"Clouds, you doubtless know, are ma.s.ses of vapor from water. Now, when these vapors are sufficiently condensed to acquire a certain weight, they can no longer float in the atmosphere, and they fall in the form of rain. But they fall in rain because they have to traverse the air in order to fall to the ground. Now, the air offers such a resistance to this water that it is obliged to separate, to divide itself into small drops. If there were no air between the water and the ground, the water would not fall in drops of rain, but in a ma.s.s, like a solid body; and I am going to prove that to you, so as to convince Miss Miette."
Among the various instruments unpacked from the box, Monsieur Roger chose a round tube of gla.s.s, closed at one end, tapering, and open at the other end. He introduced into this tube a certain quant.i.ty of water so as to half fill it. Then he placed the tube above a little alcohol lamp, and made the water boil.
"Remark," said he, "how fully and completely the vapors from the water, which are formed by the influence of heat, force out the air which this tube encloses in escaping by the open end of the tube."
When Monsieur Roger judged that there no longer remained any air in the tube, he begged Monsieur Dalize to hand him the blowpipe. Monsieur Dalize then handed to his friend a little instrument of bra.s.s, which was composed of three parts,--a conical tube, furnished with a mouth, a hollow cylinder succeeding to the first tube, and a second tube, equally conical, but narrower, and placed at right angles with the hollow cylinder. This second tube ended in a very little opening.
Monsieur Roger placed his lips to the opening of the first tube, and blew, placing the little opening of the second tube in front of the flame of a candle, which Monsieur Dalize had just lit. A long and pointed tongue of fire extended itself from the flame of the candle.
Monsieur Roger placed close to this tongue of fire the tapering and open end of the tube in which the water had finished boiling. The air, forced out of the blowpipe and thrust upon the flame of the candle, bore to this flame a considerable quant.i.ty of oxygen, which increased the combustion and produced a temperature high enough to soften and melt the open extremity of the tube, and so seal it hermetically.
"I have," said Monsieur Roger, "by the means which you have seen, expelled the air which was contained in this tube, and there remains in it only water. In a few moments we will make use of it. But it is good to have a comparison under your eyes. I therefore ask Miss Miette to take another tube similar to that which I hold."
"Here it is," cried Miette.
"Now I ask her to put water into it."
"I have done so."
"Lastly, I ask her to turn it over quickly, with her little hand placed against its lower side in order to prevent the water from falling upon the floor."
Miss Miette did as she was commanded. The water fell in the tube, dividing itself into drops of more or less size. It was like rain in miniature.
"The water, as you have just seen," said Monsieur Roger, "has fallen in Miss Miette"s tube, dividing itself against the resistance of the air.
In the tube which I hold, and in which there is no longer any air, you will see how water falls."
Monsieur Roger turned the tube over, but the water this time encountered no resistance from the air. It fell in one ma.s.s, and struck the bottom of the tube with a dry and metallic sound.
"It made a noise almost like the noise of a hammer," said Paul Solange.
"Exactly," answered Monsieur Roger. "Scientists have given this apparatus the name of the water-hammer." And looking at Miette, who in her astonishment was examining the tube without saying anything, Monsieur Roger added, smiling, "And this hammer has struck Miss Miette with surprise."
[Ill.u.s.tration]
[Ill.u.s.tration]
CHAPTER XVI.
AMUSING PHYSICS.
Hearing Monsieur Roger"s jest, Miette raised her head, and said,--
"Yes, it is very curious to see water fall like that, in a single ma.s.s; and, besides, it fell quicker than the water in my tube."
"Of course: because it did not encounter the resistance of the air. This resistance is very easy to prove; and if Miss Miette will give me a sheet of any kind of paper----"
Miss Miette looked at Monsieur Roger, seeming to be slightly nettled,--not by the errand, but by something else.
Then she went in search of a sheet of letter-paper, which she brought back to Monsieur Roger. He raised his hand and dropped the paper.
Instead of falling directly towards the earth, as a piece of lead or stone would do, it floated downward from the right to the left, gently balanced, and impeded in its fall by the evident resistance of the air.
When this bit of paper had at last reached the ground, Monsieur Roger picked it up, saying,--
"I am going to squeeze this bit of paper in such a way as to make it a paper ball; and I am going to let this paper ball fall from the same height as I did the leaf."
The paper ball fell directly in a straight line upon the floor.
"And yet it was the same sheet," said he, "which has fallen so fast. The matter submitted to the action of gravity remains the same; there can be no doubt on that point. Therefore, if the sheet of paper falls more quickly when it is rolled up into a ball, it is certainly because it meets with less resistance from the air; and if it meets with less resistance, it is because under this form of a ball it presents only a small surface, which allows it easily to displace the air in order to pa.s.s."
"That is so," said Miss Miette, with a certainty which made every one smile.
Miette, astonished at the effect which she had thus produced, looked at her friend Paul, who remained silent, but very attentive.
"Well, Paul," said she, "is not that certain?"
"Yes," answered Paul.
"Hold," returned Monsieur Roger. "I am going to show you an example still more convincing of the resistance of the air,--only I must have a pair of scissors; and if Miss Miette will have the kindness to----"
Miss Miette looked again at Monsieur Roger with a singular air. None the less, she ran off in search of the scissors. Then Monsieur Roger pulled from his pocket a coin, and with the aid of the scissors cut a round bit of paper, a little smaller than the coin. That done, he placed the circular bit of paper flat upon the coin, in such a manner that it did not overlap, and asked Miss Miette to take the coin between her thumb and her finger.
"Now," said he, "let it all fall."
Miette opened her fingers, and the coin upon which he had placed the bit of paper fell. Coin and paper reached the ground at the same time.
"Why," asked Monsieur Roger, "does the paper reach the ground as soon as the coin?"
And as Miette hesitated to answer, Monsieur Roger continued:
"Because the fall of the bit of paper was not interfered with by the resistance of the air."
"Of course," cried Miette, "it is the coin which opened the way. The paper was preserved by the coin from the resistance of the air."
"Exactly so," said Monsieur Roger; "and these simple experiments have led scientists to ask if in doing away entirely with the resistance of the air it would not be possible to abolish the differences which may be observed between the falling of various bodies,--for instance, the paper and the coin, a hair and a bit of lead. And they have decided that in a vacuum--that is to say, when the resistance of the air is abolished--the paper and the coin, the hair and the lead would fall with exactly the same swiftness; all of them would traverse the same s.p.a.ce in the same time."
[Ill.u.s.tration]
"The hair falls as fast as lead," said Miette, in a tone which seemed to imply, "I would like to see that."
Monsieur Roger understood the thought of Miette, and answered by saying,--
"Well, I am going to show you that."
He chose a long tube of gla.s.s, closed by bits of metal, one of which had a stop-c.o.c.k. He put in this tube the coin, the round bit of paper, a bit of lead, and a strand of hair from Miss Miette"s head. Then he fastened the tube by one of its ends upon the disk of the air-pump and worked the pistons. As soon as he thought that the vacuum had been made, he closed the stop-c.o.c.k of the tube, to prevent the exterior air from entering. He withdrew the tube from the machine, held it vertically, then turned it briskly upsidedown. Everybody saw that the paper, the coin, the hair, and the lead all arrived at the same time at the bottom of the tube. The experiment was conclusive. Then Monsieur Roger opened the stop-c.o.c.k and allowed the air to enter into the tube. Again he turned the tube upsidedown: the coin and the bit of lead arrived almost together at the bottom of the tube, but the paper, and especially the strand of hair, found much difficulty on the way and arrived at the bottom much later.
"Why, how amusing that is!" cried Miette; "as amusing as anything I know. I don"t understand why Paul wishes to have nothing to do with physical science."