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 mass;
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
pass."
"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 space in the same
time."
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"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 glass, closed by bits of metal, one of which had
a stop-cock. 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-cock 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-cock 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."
But Miette was mistaken this time, for Paul was now very anxious to
learn more.
"Very well," said Monsieur Roger, "as all this has not wearied you, I
am, in order to end to-day, going to make another experiment which will
not be a bit tiresome, and which, without any scientific apparatus,
without any air-pump, will demonstrate to you for the last time the
existence of the pressure, of the weight of the atmosphere."
Monsieur Roger stopped and looked at Miette, whose good temper he was
again going to put to the test. Then he said,--
"I need a carafe and a hard egg; and if Miss Miette will only be kind
enough to----"
This time Miette seemed still more uneasy than ever, more embarrassed,
more uncomfortable; still, she fled rapidly towards the kitchen. During
her absence, Monsieur Roger said to Madame Dalize,--
"Miette seems to think that I trouble her a little too often."
"That is not what is annoying her, I am certain," replied Madame Dalize;
"but I do not understand the true cause. Let us wait."
At this moment Miette returned, with the carafe in one hand, the
hard-boiled egg (it was not boiled very hard, however) in the other.
Monsieur Roger took the shell off the egg and placed the egg thus
deprived of its shell upon the empty carafe, somewhat after the manner
of a stopper or cork.
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"What I want to do," said he, "is to make this egg enter the carafe."
"Very well," said Miette; "all you have to do is to push from above: you
will force the egg down."
"Oh, but nobody must touch it. It must not be a hand that forces it
down, but by weight from above. No, the atmosphere must do this."
Monsieur Roger took off the egg, and lit a bit of paper, which he threw
into the empty carafe.
"In order to burn," said he, "this paper is obliged to absorb the oxygen
of the air in the carafe,--that is to say, it makes a partial vacuum."
When the paper had burned for some moments, Monsieur Roger replaced the
egg upon the carafe's neck, very much in the manner you would place a
close-fitting ground-glass stopper in the neck of a bottle, and
immediately they saw the egg lengthen, penetrate into the neck of the
carafe, and at last fall to the bottom. "There," said he, "is
atmospheric pressure clearly demonstrated. When a partial vacuum had
been made in the carafe,--that is to say, when there was not enough air
in it to counterbalance or resist the pressure of the exterior
air,--this exterior air pressed with all its weight upon the egg and
forced it down in very much the same way as Miss Miette wished me to do
just now with my hand."
In saying these last words, Monsieur Roger looked towards Miette.
"By the way," he said, "I must apologize to you, Miss Miette, for having
sent you on so many errands. I thought I saw that it annoyed you a
little bit."
Miss Miette raised her eyes with much surprise to Monsieur Roger.
"But that was not it at all," said she.
"Well, what was it?" asked Monsieur Roger.
And Miette replied timidly, yet sweetly,--
"Why, I only thought that you might stop calling me Miss. If you please,
I would like to be one of your very good friends."
"Oh, yes; with very great pleasure, my dear little Miette," cried
Monsieur Roger, much moved by this touching and kindly delicacy of
feeling, and opening his arms to the pretty and obliging little child of
his friends.
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