Isaac Newton (1642-1727)

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In addition to combining mathematical genius and profound physical insight, Newton also possessed practical skills. He built the furnaces in his own small laboratory in Trinity College, where he personally carried out alchemical experiments. He also constructed a novel kind of reflecting telescope, for which he was elected a Fellow of the Royal Society. However, Newton was a solitary and difficult person who has often been described as neurotic.

Figure 1.8 Trinity College, Cambridge around 1690 Click here for larger image (24.38kb)

He reacted badly to criticism and expected to get full credit for his discoveries even though he often did little to publicize them. He became involved in a number of bitter disputes over priority. Newton also harboured unconventional religious views (he was essentially a Unitarian) which prevented him from becoming the Master of his college. In 1678 he apparently suffered a nervous breakdown and for several years thereafter concentrated on alchemy and scriptural studies.

Newton was recalled to natural philosophy in 1684 by the young astronomer Edmond Halley who asked how a planet would move if it was attracted towards the Sun by a force that weakened in proportion to the inverse square of its distance from the Sun: in symbols,
.
(This means, for example, that increasing the distance by a factor of three decreases the force by a factor of nine.)
Newton is said to have immediately told Halley the answer (an ellipse) having worked it out during the plague years. Halley persuaded Newton to recreate his calculations and publish them. The result, in 1686, was what is widely regarded as the most influential book in the history of science, Newton's Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), a work usually referred to simply as Principia. In the opening pages of this book, Newton presented his definitions of force and mass, and his three laws of motion. He then went on to demonstrate that a body attracted towards a fixed point by a force that varied in proportion to the inverse square of its distance from that point would, in many circumstances, follow

Figure 1.9 Principia - Newton's masterpiece Click here for larger image (25.45kb)

an elliptical path. After establishing many other results Newton presented, in Part 3 of the book, his System of the World in which he proposed that gravity was a universal force, acting between any two particles of matter, with a magnitude that is proportional to the product of their masses and the inverse square of their separation - just the kind of inverse square law that Halley had asked about. Thus Newton was able to explain the observed motion of the planets. He went on to consider the Moon's motion in detail (taking account of the gravitational influence of both the Earth and the Sun), the behaviour of comets, and the gravitational origin of the Earth's oceanic tides. The scope and power of Principia caused a sensation, and made Newton the foremost scientist of his time, or perhaps any time.

Newton suffered another breakdown in 1693 and subsequently quit Cambridge and the academic life in favour of London and the world of affairs. He became Warden of the Mint in 1696 and successfully oversaw the introduction of a new coinage. As a consequence he was appointed to a lucrative position as Master of the Mint and devoted much of his remaining time to theology and biblical chronology. He was elected President of the Royal Society in 1703, published his last great scientific work Opticks in 1704 (based on work performed many years earlier), and was knighted in 1705. He died, in London in 1727, and is buried in Westminster Abbey.