AT THE CENTRE OF THE EARTH.
Monsieur Roger, hiding his satisfaction, seemed to attach no importance
to this request of Miette under the assent given by Paul. Wishing to
profit by the awakened curiosity of his little friend, he hastened to
continue, and said,--
"Who wants to bring me a bit of cork and a glass of water?"
"I! I!" cried Miette, running.
When Miette had returned with the articles, Monsieur Roger continued:
"I told you a moment ago that if balloons and smoke and clouds do not
fall, it is because they find themselves in the midst of air which is
heavier than they are. I am going to try an experiment which will make
you understand what I have said."
Monsieur Roger took the cork, raised his hand above his head, and opened
his fingers: the cork fell.
"Is it a heavy body?" said he. "Did it fall to the ground?"
"Yes," cried Paul and Miette together.
Then Monsieur Roger placed the glass of water in front of him, took the
cork, which Miette had picked up, and forced it with his finger to the
bottom of the glass; then he withdrew his finger, and the cork mounted
up to the surface again.
"Did you see?" asked Monsieur Roger.
"Yes," said Miss Miette.
"You remarked something?"
"Certainly: the cork would not fall, and you were obliged to force it
into the water with your finger."
"And not only," continued Monsieur Roger, "it would not fall, as you
say, but it even hastened to rise again as soon as it was freed from the
pressure of my finger. We were wrong, then, when we said that this same
cork is a heavy body?"
"Ah, I don't know," said Miette, a little confused.
"Still, we must know. Did this cork fall just now upon the ground?"
"Yes."
"Then it was a heavy body?"
"Yes."
"And now that it remains on the surface of the water, that it no longer
precipitates itself towards the earth, it is no longer a heavy body?"
This time Miette knew not what to answer.
"Well, be very sure," continued Monsieur Roger, "that it is heavy. If it
does not fall to the bottom of the water, it is because the water is
heavier than it. The water is an obstacle to it. Nevertheless, it is
attracted, like all bodies, towards the earth, or, more precisely,
towards the centre of the earth."
"Towards the centre of the earth?" repeated Miette.
"Yes, towards the centre of the earth. Can Miss Miette procure for me
two pieces of string and two heavy bodies,--for example, small pieces of
lead?"
"String, yes; but where can I get lead?" asked Miette.
"Look in the box where I keep my fishing-tackle," said Monsieur Dalize
to his daughter, "and find two sinkers there."
Miette disappeared, and came back in a moment with the articles desired.
Monsieur Roger tied the little pieces of lead to the two separate
strings. Then he told Miette to hold the end of one of these strings in
her fingers. He himself did the same with the other string. The two
strings from which the sinkers were suspended swayed to and fro for some
seconds, and then stopped in a fixed position.
[Illustration]
"Is it not evident," said Monsieur Roger, "that the direction of our
strings is the same as the direction in which the force which we call
weight attracts the bodies of lead? In fact, if you cut the string, the
lead would go in that direction. The string which Miss Miette is
holding and that which I hold myself seem to us to be parallel,--that is
to say, that it seems impossible they should ever meet, however long the
distance which they travel. Well, that is an error. For these two
strings, if left to themselves, would meet exactly at the centre of the
earth."
"Then," said Miette, "if we detach the sinkers, they would fall, and
would join each other exactly at the centre of the earth?"
"Yes, if they encountered no obstacle; but they would be stopped by the
resistance of the ground. They would attempt to force themselves
through, and would not succeed."
"Why?"
"Why, if the ground which supports us did not resist, we would not be at
this moment chatting quietly here on the surface of the earth; drawn by
gravity, we would all be----"
"At the centre of the earth!" cried Miette.
"Exactly. And it might very well happen that I would not then be in a
mood to explain to you the attraction of gravity."
"Yes, that is very probable," said Miss Miette, philosophically. Then
she added, "If, instead of letting these bits of lead fall upon the
ground, we let them fall in water?"
"Well, they would approach the centre of the earth for the entire depth
of the water."
Miette had mechanically placed the sinker above the glass of water. She
let it fall into it; the cork still swam above.
"Why does the lead fall to the bottom of the water, and why does the
cork not fall?"
"Why," said Albert, "because lead is heavier than cork."
Miette looked at her brother, and then turned her eyes towards Monsieur
Roger, as if the explanation given by Albert explained nothing, and
finally she said,--
"Of course lead is heavier than cork; but why is it heavier?"
"My child, you want to know a great deal," said Madame Dalize.
"Ah, mamma, it is not my fault,--it is Paul's, who wants to know, and
does not like to ask. I am obliged to ask questions in his stead."
That was true. Paul asked no questions, but he listened with attention,
and his eyes seemed to approve the questions asked by his friend Miette.
Monsieur Roger had observed with pleasure the conduct of his young
friend, and it was for him, while he was looking at Miette, the latter
continued:
"Tell us, Monsieur Roger, why is lead heavier than cork?"
"Because its density is greater," answered Monsieur Roger, seriously.
"Ah!" murmured Miette, disappointed; and, as Monsieur Roger kept silent,
she added, "What is density?"
"It would take a long time to explain."
"Tell me all the same."
Monsieur Roger saw at this moment that Paul was beckoning to Miette to
insist.
"Goodness!" said he, smiling at Paul; "Miss Miette was right just now.
It is you that wish me to continue the questions!"
[Illustration]
[Illustration]