Newton, SIR ISAAC, the greatest of natural philosophers, was born on 25th December (o.s.) 1642—year remarkable in English history for the breaking out of the Civil War, and doubly remarkable in the history of science by the birth of Newton and the death of Galileo. The farmhouse he was born in, still preserved religiously, is at the hamlet of Woolsthorpe in Coterworth parish, Lincolnshire, 8 miles S. of Grantham (q.v.), at whose grammar-school the boy received his early education. On the 5th of June 1661 he left home for Cambridge, where he was admitted as subsizar at Trinity College. On the 8th of July following he matriculated as sizar of the same college. He immediately applied himself to the mathematical studies of the place, and within a very few years must have not only made himself master of most of the works of any value on such subjects then existing, but had also begun to make some progress in the methods for extending the science. In 1665, in which year he took his B.A., he committed to writing his first discovery on fluxions; and in 1666, according to Voltaire's Lettres sur les Anglais (1733), the fall of an apple, as he walked in the garden at Woolsthorpe, suggested the most magnificent of his subsequent discoveries—the law of universal gravitation. On his first attempt, however, by means of the law so suggested to his mind, to explain the lunar and planetary motions, he employed an estimate then in use of the radius of the earth which was so erroneous as to produce a discrepancy between the real force of gravity and that required by theory to explain the motions, corresponding to the respective figures 16·1 and 13·9.
He accordingly abandoned the hypothesis for other studies. These other pursuits to which he thus betook himself consisted chiefly of investigations into the nature of light, and the construction of telescopes. By a variety of ingenious and interesting experiments upon sunlight refracted through a prism in a darkened apartment, he was led to the conclusion that rays of light which differ in colour differ also in refrangibility. This discovery enabled him to explain an imperfection of the telescope, which had not till then been accounted for. The indistinctness of the image formed by the object-glass was not necessarily due to any imperfection of its form, but to the fact of the different coloured rays of light being brought to a focus at different distances. He concluded rightly that it was impossible for an object-glass consisting of a single lens to produce a distinct image. He went further, and too hastily concluding, from a single experiment, that the dispersive power of different substances was proportional to their refractive power, he pronounced it impossible to produce a perfect image by a combination of lenses. This conclusion—since proved erroneous by the discovery of the achromatic telescope (see ACHROMATISM)—turned Newton's attention to the construction of reflecting telescopes; and the form devised by him is the one which, at later periods, reached such perfection in the hands of Sir William Herschel and Lord Rosse.
Newton became a Fellow of Trinity in 1667, and Lucasian professor of Mathematics in 1669; and it was on 11th January 1671 that he was elected a member of the Royal Society, having become known to that body from his reflecting telescopes. At what period he resumed his calculations about gravitation, employing the more correct measure of the earth obtained by Picard in 1670, does not clearly appear; but it was in the year 1684 that it became known to Halley that he was in possession of the whole theory and its demonstration. It was on the urgent solicitation of Halley that he was induced to commit to a systematic treatise these principles and their demonstrations. The principal results of his discoveries were set down in a treatise called De Motu Corporum, and were afterwards more completely unfolded in the great work entitled Philosophiæ Naturalis Principia Mathematica, which was finally published about midsummer 1687.
Shortly before the Principia was given to the public Newton had been called to take an active part in defending the rights of the university against the illegal encroachments of James II. The conspicuous part which he had taken on that occasion procured him a seat in the Convention Parliament, in which he sat from January 1689 to its dissolution in 1690. In 1696 he was appointed Warden of the Mint, and was afterwards promoted to the office of Master of the Mint in 1699, an office which he held till the end of his life. He again took a seat in parliament in the year 1701 as the representative of his university. Thus engaged in the public service, he had little time left for mere scientific studies—pursuits which he always held of secondary importance to the public duties in which he was engaged. In the interval of public duty, however, Newton showed that he still retained the scientific power by which his great discoveries had been made. This was shown in his solution of two celebrated problems proposed in June 1696 by John Bernoulli, as a challenge to the mathematicians of Europe. A similar mathematical feat is recorded of him so late as 1716, in solving a problem proposed by Leibnitz for the purpose, as he expressed it, of feeling the pulse of the English analysts. When in parliament Newton recommended the public encouragement of the invention of a method for determining the longitude—the first reward in consequence being gained by John Harrison for his chronometer. He was president of the Royal Society from 1703 till his death, a period of twenty-five years, being each year re-elected. In this position he could do much for the advancement of science; and one of his most important works during this time was the superintendence of the publication of Flamsteed's Greenwich Observations—a task, however, not accomplished without much controversy and some bitterness between himself and that astronomer. The controversy between Newton and Leibnitz as to priority of discovery of the differential calculus, or the method of fluxions, was raised rather through the partisanship of jealous friends than through the anxiety of the philosophers themselves, who were, however, induced to enter into and carry on the dispute with some degree of bitterness and mutual recrimination. The verdict of the impartial historian of science must be that the methods were invented quite independently, and that, although Newton was the first inventor, a greater debt is owing by later analysts to Leibnitz, on account of the superior facility and completeness of his method. In 1699 Newton was elected a foreign associate of the Academy of Sciences, and in 1703 he received the honour of knighthood from Queen Anne. He died at Kensington on 20th March 1727, and his remains received a resting-place in Westminster Abbey, where a monument was erected to his memory in 1731. Roubilliac's magnificent full-length statue was erected in 1755 in the antechapel of Trinity College, Cambridge.
Besides the first edition of the Principia, other editions appeared in 1713, 1726, 1729, 1730; and at Geneva the Jesuits' edition (1739-42; republished at Glasgow, 1822). An admirable reprint is that by Lord Kelvin and Professor Blackburn (Glasgow, 1871). Clarke's Latin translation of the Optics appeared in 1706; the Optical Lectures in 1728; the Fluxions in 1736; and Horsley edited an edition of his collected works (5 vols. 4to 1779-85). Newton was a student of Alchemy (q.v.); and he left a remarkable monument of his interest in theology, especially prophecy, a MS. work on the prophecies of Daniel and on the Apocalypse, a history of the Creation, and a number of tracts. See the articles in this work on ASTRONOMY, FLUXIONS, GRAVITATION, LIGHT, MOTION (LAWS OF), OPTICS, SPECTRUM; Sir David Brewster's Life of Newton (1855); and Augustus de Morgan's Newton, his Friend, and his Niece (1885), that friend being John Conduitt (1688-1737), Newton's successor as master of the mint, who in 1717 married Newton's niece, Katherine Barton, the widow probably of the Earl of Halifax.
NEWTON'S RINGS.—In his investigations of the colours produced by thin plates of any material, solid, fluid, or gaseous, Sir Isaac Newton hit upon the following mode of exhibiting the colours produced by reflection from a film of air. He took two lenses, one convex-plane, its convex side having a radius of 14 feet, the other equi-convex, with the radii of its surfaces 50 feet, and laid the first with its plane surface downwards on the top of the second, thus producing a thin film of air between the lenses; the film being thinnest near the centre, and becoming gradually thicker outwards. On slowly pressing the upper lens against the under one, a number of concentric coloured rings, having the point of contact of the lenses for their centre, appeared, and increased in size when the pressure was increased. These rings, or more properly systems of rings, are in this form of the experiment seven in number, and each of them is composed of a number (ranging from eight in the first or smallest ring to two in the outermost) of rings of different colours, the colours, though different in each of the systems of rings, preserving the same arrangement as the colours of the spectrum; thus, in the second ring the inside colour is violet, and the outside scarlet red. The colours are very distinct in the first three systems of rings, but become gradually confused and dull towards the outside, till they almost fade away in the seventh system. The centre is deep black. The thickness of the air-film at the centre is about half a millionth of an inch, and increases gradually to nearly of an inch, when the colours disappear. See INTERFERENCE.