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.
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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.
Newtons Telescope
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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.
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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.