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Astro*Dictionary by Michael Erlewine





1 article for "Newton"

Newton, Sir Isaac [Astro*Index]

(1642-1727) English scientist, mathematician, astronomer, and astrologer.

He developed the Binomial Theorem in mathematics. Escaping the plague which hit London, Newton left Cambridge University to live at his mother's farm. According to his own writings, he there observed an apple fall to the ground, and speculated that the same force which pulled upon the apple might keep the Moon locked into its orbit about the Earth. Using an incorrect value for the distance of the Moon, he arrived at a rate of fall for the Moon which was only 7/8ths of the observed value. He was also concerned with the problem of whether the attraction could be computed (with sufficient accuracy) by considering the Earth to be a mass-point, ignoring the extended mass of the Earth. This problem was not to be resolved until after his development of the Calculus, some 15 years later. He advanced a particle theory of light, and developed a reflecting telescope using a parabolic mirror. When Robert Hooke, Newton's arch-rival, boasted to Wren and Halley that he had derived a set of 'laws' which explained planetary motions, Wren was unimpressed and offered a prize to anyone who could solve the problem. Halley, Newton's friend, took the problem to Newton asking what shape the orbit of a planet would assume if there were a force of attraction between two bodies that diminished as the square of the distance. Newton immediately replied, that the orbit would be an ellipse. Excited by this statement, Halley encouraged Newton to, again, consider the problem of gravitation. By this time, Newton had developed his Calculus to the point that he was able to show that spherical bodies (such as the Earth) could be treated as if their mass were concentrated at a point located at the center of the sphere. And using Picard's improved value for the size of the Earth, he was able to derive a value for the rate of fall of the Moon which agreed with observation. His massive work was completed in 18 months, and published in 1687 under the title Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), and is usually known by is contracted title, Principia Mathematica. Written in Latin, an English version did not appear until 2 years after Newton's death. In spite of his invention of the Calculus, which would have greatly simplified his task, Newton chose to prove the various propositions in this work by geometrical reasoning. In this work, he set forth the three propositions which have become known as the 'laws' of Newton:

(1) A body at rest remains at rest, while a body in motion continues in uniform motion (constant velocity) in a straight line, unless it is acted upon by an external force;

(2) When a force acts upon a body, the state of rest or motion is changed in the direction in which the force acts, with the rate of change of momentum being proportional to the force. (If the mass is taken to be constant, this leads to the formula: F = ma, in which the force, F,and the acceleration, a, are vectors.);

(3) To every action there is an equal and opposite reaction. From these laws, he was able to derive an expression for the 'force' of gravitation: F = Gm1m2r/r3, where F and r are vectors.

Newton guessed that this law could also be applied between any two bodies throughout the universe, and this law became known as the Universal 'Law' of Gravitation. Correct determination of the value of the constant G was not made until a century later with the work of Cavendish, but Newton's guess was reasonably accurate and allowed him to estimate the mass of Jupiter and Saturn quite well. Newton's Theory of Universal Gravitation explained Kepler's laws, the Precession of the Equinoxes, and the flattening of the poles of the Earth. Remaining discrepancies in the observed positions of celestial bodies were attributed to Perturbations (minor gravitational attractions) which resulted from considerations involving more than two bodies. The Royal Society offered to publish Newton's great work, but due to a shortage of funds and the controversy raised by Hooke (who claimed prior discovery), backed out on its agreement. But, Halley rose to the occasion, paid for the publication, and even assisted in reading the galley proofs. Newton's work completed the revolution begun by Copernicus and advanced by Kepler and Galileo, and led the the modern conception of the solar system: heliocentric, with the bodies in elliptical orbits, and governed by mathematically formulated 'laws' of gravitation and motion. Notwithstanding the spectacular successes achieved by astronomers in applying Newtonian Gravitation to the motion of heavenly bodies, Newton's 'law' of gravitation is, in fact, only a theory--one which has been shown to be seriously flawed. The motion of perihelion of Mercury, for example, exhibits a motion which cannot be accounted for by the Newtonian theory. The Gravitational Theory of Einstein was able to account for discrepancy, but required some fundamental revisions in our concept of space and time. Astronomers avoid the resulting embarrassments by treating the effects of Relativity as small "corrections" to the Newtonian Theory of Gravitation.

While this practice can be justified as leading to simplifications in computational procedures, it is, at once, both deceptive and deceitful, as it continues to promote the myth of Newton's view of gravitation as a 'law', rather than a mere theory. Newton also wrote over a million words on Chemistry (which include recipes for the manufacture of gold by transmutation). He also wrote over a million and a half words on mystical passages of the Bible, setting the Day of Creation in BC3500.

See also:
♦ Gravitation ♦ Picard, Jean ♦ Halley, Edmund


Astro*Index Copyright © 1997 Michael Erlewine