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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