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

    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