Much of today's science of physics is based on Newton's discovery of the three laws of mot

ion and his theory of gravity (引力). Newton also developed one of the most powerful tools of mathematics. It is the method we call calculus (微积分). Late in his life, Newton said of his work: "If I saw further than other men, it was because I stood on the shoulders of giants." One of those giants was the great Italian scientist, Galileo. Galileo died the same year Newton was born. Another of the giants was the Polish scientist Nicholas Copernicus. He lived a hundred years before Newton. Copernicus had begun a scientific revolution. It led to a completely new understanding of how the universe worked. Galileo continued and expanded the work of Copernicus. Isaac Newton built on the ideas of these two scientists and others. He found and proved the answers for which they searched.

At that time, a deadly plague was spreading across England. To escape the disease, Newton returned to the family farm. He did more thinking than farming. In doing so, he found the answers to some of the greatest mysteries of science. Newton used his great skill in mathematics to form. a better understanding of the world and the universe. He used methods he had learned as a boy in making things. He experimented. Then he studied the results and used what he had learned to design new experiments. Newton's work led him to create a new method in mathematics for measuring areas curved in shape. He also used it to find how much material was contained in solid objects. The method he created became known as integral calculus.

Isaac Newton was born in Woolsthorpe, England, on December twenty-fifth, sixteen forty-two. He was born early. He was a small baby and very weak. No one expected him to survive. But he surprised everyone. He had one of the most powerful minds in history. And he lived until be was eighty-four. Newton's father died before he was born. His mother married again a few years later. She left Isaac with his grandmother. The boy was not a good student. Yet he liked to make things, such as kites and clocks and simple machines.

Newton also enjoyed finding new ways to answer questions or solve problems. As a boy, for example, he decided to find a way to measure the speed of the wind. On a windy day, he measured how far he could jump with the wind at his back. Then he measured how far he could jump with the wind in his face. From the difference between the two jumps, he made his own measure of the strength of the wind. Strangely, Newton became a much better student after a boy kicked him in the stomach. The boy was one of the best students in the school. Newton decided to get even by getting higher marks than the boy who kicked him. In a short time, Newton became the top student at the school.

Newton left school to help on the family farm. It soon became clear, however, that the boy was not a good farmer. He spent his time solving mathematical problems, instead of taking care of the crops. He spent horns visiting a bookstore in town, instead of selling his vegetables in the market. An uncle decided that Newton would do better as a student than as a farmer. So he helped the young man enter Cambridge University to study mathematics. Newton completed his university studies five years later, in sixteen sixty-five. He was twenty-two years old.

One day, sitting in the garden, Newton watched an apple fall from a tree. He began to wonder if the same force that pulled the apple down also kept the moon circling the earth. Newton believed it was. And he believed it could be measured. He called the force "gravity". He began to examine it carefully. He decided that the strength of the force keeping a planet in orbit around the sun depended on two things. One was the amount of mass in the planet and the sun. The other was how far apart they were.

Newton was able to find the exact relationship be

A．Y

B．N

C．NG