Newton, Sir Isaac (1642-1727)

(click here to go to "Newton's approach to science")    

      English physical scientist and mathematician, one of the greatest figures in the entire history of science, was born at Woolsthorpe, near Grantham in Lincolnshire, on December 25, 1642. His father had died the previous October. In 1645, Newton’s mother remarried, moved to her new husband’s home and left her son in the care of her mother. Newton was an indifferent scholar until a successful fight with another boy aroused his spirit and led to his becoming the best student of the school.

      When Newton was 14 years old (1656), his mother became widowed for the second time, returned to Woolsthorpe and brought the boy home from school to run the farm. He proved to be an absent-minded farmer, occupying himself with mathematics instead of attending to his work. His uncle, William Ayscough, rector of Burton Coggles, Cambridge, and in 1660 by his advice Newton was sent to school to prepare for Cambridge. On June 5, 1661, he matriculated as a subizar at Trinity College. Three years later he was elected as scholar and in January 1665, took the B.A. degree. In 1667 he was elected a fellow of the college. In the autumn of that year the spread of the Great Plague caused the closing of the university. Until its reporting in the spring of 1667 Newton remained at Woolsthrope. During those 18 months he laid the foundations for his famous discoveries in mathematics and physical science.

Early basis discoveries

      During the first of these months at Woolsthope, Newton discovered what is now called the binomial theorem, and soon thereafter the method of “fluxions,” later known as the different calculus, the most important mathematical innovation made since the time of the ancient Greeks. In May of 1666, he related, “I had entrance into the inverse method of fluxions,” or the principle of the integral calculus, the method of calculating areas under curves and the volumes of solid figures.

      Thee discoveries alone would have entitled him to one of the highest places in the history of sciences. But two others accompanied them, each of equal significance. One was an analysis by experiment of composition of white light and the nature of colors. The other was the discovery of gravitational force holding the moon on its orbit, though nothing of his was published for almost 20 years (see work on gravitation and astronomy, bellow). Newton later said that during those two years, “I was in the prime of my age for invention, and minded mathematics and philosophy more that at any time since.”

      Newton returned to Cambridge and to Trinity College in 1667n, and did not publish discoveries. But his teacher, Isaac Barrow, a man who distinguished himself the fields of optics, mathematics and theology, recognized the superiority of his gifted pupil and resigned his chair, the Lucasian professorship of the mathematics so that Newton, at the age of 26, might succeed him. In a book on optics published in that year, Barrow recorded his indebtedness to Newton, calling him a “man of quite exceptional ability.”

Work on the telescope and optics--at this time the subject of optics was Newton’s chief scientific interest. He worked at the problem of grinding lenses with non-spherical surfaces and continued to experiment with prisms.

 One result of his research was a new type of telescope, called the reflecting telescope because its principle light-gathering component was a mirror rather than the lens system of the refracting telescope. News of this invention came to the royal society of London. Newton constructed a telescope and sent it to the society, to which he was elected a fellow. A week later, he suggested that he would like to present an account of the scientific discovery that had led him to design the new instrument, a discovery, in his words, “being in my judgment the oddest, if not the most considerable detection, which has hitherto been made in the operations of nature.”

      The main points of Newton’s discovery were these. He found that if narrow beam of “white light,” e.g. sunlight, is allowed to pass through a slit into a prism, it will be decomposed into light of many colors, or it will produce a spectrum. Separate out any single color from that spectrum, as by placing a board with a slit in the path of the light leaving the prism, and allow that monochromatic light to pass through a second prism. The result is that that the beam is bent but its color is uncharged. Hence, those were wrong who had argued that the production of a spectrum by a prism arose from a “standing” action of the prism. Rather, as Newton’s experiments showed, all light is bent or refracted as it goes from one medium to another (save in a direction perpendicular to the interface between the two mediums). Newton showed that white light is a mixture of light of all colors and that the prism separated the mixture into its component parts because the light of each color is refracted b the prism y a different amount. But if light of a single color were to be separated out in the spectrum, its color would not change as it passed through another prism since it would not be a mixture but would be (to use Newton’s own phrase) “homogeneal.”

      Knowing that whiter light is a mixture of light of all colors and the prism separates light into this component colors, Newton could then explain many color phenomena. For instance, a piece of white paper when illuminated with light of single color (say, red, green or yellow) will no longer appear to be white (but rather red, green or yellow).the colors of objects thus are related to the light by which they are seen, because “natural bodies… are variously qualified to reflect one sort of light in greater plenty than another.” On this research are founded the science of color and the technique of spectrum analysis.

      In one set of experiments, Newton studied the phenomenon known now as chromatic aberration. Since the prism experiments had shown that each color has its own index of refraction, Newton concluded that the image of a body illuminated by white light (as sun light) will not be sharp, there being a different focus for each color. Thus an ordinary biconvex lens forms an image with an edge colored like a miniature rainbow. Newton concluded erroneously from experiments that no one could ever make a lens system free of these color fringes—free of chromatic aberration. He claimed to have shown by experiment that there is such a relation between the bending of light beams (mean deviation) and the spreading out into colors (dispersion) that even a system of two or more lenses could never give an image without these unwanted color effects. In this, he was mistaken; prisms and lenses can be made of different kinds of glass in pairs so that there is no dispersion although there is a net deviation or bending of light rays from their original paths.

      In order to prevent chromatic aberration from spoiling the quality of the telescopic image, Newton devised a telescope in which the principle element was a concave or magnifying mirror. Yet, as Christian Huygens pointed out, the full potentialities of Newton’s reflecting telescope could not be released until there was a method of grinding parabolic mirrors. (The most powerful telescopes at Mount Wilson and Palomar observatories and reflecting telescopes.) The telescope Newton made for the royal society, one of their most prized possessions, is 9 inches long and has a two-inch mirror.

      When Newton sent his paper on light and colors to the Royal Society, a committee was appointed to study the question further. One committee member, Robert Hooke, the originator of a theory of light and color of considerable merit, had written a book dealing in part with the same type of phenomena Newton had studied, the Micrographia (1664). Hooke admitted the accuracy of Newton’s experiments, but doubted Newton’s conclusions. Huygens also held to his own theory of color, and as E. N. DA Costa Andrade has explained, “he failed to understand…that Newton was not arguing about the nature of color, about matters of doctrine, but describing experiments to show how white light and colored light behaved, to show what were the measurable properties.” Other critics arrows; some misunderstood the experiments, but there was chiefly disagreement on Newton’s theory. Three of Newton’s comments explain his position clearly: “… the Theory, which I propounded, was evinced but me, not inferring ‘tis thus because not otherwise, that is, not by deducing it only from a confutation of contrary suppositions, but by deriving it from Experiments concluding positively and directly.” “For the best and safest method of philosophizing seems to be, first to enquire diligently into the properties of things and of establishing these properties by experiment, and then to proceed more slowly to hypotheses for the explanation of them.” As to “certain properties of light, which, now discovered, I think easy to be proved… which if I had not considered then as true, I would rather have them rejected as vein and empty speculation, then acknowledged even as a hypothesis.”

      Discussions about Newton’s paper lasted until well into 1675. In December of that year he wrote, “I was so persecuted with discussions arising out of my theory of light that I blamed my own imprudence for parting with so substantial a blessing as my quiet to run after a shadow.”

      One effect of the controversy was that Newton was led to investigate other effects of color, to inquire how light was produced and to develop the emissions or corpuscular theory of light, according to which light is cause by the emission by a luminous body of a host of tiny particles traveling in empty space with a 186000 mi. per second; the laws of reflection and refraction were developed on mechanical principles, aided only by a supplementary hypothesis as to why, when falling on a transparent surface, some of the particles are reflected—bent back into the medium from which they have come—and others are refracted, along a new path inclined to the old , into the medium toward which they are traveling. It is a consequence of this theory that light travels more slowly in a dense medium such as glass and in air. The theory was also applied to explain the colors seen when light is reflected from a thin film, a soap film or the thin layer of air between a convex lens of large radius and a flat reflecting surface on which it rests; in this case, when viewed in reflected light of a definite color a series of dark and light rings circling round a central black spot is seen. Newton determined the law connecting the radius of a bright ring and the color of the light. Since the radius depends on the color, the bright rings for the various colors, when white light is used, will be different at the observer will see a series of colored rings surrounding the central black spot. This phenomenon is known as “Newton’s rings.”

      Hooke was again a critic; in his Micrographia he had adopted a kind of wave theory of light, according to which light consists of a series of pulses transmitted through a medium pervading space, the universal ether, and had endeavored to explain rectilinear propagation reflection and refraction as well as dispersion and the colors of thin plates. Newton, in his explanation of optical phenomena showed how the corpuscles of light might be guided by waves in an ethereal medium; yet he thought little of Hooke’s attempts at explanation. From the work of Thomas Young in 1804 and the brilliant work of the French genius Augustin Fresnel a few years later came the explanation on the wave theory of all the phenomena of light as then observed. Young drew on Newton’s concepts of waves as much as on the views of Christian Huygens.

      Newton rejected a simple wave theory of light because it could not account for rectilinear propagation or for polarization. As Newton demonstrated all wave phenomena—for instance, sound—carry the disturbance into the region of the shadow, or around obstacles. It never occurred to him that the waves of light might be exceedingly small. Yet in studying the colors of thin plates, Newton provided much of the necessary information for the later wave theorists. Thomas Young showed that Newton’s careful measurements led to an accurate determination of the wavelength of the several colors. In his early papers, and later on in his Opticks (first edition 1704) Newton advanced an explanation of optical phenomena that was neither a pure corpuscular theory nor a pure wave theory. According to Newton it seemed probable that light consists of a series of corpuscles emanating from luminous bodies. These corpuscles give rise to waves as they travel through the ether and many optical phenomena (such as the colors of thin plates) a rise from the interaction of the waves and corpuscles. This explanation fell from favor during the 19^th century, when the wave theory of light was universally accepted. But since Einstein’s theory of photons of 1905, many writers have called attention to a similarity between Newton’s views and those of the 20^th century, in which there is a fusion of elements of both wave and corpuscular theories of light.

      Work on gravitation and astronomy. —Since the early years at Woolsthrope, Newton had been considering the main problem of motion: what force is it that keeps the planets moving about the sun in the Copernican system? Newton showed that one and the same force of the universal gravitation caused the planets to revolve about the sun in elliptical paths according to Kepler’s laws. Furthermore, this force, which varies as the inverse square of the distance, keeps the moon in motion about the earth and causes objects to fall to earth.

      Newton related that the occasion of this discovery was the fall of an apple. What did he mean? If the moon moves in an orbit around the Earth, and does not fly off in a straight line along a tangent to the orbit, there must be a force directed to the Earth, a “centripetal” force   pulling the moon to the center of the Earth. The situation is similar to that of a ball whirling in a circle at the end of a string; if the string breaks, the centripetal force ceases to be exerted, and the ball flies off along a tangent. Expressed differently, the moon is continually drawn away from its rectilinear tangential path by a force; this force causes the moon to fall continually away from a straight line and to follow its observed orbit. Newton computed the distance the moon must fall in each second. If the force that makes the moon fall varies inversely as the square of the distance, then, since the moon is at a distance of 60 earth radii from the earth’s center, the earth’s force is 1/60² or 1/3600 of what it would be if the moon were at the Earth’s surface. Hence, assuming that the force of gravity keeps the moon in its orbit and that this force varies inversely as the distance, Newton could predict the rate of fall of an object to the Earth. This proved to be approximately what is observed: as Newton expressed it, the observation agreed “pretty nearly” with the theory. He also was able to show that Kepler’s laws implied a central force that varied as the square of the distance. Conversely, by assuming a single force exerted between sun and planets proportional to the masses of the sun and the planet involved and inversely proportional to the square of the distance between them, one could derive Kepler’s laws and show that one and the same force acted between the planets and the sun, between any planet and its satellite, between the oceans and sun and moon (so as to produce the tides) and, in general, between any two bits of matter in the universe.

      In London, there were great debates about planetary motions and about the orbits that would result from specified types of forces. Discussions went on at a Royal society or in the houses of the members—Sir Christopher Wren, Hooke, Edmond Halley and others were active in the society, until one Wednesday in January 1684 Halley met Wren and Hooke and the latter declared “that he had demonstrated all the laws of the celestial motions.” Halley confessed his ignorance and Sir Christopher “to encourage enquiry said he would he would give Hooke or me”—the quotation is from a letter of Halley to Newton—“two months to bring him a convincing demonstration.” Sir Christopher offered to give “a book of 40 shillings” to the one who first found the solution. So it remained until August, When Halley visited Newton at Cambridge and put the question, what would be the path of a body moving under the action of a central force which varied as the inverse square of the distance from the center. Halley wrote that Newton knew the answer and “had brought this demonstration to perfection.” Newton promised to look for the old proof but could not find it, “and not finding it did it again.” Halley retuned to Cambridge and persuaded Newton to put his work in form for the Royal society. On December 10, 1684, Halley informed the society that he had lately seen Newton, who had showed him a curious treatise, De Motu, which, upon Halley’s desire, was sent to the society to be entered on their register.

      Newton then attacked and solved a major problem. Hitherto his calculations had proceeded on the assumption that the sun and the planets could each be treated as though they were points, with all their matter concentrated at their respective centers. But was this true or was it merely an approximation resulting from the fact that the planetary distances were so immense that even a great sphere like the sun could in comparison be treated as a point?

      Newton proceeded to work this out, the assumption that each particle of the sun attracted an external particle with a force proportional to the product of the masses of the two and inversely proportional to the square of the distance between them. Thus he proved that if the sun were of uniform density then the resultant force on the external particle was the same as that which would be exerted by the whole mass of that concentrated at the center.

      Some scholars have held that it was the difficulty of solving this problem that had caused Newton in 1665 to lay aside his astronomical calculations. Others agree with H. Pemberton’s remark that a poor value for the earth’s radius was responsible for the delay. In any event, the calculations were resumed with a more correct knowledge of the moon’s distance.

      The writing of the Principia was begun in March 1686. Entitled Philosophiae Naturalis Principia Mathematica, or “mathematical principles of natural philosophy,” the work was first published in the summer of 1687. At the time the Royal society was in difficulties as to funds and Halley took the whole cost on himself. Hooke, when the first book was presented, claimed that he had forestalled Newton in part of it, and in the correspondence that followed Halley did all he could to smooth over the difficulties and persuade Newton to continue his work.

      The Principia set the seal to Newton’s reputation. Ti explained for the first time the way in which a single mathematical law could account for phenomena of the heavens, the tides, and the motion of objects on the earth. The whole development of modern sciences begins with this great book. For more that two hundred years it reigned supreme, and all the theories of cosmogony were based on the principles laid down by Newton. His mechanics guided astronomers and men of science in their search for natural knowledge.

Religious Beliefs.—Newton was profoundly interested in religious matters. He studied carefully the writings of the church fathers, the early writers on Christianity, and sought evidence to bolster his own principles of faith, which were anti-Trinitarian. John Maynard Keynes, who studied Newton’s writings on esoteric and theological matters, concluded that Newton was “a Judaic monotheist of the school of Maimonids.” very likely this was the reason that Newton reused holy orders and had to be given a special dispensation to hold his professorship. He kept his religious convictions, like his experiments on alchemy, secret. Unfortunately, the amount of time and energy that he devoted to alchemy revaled that given to physics or to mathematics. So well did Newton keep his secret that his activities in these two realms are not generally and fully known.

Middle and Latter Life.—in 1687 James II tried to force the university to admit as a master of arts Father Alban Francis, a Benedictine monk, without taking the oaths of allegiance and supremacy. Newton was one of those who led the resistance to the royal action, and appeared before Lord Jeffreys to argue the case for Cambridge. In the end the deputies were reprimanded and John Peachell, the vice-chancellor, was deprived of his office. Newton’s share in the affair led to his being elected member of the parliament for the university in 1689, retaining the seat till the dissolution next year. He was elected again in 1701, but he never took any prominent part it politics.

      Upon the dissolution for parliament in 1690 he returned to Cambridge and continued for a time his mathematical work; this was interrupted in 1692-94 by a serious illness. He was suffering from insomnia and nervous trouble. There was a report that he was going out of his mind. In June 1694 Huygens wrote to G. W. Leibniz, “I do not know if you are acquainted with the accident to the good Mr. Newton, namely, that he has had an attack of Phrenitis which lasted 18 months and of which they say his friends have cured him by means of remedies and keeping him shut up.” For some time his friends had been anxious to obtain same recognition of his work; this came in 1695. Charles Montague, latter earl of Halifax, a former fellow of Trinity who was Chancellor of the Exchequer, offered him the post of warden of the mint. This he accepted and four years latter he became master. In the same year he was elected one of the eight foreign associates of the French Academy of Science.

      In 1696 John Bernoulli addressed a letter to the mathematicians of Europe, challenging them to solve two problems and giving six months for the solution. On January 29, 1697 Newton received from France two copies of the printed papers containing the problems and the following day sent the solution to the Royal society. They were transmitted anonymously to Bernoulli, who, as he said, recognized the lion by his talon, “tanquam ex ungue leonem.”

      As warden of the mint Newton had retained his Cambridge offices, but soon after his appointment as master he named a deputy, and in 1701 resigned his professorship and the fellowship at Trinity. He had moved to London, where he continued his duties as master with marked efficiency until his death in 1727. In 1703 Newton became president of the Royal society and was re-elected annually until his death. Queen Anne visited Cambridge in 1705 and on this occasion Newton was knighted. About the same time the controversy with Leibniz was a plagiarist had no foundation. Early in 1727 Newton was taken seriously ill; he died on March 20, 1727, and was buried in Westminster abbey on March 28.

 Published works—since the first issue of principia in 1687 (see above), there have been many editions. In 1708 Newton consented to have Roger Cotes, a fellow of Trinity, help him prepare a second edition, which was published in 1713; a third edition made with the aid of Henry Pemberton appeared in 1726. This Latin edition was reprinted in Geneva in 1739-42 with an excellent commentary by two minims, Le Sueur and Jaquier; often reprinted, this is known incorrectly as the “Jesuits’ edition.” An English translation first published by A. Motte as Mathematical Principles of Natural Philosophy (1729) was revised and republished (1803) revised again by Florian Cajory and reprinted together with Newton’s System of the World.

      The optics, first published in 1704, went through three editions in Newton’s lifetime; a modern edition appeared in 1952.

      The scientific papers published by Newton in his lifetime are collected in Isaac Newton’s Papers and Letters on Natural Philosophy, edited by I. Bernard Cohen (1958). The most recent edition of Newton’s writings, edited by S. Horsely in five volumes under title Opera quae extant omina (1779-85).

      Correspondence of Scientific Men of the 17^th Century, etc. From the Originals in the Collection of the Earl of Macclesfield, edited by S.P. Rigaud (1841); and Correspondence of Sir Isaac Newton and Professor Cotes, Including Letters oh Other Eminent Men. (1850), edited by J. Edleston, contain many of Newton’s letters and the latter volume contains a synopsis of his life. A Lachlan (ed.), Theological Manuscripts (1950); earlier published religious writings were Chronology of Ancient Kingdoms Amended (1728) and the Apocalypse of St. John (1733).

      The Royal society has undertaken an edition of the Correspondence of Isaac Newton, of which the first two volumes (1959, 1960), edited by H,W. Turnbull, cover the years 1661-75, 1676-87.

----------------------------------------------------------------