Isaac Newton: The Man Who Unified the Heavens and the Earth

Isaac Newton is the greatest natural philosopher who ever lived. He is the figure who, more than any other, completed the Scientific Revolution: who gave it its mathematical form, its empirical reach, and its philosophical foundation. The Philosophiae Naturalis Principia Mathematica of 1687 — the Principia, as it is usually called — is the most important single work in the history of the physical sciences. It is the book in which Newton set out the three laws of motion and the law of universal gravitation, and from which he derived Kepler’s three laws of planetary motion, explained the tides and the motion of the Moon, and demonstrated that the force that held the planets in their orbits was the same force that made a stone fall to the ground. The unification of celestial and terrestrial mechanics, which had been the central project of the Scientific Revolution since Copernicus, was completed in the Principia. Newton was also a difficult and complicated man. He was a brilliant mathematician, a brilliant experimentalist, and a brilliant writer of polemical Latin prose, and he was also an alchemist, a theologian, an accountant at the Royal Mint, a Member of Parliament, a sometimes cruel man who punished his enemies with care, and a reclusive figure who, toward the end of his life, was widely regarded as the greatest Englishman of his generation. the lonely genius at Cambridge, the apple falling from the tree, the universal law of gravitation — is partly true and partly misleading. The reality is more interesting. This page is an introduction to Newton and to the work that bears his name. Three articles treat specific aspects in detail: What Is in Newton’s Principia Mathematica? covers the contents of the Principia; How Did Newton Discover Gravity? covers the discovery of universal gravitation; and What Did Newton Contribute to Optics? covers the prism experiments and the Opticks. The broader context in which Newton worked is the page on the key figures of the Scientific Revolution and the Laws of Motion and Gravity section in the discoveries section.

Early Life

Isaac Newton was born in Woolsthorpe, a small village in Lincolnshire, England, on 25 December 1642 (old style) or 4 January 1643 (new style). He was born prematurely, and he was a small and sickly infant; the story that he was small enough to fit into a quart pot may be exaggerated, but it is a striking image. His father, also Isaac, had died three months before his birth, and he was raised by his mother, Hannah Ayscough, and his grandmother. When Newton was three, his mother remarried and moved to a nearby village, leaving Newton in the care of his grandmother. He hated his stepfather, and the experience may have contributed to the difficult temperament that would plague him throughout his life. He attended the local grammar school, the King’s School in Grantham, where he was a competent but not outstanding student. He was interested in mechanical devices and built a number of small models; the story that he was badly beaten by a bully at school and resolved to outperform the bully in class is probably apocryphal, but it is a striking image. In 1661, at the age of eighteen, Newton was admitted to Trinity College, Cambridge. He came up as a subsizar — a student who worked for the college in exchange for his room and board. He was, in his own way, a typical undergraduate: he read the standard curriculum, but he also read widely outside it, including the works of Descartes, Gassendi, Boyle, and others. He was particularly influenced by the Cartesian natural philosophy, which held that the physical world could be explained by the motion of corpuscles of matter. The Cartesian philosophy was, in the 1660s, the leading natural philosophy in Europe, and it was the framework within which Newton work, and against which he would, eventually, define his own.

The Plague Years (1665–1667)

In the summer of 1665, the bubonic plague reached Cambridge, and the university was closed. Newton returned to the family farm at Woolsthorpe. He remained there, with occasional visits to Cambridge, until the spring of 1667, when the plague had subsided and the university reopened. The two plague years were, by Newton’s own later account, the most productive of his life. In a famous passage, written late in life, Newton recalled that in these two years he had “begun to think of gravity extending to the orb of the Moon” and had “deduced that the forces which keep the planets in their orbs must [be] reciprocally as the squares of their distances from the centres about which they revolve.” He also worked out the binomial theorem, the beginnings of the calculus, the composition of white light, and the law of cooling. Whether all of these were actually accomplished in the plague years, or were rather the result of work done over the next two decades, has been a subject of historical debate, but Newton’s own account is striking. Newton’s first run at the gravitational problem is particularly interesting. He had tried to compare the force that held the Moon in its orbit (computed from the Moon’s orbital period and distance) with the force of gravity at the Earth’s surface. The comparison was, in principle, the inverse-square law: if the force of gravity falls off as the square of the distance, then the force at the Moon’s distance should be about 1/3600 of the force at the Earth’s surface. The Earth’s radius was about 3,960 miles, and the Moon’s distance was about 60 Earth radii, so the ratio was about 1/3600, which was consistent with the orbital calculation. The comparison required, however, an accurate value for the Earth’s radius, and the value Newton had (the value used in the 1660s) was about 15 percent off. The comparison did not quite work out, and Newton set the problem aside. The story is told in more detail in How Did Newton Discover Gravity?.

Cambridge and the Lucasian Chair (1669–1696)

Newton returned to Cambridge in 1667 and was elected a fellow of Trinity College in 1668. In 1669, he was appointed Lucasian Professor of Mathematics, the most prestigious academic position in England. The Lucasian chair had been founded in 1663, and Newton was only the second holder. Newton’s first years in the Lucasian chair were not, on the surface, particularly productive. He gave the standard lectures on optics, geometry, and astronomy. He did some experimental work in alchemy. He corresponded with a small circle of natural philosophers, including Robert Hooke, who was the Curator of Experiments at the Royal Society. He did not, however, publish anything of note. The lack of publication was, in part, Newton’s temperament: he was reluctant to publish, and he was afraid of criticism. It was also, in part, a consequence of the state of the sciences: the problems that interested him most were not yet ripe for solution. The picture changed in the 1670s. Newton built a reflecting telescope, the first practical one ever made, and he sent it to the Royal Society. The Royal Society, in response, elected him a fellow in 1672. Newton, in turn, sent the Society a paper on his experiments with prisms, in which he argued that white light is a mixture of the colors of the spectrum, and that each color is refracted by a glass prism at a slightly different angle. The paper provoked a long dispute with Hooke, who had his own theory of light, and the dispute was one of the formative episodes of Newton’s career. It is described in What Did Newton Contribute to Optics?. In 1679, Newton received a letter from Hooke, in his capacity as Secretary of the Royal Society, asking Newton’s views on a number of topics. The letter included a question about the path of a body under the action of a central force, and it provoked Newton to return to the gravitational problem. The exchange of letters that followed is the basis for the famous dispute between Newton and Hooke over the priority of the inverse-square law. The story is told in How Did Newton Discover Gravity?.

The Principia (1687)

The decisive event of Newton’s career was the visit of Edmund Halley in 1684. Halley, the Astronomer Royal, was discussing the planetary orbits with Robert Hooke and Christopher Wren. The question was: what curve would a planet trace if it were attracted to the Sun by a force varying inversely with the square of the distance? Hooke claimed to have solved the problem, but he would not say how. Halley went to Cambridge to ask Newton. Newton told Halley that the curve was an ellipse. Halley, in some astonishment, asked how he knew. Newton replied that he had computed it. Halley asked to see the computation. Newton, rummaging through his papers, could not find the relevant ones, and he wrote to Halley promising to redo the calculation and send it on. The result was a short treatise, De Motu Corporum in Gyrum (“On the Motion of Bodies in Orbits”), which Halley received in November 1684. Halley was impressed, and he urged Newton to develop the argument into a full book. The result was the Principia, published in 1687 under the imprimatur of the Royal Society and at Halley’s expense. The Principia is one of the most consequential books in this history. Its full contents are surveyed in What Is in Newton’s Principia Mathematica?. Briefly, the book is divided into three parts. Book I, “On the Motion of Bodies,” sets out the mathematical framework: the laws of motion, the geometry of curves, the theory of motion under the action of central forces, and the motion of bodies in resisting and non-resisting media. Book II continues the analysis of motion in resisting media, including fluids, pendulums, and projectiles, and it ends with a devastating critique of Descartes’ vortex theory of the planetary system. Book III, “The System of the World,” applies the mathematical framework to the actual solar system: it shows that the inverse-square law of gravitation implies Kepler’s three laws, explains the motion of the Moon, the tides, and the figure of the Earth, and analyzes the orbits of comets. The book made Newton famous. It was read across Europe, and it transformed the practice of natural philosophy. The book also made many enemies, particularly among the Cartesians on the Continent, who rejected the gravitational theory as an “occult quality” — a return to the scholastic philosophy that Descartes had been trying to replace. The dispute with the Cartesians would occupy Newton for the rest of his life.

The Opticks and the Calculus Dispute (1704–1716)

The Opticks was published in 1704, in English, with a Latin translation in 1706. The book was a complement to the Principia: it set out Newton’s experimental work on light and color, and it included, in the famous “Queries” at the end, a series of speculations about the nature of light, the structure of matter, and the possibility of a unified physics. The book is the subject of What Did Newton Contribute to Optics?. The calculus dispute with Leibniz broke out in the 1690s and lasted for the rest of Newton’s life. Newton had developed the calculus, in the form of “fluxions,” in the plague years of the 1660s, but he had not published the work. Leibniz, independently, had developed the calculus, in the form of differentials and integrals, and he had published first, in 1684. The dispute was, in part, a question of priority: who had invented the calculus first? And in part, a question of national prestige: the English Newtonians and the Continental Leibnizians fought for the honor of their respective champions. Newton, who had a powerful memory for enemies, was convinced that Leibniz had plagiarized him, and he used his influence at the Royal Society to have a committee report prepared, in 1713, that upheld Newton’s priority. The report was written by Newton himself, in effect, although the cover of anonymity was preserved. The calculus dispute was a disaster for English mathematics. The Newtonian “fluxions” notation was less flexible than the Leibnizian differential notation, and the English mathematical community, in the eighteenth century, lost its leadership of European mathematics to the Continental tradition, which used the Leibnizian notation. The dispute also did lasting damage to Newton’s reputation, as it became clear, in the nineteenth century, that the priority claims on both sides were exaggerated.

The Royal Mint and the Presidency of the Royal Society (1696–1727)

In 1696, Newton accepted an appointment as Warden of the Royal Mint. The appointment was, in part, a recognition of Newton’s talents and, in part, a political maneuver by his friends. The Mint was in a state of crisis: the English silver coinage was being clipped, counterfeited, and exported, and a major recoinage was needed. Newton threw himself into the work with characteristic energy. He supervised the recoinage, hunted down counterfeiters (one of whom, William Chaloner, was hanged in 1699 largely on Newton’s evidence), and was promoted to Master of the Mint in 1700. The Mint was a lucrative post, and Newton became a wealthy man. Newton was also a Member of Parliament, briefly, for the University of Cambridge, in 1689 and again in 1701. He was not a particularly active Member. He was, however, President of the Royal Society from 1703 until his death in 1727. The presidency gave him a powerful platform, and he used it to promote his own views, to control the publication of the Philosophical Transactions, and to punish his enemies (most notably Hooke, who died in 1703, and whose portrait was removed from the walls of the Royal Society on Newton’s orders). Newton was also a widely respected public figure. He was knighted in 1705 by Queen Anne, becoming Sir Isaac Newton.

The Private Newton

The public Newton is one of the great figures of the Enlightenment. The private Newton is a more complicated and more interesting figure. He was a lifelong bachelor, and he seems to have had few close personal relationships. He was a deeply religious man, in a heterodox way: he rejected the Trinity, and he was a kind of antitrinitarian heretic. He wrote extensively on biblical chronology, on the prophecies of Daniel and the Revelation of St John, and on the history of the early Church. He left a substantial body of unpublished theological work, much of which has been published only in the twentieth century. Newton was also, throughout his life, an alchemist. He kept an alchemical laboratory in his rooms at Trinity, and he conducted hundreds of alchemical experiments. The alchemical work was, in part, an attempt to understand the structure of matter in a way that the mechanical philosophy did not. It was also, in part, a search for the philosopher’s stone, and Newton left a substantial body of alchemical manuscripts. The alchemical work was kept private, partly because it was potentially embarrassing, and partly because it was illegal under English law (the multiplication of gold was considered a form of counterfeiting). The full extent of Newton’s alchemical work has been revealed only in recent decades, and it has complicated the standard image of Newton as the founder of modern physics.

The Last Years and Legacy

Newton spent the last years of his life at his house in Kensington, where he had moved in 1725. He was increasingly frail, and he suffered from kidney stones and gout. He died on 20 March 1727, and was buried in Westminster Abbey on 4 April 1727. The Latin inscription on his monument, written by his friend and biographer William Whiston, begins, “Mortals, congratulate yourselves that so great a man has lived for the honor of the human race.” Newton’s influence on the subsequent history of science is difficult to overstate. The Principia was the dominant text in theoretical physics for two hundred years. The three laws of motion, the law of universal gravitation, and the methods of mathematical physics that Newton developed became the foundation of classical mechanics. The calculus, in both its Newtonian and Leibnizian forms, became the language of physics. The Opticks became the foundation of the wave-particle debate in optics. Even Newton’s alchemical and theological work, which was kept private, has had a complex influence on the history of ideas. is partly true. Newton was, by any reasonable standard, a genius. The law of universal gravitation is one of the great achievements of the human mind. The story of the apple is probably apocryphal, but it is true that the discovery of universal gravitation required a combination of careful observation, mathematical analysis, and intellectual boldness that is rare in any age. The combination of those qualities is Newton’s legacy, and it is the central story of the Scientific Revolution.

Sources and Further Reading

The standard one-volume biography of Newton is Richard Westfall, Never at Rest: A Biography of Isaac Newton (Cambridge University Press, 1980; corrected reprint 1983), which remains indispensable. The shorter and more recent Stephen Snobelen, “Newton,” in the Stanford Encyclopedia of Philosophy (2024), is a reliable online starting point. The most useful collection of Newton’s writings in accessible form is I. Bernard Cohen and Richard Westfall, Newton: Texts, Backgrounds, Commentaries (Norton, 1995). The alchemical work is treated in William R. Newman, Newton the Alchemist: Science, Enigma, and the Quest for Nature’s “Central Fire” (Princeton University Press, 2019), which supersedes the older Betty Jo Teeter Dobbs, The Janus Faces of Genius: The Role of Alchemy in Newton’s Thought (Cambridge, 1991). The theological work is treated in James E. Force and Richard H. Popkin, Newton and Religion: Context, Nature, and Influence (Kluwer, 1999). The calculus priority dispute is treated separately in The Newton–Leibniz Calculus Controversy.

Related Articles

• What Is in Newton’s Principia Mathematica?
• How Did Newton Discover Gravity?
• What Did Newton Contribute to Optics?
• The Newton–Leibniz Calculus Controversy
• Key Figures of the Scientific Revolution
• Johannes Kepler: The Celestial Harmonist
• Galileo Galilei: The First Modern Scientist
• The Laws of Motion and Gravity