part 8

84 The answer is: "Because it is going round the earth." This is a cord in my hand. The cord has a weight at its end. The weight is hanging down on the cord which is in my hand. I make the weight go round on the cord. I keep the end of the cord in my hand. Now I let the end of the cord in my hand go. The weight goes off in a straight line. It takes the cord with it.

85 The pull of the cord in my hand kept the weight from going off in a straight line. The attraction between the earth and the moon keeps the moon from going off in a straight line. The moon goes round and round the earth… month after month It does not get farther from the earth, or nearer to the earth. It keeps about the same distance from the earth.

86 Here is Sir Isaac Newton, the great man of science. Newton had a great mind. He is under an apple tree. It is the year 1666. Those are apples which are over his head. The seat has three legs. Here is an apple which was over his head. The apple was on a branch of the tree. The apple came off the branch. It came down. It came down on Newton's head.

87 That is the story. The story may be true or it may not be true. But that is the story. It comes from the great writer, Voltaire. True? 2 + 2 = 4. That is true. 2 + 2 = 5. That is not true. It is a false statement. "Apples are fruit." That statement is true. "Apples are animals." That statement is false. In this story the fall of the apple on Newton's head was the cause of the idea. The blow which the apple gave to Newton's head gave an idea to Newton. It made a question come into Newton's mind. This was the question: "Have the fall of the apple and the motion of the moon the same cause?"

88 Here is a ball. It is hanging on a cord. I will give a blow to the ball with this stick. I gave the blow. Now the ball is in motion. What was the cause of the motion? The blow of the stick was the cause of the motion. The ball was not in motion before the blow. It was at rest. It was hanging on the end of the cord. The blow was the cause of the motion. After the blow the ball was in motion. The motion came from the blow. The motion was the effect of the blow.

93 What is this? The man has an umbrella in his hand. It is open. He has it over his head. Why? Because it is raining. Water is coming down from the sky. The water is rain. Rain is coming down. Rain is falling. It is raining. The rain made the man put up his umbrella. That was the effect of the rain. Today is Monday. Yesterday (Sunday) the sun was bright. There were no clouds in the sky. Today there are dark clouds in the sky. They come between us and the sun. The dark clouds keep the light of the sun from us.