8 Isaac Newton 8.1 Potted biography Rural background Woolsthorpe Manor • 1642: born in Lincolnshire, East Midlands of England. • He was a small & weak baby. • Father died before birth. Mother remarried when he was 2, and moved to live with new husband, leaving N. with his grandparents on the farm until he was 12. • Indifferent performance at school until there was an altercation with another student, after which time N. applied himself and came top of the class. • Major interest was making models and mechanical toys, but also was always absorbed in reading, and developed a life-long habit of keeping a diary. School years Cambridge University • Left school at 16 and was meant to take over running the • 1661: went to Trinity College Cambridge as a sizar. farm, but showed no aptitude or interest and was a At this time Cambridge was rather backward intellectually, disaster. • and new ideas of Copernicus, Galileo, Kepler, Descartes • His mother realized that Newton should go to largely hadn’t penetrated: scholarship was focused on Aristotle university--with strong encouragement of his school and on voluminous theological studies. headmaster, and so arranged for him to finish school. • However, Trinity was a hotbed of Cartesian philosophy. • This required boarding with a family in nearby town of Grantham. • The University (and the country) were also just recovering from the Puritanism of the Protectorate & Charles II was • Husband of this family was a pharmacist and Newton proclaimed monarch in 1661. developed a lifelong interest in chemistry, as well as Newton would have studied arithmetic, Euclid, and doctoring himself with various chemical remedies. • trigonometry, classical & medieval Latin, logic & ethics. • Also fell in love with a Miss Storey, a stepdaughter of his But he also studied optics with his tutor, read Kepler’s Optics host, and became engaged to marry her ca. 1661. • and struggled through Descartes’ Analytical Geometry. • 1665 graduated with B.A. degree. Back in Woolsthorpe Newton’s telescope • In 1665 the university was closed due to a resurgence of the Plague. • Newton spent much of the next two years back at the family manor, quietly reading and thinking. • During these “golden years” he made three classic discoveries that revolutionized the future of science: ! the mathematical method of “fluxions,” i.e. the calculus, ! understanding the composition of light, & ! the law of universal gravitation. • The chromatic aberration of refracting telescope led to his invention of a reflecting telescope. Cambridge professor Scientific disputes • His publication on light also began a long dispute with • In 1667 Newton returned to Cambridge as a Fellow of Robert Hooke, who claimed priority in Newton’s Trinity. discoveries in optics. (There were more to follow.) • Engagement to Miss Storey ended (or faded away). • A result of these disputes was to strengthen Newton’s • In 1669 he was appointed (2nd) Lucasian Professor. opposition to publishing his work, believing that others would draw him into further disputes which he • First lecture course was on optics. considered a waste of time. • His invention of the reflecting telescope brought • A major difference in outlook between Newton, fellowship in the Royal Society in 1671. Huygens, & Hooke was Newton’s insistence on • A year later he published a letter in the Transactions of the quantitative measurement, rather than qualitative Royal Society on his “new theory of light and colours.” speculation. • Huygens appears not to have appreciated the significance • He did not send any further papers to the Royal Society of this work, nor completely understood it. on optics, and in 1675 offered his resignation as as Fellow, in part because he believed the Society had not This was quite a disappointment to Newton. • supported his ideas. Problems with orthodoxy Life in Cambridge • Newton had always done much theological reading and thinking, and as a result became convinced that the doctrine of • At the request of one of his friends, in 1676 Newton the Trinity was not Biblical. exchanged two letters with Gottfried Leibniz describing some of his mathematical discoveries. • This (Arian heresy) was a major problem for him: if this were to become known he would have lost his college fellowship. • These were courteous and open, but later would become part of a long controversy over priority in discovery of • The law required that the Lucasian Professor become ordained the calculus. in the Church of England, which would mean affirming the 39 Articles of Religion, including the doctrine of the Trinity, which • During this period (from ca. 1669) Newton did much he refused to do. experimentation in chemistry & alchemy (i.e. transmutation of metals and finding an elixir for • By 1675 he had given up hope, but at the last minute the King immortality), having studied all the ancient alchemical issued a royal dispensation, lifting the requirement that the treatises. Lucasian Professor must take holy orders. • Newton’s lifestyle was largely solitary. His concentration • Thus Charles II saved from oblivion one of the greatest scientists was extraordinary: he would become so engaged on a of all time. problem he would forget to eat and sleep. Publication of the Principia Parliamentary service In 1684 Edmund Halley visited Newton and asked what • In 1687 James II became King. the shape of a planetary orbit would be if the force • between it and the Sun varied as the inverse square of • He was a devout Roman Catholic and eventually the distance between them. declared his intent to overthrow the English Church. • Newton replied that it would be an ellipse, and that he • As an example the monarch sent a letter to Cambridge had worked it out years before. commanding that a Benedictine monk should be given an M.A. degree without requiring him to sign the 39 He later produced a proof for Halley, in the course of • Articles of Religion of the Anglican Church. which he began developing a book-length discussion on the subject of motion of bodies in orbit. • Newton encouraged the University to resist, and in the end the King backed down. • This was written out during 1685 & 1686 into his magnum opus. • In 1688 the University chose Newton to represent them in the House of Commons for two years. • In 1687 Newton published the Philosophiae Naturalis Principia Mathematica (Mathematical Principles of • He seems to have especially enjoyed this period in Natural Philosophy). London and participation in the halls of government. Newton’s breakdown Newton: portrait of • In 1689 Newton’s mother died. • In 1692 a young Swiss mathematician, Fatio de Duillier 1689 who was an admirer and had proposed to edit a new edition of the Principia, abruptly ended his friendship. (aged 46) • In this period Newton also became obsessed with obtaining a government position, and felt let down by his friends when a position was not forthcoming. • In 1692 he suffered a major mental breakdown. • By 1693 he seems to have recovered, but had no interest in creative scientific work, despite the fact that the Principia was out of print and others were following up his ideas. Life in London The Great Man • In 1699 the dispute between Leibniz and Newton became • In 1694 one of Newton’s former Trinity students, Charles a major international conflict. Montague (later Lord Halifax), became Chancellor of the Yet another major quarrel erupted between Newton & Exchequer. • John Flamsteed, the Astronomer Royal. One of his decisions was the recoinage of English • In 1703 Newton was elected President of the Royal currency. • Society, and continued so until he died. In 1696 Newton was appointed Warden of the Mint, and • In 1704 Newton published his Opticks (in English), & the the recoinage project was executed with great success. • Latin translation in 1706. It was wildly popular. He moved to London and set up house with his niece, • In 1705 he was knighted. Catharine Barton. • By this time Newton had become one of the most In 1699 Newton was appointed Master of the Mint, and • • celebrated persons of his time. held this position until his death. In 1727 Newton died and was buried in a spectacular There is no doubt he carried out his duties as a civil • • tomb at Westminster Abbey. servant with distinction. Newton’s tomb, Newton, 1726 Westminster Abbey 8.2 The Principia Newton’s title page changes for the 2nd edition of the Principia Principia summary • Book I ! Laws of motion • Book II ! Hydrostatics and hydrodynamics, in which Newton demolishes Descartes’ vortex model for the planets. • Book III ! Law of universal gravitation ! Tides ! Accounts of oblate shapes of the Earth & other planets ! Masses of celestial objects in terms of mass of the Earth. The Principia The Principia, cont’d • Using his laws of motion and gravitation, Newton • In short, Newton’s laws of motion and the law of showed that he could deduce mathematically all three of universal gravitation not only described precisely the Kepler’s laws of planetary motion (which Kepler had of motions of planets orbiting the Sun, they enabled people course worked out painstakingly by years of analysis of calculate things they had not previously thought were decades of observations). possible. • He also showed how his laws of motion and gravitation • Comparison of predictions of Newton’s theory with could explain new phenomena: observations confirmed the validity of Newton’s ideas. ! the tides • Newton could predict from his theory all the observational work of centuries. ! the oblate shapes of Earth and other planets. • This was a spectacular achievement, something no one ! He calculated the mass of a planet in terms of the had ever done before. Earth’s mass. • And so it is not surprising that Newton was regarded as ! And he showed that the Great Comet of 1680 was in one of the great intellectual giants of all time.