Sir Isaac Newton

Sir Isaac Newton, the culminating figure in the scientific revolution of the 17th century, was born on Jan. 4, 1643 (N.S.; Dec. 25, 1642, O.S.), in the manor house of Woolsthorpe, near Grantham, Lincolnshire, England.Perhaps the greatest scientific genius of all time, Newton made fundamental contributions to every major area of scientific and mathematical concern to his generation.

Newton came from a family of modest yeoman farmers. His father died several months before he was born. Three years later his mother remarried and moved to a nearby village, leaving Isaac in the care of his maternal grandmother.

Upon the death of his stepfather in 1656, Newton's mother removed him from grammar school in Grantham in hopes of training him to manage her now much enlarged estate, but even then Newton's interests ran more toward books and mathematical diversions. His family decided that he should be prepared for the university, and he entered Trinity College, Cambridge, in June 1661.

Even though instruction at Cambridge was still dominated by the philosophy of Aristotle, some freedom of study was permitted in the student's third year. Newton immersed himself in the new mechanical philosophy of Descartes, Gassendi, and Boyle; in the new algebra and analytical geometry of Vieta, Descartes, and Wallis; and in the mechanics and Copernican astronomy of Galileo. At this stage Newton showed no great talent. His scientific genius emerged suddenly when the plague closed the university in the summer of 1665 and he had to return to Lincolnshire. There, within 18 months he began revolutionary advances in mathematics, optics, physics, and astronomy.

Newton's initial lectures as Lucasian Professor dealt with optics, including his remarkable discoveries made during the plague years. He had reached the revolutionary conclusion that white light is not a simple, homogeneous entity, as natural philosophers since Aristotle had believed. When he passed a thin beam of sunlight through a glass prism, he noted the oblong spectrum of colors--red, yellow, green, blue, violet--that formed on the wall opposite. Newton showed that the spectrum was too long to be explained by the accepted theory of the bending (or refraction) of light by dense media. The old theory said that all rays of white light striking the prism at the same angle would be equally refracted.

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Newton argued that white light is really a mixture of many different types of rays, that the different types of rays are refracted at slightly different angles, and that each different type of ray is responsible for producing a given spectral color. A so-called crucial experiment confirmed the theory. Newton selected out of the spectrum a narrow band of light of one color. He sent it through a second prism and observed that no further elongation occurred. All the selected rays of one color were refracted at the same angle.

Newton's greatest achievement was his work in physics and celestial mechanics, which culminated in the theory of universal gravitation. Even though Newton also began this research in the plague years, the story that he discovered universal gravitation in 1666 while watching an apple fall from a tree in his garden is a myth. By 1666, Newton had formulated early versions of his three laws of motion. He had also discovered the law stating the centrifugal force (or force away from the center) of a body moving uniformly in a circular path. However, he still believed that the earth's gravity and the motions of the planets might be caused by the action of whirlpools, or vortices, of small corpuscles, as Descartes had claimed. Moreover, although he knew the law of centrifugal force, he did not have a correct understanding of the mechanics of circular motion. He thought of circular motion as the result of a balance between two forces--one centrifugal, the other centripetal (toward the center)--rather than as the result of one force, a centripetal force, which constantly deflects the body away from its inertial path in a straight line.

Newton's great insight of 1666 was to imagine that the Earth's gravity extended to the Moon, counterbalancing its centrifugal force. From his law of centrifugal force and Kepler's third law of planetary motion, Newton deduced that the centrifugal (and hence centripetal) force of the Moon or of any planet must decrease as the inverse square of its distance from the center of its motion. For example, if the distance is doubled, the force becomes one-fourth as much; if distance is trebled, the force becomes one-ninth as much. This theory agreed with Newton's data to within about 11%.

In 1684 the young astronomer Edmond Halley, tired of Hooke's fruitless boasting, asked Newton whether he could prove Hooke's conjecture and to his surprise was told that Newton had solved the problem a full 5 years before but had now mislaid the paper. At Halley's constant urging Newton reproduced the proofs and expanded them into a paper on the laws of motion and problems of orbital mechanics.

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Newtons Telescope

Finally Halley persuaded Newton to compose a full-length treatment of his new physics and its application to astronomy. After 18 months of sustained effort, Newton published (1687) the Philosophiae naturalis principia mathematica (The Mathematical Principles of Natural Philosophy), or Principia, as it is universally known.

By common consent the Principia is the greatest scientific book ever written. Within the framework of an infinite, homogeneous, three-dimensional, empty space and a uniformly and eternally flowing "absolute" time, Newton fully analyzed the motion of bodies in resisting and nonresisting media under the action of centripetal forces. The results were applied to orbiting bodies, projectiles, pendula, and free-fall near the Earth. He further demonstrated that the planets were attracted toward the Sun by a force varying as the inverse square of the distance and generalized that all heavenly bodies mutually attract one another. By further generalization, he reached his law of universal gravitation: every piece of matter attracts every other piece with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.

 

Newton died in London on Mar. 31 (N.S.; Mar. 20, O.S.), 1727, having singlehandedly completed the scientific revolution and molded much of the content and the image of modern science.

John A. Schuster

 

Bibliography: Andrade, E. N., Isaac Newton (1950; repr. 1979); Bechler, Z., Contemporary Newtonian Research (1982); Christianson, G. E., In the Presence of the Creator: Isaac Newton and His Times (1984); Cohen, J B., and Westfall, R. S., eds., Newton Texts, Backgrounds, Commentaries (1994); Gjertson, D., The Newton Handbook (1987); Hall, A. R., Isaac Newton (1992); Manuel, F. E., A Portrait of Isaac Newton (1990); Maury, J.-P., Newton, trans. by P. Mark (1992); Westfall, R. S., The Life of Isaac Newton (1993).

Last modified on: Thursday, October 30, 1997.