Most of you, no doubt, know the story of Newton and the falling apple and how it led to his discovery of the law of gravity. But how much do you know beyond that? Do you know what kind of man this great scientist was? or where he stands in the history of science? If you don't, or even if you do, read the following lesson.

Isaac Newton was born on Christmas Day, 1642. He grew up in the English countryside. From the very first Newton was very much interested in the mysteries of nature. One of the most difficult scientific problems of Newton's day was about the question of motion¹. Why did objects move? Scientists could see that stones rolled down hills, that wind blew leaves along the ground, and heavy objects fell to the earth when dropped.

After Copernicus, they began to admit that the earth itself moved. "Were there laws that govern these various kinds of motion?" they asked themselves. The Greeks had believed there were different rules for motion on earth and in space, and that there were unnatural² movements on the surface of the earth.

Galileo was the first person to challenge this Greek view of motion. This Italian scientist was a follower³ of Copernicus. It didn't make much sense to Galileo to have different rules for motion on earth and in space. He made two important discoveries. First, he showed that motion was not unnatural. On the contrary, an object once in motion would tend to continue in motion. Second, Galileo worked out a mathematical⁴ formula⁵ for the motion of all objects that fell to the earth.

Galileo, however, did not explain how all motion in the universe worked. Much work had been done since Copernicus to observe and record the movements in the solar system. It remained now for some great mathematical mind to pull this work all together and put it into universal laws.

At the age of twenty-three Isaac Newton moved from Cambridge to his country home. There his thoughts turned to the problems of motion. As Newton himself later told the story, he was sitting in the garden one evening, thinking, when he noticed a falling apple. The apple set him to wondering about the movement of falling things.

It occurred to him that the force which caused fruit to fall from trees worked quite as well at greater distances from the center of the earth -- on top of buildings or even on top of mountains. Perhaps, thought Newton, this same force reached out much farther⁶ still, even to the moon. Was it this force which kept the moon going around the earth? And if so, could not the same force explain the movements of the planets⁷ around the sun? Newton began to search for a mathematical expression of his idea.