NEWTON, ISAAC (b. Woolsthorpe, England, 25 December 1642; d. London, England, 20 March 1727), mathematics, dynamics, celestial mechanics, astronomy, optics, natural philosophy.

    several colors. In query 15 Newton discussed binocular vision, along with other aspects of seeing, while in query 16 he took up the phenomenon of persistence of vision.

Newton has been much criticized for believing dispersion to be independent of the material of the prism and for positing a constant relation between deviation and dispersion in all refractive substances. He thus dismissed the possibility of correcting for chromatic aberration in lenses, and directed attention from refraction to reflecting telescopes.103

Newton is often considered to be the chief advocate of the corpuscular or emission theory of light. Lohne has shown that Newton originally did believe in a simple corpuscular theory, an aspect of Newton's science also forcibly brought out by Sabra. Challenged by Hooke, Newton proposed a hypothesis of ether waves associated with (or caused by) these corpuscles, one of the strongest arguments for waves probably being his own discovery of periodicity in “Newton's rings.” Unlike either Hooke or Huygens, who is usually held to be the founder of the wave theory but who denied periodicity to waves of light, Newton postulated periodicity as a fundamental property of waves of (or associated with) light, at the same time that he suggested that a particular wavelength characterizes the light producing each color. Indeed, in the queries, he even suggested that vision might be the result of the propagation of waves in the optic nerves. But despite this dual theory, Newton always preferred the corpuscle concept, whereby he might easily explain both rectilinear propagation and polarization, or “sides.” The corpuscle concept lent itself further to an analysis by forces (as in section 14 of book I of the Principia), thus establishing a universal analogy between the action of gross bodies (of the atoms or corpuscles composing such bodies), and of light. These latter topics are discussed below in connection with the later queries of the Opticks.

Dynamics, Astronomy, and the Birth of the “Principia.”

Newton recorded his early thoughts on motion in various student notebooks and documents.104 While still an undergraduate, he would certainly have studied the Aristotelian (or neo-Aristotelian) theory of motion and he is known to have read Magirus' Physiologiae peripateticae libri sex; his notes include a “Cap:4. De Motu” (wherein “Motus” is said to be the Aristotelian ἐντελέχεια). Extracts from Magirus occur in a notebook begun by Newton in 1661;105 it is a repository of jottings from his student years on a variety of physical and nonphysical topics. In it Newton recorded, among other extracts, Kepler's third law, “that the mean distances of the primary Planets from the Sunne are in sesquialter proportion to the periods of their revolutions in time.”106 This and other astronomical material, including a method of finding planetary positions by approximation, comes from Thomas Streete's Astronomia Carolina.

Here, too, Newton set down a note on Horrox' observations, and an expression of concern about the vacuum and the gravity of bodies; he recorded, from “Galilaeus,” that “an iron ball” falls freely through “100 braces Florentine or cubits [or 49.01 ells, perhaps 66 yards] in 5? of an hower.” Notes of a later date—on matter, motion, gravity, and levity—give evidence of Newton's having read Charleton (on Gassendi), Digby (on Galileo), Descartes, and Henry More.

In addition to acquiring this miscellany of information, making tables of various kinds of observations, and supplementing his reading in Streete by Wing (and, probably, by Galileo's Sidereus nuncius and Gassendi's epitome of Copernican astronomy), Newton was developing his own revisions of the principles of motion. Here the major influence on his thought was Descartes (especially the Principia philosophiae and the Latin edition of the correspondence, both of which Newton cited in early writings), and Galileo (whose Dialogue he knew in the Salusbury version, and whose ideas he would have encountered in works by Henry More, by Charleton and Wallis, and in Digby's Two Essays).

An entry in Newton's Waste Book,107 dated 20 January 1664, shows a quantitative approach to problems of inelastic collision. It was not long before Newton went beyond Descartes's law of conservation, correcting it by algebraically taking into account direction of motion rather than numerical products of size and speed of bodies. In a series of axioms he declared a principle of inertia (in “Axiomes” 1 and 2); he then asserted a relation between “force” and change of motion; and he gave a set of rules for elastic collision.108 In “Axiome” 22, he had begun to approach the idea of centrifugal force by considering the pressure exerted by a sphere rolling around the inside surface of a cylinder. On the first page of the Waste Book, Newton had quantitated the centrifugal force by conceiving of a body moving along a square inscribed in a circle, and then adding up the shocks at each “reflection.” As the number of sides were increased, the body in the limiting case would be “reflected by the sides of an equilateral circumscribed polygon of an infinite number of sides (i.e. by the circle it selfe).” Herivel has pointed out the near equivalence of such results to the early proof mentioned by Newton at the end of the scholium to proposition 4, book I, of the