Sir Isaac Newton (1642-1727) was an English scientist and mathematician. He made major contributions in mathematics and theoretical and experimental physics and achieved a remarkable synthesis of the work of his predecessors on the laws of motion, especially the law of universal gravitation.

Isaac Newton was born on Christmas Day, 1642, at Woolsthorpe, a hamlet in southwestern Lincolnshire. In his early years Lincolnshire was a battle-ground of the civil wars, in which the challenging of authority in government and religion was dividing England's population. Also of significance for his early development were circumstances within his family. He was born after the death of his father, and in his third year his mother married the rector of a neighboring parish, leaving Isaac at Woolsthorpe in the care of his grandmother.

After a rudimentary education in local schools, he was sent at the age of 12 to the King's School in Grantham, where he lived in the home of an apothecary named Clark. It was from Clark's stepdaughter that Newton's biographer William Stukeley learned many years later of the boy's interest in her father's chemical library and laboratory and of the windmill run by a live mouse, the floating lanterns, sundials, and other mechanical contrivances Newton built to amuse her. Although she married someone else and he never married, she was the one person for whom Newton seems to have had a romantic attachment.

At birth Newton was heir to the modest estate which, when he came of age, he was expected to manage. But during a trial period midway in his course at King's School, it became apparent that farming was not his métier. In 1661, at the age of 19, he entered Trinity College, Cambridge. There the questioning of long-accepted beliefs was beginning to be apparent in new attitudes toward man's environment, expressed in the attention given to mathematics and science.

After receiving his bachelor's degree in 1665, apparently without special distinction, Newton stayed on for his master's; but an epidemic of the plague caused the university to close. Newton was back at Woolsthorpe for 18 months in 1666 and 1667. During this brief period he performed the basic experiments and apparently did the fundamental thinking for all his subsequent work on gravitation and optics and developed for his own use his system of calculus. The story that the idea of universal gravitation was suggested to him by the falling of an apple seems to be authentic: Stukeley reports that he heard it from Newton himself.

Returning to Cambridge in 1667, Newton quickly completed the requirements for his master's degree and then entered upon a period of elaboration of the work begun at Woolsthorpe. His mathematics professor, Isaac Barrow, was the first to recognize Newton's unusual ability, and when, in 1669, Barrow resigned to devote himself to theology, he recommended Newton as his successor. Newton became Lucasian professor of mathematics at 27 and stayed at Trinity in that capacity for 27 years.

Experiments in Optics

Newton's main interest at the time of his appointment was optics, and for several years the lectures required of him by the professorship were devoted to this subject. In a letter of 1672 to the secretary of the Royal Society, he says that in 1666 he had bought a prism "to try therewith the celebrated phenomena of colours." He continues, "In order thereto having darkened the room and made a small hole in my window-shuts to let in a convenient quantity of the Suns light, I placed my prism at its entrance, that it might be thereby refracted to the opposite wall." He had been surprised to see the various colors appear on the wall in an oblong arrangement (the vertical being the greater dimension), "which according to the received laws of refraction should have been circular." Proceeding from this experiment through several stages to the "crucial" one, in which he had isolated a single ray and found it unchanging in color and refrangibility, he had drawn the revolutionary conclusion that "Light itself is a heterogeneous mixture of differently refrangible rays."

These experiments had grown out of Newton's interest in improving the effectiveness of telescopes, and his discoveries about the nature and composition of light had led him to believe that greater accuracy could not be achieved in instruments based on the refractive principle. He had turned, consequently, to suggestions for a reflecting telescope made by earlier investigators but never tested in an actual instrument. Being manually dexterous, he built several models in which the image was viewed in a concave mirror through an eyepiece in the side of the tube. In 1672 he sent one of these to the Royal Society.

Newton felt honored when the members were favorably impressed by the efficiency of his small reflecting telescope and when on the basis of it they elected him to their membership. But when this warm reception induced him to send the society a paper describing his experiments on light and his conclusions drawn from them, the results were almost disastrous for him and for posterity. The paper was published in the society's Philosophical Transactions , and the reactions of English and Continental scientists, led by Robert Hooke and Christiaan Huygens, ranged from skepticism to bitter opposition to conclusions which seemed to invalidate the prevalent wave theory of light.

At first Newton patiently answered objections with further explanations, but when these produced only more negative responses, he finally became irritated and vowed he would never publish again, even threatening to give up scientific investigation altogether. Several years later, and only through the tireless efforts of the astronomer Edmund Halley, Newton was persuaded to put together the results of his work on the laws of motion, which became the great Principia.

His Major Work

Newton's magnum opus, Philosophiae naturalis principia mathematica, to give it its full title, was completed in 18 months--a prodigious accomplishment. It was first published in Latin in 1687, when Newton was 45. Its appearance established him as the leading scientist of his time, not only in England but in the entire Western world.

In the Principia Newton demonstrated for the first time that celestial bodies follow the laws of dynamics and, formulating the law of universal gravitation, gave mathematical solutions to most of the problems concerning motion which had engaged the attention of earlier and contemporary scientists. Book 1 treats the motion of bodies in purely mathematical terms. Book 2 deals with motion in resistant mediums, that is, in physical reality. In Book 3, Newton describes a cosmos based on the laws he has established. He demonstrates the use of these laws in determining the density of the earth, the masses of the sun and of planets having satellites, and the trajectory of a comet; and he explains the variations in the moon's motion, the precession of the equinoxes, the variation in gravitational acceleration with latitude, and the motion of the tides. What seems to have been an early version of book 3, published posthumously as The System of the World, contains Newton's calculation, with illustrative diagram, of the manner in which, according to the law of centripetal force, a projectile could be made to go into orbit around the earth.

In the years after Newton's election to the Royal Society, the thinking of his colleagues and of scholars generally had been developing along lines similar to those which his had taken, and they were more receptive to his explanations of the behavior of bodies moving according to the laws of motion than they had been to his theories about the nature of light. Yet the Principia presented a stumbling block: its extremely condensed mathematical form made it difficult for even the most acute minds to follow. Those who did understand it saw that it needed simplification and interpretation. As a result, in the 40 years from 1687 to Newton's death the Principia was the basis of numerous books and articles. These included a few peevish attacks, but by far the greater number were explanations and elaborations of what had subtly evolved in the minds of his contemporaries from "Mr. Newton's theories" to the "Newtonian philosophy."

London Years

The publication of the Principia was the climax of Newton's professional life. It was followed by a period of depression and lack of interest in scientific matters. He became interested in university politics and was elected a representative of the university in Parliament. Later he asked friends in London to help him obtain a government appointment. The result was that in 1696, at the age of 54, he left Cambridge to become warden and then master of the Mint. The position was intended to be something of a sinecure, but he took it just as seriously as he had his scientific pursuits and made changes in the English monetary system that were effective for 150 years.

Newton's London life lasted as long as his Lucasian professorship. During that time he received many honors, including the first knighthood conferred for scientific achievement and election to life presidency of the Royal Society. In 1704, when Huygens and Hooke were no longer living, he published the Opticks, mainly a compilation of earlier research, and subsequently revised it three times; he supervised the two revisions of the Principia; he engaged in the regrettable controversy with G. W. von Leibniz over the invention of the calculus; he carried on a correspondence with scientists all over Great Britain and Europe; he continued his study and investigation in various fields; and, until his very last years, he conscientiously performed his duties at the Mint.

His "Opticks"

In the interval between publication of the Principia in 1687 and the appearance of the Opticks in 1704, the trend was away from the use of Latin for all scholarly writing. The Opticks was written and originally published in English (a Latin translation appeared 2 years later) and was consequently accessible to a wide range of readers in England. The reputation which the Principia had established for its author of course prepared the way for acceptance of his second published work. Furthermore, its content and manner of presentation made the Opticks more approachable. It was essentially an account of experiments performed by Newton himself and his conclusions drawn from them, and it had greater appeal for the experimental temper of the educated public of the time than the more theoretical and mathematical Principia.

Of great interest for scientists generally were the queries with which Newton concluded the text of the Opticks--for example, "Do not Bodies act upon Light at a distance, and by their action bend its rays?" These queries (16 in the first edition, subsequently increased to 31) constitute a unique expression of Newton's philosophy; posing them as negative questions made it possible for him to suggest ideas which he could not support by experimental evidence or mathematical proof but which gave stimulus and direction to further research for many generations of scientists. "Of the Species and Magnitude of Curvilinear Figures," two treatises included with the original edition of the Opticks, was the first purely mathematical work Newton had published.

Mathematical Works

Newton's mathematical genius had been stimulated in his early years at Cambridge by his work under Barrow, which included a thorough grounding in Greek mathematics as well as in the recent work of René Descartes and of John Wallis. During his undergraduate years Newton had discovered what is known as the binomial theorem; invention of the calculus had followed; mathematical questions had been treated at length in correspondence with scientists in England and abroad; and his contributions to optics and celestial mechanics could be said to be his mathematical formulation of their principles.

But it was not until the controversy over the discovery of the calculus that Newton published mathematical work as such. The controversy, begun in 1699, when Fatio de Duillier made the first accusation of plagiarism against Leibniz, continued sporadically for nearly 20 years, not completely subsiding even with Leibniz's death in 1716.

The inclusion of the two tracts in the first edition of the Opticks was certainly related to the controversy, then in progress, and the appearance of other tracts in 1707 and 1711 under the editorship of younger colleagues suggests Newton's release of this material under pressure from his supporters. These tracts were for the most part revisions of the results of early research long since incorporated in Newton's working equipment. In the second edition of the Principia, of 1713, the four "Regulae Philosophandi" and the four-page "Scholium Generale" added to book 3 were apparently also designed to answer critics on the Continent who were expressing their partisanship for Leibniz by attacking any statement of Newton's that could not be confirmed by mathematical proof; the "Scholium" is of special interest in that it gives an insight into Newton's way of thought which the more austere style of the main text precludes.

Other Writings and Research

Two other areas to which Newton devoted much attention were chronology and theology. A shortened form of his Chronology of Ancient Kingdoms appeared without his consent in 1725, inducing him to prepare the longer work for publication; it did not actually appear until after his death. In it Newton attempted to correlate Egyptian, Greek, and Hebrew history and mythology and for the first time made use of astronomical references in ancient texts to establish dates of historical events. In his Observations upon the Prophecies of Daniel and the Apocalypse of St. John, also posthumously published, his aim was to show that the prophecies of the Old and New Testaments had so far been fulfilled.

Another of Newton's continuing interests was the area in which alchemy was evolving into chemistry. His laboratory assistant during his years at Cambridge wrote of his chemical experiments as being a major occupation of these years, and Newton's manuscripts reflect the importance he attached to this phase of his research. His Mint papers show that he made use of chemical knowledge in connection with the metallic composition of the coinage. Among the vast body of his manuscripts are notes indicating that his Chronology and Prophecy and also his alchemical work were parts of a larger design that would embrace cosmology, history, and theology in a single synthesis.

The mass of Newton's papers, manuscripts, and correspondence which survives reveals a person with qualities of mind, physique, and personality extraordinarily favorable for the making of a great scientist: tremendous powers of concentration, ability to stand long periods of intense mental exertion, and objectivity uncomplicated by frivolous interests. The many portraits of Newton (he was painted by nearly all the leading artists of his time) range from the fashionable, somewhat idealized, treatment to a more convincing realism. All present the natural dignity, the serious mien, and the large searching eyes mentioned by his contemporaries.

When Newton came to maturity, circumstances were auspiciously combined to make possible a major change in men's ways of thought and endeavor. The uniqueness of Newton's achievement could be said to lie in his exploitation of these unusual circumstances. He alone among his gifted contemporaries fully recognized the implications of recent scientific discoveries. With these as a point of departure, he developed a unified mathematical interpretation of the cosmos, in the expounding of which he demonstrated method and direction for future elaboration. In shifting the emphasis from quality to quantity, from pursuit of answers to the question "Why?" to focus upon "What?" and "How?" he effectively prepared the way for the age of technology. He died on March 20, 1727.

Further Reading

• Newton's writings are available in many editions, several of which contain scholarly introductions and notes of great value. Louis T. More, Isaac Newton (1934), is the major biography written in this century, but it lacks the benefit of recent scholarship. Two good newer accounts are Herbert D. Anthony, Sir Isaac Newton (1960), a short but comprehensive and interestingly presented biography, and Frank Manuel, Isaac Newton (1968), an illuminating psychological study of Newton.
• A convenient biographical introduction in John David North's brief study, Isaac Newton (1968), which relates the highlights of Newton's life and work. A psychologically oriented essay on Newton is in Dunkwart A. Rustow, ed., Philosophers and Kings: Studies in Leadership (1970). Among the older works, William Stukeley's Memoirs of Sir Isaac Newton's Life, for which he collected material during Newton's last years but which was not published until 1936, is an interesting compilation of anecdotes and observations. Sir David Brewster, Memoirs of the Life, Writings and Discoveries of Sir Isaac Newton (1855; repr. 1965), is still a useful biographical source.
• Useful evaluations of Newton's work include Edward N. da C. Andrade, Isaac Newton (1954), available in paperback; the chapter on Newton in James G. Crowther, Founders of British Science (1960); Arthur E. Bell, Newtonian Science (1961); and Alexandre Koyré, Newtonian Studies (1965).