Electronic edition published by Cultural Heritage Langauge Technologies (with permission from Charles Scribners and Sons) and funded by the National Science Foundation International Digital Libraries Program. This text has been proofread to a low degree of accuracy. It was converted to electronic form using data entry.
NEWTON, ISAAC (b. Woolsthorpe, England,
25 December 1642; d. London, England, 20 March
1727), mathematics, dynamics, celestial mechanics,
astronomy, optics, natural philosophy.
Optics.
Rays, by virtue of their different Refrangibility or
Reflexibility”; the study of color thus becomes
“a Speculation as truly mathematical as any other
part of Opticks.”101
In part 3 of book II, Newton analyzed “the
permanent Colours of natural Bodies, and the Analogy
between them and the Colours of thin transparent
Plates.” He concluded that the smallest possible
subdivisions of matter must be transparent, and their
dimensions optically determinable. A table accompanying
proposition 10 gives the refractive powers of
a variety of substances “in respect of ... Densities.”
Proposition 12 contains Newton's conception of
“fits”:
Every Ray of Light in its passage through any
refracting Surface is put into a certain transient
Constitution or State, which in the progress of the Ray
returns at equal Intervals, and disposes the Ray at
every return to be easily transmitted through the next
refracting Surface, and between the returns to be easily
reflected by it.
The succeeding definition is more specific: “The
returns of the disposition of any Ray to be reflected
I will call its Fits of easy Reflection, and those of its
disposition to be transmitted its Fits of easy Transmission,
and the space it passes between every return
and the next return, the Interval of its Fits.”
The “fits” of easy reflection and of easy refraction
could thus be described as a numerical sequence;
if reflection occurs at distances 0, 2, 4, 6, 8, ..., from
some central point, then refraction (or transmission)
must occur at distances 1, 3, 5, 7, 9, .... Newton did
not attempt to explain this periodicity, stating that
“I do not here enquire” into the question of “what
kind of action or disposition this is.” He declined to
speculate “whether it consists in a circulating or a
vibrating motion of the Ray, or of the Medium, or
something else,” contenting himself “with the bare
Discovery, that the Rays of Light are by some cause
or other alternately disposed to be reflected or
refracted for many vicissitudes.”
Newton thus integrated the periodicity of light into
his theoretical work (it had played only a marginal
part in Hooke's theory). His work was, moreover,
based upon extraordinarily accurate measurements—so
much so that when Thomas Young devised an
explanation of Newton's rings based on the revived
wave theory of light and the new principle of interference,
he used Newton's own data to compute the
wavelengths and wave numbers of the principal colors
in the visible spectrum and attained results that are
in close agreement with those generally accepted today.
In part 4 of book II, Newton addressed himself to
“the Reflexions and Colours of thick transparent
polish'd Plates.” This book ends with an analysis of
halos around the sun and moon and the computation
of their size, based on the assumption that they are
produced by clouds of water or by hail. This led him
to the series of eleven observations that begin the
third and final book, “concerning the Inflexions of the
Rays of Light, and the Colours made thereby,” in
which Newton took up the class of optical phenomena
previously studied by Grimaldi,102 in which “fringes”
are produced at the edges of the shadows of objects
illuminated by light “let into a dark Room through a
very small hole.” Newton discussed such fringes surrounding
the projected shadows of a hair, the edge
of a knife, and a narrow slit.
Newton concluded the first edition of the Opticks
(1704) with a set of sixteen queries, introduced “in
order to a further search to be made by others.” He
had at one time hoped he might carry the investigations
further, but was “interrupted,” and wrote that
he could not “now think of taking these things into
farther Consideration.” In the eighteenth century and
after, these queries were considered the most important
feature of the Opticks—particularly the later ones,
which were added in two stages, in the Latin Optice
of 1706 and in the second English edition of 1717-1718.
The original sixteen queries at once go beyond mere
experiments on diffraction phenomena. In query 1,
Newton suggested that bodies act on light at a distance
to bend the rays; and in queries 2 and 3, he attempted
to link differences in refrangibility with differences in
“flexibility” and the bending that may produce color
fringes. In query 4, he inquired into a single principle
that, by “acting variously in various Circumstances,”
may produce reflection, refraction, and inflection,
suggesting that the bending (in reflection and
refraction) begins before the rays “arrive at the
Bodies.” Query 5 concerns the mutual interaction of
bodies and light, the heat of bodies being said to
consist of having “their parts [put] into a vibrating
motion”; while in query 6 Newton proposed a reason
why black bodies “conceive heat more easily from
Light than those of other Colours.” He then discussed
the action between light and “sulphureous” bodies,
the causes of heat in friction, percussion, putrefaction,
and so forth, and defined fire (in query 9) and flame
(in query 10), discussing various chemical operations.
In query 11, he extended his speculations on heat and
vapors to sun and stars. The last four queries (12 to 16)
of the original set deal with vision, associated with
“Vibrations” (excited by “the Rays of Light”) which
cause sight by “being propagated along the solid
Fibres of the optick Nerves into the Brain.” In query 13
specific wavelengths are associated with each of