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.
raised to any given power, and taken together, may
make everywhere the same sum.”72
FIGURE 2. Newton's drawing of the crucial experiment
(University Library, Cambridge, MS Add. 4002, fol. 128a).
Newton himself was a careful draftsman, but the diagrams
have become so corrupt in later editions as to violate the
fundamental laws of optics.
Newton's analytic solution of the curve of least
descent is of particular interest as an early example of
what became the calculus of variations. Newton had
long been concerned with such problems, and in the
Principia had included (without proof) his findings
concerning the solid of least resistance. When David
Gregory asked him how he had found such a solid,
Newton sent him an analytic demonstration (using
dotted fluxions), of which a version was published
as an appendix to the second volume of Motte's
English translation of the Principia.73
Optics.
The study of Newton's work in optics has
to date generally been limited to his published letters
relating to light and color (in Philosophical Transactions,
beginning in February 1672), his invention of
a reflecting telescope and “sextant,” and his published
Opticks of 1704 and later editions (in Latin and
English). There has never been an adequate edition
or a full translation of the Lectiones opticae. Nor,
indeed, have Newton's optical manuscripts as yet
been thoroughly studied.74
Newton's optical work first came to the attention
of the Royal Society when a telescope made by him
was exhibited there. Newton was elected a fellow
shortly thereafter, on 11 January 1672, and responded
by offering the Society an account of the discovery
that had led him to his invention. It was, he proudly
alleged, “the oddest if not the most considerable detection
yet made in the operations of nature”: the analysis
of dispersion and the composition of white
light.
In the published account Newton related that in
1666 (“at which time I applyed myself to the grinding
of Optick glasses of other figures than Spherical”) he
procured a triangular glass prism, “to try therewith
the celebrated Phaenomena of Colours.” Light from
a tiny hole in a shutter passed through the prism; the
multicolored image--to Newton's purported surprise--was
of “an oblong form,” whereas “according to
the received laws of Refraction, I expected [it] should
have been circular.” To account for this unexpected
appearance, Newton looked into a number of possibilities,
among them that “the Rays, after their
trajection through the Prisme did not move in
curve lines,” and was thereby led to the famous
“experimentum crucis.”75 In this experiment
Newton used two prisms: the first was employed
to produce a spectrum on an opaque board
(BC) into which a small hole had been drilled; a
beam of light could thus pass through the hole to
a second board (DE) with a similar aperture; in this
way a narrow beam of light of a single color would
be directed to a second prism, and the beam emerging
from the second prism would project an image on
another board (Fig. 2). Thus, all light reaching the final
board had been twice subjected to prismatic dispersion.
By rotating the first prism “to and fro slowly about its
Axis,” Newton allowed different portions of the
dispersed light to reach the second prism.
Newton found that the second prism did not
produce any further dispersion of the “homogeneal”
light (that is, of light of about the same color); he
therefore concluded that “Light it self is a Heterogeneous
mixture of differently refrangible Rays”; and
asserted an exact correspondence between color and
“degree of Refrangibility” (the least refrangible rays
being “disposed to exhibit a Red colour,” while those
of greatest refrangibility are a deep violet). Hence,
colors “are not Qualifications of Light, derived from
Refractions, or Reflections of natural Bodies,” as
commonly believed, but “Original and connate
properties,”
differing in the different sorts of rays.76