Who Was Isaac Newton? Read online

  Another subject that always interested Newton was light. He had bought himself a prism at Stourbridge Fair. This was a specially shaped piece of glass. When light shone through it, the light turned into a rainbow of color. (We call this the spectrum.) Newton began playing around with his prism, testing what he had learned about light.

  Aristotle taught that in its basic form, light was pure white. All other colors came from making changes to white light. If you changed it a little, you got red. Changing it a little more gave you orange, and so on through all the colors. But by now, Newton knew Aristotle was sometimes wrong. Maybe he was wrong about light.

  Newton knew that when you shine white light through a prism, the light breaks up into all the colors of the spectrum. What would happen if you sent the broken-up spectrum through a second prism? If white light was really being changed to turn into all the colors, a second prism should change the light even more. Newton discovered that, in fact, this didn’t happen. A second prism brought all the colors back together to create a single beam of white light again.

  This made Newton think of other questions. What would happen if you shone just a single color of light through a second prism? He created an experiment to find out. First he passed a ray of white light through a prism, to get the whole spectrum. Then he took just the green light and sent it through a second prism. If Aristotle was right, the first prism had already done something to the white light that had turned it green. What would the second prism do? Would it break the green light up into the whole spectrum again? Would it just change the green a little more, so it turned blue? Instead, Newton discovered that the second prism made no change at all. The green beam stayed green.

  His experiments told Newton that Aristotle was wrong. White light was not the basic form of light. Instead, white light was made up of all the different colors put together. The prism wasn’t making changes to the white light. It was breaking it up and separating it into its different parts.

  From what he figured out about light, Newton was able to explain a mystery. Until Newton, no one understood what made rainbows appear in the sky. Newton realized that drops of water in the air could act like prisms, breaking the white light of the sun into red, orange, yellow, green, blue, indigo, and violet. He was able to explain how, when sunlight passed through these natural prisms, it created a rainbow.

  Chapter 4

  Falling Apples

  Newton’s year at his mother’s house came to be called his annus mirabilis. In Latin that means miraculous year. It seemed like a miracle that one young man could figure out so much in so short a time. Discovering the true nature of light and inventing calculus was just the beginning. He also began the work that would lead to the laws of motion named after him and to the theory of gravity. The famous story about Newton tells how a falling apple led him to discover gravity. This story may even be true. In his later years, Newton himself said his first notion of gravity was “occasioned by the fall of an apple,” and there were apple trees at Woolsthorpe.

  Aristotle taught that the reason things fall is because heavy objects have a natural tendency to move downward. Again it seemed to Newton that Aristotle was wrong. He didn’t think it made sense to say that objects had a built-in need to fall down. He thought there must be some kind of force that pulled things toward the Earth.

  If there was such a force, how far up could it reach? Newton decided that maybe the force didn’t have any limits. The very same force that pulled on the apple could also be pulling on the moon and the planets as well.

  This was a brand-new and amazing idea. In Newton’s time, people thought the universe was divided into two parts. There were forces that worked here on Earth and there were forces out beyond the moon. They were completely different. Because people couldn’t travel to outer space, there was no way to study these forces. This meant no one could ever learn how the universe worked beyond the small part people could reach.

  Now Newton had decided that if he studied the falling apple, he could learn about the forces at work on everything in the universe. The more he thought about it, the more certain he became. The force that made an apple fall from a tree was the very same force that made the moon circle around the Earth instead of flying off into space.

  No one knows exactly how far Newton got in figuring out all these ideas during his miraculous year, or how much he worked out later. It was a long time before Newton shared his thoughts with anyone else.

  All his life Newton hated going public with his discoveries. He didn’t like to tell anyone else until he was positive he had worked out every detail perfectly. He wanted to be sure no one could possibly catch him making a mistake. He also seemed to like keeping his bold, exciting ideas all to himself.

  Chapter 5

  The Wonderful Telescope

  When the plague finally ended in 1667, Newton went back to Cambridge. Here one of his teachers encouraged him to share at least one of his discoveries with the world. This teacher was Isaac Barrow, the first-ever professor of mathematics at Cambridge.

  In 1669, Newton showed Barrow a paper he had written on his method of fluxions. Barrow was amazed by this wonderful new mathematical tool. He thought it was too important for Newton to keep all to himself. Newton reluctantly let Barrow show the paper to a very small number of people, but he absolutely refused to let it be published.

  In October 1669, Barrow left Cambridge. He thought so highly of Newton that he arranged for Newton to take his place as professor of mathematics. Thanks to Barrow, Newton was finally able to live exactly the kind of life he wanted. His duties didn’t take much time or energy. All he had to do was give a few lectures. He was a very dull lecturer and difficult to understand. Almost no one went to hear him.

  Newton didn’t care. He wasn’t interested in the other students or professors. He spent most of his time wandering around the university in badly fitting clothing, with his long silver hair hanging uncombed.

  Newton was often so busy thinking that he would forget whether or not he had eaten. The rumor at Cambridge was that his cat got fat from the meals Newton left sitting on his table. He slept only a few hours a night and often not in his bed.

  Newton wanted to learn more about the way planets moved. To do this, he needed a powerful telescope, but the telescopes of his time weren’t good enough for him. They worked by collecting light from a wide area and then focusing it through a glass lens. The images they produced were fuzzy, with a fringe of colors.

  Newton wanted a telescope that gave a clearer image. He used what he had discovered about light to solve the problem. The trouble was the lens, he realized. When white light passed through a lens, the lens acted like a prism and broke the light into separate colors. This caused the light to become unfocused, and the image would blur.

  Newton had read about another possible way to make a telescope, one that used a mirror. This might get around the problem, because the light would be reflected, instead of passing through a lens. But no one had ever managed to actually build such a telescope.

  Newton had loved to build models when he was a child. He used the skills he had learned then to make a reflecting telescope that worked as well as telescopes ten times its size.

  Chapter 6

  Fighting about Light

  Newton’s wonderful telescope caught the interest of an important club in London. It was called the Royal Society. Founded in 1660, this was a group of scholars who met every week to watch experiments and talk about science.

  The Royal Society thought the best way to advance knowledge was to discuss ideas, so each man could build on—or knock down—what the others were thinking. Their motto was Nullius in verba, which means roughly, “Don’t take anyone’s word for it.”

  Clubs like the Royal Society were springing up all over in Newton’s time. This period is often called the Age of Enlightenment. Enlightenment means learning the kind of important knowledge that c
hanges the way people think. The great scholars of the time believed in working together. They wanted to deal with issues of all kinds using reason, logic, and observation—not superstition or religion.

  Newton is considered one of the Enlightenment’s greatest figures, but his personality didn’t fit the Enlightenment ideal very well. He didn’t want advice from other people. He wanted to keep his work to himself until it was perfect. Even then, he hated talking about it with other people. If they questioned him—or even worse, thought he might be wrong—he lost his temper.

  Still it was flattering for Newton to have such an important group interested in his telescope. He let himself be persuaded to share. In 1671, Barrow displayed the telescope in London, where it was a huge hit—even with the king. Newton donated a telescope to the Royal Society. In return, the society made him a member.

  Joining the Royal Society in 1672 led Newton to take another important step. He would try to behave more like an Enlightenment scholar. Instead of keeping his research secret, he would share it with others. He sent the fellows of the Royal Society a paper about the research on light he had done five years earlier. He couldn’t resist bragging a little about how important the work was. He proudly described it as “the oddest if not the most considerable detection which hath hitherto been made in the operations of nature.” He described the experiments he had done and asked the society members to see if they could get the same results.

  At first, all seemed well. One member wrote to Newton that his paper had “met with a singular attention and uncommon applause.” However, not everyone agreed with everything he said. They had questions. Some people tried his experiments and claimed they didn’t work. Newton felt as if they were attacking him, and he fought back.

  One member of the Royal Society in particular made him very angry. This was a man named Robert Hooke. His job was to demonstrate experiments at the society’s meetings. Hooke actually agreed with much of what Newton said. But he didn’t believe that Newton’s experiments really proved what Newton said they did.

  Disagreement of this kind is common among scientists—it’s an important way to work out the problems with an idea and to make new discoveries. Unfortunately, both Hooke and Newton were very sensitive and proud. They didn’t just discuss ideas—they had fights. As the arguments grew worse, they insulted each other, and each accused the other of stealing ideas. They became enemies for life.

  Newton never learned to enjoy give-and-take arguments with his fellow scholars. He missed working alone, entirely for his own satisfaction. “I desire to decline being involved in such troublesome & insignificant Disputes,” he proclaimed. He went back to working all by himself.

  Chapter 7

  A Secret Life

  Arguing with other scholars was not Newton’s only problem. He also had a more personal difficulty. Newton was a fellow of Cambridge University. Being a fellow meant the university gave him money to live and work there, safe from the world outside. Cambridge was part of the Church of England. Every fellow had to become a minister in the church within seven years. By 1674, Newton’s seven years were almost up. But he couldn’t become a minister because, secretly, he didn’t accept the teachings of the church.

  Newton was a Christian and very serious about his religion. However, being Newton, he wasn’t willing to just accept someone else’s explanation about anything important.

  Newton read the Bible with the same fierce, questioning mind he turned on the natural world. He decided that he did not agree with the Church of England about the Holy Trinity. The church said that God was one being, made up of the Father, the Son, and the Holy Ghost, and all three were divine. To stay at Cambridge, Newton would have to swear that he accepted this idea. But he didn’t—he thought it was wrong to call Christ God. If he refused to agree with what the church said, he would be forced to leave Cambridge in disgrace, but he didn’t want to lie about something so important.

  In 1675, he approached King Charles II. He thought the king might be able to help him because he was the head of the Church of England. Newton didn’t want to tell the king the real reason for his problem. Instead he explained that he wasn’t just a fellow of the university. He was also a professor of mathematics. According to Newton, this meant he should not have to become a minister. This argument didn’t really make sense. Fortunately, King Charles didn’t care. Newton didn’t have to become a minister, the king decided. He was able to stay at Cambridge without having to lie.

  Just as he had a secret religious life, Newton also had a secret scientific life. He wanted to unlock the mysteries of alchemy. Alchemy was part magic, part religion, and part science. In secret, alchemists searched for the Philosopher’s Stone, which would turn other metals into gold, and the Elixir of Life, which would grant immortality.

  Newton spent even more time and energy on alchemy than he did on ordinary science. His servant reported that Newton often sat up all night in his private lab at Cambridge, bent over a roaring fire, working on mysterious experiments.

  This might seem odd and puzzling. Why was a scientist involved with secret rituals and magic? Actually, it’s not hard to guess why alchemy might appeal to him. He hated to have his work criticized in public. Alchemy offered him a perfect excuse to keep it secret. Alchemists considered themselves special, much wiser than ordinary people. Newton liked seeing himself as part of this select group.

  But there was more to Newton’s interest than that. In Newton’s time, science was still in an early stage. It was not always possible to separate myths from facts. Alchemists believed they could turn other metals into gold because they thought that everything was made up of tiny particles that could be separated and recombined to make something else.

  The questions the alchemists asked were not foolish. Some of their knowledge would eventually lead to modern chemistry and contribute to our knowledge of how atoms combine to form molecules.

  Still, this was the Age of Enlightenment. Serious thinkers were turning away from the idea of special, secret wisdom available only to the chosen few. After Newton died, the Royal Society discovered he had written over a million words about alchemy. They were so embarrassed by this that they marked the papers “not fit to be printed.” Newton’s writings about alchemy were not published until 2004.

  Chapter 8

  A Competition

  After his fight with the Royal Society, Newton withdrew into himself. He concentrated on his secret study of alchemy. He claimed he wasn’t interested in scientific research anymore. Maybe he meant what he said at the time, but his greatest work was still ahead of him.

  In 1684, three members of the Royal Society were chatting in a coffeehouse about current scientific issues. These three were Newton’s enemy Hooke, a young astronomer named Edmond Halley, and Christopher Wren, a famous architect. Wren had been trying to understand how and why planets orbited the sun. Now he asked the other two men for help.

  People already knew what path an orbiting planet actually followed. Johannes Kepler had shown in 1609 that it was an ellipse. They also knew that the amount of force between the planet and the sun decided the path of the orbit. But something else was involved that no one could figure out. The strength of the force changed in a complicated way, depending on how far apart the two bodies were. The force got weaker as the planet and the sun got farther apart. That made sense, but the force and the distance didn’t seem to change at the same rate. The force changed faster and faster the more the distance grew. No one could figure out exactly what the relationship between the distance and the force was.

  Scholars had come up with various ideas to explain the relationship. One suggestion was a mathematical relationship called the inverse square rule. Wren thought this might be the right one, but he had tried to prove it, and he couldn’t.

  Wren put the problem to his friends. Could they prove—using mathematics—that the inverse square rule would produce an elliptica
l orbit? If so, they would have created an important new law about the way the planets moved.

  Hooke bragged that he had already done this, but he wasn’t ready to tell the others how. First he wanted them to try and fail. Then he would show them. Wren and Halley didn’t take Hooke very seriously. (When Newton had produced his wonderful telescope, Hooke claimed that he had already made a telescope that worked even better and was so small he could hang it from his watch chain.) Wren offered a prize—a valuable book—to whoever could show him the mathematical proof first.

  After two months, Hooke still hadn’t shown him anything. Nervously, Halley decided to approach the prickly Newton. Like Hooke, Newton said he had already proved that the inverse square rule would produce an elliptical orbit, years before. Unfortunately he wasn’t sure where he had put the proof. He had only done it for his own amusement. He promised to send it to Halley as soon as he found it. Unlike Hooke, Newton wasn’t just bragging. Within a few months, Newton was able to send Halley his proof.

  HALLEY’S COMET

  A COMET IS A BRIGHT OBJECT LIKE A STAR IN THE SKY, OFTEN WITH A LONG TAIL. IN NEWTON’S TIME, PEOPLE BELIEVED COMETS WERE SIGNS FROM HEAVEN THAT SOMETHING TERRIBLE (OR WONDERFUL) WAS GOING TO HAPPEN. IN 1682, A BRIGHT COMET APPEARED. NEWTON’S FRIEND EDMOND HALLEY READ OLD REPORTS FROM ASTRONOMERS GOING BACK FOR MANY YEARS. HE NOTICED THAT THERE WERE REPORTS OF SOME KIND OF BRIGHT OBJECT APPEARING IN THE SKY JUST ABOUT EVERY SEVENTY-SIX YEARS. HE MADE A BRILLIANT LEAP AND GUESSED THAT IT WAS ACTUALLY THE SAME COMET COMING BACK OVER AND OVER. THIS WOULD MEAN COMETS ORBITED THE SUN, JUST LIKE THE PLANETS—ONLY COMETS HAD A MUCH LONGER ORBIT. HE PREDICTED THAT IT WOULD APPEAR AGAIN IN 1758. HALLEY WAS ALREADY DEAD BY THEN, BUT WHEN THE COMET REAPPEARED JUST AS HE SAID IT WOULD, IT WAS NAMED IN HIS HONOR.