up into the garret, and brought the feathers.

They carried them to their mother. She said that they would answer very well, and she laid them gently down upon the table.

Then she took up her scissors, and began to cut off some of the lightest down, saying, at the same time,--

"Now, children, I am going to give you some writing to do, about _the air_."

"Writing?" said Rollo.

"Yes," said his mother. "I am going to explain to you something about the air, and then you must write down what I tell you."

"But I can't write," said Nathan.

"No," said his mother, "but you can tell Rollo what you would wish to say, and he will write it for you."

"Why, mother," said Rollo, "I don't think that that will be very good play."

"No," replied his mother, "I don't give it to you for play. It will be quite hard work. I hope you will take hold of it energetically, and do it well.

"First," said she, "I am going to perform some experiments for you, before I tell you what I want you to write."

By this time, she had cut off the downy part of several feathers, and had laid them together in a little heap. Then she took a fine thread, and tied this little tuft of down to the end of it. Then she took up the thread by the other end, and handed it to Rollo.

"There, Rollo," said she. "Now, do you remember what your father told you, the other day, about the effect of heat upon air?"

"It makes it light," said Rollo.

"And why does it make it light?" asked his mother.

"Why, I don't exactly recollect," said Rollo.

"Because it swells it; it makes it expand; so that the same quant.i.ty of air spreads over a greater s.p.a.ce; and this makes it lighter, But cool or cold air is heavier, because it is more condensed.

"Now, wherever there is heat," continued his mother, "the air is made lighter, and the cool and heavy air around presses in under it, and buoys it up. This produces currents of air. You recollect, don't you, that your father explained all this to you the other day?"

"Yes," said Rollo, "I remember it."

"Well," said his mother, "now you and Nathan may take this little tuft, and carry it about to various places, and hold it up by its thread, and it will show you the way the air is moving; and then you may come to me, and I will explain to you why it moves that way."

"Well," said Rollo, "come, Nathan, let us go. First we will hold it at the key-hole of the door."

Rollo held the end of the thread up opposite to the door, in such a way, that the tuft was exactly before the key-hole. The tuft was at once blown out into the room.

"O, see, Nathan, how it blows out. The air is coming in through the key-hole."

"Yes," said his mother; "when there is a fire in the room, and none in the entry, then the cold air in the entry runs down through the key-hole into the room."

"It don't run down, mother," said Rollo; "it blows right in straight."

"Perhaps I ought to have said it spouts in," said his mother, "just as the water did from the hole in your dam. And, now," she continued, "come and hold the tuft near the chimney."

Rollo did so; and he found that it was carried in, proving, as their father had showed them before, that the heavy, cold air, pressing into the room, crowded the warm, light air up the chimney.

"Now, should you think," said their mother, "that the cold air could come in through the key-hole, as fast as it goes up the chimney?"

Both Rollo and Nathan thought that it could not.

"Then go all around the room," said she, "and see if you can find any other place, where it comes in. For it is plain, you see, that the light air cannot be driven up chimney any faster than cold and heavy air comes in to drive it up and take its place."

So Rollo and Nathan went around the room, holding their tuft at all the places they could find, where they supposed there could be openings for the cold air to press in. They found currents coming in around the windows, and by the hinges of the doors; and at length Rollo said, he meant to open the window a little way, and see if the cold air from out of doors would not press in there too. He did so, and the tuft was blown in very far, showing that the cold air from out of doors pressed in very strongly.

"Now, if all these openings were to be stopped," said their mother, "then no cold air could crowd into the room; and of course the hot air could not be buoyed up into the chimney, and a great deal of the hot air and smoke would come into the room. This very often happens when houses are first built, and the rooms are very tight.

"But now, Rollo," she continued, "suppose that the door was opened wide; then should not you think that _more_ cold and heavy air would press in, than could go up the chimney?"

"Yes, mother, a great deal more," said Rollo.

"Try it," said his mother.

So Rollo opened the door, and held his tuft in the pa.s.sage-way; and he found that the air was pressing in very strongly through the open s.p.a.ce.

Wherever he held it, it was blown into the room a great deal, showing that the heavy air pressed in, in a torrent.

"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."