Part 16 (1/2)
”Master Paul is right,” replied Monsieur Roger. ”It has been found that in falling for two seconds a body falls sixteen feet and one inch multiplied by twice two,--that is to say, sixty-four feet and four inches. In falling three seconds a body traverses sixteen feet and one inch multiplied by three times three,--that is to say, by nine. In falling four seconds it traverses sixteen feet and one inch multiplied by four times four,--that is to say, by sixteen; and so on. This law of falling bodies which learned men have discovered teaches us that in order to calculate the s.p.a.ce traversed by a body in a certain number of seconds it is necessary to multiply sixteen feet and one inch by the arithmetical square of that number of seconds. And Master Paul must know, besides, that the square of a number is the product obtained by multiplying this number by itself.”
Paul bent his head.
”And now you must also know,” continued Monsieur Roger, ”how I could calculate the height of the tower of Heurtebize. The stone which you let fall, according to my watch, took two seconds before it reached the soil. The calculation which I had to make was easy, was it not?”
”Yes, sir: it was necessary to multiply sixteen feet and one inch by two times two,--which gives about sixty-four feet and four inches as the height of the tower.”
”You are right, and, as you may judge, it was not a very difficult problem.”
”Yes,” added Monsieur Dalize; ”but it was interesting to know why the apple fell, and you have taught us.”
”That is true,” cried Miette; ”only you have forgotten to tell us why the moon does not fall.”
”I have not forgotten,” said Monsieur Roger; ”but I wished to avoid speaking of the attraction of the universe. However, as Miette obliges me, I shall speak. You see that all earthly bodies are subject to a force which has been called gravity, or weight. Now, gravity can also be called attraction. By the word attraction is meant, in fact, the force which makes all bodies come mutually together and adhere together, unless they are separated by some other force. This gravity or attraction which the terrestrial ma.s.s exerts upon the objects placed on its surface is felt above the soil to a height that cannot be measured.
Learned men have, therefore, been led to suppose that this gravity or attraction extended beyond the limits which we can reach; that it acted upon the stars themselves, only decreasing as they are farther off. This supposition allows it to be believed that all the stars are of similar phenomena, that there is a gravity or attraction on their surface, and that this gravity or attraction acts upon all other celestial bodies.
With this frame of thought in his mind, Newton at last came to believe that all bodies attract each other by the force of gravity, that their movements are determined by the force which they exert mutually upon one another, and that the system of the universe is regulated by a single force,--gravity, or attraction.”
”But that does not explain to us why the moon does not fall,” said Monsieur Dalize.
Monsieur Roger looked at his friend.
”So you also,” said he, smiling,--”you also are trying to puzzle me?”
”Of course I am; but I am only repeating the question whose answer Miette is still awaiting.”
”Yes,” said Miette, ”I am waiting. Why does not the moon fall?”
”Well, the moon does not fall because it is launched into s.p.a.ce with so great a force that it traverses nearly four-fifths of a mile a second.”
Miette ran to open the door of the vestibule. The park was bathed in the mild light of a splendid moon.
”Is it of that moon that you are speaking,--the moon which turns around us?”
”Certainly, as we have no other moon.”
”And it turns as swiftly as you say?”
”Why, yes. And do you know why it turns around us, a prisoner of that earth from which it seeks continually to fly in a straight line? It is because----”
Monsieur Roger stopped suddenly, with an embarra.s.sed air.
”What is the matter?” asked Miette.
”Why, I am afraid I have put myself in a very difficult position.”
”Why?”
[Ill.u.s.tration]