Newton , Sir Isaac

(1642–1727) English physicist and mathematician

Newton's father, the owner of the manor of Woolsthorpe in Lincolnshire, died three months before Newton was born. The family had land but were neither wealthy nor gentry. Left by his mother in the care of his grandmother, the young Newton is reported to have been quiet, unwilling to play with the village boys, and interested in making things. His mother returned to Woolsthorpe in 1656 after the death of her second husband. By this time Newton was at school in Grantham where he stayed until 1658, lodging with a local apothecary. There is no evidence that he was especially gifted at this time, although he was certainly skillful for he made a water clock, sundials (which still survive at Woolsthorpe), and model furniture for his stepsisters. After two years helping his mother to run the family farm, he went to Cambridge University in 1661, where he stayed for nearly 40 years.

Not much is known of Newton's student life. In 1665 he was forced by the plague to leave Cambridge and return to Woolsthorpe. Here, during his so-called annus mirabilis(miraculous year), he began to develop the ideas and insights for which he is so famous. Here he first began to think about gravity, and also devoted time to optics, grinding his own lenses and considering the nature of light. During this period he also worked out his mathematical ideas about ‘fluxions’ (the calculus).

When he returned to Cambridge after the plague had died down he was elected a fellow of his college, Trinity, in 1667, and in 1669 he succeeded Barrow as Lucasian Professor. He served as member of parliament for the university for the periods 1689–90 and 1701–02, although he does not appear to have been politically very active. His public career was pursued through Charles Montague, first earl of Halifax, who was able to introduce Newton into court and society circles. When Montague became chancellor of the exchequer he was able to offer Newton the post of warden of the Mint in 1696. He was made master of the Mint in 1699 and knighted for his services in 1705. From this time he did virtually no new science apart from publishing and revising works already written. He did concern himself with the affairs of the Royal Society, of which he became president in 1703. He resigned his Cambridge post in 1701.

At the Mint, his first task was to supervise ‘the great recoinage’ – the replacement of the old hammered coins with new pieces with milled edges. It was also Newton's business to pursue the counterfeiters and clippers of his day. As ever, he took his duties seriously and could be found regularly visiting suspects in Newgate and other prisons. Between June 1698 and Christmas 1699 he interviewed 200 witnesses on 123 separate occasions. In the same period 27 counterfeiters were executed. Other major tasks undertaken by Newton included the introduction of a union coinage in 1707 following the union of the Kingdoms of England and Scotland, the issue of new copper coins in 1718, the revaluation of the guinea to 21 shillings in 1717, and a general improvement in the assaying of the currency. The Mint made Newton a wealthy man. In addition to a salary of £600 a year he also received a commission on the amount of silver minted, which brought in on average £1000 a year. At the time of his death Newton had accumulated £30,000 in cash and securities.

Much of Newton's later life was also spent in needless priority disputes. These arose largely through his reluctance to publish his own work. It was not until 1704, when Newton was over 60, that he actually published a mathematical text. Even then his main work on the calculus, Methodis fluxionum (Method of Fluxions), composed between 1670 and 1671, was only published posthumously in 1736. At the same time manuscripts of unpublished works were shown to friends and colleagues.

When, therefore, Leibniz published his own work on the differential and integral calculus in 1684, he felt no need to acknowledge any unpublished work of Newton. He had developed his methods and notation largely from his own vast intellectual resources. He had seen some Newtonian manuscripts on a visit to London in 1673, and letters from Newton in 1676 contained further details. None of this, it is now accepted, was sufficient to account for Leibniz's 1684 paper. The dispute began in 1700 when Leibniz objected to the practice of the Newtonians referring to him as the ‘second inventor’ of the calculus. The dispute dragged on until the 1720s, long outlasting the death of Leibniz in 1716. After a decade of bitter and anonymous dispute Leibniz unaccountably applied to the Royal Society in 1712 to conduct an inquiry into the matter. Newton behaved quite shamelessly. He appointed the committee, decided what evidence it should see, and actually drafted the published report himself. Thereupon, in later stages of the dispute, he would appeal to the report, the Commercium epistolicum (1713; On the Exchange of Letters), as an independent justification of his position.

Newton is best known for his work on gravitation and mechanics. The most famous story in the history of science has the unusual distinction of being true, at least according to Conduit, who married Newton's niece Catherine. He reported that “In the year 1665, when he retired to his own estate on account of the plague, he first thought of his system of gravity, which he hit upon by observing an apple fall from a tree.” His ideas were not published until 1684 when Edmond Halley asked Newton to find what force would cause a planet to move in an elliptical orbit. Newton replied that he already had the answer. Finding that he had lost his proof, he worked it out again.

His result was that two bodies – such as the Sun and a planet, or the Earth and the Moon – attract each other with a force that depends on the product of their masses and falls off as the square of their distance apart. Thus the force is proportional to m₁m₂/d², where m₁ and m₂ are the masses and d is their distance apart. Originally he applied this to point masses but in 1685 he proved that a body acted as if its mass were a point mass of the same magnitude acting at the center of the body (for a symmetrical body).

Newton's original work on gravity, in 1665, had been applied to the motion of the Moon. His insight was that the Moon in its motion ‘falls’ to the Earth under the same cause as the apple falls. His calculations at this time used an erroneously low value for the Earth's radius and it was possibly this that made him lay aside his calculations until 1684.

Then in 1684 he took up the subject again and began to write his great work Philosophiae Naturalis Principia Mathematica(Mathematical Principles of Natural Philosophy) – known as thePrincipia. The first edition was published in 1687. Here he set out his three laws of motion. His first law states that a body at rest or in uniform motion will continue in that state unless a force is applied. His second law gives a definition of force – that it equals the mass of a body multiplied by the acceleration it produces in the body. His third law puts forward the idea that if a body exerts a force (action) on another there is an equal but opposite force (reaction) on the first body.

What Newton did in his work in mechanics was to establish a unified system: one in which a simple set of basic laws explained a range of diverse phenomena – the motion of the Moon and planets, motion of the Earth, and the tides. Newton did not give any explanation of what gravity actually is. How it acts, its mechanism, and its cause were matters that Newton claimed we should not frame hypotheses on. That it has a cause Newton was sure of, for the idea that a body may act on another through a vacuum over a long distance “without the mediation of anything else … is to me so great an absurdity that I believe no man can ever fall into it. Gravity must be caused … but whether this agent be material or immaterial I have left to the consideration of my reader.” Newton did not always obey his own injunction and in the 1713 edition of the Principia speculated about the existence of “certain very subtle spirits that pervade all dense bodies,” which might explain light, electricity, sensation, and much besides.

Newton's reluctance to provide a gravitational mechanism was seen as a basic weakness of his system by the Cartesians. Whatever the defects of the physics of René Descartes at least he provided mechanisms, in the form of vortices, to explain all movements. To some Newton's gravity seemed a retrograde step in that it was reintroducing into physics the occult, meaningless forces that Descartes had recently eliminated. Nevertheless, Newton's system received great acclaim in England and was to become the model for all succeeding scientific theory.

Newton also worked extensively on light. He began by rejecting the Cartesian account of color. For Descartes white light was natural light; colored light was the modification produced in light by the medium through which it passes. Thus light passing through a prism is spread into a spectrum because the light has been differentially modified by the varying thickness of the prism.

Newton published his own account in 1672 in his first published paper, New Theory about Light and Colours. “I procured me a Triangular glass-Prisme to try therewith the celebrated Phenomena of Colours,” he began. When he passed a ray of light through a prism he found that it formed an oblong, not a circular image, five times longer than its breadth. He found that, as was well known, light passing through a prism was dispersed and formed a colored spectrum. But when a second prism was taken and colored light rays passed through it, no further change was discernible. Red light remained red, and blue light blue. From this, his famous experimentum crucis (cross experiment), he derived two important conclusions: firstly, ordinary white light was composite, a mixture of the various colors of the spectrum; secondly, he concluded, “Light consists of Rays differently Refrangible,” and it was this difference in refrangibility that produced the oblong image which had so puzzled Newton.

Newton's views found little favor and over the next few years he was repeatedly called upon to explain and defend his position. By 1676 he had had enough. “I see a man must either resolve to put out nothing new or become a slave to defend it,” he wrote to Oldenburg, and published no more on light until 1704.

He had, however, already in 1675 sent a paper to the Royal Society entitled An Hypothesis Explaining the Properties of Light. He refused to allow it to be published and it first appeared in 1757, long after Newton's death. The paper contains Newton's analysis of light as “multitudes of unimaginable small and swift corpuscles of various sizes, springing from shining bodies.” He dismissed the view that light, like sound, could consist of waves, because light unlike sound could not travel around corners. The paper also contained an account of what have since become known as Newton's rings. These consist of a series of concentric colored rings and can be produced by putting a plano-convex lens of large radius of curvature on a flat reflecting surface. They were explained by Newton with some ingenuity and some difficulty in terms of his corpuscular theory of light. Newton's mature views on these and many other matters were presented in his Opticks(1704).

Not all of Newton's work on light was of a theoretical kind. He was an extremely talented experimentalist and in the late 1660s he designed and built the first reflecting telescope. This involved grinding and polishing the mirrors himself. The idea of a reflecting telescope had occurred earlier to James Gregory but his attempts at constructing a model, despite receiving professional help, led nowhere. The advantage of the Newtonian telescope over the refractor of Galileo is that mirrors do not suffer from chromatic aberration.

But above all else Newton was a mathematician of incomparable power. In 1696 Johann Bernoulli posed a problem to the mathematicians of Europe, allowing them six months to solve it. Newton solved the problem in a single night and published the result anonymously in the Transactions of the Royal Society. Bernoulli was not fooled, claiming to recognize the author or, “the lion by his claw.” Again in 1716 Leibniz issued another difficult problem, which Newton solved before going to bed after a day's work at the Mint.

Newton communicated the generalized form of the binomial theorem to Henry Oldenbourg in 1676. It was also in that year that he deposited with Oldenbourg his epistola prior (first letter) claiming discovery of his method of fluxions in an anagram. The terminology arose from his considering the path of a continuously moving body as a curve made by a continuously moving point. The moving point he called a fluent and its velocity he called a fluxion. This he symbolized by ẋ and its acceleration as ⎕. This, independently of Leibniz, was Newton's discovery of the calculus, although Leibniz's notation was the one eventually adopted.

Throughout his life Newton also displayed a deep interest in two other areas: religion and alchemy. At his death over 1000 manuscript pages, running to nearly 1.5 million words, and two completed books were discovered, devoted entirely to religious matters. Newton was a unitarian, a matter kept fairly secret during his life as it would have excluded him from his Lucasian chair and his post at the Mint. Much of his life was spent on deep studies of church history, the Bible, and ancient chronology. His aim was to show that the text of the Bible had been corrupted by later trinitarian editors, and that the history of the early church revealed a similar corruption introduced by Athanasius in the fourth century. The matter was dealt with at length in his Two Notable Corruptions of Scripture (1754) and in numerous manuscripts.

Equally extensive were Newton's alchemical manuscripts. In his library were 138 books on alchemy, and his manuscripts on the subject exceed 600,000 words. It is less clear, however, whether Newton was a genuine alchemist committed to dreams of transmutation and the philosopher's stone, or whether he was merely using whatever sources he could find to further his chemical interests. His interests in chemistry were sufficient to lead him to establish a laboratory in Trinity College and for a while in the 1680s, it was reported, “the laboratory fire scarcely went out night or day.” He published during his life just one brief work on chemistry, De natura acidorum (1710; On the Nature of Acids). There are, however, several passages devoted to chemistry scattered among the Queries added by Newton to hisOpticks (1704).

Newton died in 1727 at the age of 85 after a fairly short illness. He managed to preside over a meeting of the Royal Society a fortnight before his death. Shortly after he was diagnosed as having a stone in the bladder and seems to have spent the last days of his life in great pain. He was buried in Westminster Abbey where a most unattractive monument can still be seen. Many words have been written about his greatness as a scientist; the most apposite remain the often quoted words of Alexander Pope, composed for Newton's tomb but, for some reason, rejected: Nature and Nature's laws lay hid in night:

God said, let Newton be! and all was light.