Monsieur Roger, hiding his satisfaction, seemed to attach no importance to this request of Miette under the a.s.sent 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 gla.s.s 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 gla.s.s 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 gla.s.s; 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.
[Ill.u.s.tration]
"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 gla.s.s 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?"