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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.
Optics.
as a sort of scenario by which Newton attempted to
convey the impression of a logical train of discovery
based on deductions from experiment. The historical
record, however, shows that Newton's great leap
forward was actually a consequence of implications
drawn from profound scientific speculation and
insight.93
In any event, Newton himself did not publish the
Lectiones opticae, nor did he produce his planned
annotated edition of at least some (and maybe all) of
his letters on light and color published in the
Philosophical Transactions.94 He completed his English
Opticks, however, and after repeated requests that
he do so, allowed it to be printed in 1704, although
he withheld his name, save on the title page of one
known copy. It has often been alleged that Newton
released the Opticks for publication only after Hooke—the
last of the original objectors to his theory of light
and colors—had died. David Gregory, however,
recorded another reason for the publication of the
Opticks in 1704: Newton, Gregory wrote, had been
“provoked” by the appearance, in 1703, of George
Cheyne's Fluxionum methoda inversa “to publish his
[own tract on] Quadratures, and with it, his Light &
Colours, &c.”95
In the Opticks, Newton presented his main discoveries
and theories concerning light and color in
logical order, beginning with eight definitions and
eight axioms.96 Definition 1 of book I reads: “By the
Rays of Light I understand its least Parts, and those
as well Successive in the same Lines, as Contemporary
in several Lines.” Eight propositions follow, the first
stating that “Lights which differ in Colour, differ also
in Degrees of Refrangibility.” In appended experiments
Newton discussed the appearance of a paper
colored half red and half blue when viewed through
a prism and showed that a given lens produces red
and blue images, respectively, at different distances.
The second proposition incorporates a variety of
prism experiments as proof that “The Light of
the Sun consists of Rays differently refrangible.”
The figure given with experiment 10 of this series
illustrates “two Prisms tied together in the form
of a Parallelopiped” (Fig. 3). Under specified conditions,
sunlight entering a darkened room through a
small hole F in the shutter would not be refracted
by the parallelopiped and would emerge parallel to the
incident beam FM, from which it would pass by
refraction through a third prism IKH, which would
by refraction “cast the usual Colours of the Prism
upon the opposite Wall.” Turning the parallelopiped
about its axis, Newton found that the rays producing
the several colors were successively “taken out of the
transmitted Light” by “total Reflexion”; first “the
Rays which in the third Prism had suffered the
greatest Refraction and painted [the wall] with violet
and blew were ... taken out of the transmitted Light,
the rest remaining,” then the rays producing green,
yellow, orange, and red were “taken out” as the
parallelopiped was rotated yet further. Newton thus
experimentally confirmed the “experimentum crucis,”
showing that the light emerging from the two prisms
“is compounded of Rays differently Refrangible,
seeing [that] the more Refrangible Rays may be
taken out while the less Refrangible remain.” The
arrangement of prisms is the basis of the important
discovery reported in book II, part 1, observation 1.
FIGURE 3
In proposition 6 Newton showed that, contrary
to the opinions of previous writers, the sine
law actually holds for each single color. The first part
of book I ends with Newton's remarks on the impossibility
of improving telescopes by the use of color-corrected
lenses and his discussion of his consequent
invention of the reflecting telescope (Fig. 4).
In the second part of book I, Newton dealt with
colors produced by reflection and refraction (or
transmission), and with the appearance of colored
objects in relation to the color of the light illuminating
them. He discussed colored pigments and their
mixture and geometrically constructed a color wheel,
drawing an analogy between the primary colors in a
compound color and the “seven Musical Tones or
Intervals of the eight Sounds, Sol, la, fa, sol,
la,
mi, fa, sol....”97
Proposition 9, “Prob. IV. By the discovered
Properties of Light to explain the Colours of the
Rain-bow,” is devoted to the theory of the rainbow.
FIGURE 4. Newton's method “To shorten Telescopes”: efg
represents the prism, abcd the speculum, and h the lens.
Descartes had developed a geometrical theory, but had