Great Astronomers: Newton
Great Astronomers in Modern English
by Sir Robert S. Ball, 1895 (paraphrased by Leslie Noelani Laurio)
To view the table of contents for the rest of this book, click here.
Sir Isaac Newton, 1642/3-1727
Discovered gravity, the three laws of motion, and calculus.
It was only a year after the death of Galileo that Isaac Newton was born. Compared with the fame of Newton, even Galileo has to take second place to the philosopher/scientist who first explained the accurate theory of the universe.
Isaac Newton was born Dec. 25, 1642 [old style; with dates adjusted according to differences in the Gregorian and Julian calendar after 1752, his birthday becomes Jan 4, 1643] at Woolsthorpe in Lincolnshire county, England. His father, Isaac Sr., had died a few months after his marriage to Harriet Ayscough, young Isaac's mother. The baby was so frail and weak that his mother didn't expect him to live. But she tended him so carefully that he thrived beyond expectation, and even lived a longer lifespan than most people of his era.
For the first three years of his life he lived in Woolsthorpe with his widowed mother. She supplemented their income with revenue from a small estate nearby in Leicestershire.
In 1645, his mother married Rev. Barnabas Smith and moved to a new home about a mile from Woolsthorpe. Little Isaac went to live with his maternal grandmother. He went to the public school at Grantham, where his teacher was Mr. Stokes. In order to be closer to the school, he boarded at the home of Mr. Clark, an apothecary at Grantham. Isaac Newton later wrote that he was near the bottom of his class, and was by no means the kind of model schoolboy who finds favour with his teacher by diligently studying his Latin grammar. In fact, the first time he seems to have been motivated to study was after a boy who was above him in class severely kicked him. This indignity stimulated young Isaac so much that he not only passed ahead of the bully who had mistreated him, but he continued to progress until he was at the top of the entire school.
[View images of Isaac Newton's boyhood church and a historic sundial he made at 9 years old here.]
Young Isaac didn't spend his free time playing like the other boys. He preferred to make mechanical toys and clever inventions. When some workmen built a windmill near his school, he watched with interest every day -- and then made a working model of a windmill himself! This little model was admired, and indicated a natural aptitude for mechanics. He built some other imaginative contrivances, too -- such as a carriage with wheels that the driver put in motion with a handle from the inside. He also made a clock that used water to keep the time. He won the respect of his friends by his skill at making paper kites, and, like a true engineer, he experimented with the best method of attaching the string and placement of the tail. He made paper lanterns to light his way to school in the dark winter mornings.
The only love interest of his life seems to have been when he was very young. David Brewster's "Life of Newton" says that at the house where he boarded, there were some girls also lodging. One was Miss Storey, the young sister of a doctor near Colstersworth. She was two or three years younger than Isaac Newton and gifted enough to attract his notice. He preferred to spend his time with her and her friends over playing with his own schoolmates, making them little tables and cupboards and things for their dolls. He lived for almost six years in the same house with Miss Storey, and there is evidence that their friendship developed into something more, but neither of them had enough money to marry. Miss Storey later married twice and became Mrs. Vincent. Isaac Newton always remained a friend. He regularly visited her when he went to Lincolnshire, and helped her and her family financially when she was in need.
When he was fourteen years old, his stepfather died. His mother returned to the old family home at Woolsthorpe along with her three children from her second marriage. There was little money, so Isaac was called home from school. He had begun to do well in school, and his mother hoped he was far enough along to lay aside his books and the silent musings he loved so much, and take care of the farm. But during his routine country duties, he was so distracted studying nature and so fascinated with learning things that he couldn't attend to anything else. It was plain that he would never make a good farmer. He preferred experimenting on his waterwheels to supervising farmhands, and he found calculating math equations behind a hedge much more interesting than bickering about the price of cows in the market place. Fortunately, his mother recognized his genius and was determined to let his mind have the scope it needed. So she sent him back to Grantham school to train for admission to the University of Cambridge.
In June, 1660, at the age of eighteen, Isaac Newton was enrolled at Trinity College, Cambridge. His mother had no idea that he would be the most famous student the school ever had. Isaac Newton himself didn't know that, one day, a statue of him in the ante-chapel of his college would be considered one of the main art treasures of Cambridge University. His early days at Cambridge didn't seem unusually promising or brilliant. He was an unknown youth from an obscure town. Although he enjoyed reflecting on weighty philosophical matters, his school education had not given him the routine knowledge normally expected of a University student.
Even from the beginning of his college years, Isaac Newton's interest seems to have been mathematics. He started to see a connection between mathematics and the deep secrets of nature. In fact, a century later, Laplace said that Newton's immortal work in mathematics surpassed all other work of the human mind. But even though he was one of the greatest mathematicians who ever lived, he wasn't interested in it for its own sake. For him, it was merely a tool for discovering the laws of nature. His work and genius attracted the attention of the University, and in 1664, they offered him a scholarship.
Two years later, in 1666, the plague broke out and many University residents left temporarily. Isaac Newton went home to Woolsthorpe. In 1667 he went back to Cambridge -- this time as a Fellow of Trinity College [a 'fellow' is a graduate selected to receive a grant for research.] His reputation as a mathematician and natural philosopher [scientist] steadily grew. By 1669, at the age of 27, he was appointed as Lucasian Professor of Mathematics at Cambridge with time to continue his research and discoveries of the principles of the natural world.
His first great achievement was detecting the refracted colors of light. He was the first to discover that an ordinary beam of sunlight is actually a combination of different colors of light.
This is a diagram from Newton's book, Opticks, published in 1704 [in Latin] to explain the composition of light.
One of his experiments was to let a beam of sunlight into a darkened room through a small hole. If nothing is in its path to interfere with it, the beam will travel in a straight line and project an exact replica of the small hole onto a screen. But if a glass prism interrupts the sunbeam, the beam is deflected and bends slightly from its original path. When it reaches the screen, that one white beam has spread into a long beautiful band representing all the colours of the rainbow. At the top is violet, followed by indigo, blue, green, yellow, orange, and red.
The part of this experiment that fascinated Newton was the spreading of light from a small spot to an elongated beam. Without the prism, the spot projected on the screen was circular, but with the prism, the light became five times as long as the original spot. What? Why? Perhaps the thickness of the glass was the cause, or maybe it was the angle of the prism. But with more trials, this didn't seem to be the cause. It took Newton much patient labour to finally figure out what was happening. Although a spot of sunlight appears to be a beam of pure, white light, it's actually composed of rays of various colors all blended together. The individual colours are blended so closely that they can't be detected, but the prism untangles and separates them into their original rays. The rays at the blue end deflect at a greater angle and bend more than the rays at the red end of the spectrum. Each coloured ray -- red, orange, yellow, green, blue, indigo, violet -- is deflected at a different angle, so it ends up on a different part of the screen. Thus, the prism shows us what a blended beam of white light is made of.
In our day, this seems obvious, but it was a revolutionary new idea at the time, and Isaac Newton didn't accept it hastily. He tested and re-tested, verifying his suspicion with various experiments until he was sure of what he was seeing. For one of his tests, he made a hole in his screen where the violet rays fell so that all of the rays would fall on the screen except the violet. The violet ray would pass through the hole, and he would be able to experiment with it in isolation. He ran that violet ray through a prism to see how much it was deflected and bent. Then he tried the same thing at the opposite end of the spectrum, with the red ray of light. Would one ray deflect more than the other? As he expected, the violet ray was more deflected by the second prism than the red ray. This confirmed that various hues of the rainbow were each bent by the prism at a different extent. The violet had more of a bend, and red had the least.
What would happen if a rainbow beam of different coloured light went through a second prism? Would the rays deflect back into a single white light? Newton turned a second prism upside down to find out. And that's exactly what happened! The second prism worked backwards to reunite the different colours back into the original beam of white light. He illustrated this action with a few other demonstrations. It was such a startling idea, that white light was actually a collection of all the hues of the rainbow that could be sorted into their different hues, and then brought back together again.
He had noticed before that bright sunlight falling on a white sheet of paper makes the paper look gray from a distance -- not white, and not multi-coloured. What would happen to sunlight falling on white paint? He combined coloured pigment and, although it wasn't exactly white, it was close -- more of a grayish white. Would sunlight affect paper differently with whitish gray pigment vs no pigment? He put a splotch of this gray blend of paint on a sheet of paper. Then he set it beside a plain white sheet of paper on his floor and allowed sunshine to fall on both sheets of paper. It seemed to him as if the illuminated splotch of paint looked whiter than the white paper with sunshine streaming on it! He even asked a friend to come look to see if he saw the same thing. [You can read more about colour mixing and colour vision at UNSW.]
With these kinds of repeated demonstrations, Isaac Newton was able to confirm his great discovery that white light is a blend of coloured rays. He recognized that this knowledge could influence the way a telescope was constructed. Astronomers knew that imperfections made it impossible to get all the various rays of light coming from the sky into focus at the same time. They supposed that it was because the glass lens wasn't the right shape. Mathematicians had demonstrated over and over again that a single lens in the right shape should conduct all the rays of light to the same focus. But they hadn't accounted for refracted light that bends different coloured rays differently. They had taken it for granted that a beam of light was a single ray with a set angle of refraction. No wonder they couldn't get a perfect telescope lens! But when Isaac Newton showed that light wasn't a single simple beam of white light, it became obvious that a single lens, no matter how excellently shaped, wasn't going to make a perfect telescope. Additional lenses would be necessary to deal with the differences in refraction in the various hues of light. Isaac Newton's findings on light finally made a perfect refractory telescope possible.
A composite lens, or "achromatic lens," made of two pieces of glass that have different properties is able to overcome this issue. [Achromatic lenses typically combine a concave lens with a convex lens; one lens corrects red light and the other corrects blue light so that both come into equal focus to the viewer.] But, although Newton recognized the problem that refracted light presented to telescope makers, he did not think it would be possible to correct the problem with a composite lens made of two pieces of glass. In that, he was proved wrong. But it was his discovery of the nature of light that enabled others to create an achromatic lens. Isaac Newton thought some other solution was needed, so he turned his focus in another direction to solve the telescope problem. He had discovered that refraction was linked to the colour of the light. But reflection was quite different. The laws of reflected light seemed to work quite independently of colour. Rays of all different colours, whether red, blue, or yellow, reflect in the same way when bounced off a mirror. What if Newton could build a telescope that relied on reflection rather than refraction? In that way, he could side-step the whole problem of light rays refracting differently.
In order to do this, Newton made a concave mirror out of a mixture of copper and tin -- a combination that shines almost like silver. When a star's light fell on the surface, a perfect image of the star would appear in the focus of this mirror, and the image could be examined with a magnifying glass. That's how Newton's famous reflecting telescope worked. You can still see the original little reflector that he constructed in the museum at the Royal Society. The tube of the telescope was only one inch in diameter. It was the forerunner of a whole series of excellent telescopes, each one bigger than the the last one, until finally Lord Rosse made a huge one in 1845 with a six-foot reflector.
[View a 4 minute video about Newton's telescope, which includes footage of his little reflecting telescope,on YouTube.]
Isaac Newton's discovery about light led to some bitter controversies. There were some well-respected scientists who attacked him over his theories. They claimed that the elongated band of light that Newton had seen through his prism was due to this or that factor, or something else -- anything except what Newton had said was the true cause. With his characteristic patience and love for truth, he responded to each and every attack. His responses made it clear how much his opponents misunderstood the subject and displayed their ignorance about light. With every point his challengers raised, he was able to refer to fresh experiments and new illustrations until his adversaries finally gave up and realized he was right.
Some have expressed surprise that, throughout his entire career, Isaac Newton took such trouble to patiently expose the fallacies of men who challenged his views, even when it was obvious that his adversaries didn't understand the subject they were discussing. A man who was a philosopher might have thought, 'I know I'm right and that's all that matters. If they're wrong, that's their problem. Why should I care if they remain in their misconception? I have better things to do with my time than argue with simpletons about their mistaken ideas.' But that wasn't Isaac Newton's way. He spent a lot of valuable time correcting objections that didn't make any sense. The persistence and even hostility, at times, of some of these attacks were exasperating for him. But he wasn't the type of person who could ignore what other people said about him. Many minds inferior to his are blessed with indifference to other people's opinions, but he didn't have that gift.
He was still fascinated with the subject of optics, and he did more investigations with light. Everyone has noticed the beautiful colors on soap bubbles, and it's no surprise that this attracted Newton's attention. He noticed a similar effect on other thin, transparent surfaces, and he wondered if the thickness of the material had something to do with it. He wasn't as successful in this research. In fact, his guesses about what caused colours in soap bubbles were incorrect. But he was, after all, a pioneer on the leading edge of a new and unknown field. His data are indisputable, but his explanations didn't turn out to be accurate when later research unveiled new knowledge.
Even if Newton hadn't done anything else after his discoveries about light, his name would have gone down in history as one as the great minds in interpreting natural science. But there was more in his future. In fact, what he was to discover next would be so monumental that it would overshadow his research about light and push it into the background. He is the genius who explained how the universe works by the law of gravitation.
It was an era of innovation and discovery, and it was the perfect atmosphere for Newton's brilliant mind. Kepler had recognized the laws that govern the movements of planets as they orbit the sun, and in various other fields, it seemed vaguely that his explanation must have something to do with the power of matter to attract other matter. But the mathematical tool to work with this subject [calculus] didn't exist yet. It would be created by Isaac Newton.
At Woolsthorpe during the plague of 1666, Newton was occupied with the subject of gravitation [as well as sunbeams]. We don't know for sure whether the story about the apple falling out of the tree and giving him the "aha" about gravitation is myth or fact, but it does provide an excellent way to illustrate gravity. Newton put it this way: The earth attracts the apple. No matter how high the tree is, when the apple falls, it will be drawn to the earth. So there must be something in the earth that draws all external things towards it, and that power, whatever it is, must extend beyond even the tallest tree on top of the highest mountain. No matter how far up we go, we can't seem to find its limit. As far away from the earth as we've ever been, the power of the earth to attract matter towards itself is still felt. Although at this writing [1895] we haven't been able to go more than a few miles in altitude above the earth, we know with certainty that gravity goes much farther than that. Isaac Newton was convinced that even if an apple fell from a hundred miles above the earth, it would be drawn down towards the earth by that attraction force, and it would gain speed as it fell. If it was a certainty at a hundred miles, it must also be true at a thousand miles, or at hundreds of thousands of miles. The intensity of that attraction force probably gets weaker the farther away you go from the earth, but it must still exist, even vaguely, at vast distances away from the earth.
It occurred to Newton that, even though the moon is more than 250,000 miles away, the attraction force of the earth must extend even as far as the moon. He was naturally inclined to think about the moon in relation to this -- not only because the moon is the closest celestial body to the earth, but because the moon is a satellite of the earth, constantly revolving around it. If the attraction force reaches as far as the moon, making it circle the earth rather than drifting away, why doesn't it fall to earth? It doesn't fall because it continues to move. If the moon stopped to rest for a moment, the attraction force of the earth would draw it in, and it would come crashing in on us within a few days. But this catastrophe is prevented because of the moon's movement as it propels around the earth. Isaac Newton was able to use known laws of mechanics -- laws that he had helped to discover -- to calculate how strong the attraction force of the earth must be in order to keep the moon moving in the specific way it moves. Then it was apparent that the same force that attracts the apple is what guides the moon and keeps it in its orbit.
Once this fact had been established, the rest became obvious. It was as if the whole scheme of the universe was unveiled before Newton's mind. If the moon is guided and controlled by the attraction force of the earth, then the earth, which is also an orbiting celestial body, must also be guided and controlled by some greater attraction force: the sun. And if this was true of the earth, it must be true of the planets, too. Their orbits could be explained with the same attraction force.
Isaac Newton's brilliance seemed to be up to any challenge. He realized that each planet's attraction force must be interfering with every other planet's, and that explained some of the irregularities in planetary orbits that had perplexed previous astronomers. [Planets sometimes appear to wobble, or even move backwards. View a brief demonstration of Ptolemy's explanation for this irregular movement on YouTube.] The mysterious way the earth's poles sway had long been an unsolved riddle, but Newton figured that out, too. It was caused by the moon pulling the bulging mass at the equatorial regions of the earth, and that made the earth's axis tilt. [Read more about axial precession on Wikipedia.] Newton explained all of these discoveries in his immortal book, Philosophiae Naturalis Principia Mathematica [Latin for 'Mathematical Principles of Natural Philosophy;' usually referred to simply as "Principia"].
Up until 1687, when Principia was published, Isaac Newton had lived the life of a recluse at Cambridge, focused obsessively on his discoveries. But that year, he had to make a trip away from Cambridge due to some circumstances of historical significance. King James II. wanted to promote Catholics to high positions at Cambridge. He commanded that Father Francis, a Benedictine monk, should be Master of Arts at the University, without even taking the oaths of allegiance and supremacy. The University refused. So the University's Vice-Chancellor was summoned to court to explain why he had not obeyed King James. Nine delegates were selected to defend the University's side of the issue before the High Court, and Isaac Newton was one of those delegates. They were able to prove that King Charles II [James's brother] had tried to issue a writ of mandate in similar circumstances and had been induced to withdraw it. This argument won the case for the University. The following year, Newton was elected by a narrow margin to represent Cambridge University in the Convention Parliament of 1689 after the "Glorious Revolution" that replaced James II. with King William III.
One morning in 1692, Isaac Newton went to early chapel and left a lighted candle at his desk back in his office. When he returned, the candle had fallen over -- tradition says his little dog "Diamond" knocked it over -- and many of his valuable papers had been burned. The loss of these manuscripts was deeply disturbing and even affected his health. In a letter to Samuel Pepys on September 13th, 1693, he writes,
"I am extremely troubled at the embroilment I am in, and have neither ate nor slept well this twelve-month, nor have my former consistency of mind."
In spite of Newton's fame from Principia and his ground-breaking research, the government had not done anything to acknowledge his achievements. Some of his friends had tried to get him promoted to some permanent position, but without success. But Mr. Montagu, one of the men who had served in Parliament with him, was appointed Chancellor of the Exchequer in 1694. He wanted to make his mark in the government, so he decided to improve the current coin, which needed it. Coins had been "clipped," forged, and had their edges shaved off for their metal. Mr. Montagu asked Isaac Newton to be warden of the Royal Mint in 1695 [the warden's official task was to enforce laws against counterfeiting]. There was a salary of five or six hundred pounds a year, and the warden generally delegated tasks, so his duties wouldn't require any more time than he was willing to spare.
Newton's knowledge of physics came in handy with his work at the Mint, and his skill at re-coining was so successful that he was promoted to Mastership of the Mint in 1697 with a yearly salary of £1200-1500. By 1701, his work at the Mint took up so much of his time that he resigned his Lucasian professorship at Cambridge and fellowship at Trinity College. This officially ended his connection with Cambridge. At one time, his friends almost got him appointed as Provost of King's College, Cambridge, but they weren't able to get around the requirement of being a Catholic in holy orders. [Isaac Newton was a Protestant.]
In those days, it was typical for illustrious mathematicians who had solved some compelling problem to publish the problem -- while withholding their solution. For example, the Brachsitochrone problem was solved by Johann Bernouilli. The problem involves finding the shape of a curve for a ball to slide from one point to another in the shortest time. [Read about this and see an illustrative gif here.] It seems obvious that the quickest route would be a straight line between point A and B -- a plane. But that isn't the case! There's a curved path that gets there even quicker. Johann Bernouilli challenged the world to find that curve. Isaac Newton solved it. He showed that it had to be the curve of a cycloid -- the curve traced in midair that a point on a wheel would make as it rolled along the ground. [See a cycloid demonstrated here.] Newton's geometrical genius enabled him to solve the problem and deliver his solution to the President of the Royal Society on the same day!
By 1703, Isaac Newton was famous around the world, and he was elected to be president of the Royal Society. He was re-elected year after year, for 25 years, until his death made him ineligible for the position. It was while acting in the capacity as president that he met Prince George of Denmark, who was a member of the Royal Society. In April 1705, Prince George's wife, Queen Anne, visited Cambridge and knighted Newton for his discoveries about gravity -- and thus he became Sir Isaac Newton.
His friends were eager to promote the spread of knowledge and urged him to publish a new edition of his Principia. His job at the Mint kept him too busy for the revision, so his friends urged him to ask Roger Coates to help with proofreading. Coates was a distinguished young mathematician at Trinity College who had been appointed Plumian Professor of Astronomy. With his help, a new edition of Principia was published in July, 1713. Newton, who was a favourite at the court, presented a copy to Queen Anne.
All his life, Newton was interested in theological studies, especially prophecy. He wrote several theological papers, and was working on a manuscript on the prophecies of Daniel and the Apocalypse of St. John until his death. [Some of his religious writings can be accessed here.] He was interested in the laws of cooling and heat transfer, as well as alchemy [using chemistry to turn cheaper metals into gold]. For relaxation, he sometimes tried to interpret Egyptian hieroglyphics [it was widely thought that they held symbolic or magical meaning]. He struggled with health issues in the final years of his life and died March 20, 1727, at the age of eighty four. He was buried in Westminster Abbey.
Isaac Newton was appreciated and honoured during his lifetime, and his astounding discoveries made him more widely known than most of his contemporaries, but after he died, his fame has only continued to increase steadily.
It's hard to say which is more amazing and admirable -- his wonderful discoveries, or the extraordinary mental processes that enabled him to make those discoveries. Either way, his Principia is undeniably the greatest work on science that has ever been written.
[See a drawing of Isaac Newton at his telescope here; it looks like the same telescope pictured above.]
by Sir Robert S. Ball, 1895 (paraphrased by Leslie Noelani Laurio)
To view the table of contents for the rest of this book, click here.
Sir Isaac Newton, 1642/3-1727
Discovered gravity, the three laws of motion, and calculus.
It was only a year after the death of Galileo that Isaac Newton was born. Compared with the fame of Newton, even Galileo has to take second place to the philosopher/scientist who first explained the accurate theory of the universe.
Isaac Newton was born Dec. 25, 1642 [old style; with dates adjusted according to differences in the Gregorian and Julian calendar after 1752, his birthday becomes Jan 4, 1643] at Woolsthorpe in Lincolnshire county, England. His father, Isaac Sr., had died a few months after his marriage to Harriet Ayscough, young Isaac's mother. The baby was so frail and weak that his mother didn't expect him to live. But she tended him so carefully that he thrived beyond expectation, and even lived a longer lifespan than most people of his era.
For the first three years of his life he lived in Woolsthorpe with his widowed mother. She supplemented their income with revenue from a small estate nearby in Leicestershire.
In 1645, his mother married Rev. Barnabas Smith and moved to a new home about a mile from Woolsthorpe. Little Isaac went to live with his maternal grandmother. He went to the public school at Grantham, where his teacher was Mr. Stokes. In order to be closer to the school, he boarded at the home of Mr. Clark, an apothecary at Grantham. Isaac Newton later wrote that he was near the bottom of his class, and was by no means the kind of model schoolboy who finds favour with his teacher by diligently studying his Latin grammar. In fact, the first time he seems to have been motivated to study was after a boy who was above him in class severely kicked him. This indignity stimulated young Isaac so much that he not only passed ahead of the bully who had mistreated him, but he continued to progress until he was at the top of the entire school.
[View images of Isaac Newton's boyhood church and a historic sundial he made at 9 years old here.]
Young Isaac didn't spend his free time playing like the other boys. He preferred to make mechanical toys and clever inventions. When some workmen built a windmill near his school, he watched with interest every day -- and then made a working model of a windmill himself! This little model was admired, and indicated a natural aptitude for mechanics. He built some other imaginative contrivances, too -- such as a carriage with wheels that the driver put in motion with a handle from the inside. He also made a clock that used water to keep the time. He won the respect of his friends by his skill at making paper kites, and, like a true engineer, he experimented with the best method of attaching the string and placement of the tail. He made paper lanterns to light his way to school in the dark winter mornings.
The only love interest of his life seems to have been when he was very young. David Brewster's "Life of Newton" says that at the house where he boarded, there were some girls also lodging. One was Miss Storey, the young sister of a doctor near Colstersworth. She was two or three years younger than Isaac Newton and gifted enough to attract his notice. He preferred to spend his time with her and her friends over playing with his own schoolmates, making them little tables and cupboards and things for their dolls. He lived for almost six years in the same house with Miss Storey, and there is evidence that their friendship developed into something more, but neither of them had enough money to marry. Miss Storey later married twice and became Mrs. Vincent. Isaac Newton always remained a friend. He regularly visited her when he went to Lincolnshire, and helped her and her family financially when she was in need.
When he was fourteen years old, his stepfather died. His mother returned to the old family home at Woolsthorpe along with her three children from her second marriage. There was little money, so Isaac was called home from school. He had begun to do well in school, and his mother hoped he was far enough along to lay aside his books and the silent musings he loved so much, and take care of the farm. But during his routine country duties, he was so distracted studying nature and so fascinated with learning things that he couldn't attend to anything else. It was plain that he would never make a good farmer. He preferred experimenting on his waterwheels to supervising farmhands, and he found calculating math equations behind a hedge much more interesting than bickering about the price of cows in the market place. Fortunately, his mother recognized his genius and was determined to let his mind have the scope it needed. So she sent him back to Grantham school to train for admission to the University of Cambridge.
In June, 1660, at the age of eighteen, Isaac Newton was enrolled at Trinity College, Cambridge. His mother had no idea that he would be the most famous student the school ever had. Isaac Newton himself didn't know that, one day, a statue of him in the ante-chapel of his college would be considered one of the main art treasures of Cambridge University. His early days at Cambridge didn't seem unusually promising or brilliant. He was an unknown youth from an obscure town. Although he enjoyed reflecting on weighty philosophical matters, his school education had not given him the routine knowledge normally expected of a University student.
Even from the beginning of his college years, Isaac Newton's interest seems to have been mathematics. He started to see a connection between mathematics and the deep secrets of nature. In fact, a century later, Laplace said that Newton's immortal work in mathematics surpassed all other work of the human mind. But even though he was one of the greatest mathematicians who ever lived, he wasn't interested in it for its own sake. For him, it was merely a tool for discovering the laws of nature. His work and genius attracted the attention of the University, and in 1664, they offered him a scholarship.
Two years later, in 1666, the plague broke out and many University residents left temporarily. Isaac Newton went home to Woolsthorpe. In 1667 he went back to Cambridge -- this time as a Fellow of Trinity College [a 'fellow' is a graduate selected to receive a grant for research.] His reputation as a mathematician and natural philosopher [scientist] steadily grew. By 1669, at the age of 27, he was appointed as Lucasian Professor of Mathematics at Cambridge with time to continue his research and discoveries of the principles of the natural world.
His first great achievement was detecting the refracted colors of light. He was the first to discover that an ordinary beam of sunlight is actually a combination of different colors of light.
This is a diagram from Newton's book, Opticks, published in 1704 [in Latin] to explain the composition of light.
One of his experiments was to let a beam of sunlight into a darkened room through a small hole. If nothing is in its path to interfere with it, the beam will travel in a straight line and project an exact replica of the small hole onto a screen. But if a glass prism interrupts the sunbeam, the beam is deflected and bends slightly from its original path. When it reaches the screen, that one white beam has spread into a long beautiful band representing all the colours of the rainbow. At the top is violet, followed by indigo, blue, green, yellow, orange, and red.
The part of this experiment that fascinated Newton was the spreading of light from a small spot to an elongated beam. Without the prism, the spot projected on the screen was circular, but with the prism, the light became five times as long as the original spot. What? Why? Perhaps the thickness of the glass was the cause, or maybe it was the angle of the prism. But with more trials, this didn't seem to be the cause. It took Newton much patient labour to finally figure out what was happening. Although a spot of sunlight appears to be a beam of pure, white light, it's actually composed of rays of various colors all blended together. The individual colours are blended so closely that they can't be detected, but the prism untangles and separates them into their original rays. The rays at the blue end deflect at a greater angle and bend more than the rays at the red end of the spectrum. Each coloured ray -- red, orange, yellow, green, blue, indigo, violet -- is deflected at a different angle, so it ends up on a different part of the screen. Thus, the prism shows us what a blended beam of white light is made of.
In our day, this seems obvious, but it was a revolutionary new idea at the time, and Isaac Newton didn't accept it hastily. He tested and re-tested, verifying his suspicion with various experiments until he was sure of what he was seeing. For one of his tests, he made a hole in his screen where the violet rays fell so that all of the rays would fall on the screen except the violet. The violet ray would pass through the hole, and he would be able to experiment with it in isolation. He ran that violet ray through a prism to see how much it was deflected and bent. Then he tried the same thing at the opposite end of the spectrum, with the red ray of light. Would one ray deflect more than the other? As he expected, the violet ray was more deflected by the second prism than the red ray. This confirmed that various hues of the rainbow were each bent by the prism at a different extent. The violet had more of a bend, and red had the least.
What would happen if a rainbow beam of different coloured light went through a second prism? Would the rays deflect back into a single white light? Newton turned a second prism upside down to find out. And that's exactly what happened! The second prism worked backwards to reunite the different colours back into the original beam of white light. He illustrated this action with a few other demonstrations. It was such a startling idea, that white light was actually a collection of all the hues of the rainbow that could be sorted into their different hues, and then brought back together again.
He had noticed before that bright sunlight falling on a white sheet of paper makes the paper look gray from a distance -- not white, and not multi-coloured. What would happen to sunlight falling on white paint? He combined coloured pigment and, although it wasn't exactly white, it was close -- more of a grayish white. Would sunlight affect paper differently with whitish gray pigment vs no pigment? He put a splotch of this gray blend of paint on a sheet of paper. Then he set it beside a plain white sheet of paper on his floor and allowed sunshine to fall on both sheets of paper. It seemed to him as if the illuminated splotch of paint looked whiter than the white paper with sunshine streaming on it! He even asked a friend to come look to see if he saw the same thing. [You can read more about colour mixing and colour vision at UNSW.]
With these kinds of repeated demonstrations, Isaac Newton was able to confirm his great discovery that white light is a blend of coloured rays. He recognized that this knowledge could influence the way a telescope was constructed. Astronomers knew that imperfections made it impossible to get all the various rays of light coming from the sky into focus at the same time. They supposed that it was because the glass lens wasn't the right shape. Mathematicians had demonstrated over and over again that a single lens in the right shape should conduct all the rays of light to the same focus. But they hadn't accounted for refracted light that bends different coloured rays differently. They had taken it for granted that a beam of light was a single ray with a set angle of refraction. No wonder they couldn't get a perfect telescope lens! But when Isaac Newton showed that light wasn't a single simple beam of white light, it became obvious that a single lens, no matter how excellently shaped, wasn't going to make a perfect telescope. Additional lenses would be necessary to deal with the differences in refraction in the various hues of light. Isaac Newton's findings on light finally made a perfect refractory telescope possible.
A composite lens, or "achromatic lens," made of two pieces of glass that have different properties is able to overcome this issue. [Achromatic lenses typically combine a concave lens with a convex lens; one lens corrects red light and the other corrects blue light so that both come into equal focus to the viewer.] But, although Newton recognized the problem that refracted light presented to telescope makers, he did not think it would be possible to correct the problem with a composite lens made of two pieces of glass. In that, he was proved wrong. But it was his discovery of the nature of light that enabled others to create an achromatic lens. Isaac Newton thought some other solution was needed, so he turned his focus in another direction to solve the telescope problem. He had discovered that refraction was linked to the colour of the light. But reflection was quite different. The laws of reflected light seemed to work quite independently of colour. Rays of all different colours, whether red, blue, or yellow, reflect in the same way when bounced off a mirror. What if Newton could build a telescope that relied on reflection rather than refraction? In that way, he could side-step the whole problem of light rays refracting differently.
In order to do this, Newton made a concave mirror out of a mixture of copper and tin -- a combination that shines almost like silver. When a star's light fell on the surface, a perfect image of the star would appear in the focus of this mirror, and the image could be examined with a magnifying glass. That's how Newton's famous reflecting telescope worked. You can still see the original little reflector that he constructed in the museum at the Royal Society. The tube of the telescope was only one inch in diameter. It was the forerunner of a whole series of excellent telescopes, each one bigger than the the last one, until finally Lord Rosse made a huge one in 1845 with a six-foot reflector.
[View a 4 minute video about Newton's telescope, which includes footage of his little reflecting telescope,on YouTube.]
Isaac Newton's discovery about light led to some bitter controversies. There were some well-respected scientists who attacked him over his theories. They claimed that the elongated band of light that Newton had seen through his prism was due to this or that factor, or something else -- anything except what Newton had said was the true cause. With his characteristic patience and love for truth, he responded to each and every attack. His responses made it clear how much his opponents misunderstood the subject and displayed their ignorance about light. With every point his challengers raised, he was able to refer to fresh experiments and new illustrations until his adversaries finally gave up and realized he was right.
Some have expressed surprise that, throughout his entire career, Isaac Newton took such trouble to patiently expose the fallacies of men who challenged his views, even when it was obvious that his adversaries didn't understand the subject they were discussing. A man who was a philosopher might have thought, 'I know I'm right and that's all that matters. If they're wrong, that's their problem. Why should I care if they remain in their misconception? I have better things to do with my time than argue with simpletons about their mistaken ideas.' But that wasn't Isaac Newton's way. He spent a lot of valuable time correcting objections that didn't make any sense. The persistence and even hostility, at times, of some of these attacks were exasperating for him. But he wasn't the type of person who could ignore what other people said about him. Many minds inferior to his are blessed with indifference to other people's opinions, but he didn't have that gift.
He was still fascinated with the subject of optics, and he did more investigations with light. Everyone has noticed the beautiful colors on soap bubbles, and it's no surprise that this attracted Newton's attention. He noticed a similar effect on other thin, transparent surfaces, and he wondered if the thickness of the material had something to do with it. He wasn't as successful in this research. In fact, his guesses about what caused colours in soap bubbles were incorrect. But he was, after all, a pioneer on the leading edge of a new and unknown field. His data are indisputable, but his explanations didn't turn out to be accurate when later research unveiled new knowledge.
Even if Newton hadn't done anything else after his discoveries about light, his name would have gone down in history as one as the great minds in interpreting natural science. But there was more in his future. In fact, what he was to discover next would be so monumental that it would overshadow his research about light and push it into the background. He is the genius who explained how the universe works by the law of gravitation.
It was an era of innovation and discovery, and it was the perfect atmosphere for Newton's brilliant mind. Kepler had recognized the laws that govern the movements of planets as they orbit the sun, and in various other fields, it seemed vaguely that his explanation must have something to do with the power of matter to attract other matter. But the mathematical tool to work with this subject [calculus] didn't exist yet. It would be created by Isaac Newton.
At Woolsthorpe during the plague of 1666, Newton was occupied with the subject of gravitation [as well as sunbeams]. We don't know for sure whether the story about the apple falling out of the tree and giving him the "aha" about gravitation is myth or fact, but it does provide an excellent way to illustrate gravity. Newton put it this way: The earth attracts the apple. No matter how high the tree is, when the apple falls, it will be drawn to the earth. So there must be something in the earth that draws all external things towards it, and that power, whatever it is, must extend beyond even the tallest tree on top of the highest mountain. No matter how far up we go, we can't seem to find its limit. As far away from the earth as we've ever been, the power of the earth to attract matter towards itself is still felt. Although at this writing [1895] we haven't been able to go more than a few miles in altitude above the earth, we know with certainty that gravity goes much farther than that. Isaac Newton was convinced that even if an apple fell from a hundred miles above the earth, it would be drawn down towards the earth by that attraction force, and it would gain speed as it fell. If it was a certainty at a hundred miles, it must also be true at a thousand miles, or at hundreds of thousands of miles. The intensity of that attraction force probably gets weaker the farther away you go from the earth, but it must still exist, even vaguely, at vast distances away from the earth.
It occurred to Newton that, even though the moon is more than 250,000 miles away, the attraction force of the earth must extend even as far as the moon. He was naturally inclined to think about the moon in relation to this -- not only because the moon is the closest celestial body to the earth, but because the moon is a satellite of the earth, constantly revolving around it. If the attraction force reaches as far as the moon, making it circle the earth rather than drifting away, why doesn't it fall to earth? It doesn't fall because it continues to move. If the moon stopped to rest for a moment, the attraction force of the earth would draw it in, and it would come crashing in on us within a few days. But this catastrophe is prevented because of the moon's movement as it propels around the earth. Isaac Newton was able to use known laws of mechanics -- laws that he had helped to discover -- to calculate how strong the attraction force of the earth must be in order to keep the moon moving in the specific way it moves. Then it was apparent that the same force that attracts the apple is what guides the moon and keeps it in its orbit.
Once this fact had been established, the rest became obvious. It was as if the whole scheme of the universe was unveiled before Newton's mind. If the moon is guided and controlled by the attraction force of the earth, then the earth, which is also an orbiting celestial body, must also be guided and controlled by some greater attraction force: the sun. And if this was true of the earth, it must be true of the planets, too. Their orbits could be explained with the same attraction force.
Isaac Newton's brilliance seemed to be up to any challenge. He realized that each planet's attraction force must be interfering with every other planet's, and that explained some of the irregularities in planetary orbits that had perplexed previous astronomers. [Planets sometimes appear to wobble, or even move backwards. View a brief demonstration of Ptolemy's explanation for this irregular movement on YouTube.] The mysterious way the earth's poles sway had long been an unsolved riddle, but Newton figured that out, too. It was caused by the moon pulling the bulging mass at the equatorial regions of the earth, and that made the earth's axis tilt. [Read more about axial precession on Wikipedia.] Newton explained all of these discoveries in his immortal book, Philosophiae Naturalis Principia Mathematica [Latin for 'Mathematical Principles of Natural Philosophy;' usually referred to simply as "Principia"].
Up until 1687, when Principia was published, Isaac Newton had lived the life of a recluse at Cambridge, focused obsessively on his discoveries. But that year, he had to make a trip away from Cambridge due to some circumstances of historical significance. King James II. wanted to promote Catholics to high positions at Cambridge. He commanded that Father Francis, a Benedictine monk, should be Master of Arts at the University, without even taking the oaths of allegiance and supremacy. The University refused. So the University's Vice-Chancellor was summoned to court to explain why he had not obeyed King James. Nine delegates were selected to defend the University's side of the issue before the High Court, and Isaac Newton was one of those delegates. They were able to prove that King Charles II [James's brother] had tried to issue a writ of mandate in similar circumstances and had been induced to withdraw it. This argument won the case for the University. The following year, Newton was elected by a narrow margin to represent Cambridge University in the Convention Parliament of 1689 after the "Glorious Revolution" that replaced James II. with King William III.
One morning in 1692, Isaac Newton went to early chapel and left a lighted candle at his desk back in his office. When he returned, the candle had fallen over -- tradition says his little dog "Diamond" knocked it over -- and many of his valuable papers had been burned. The loss of these manuscripts was deeply disturbing and even affected his health. In a letter to Samuel Pepys on September 13th, 1693, he writes,
"I am extremely troubled at the embroilment I am in, and have neither ate nor slept well this twelve-month, nor have my former consistency of mind."
In spite of Newton's fame from Principia and his ground-breaking research, the government had not done anything to acknowledge his achievements. Some of his friends had tried to get him promoted to some permanent position, but without success. But Mr. Montagu, one of the men who had served in Parliament with him, was appointed Chancellor of the Exchequer in 1694. He wanted to make his mark in the government, so he decided to improve the current coin, which needed it. Coins had been "clipped," forged, and had their edges shaved off for their metal. Mr. Montagu asked Isaac Newton to be warden of the Royal Mint in 1695 [the warden's official task was to enforce laws against counterfeiting]. There was a salary of five or six hundred pounds a year, and the warden generally delegated tasks, so his duties wouldn't require any more time than he was willing to spare.
Newton's knowledge of physics came in handy with his work at the Mint, and his skill at re-coining was so successful that he was promoted to Mastership of the Mint in 1697 with a yearly salary of £1200-1500. By 1701, his work at the Mint took up so much of his time that he resigned his Lucasian professorship at Cambridge and fellowship at Trinity College. This officially ended his connection with Cambridge. At one time, his friends almost got him appointed as Provost of King's College, Cambridge, but they weren't able to get around the requirement of being a Catholic in holy orders. [Isaac Newton was a Protestant.]
In those days, it was typical for illustrious mathematicians who had solved some compelling problem to publish the problem -- while withholding their solution. For example, the Brachsitochrone problem was solved by Johann Bernouilli. The problem involves finding the shape of a curve for a ball to slide from one point to another in the shortest time. [Read about this and see an illustrative gif here.] It seems obvious that the quickest route would be a straight line between point A and B -- a plane. But that isn't the case! There's a curved path that gets there even quicker. Johann Bernouilli challenged the world to find that curve. Isaac Newton solved it. He showed that it had to be the curve of a cycloid -- the curve traced in midair that a point on a wheel would make as it rolled along the ground. [See a cycloid demonstrated here.] Newton's geometrical genius enabled him to solve the problem and deliver his solution to the President of the Royal Society on the same day!
By 1703, Isaac Newton was famous around the world, and he was elected to be president of the Royal Society. He was re-elected year after year, for 25 years, until his death made him ineligible for the position. It was while acting in the capacity as president that he met Prince George of Denmark, who was a member of the Royal Society. In April 1705, Prince George's wife, Queen Anne, visited Cambridge and knighted Newton for his discoveries about gravity -- and thus he became Sir Isaac Newton.
His friends were eager to promote the spread of knowledge and urged him to publish a new edition of his Principia. His job at the Mint kept him too busy for the revision, so his friends urged him to ask Roger Coates to help with proofreading. Coates was a distinguished young mathematician at Trinity College who had been appointed Plumian Professor of Astronomy. With his help, a new edition of Principia was published in July, 1713. Newton, who was a favourite at the court, presented a copy to Queen Anne.
All his life, Newton was interested in theological studies, especially prophecy. He wrote several theological papers, and was working on a manuscript on the prophecies of Daniel and the Apocalypse of St. John until his death. [Some of his religious writings can be accessed here.] He was interested in the laws of cooling and heat transfer, as well as alchemy [using chemistry to turn cheaper metals into gold]. For relaxation, he sometimes tried to interpret Egyptian hieroglyphics [it was widely thought that they held symbolic or magical meaning]. He struggled with health issues in the final years of his life and died March 20, 1727, at the age of eighty four. He was buried in Westminster Abbey.
Isaac Newton was appreciated and honoured during his lifetime, and his astounding discoveries made him more widely known than most of his contemporaries, but after he died, his fame has only continued to increase steadily.
It's hard to say which is more amazing and admirable -- his wonderful discoveries, or the extraordinary mental processes that enabled him to make those discoveries. Either way, his Principia is undeniably the greatest work on science that has ever been written.
[See a drawing of Isaac Newton at his telescope here; it looks like the same telescope pictured above.]
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