Isaac Newton

Isaac Newton (1642-1727) is regarded as one of the greatest scientists of all time. With the law of universal gravitation and the three laws of motion he gave physics the foundations on which it would rest for more than two centuries; he invented calculus, revolutionised optics and built the first working reflecting telescope. He was also an alchemist, theologian, Master of the Mint and President of the Royal Society.

Childhood and Cambridge

Newton was born on Christmas Day 1642, according to the calendar then in use in England, at Woolsthorpe, a village in Lincolnshire, the posthumous son of a small landowner. Premature and frail, he had a difficult childhood: his mother remarried and left him in the care of his grandmother. After school at Grantham, where he enjoyed building sundials and model windmills, in 1661 he entered Trinity College, Cambridge, where he discovered the works of Descartes, Galileo and Kepler.

The miraculous years

In 1665 the plague forced the university to close and Newton returned to Woolsthorpe. In less than two years, still barely past twenty, he laid the foundations of his main discoveries: calculus, which he called the "method of fluxions", the theory of colours and his first ideas on gravitation. The famous anecdote of the apple dates from this period, told by Newton himself in old age to his biographer William Stukeley: seeing a fruit fall in the garden, he wondered whether the force pulling it to the ground might extend as far as the Moon. The apple tree, or a descendant of it, still stands in the garden of his birthplace, now run by the National Trust.

With experiments using prisms he showed that white light is made up of all the colours of the spectrum. In 1668 he built a reflecting telescope, which used a mirror instead of lenses to avoid chromatic aberration, and in 1669, aged just 26, he won the prestigious Lucasian chair of mathematics at Cambridge.

The Principia

In 1684 the astronomer Edmond Halley asked him what orbit a planet would follow if attracted by the Sun with a force inversely proportional to the square of the distance. Newton answered at once: an ellipse, and he had already proved it. Urged on by Halley, who paid for the printing out of his own pocket, in 1687 he published the Philosophiae Naturalis Principia Mathematica, one of the most important works in the history of science. In it he set out the three laws of motion, the principle of inertia, the relationship between force and acceleration, the principle of action and reaction, and the law of universal gravitation: the same force that makes an apple fall governs the motion of the Moon, the planets and comets, and explains the tides. For the first time heaven and earth obeyed the same mathematical laws.

In 1704 he published Opticks, in English, on his research into light. His career was also marked by bitter disputes: with Robert Hooke over the priority of certain ideas, with the Astronomer Royal John Flamsteed and above all with the German Leibniz, who had developed calculus independently. Today it is recognised that both invented it, and the notation still used is Leibniz's. In a letter to Hooke in 1675 Newton wrote the famous phrase: if he had seen further, it was "by standing on the shoulders of giants".

Alchemy, faith and the Mint

Newton devoted a great deal of time, perhaps more than to physics, to alchemy and theology: he studied biblical prophecy and ancient chronology, and secretly rejected the doctrine of the Trinity, a view that would then have cost him his career. The economist John Maynard Keynes, who bought many of his manuscripts, called him "the last of the magicians".

In 1696 he left Cambridge for London, appointed Warden and then, from 1699, Master of the Royal Mint. He took the job very seriously: he oversaw the recoinage of silver money and pursued counterfeiters relentlessly. In 1703 he became President of the Royal Society, a post he held until his death, and in 1705 Queen Anne knighted him, the first scientist to receive the honour for scientific achievement. He died in Kensington on 20 March 1727 and was buried with great ceremony in Westminster Abbey, where his monument still stands near the choir.

Legacy

Newtonian physics remained unchallenged until Einstein's relativity at the start of the 20th century, and it is still what we use to build bridges and send probes into space. The International System unit of force bears his name, the newton. Those wishing to follow in his footsteps can visit his birthplace at Woolsthorpe Manor, Trinity College in Cambridge, whose chapel holds his statue, and his tomb at Westminster.

See also the Industrial Revolution, the history of the United Kingdom and London.