besides (which
was enough for my purpose), I observed that the difference 'twixt the
length of the image and diameter of the hole through which the light was
transmitted was proportionable to their distance.

"The gradual removal of these suspicions at length led me to the
experimentum crucis, which was this: I took two boards, and, placing
one of them close behind the prism at the window, so that the light must
pass through a small hole, made in it for the purpose, and fall on the
other board, which I placed at about twelve feet distance, having first
made a small hole in it also, for some of the incident light to pass
through. Then I placed another prism behind this second board, so that
the light trajected through both the boards might pass through that
also, and be again refracted before it arrived at the wall. This done,
I took the first prism in my hands and turned it to and fro slowly about
its axis, so much as to make the several parts of the image, cast on
the second board, successively pass through the hole in it, that I might
observe to what places on the wall the second prism would refract them.
And I saw by the variation of these places that the light, tending to
that end of the image towards which the refraction of the first prism
was made, did in the second prism suffer a refraction considerably
greater than the light tending to the other end. And so the true cause
of the length of that image was detected to be no other than that LIGHT
consists of RAYS DIFFERENTLY REFRANGIBLE, which, without any respect
to a difference in their incidence, were, according to their degrees of
refrangibility, transmitted towards divers parts of the wall."(1)

THE NATURE OF COLOR

Having thus proved the composition of light, Newton took up an
exhaustive discussion as to colors, which cannot be entered into at
length here. Some of his remarks on the subject of compound colors,
however, may be stated in part. Newton's views are of particular
interest in this connection, since, as we have already pointed out, the
question as to what constituted color could not be agreed upon by
the philosophers. Some held that color was an integral part of the
substance; others maintained that it was simply a reflection from the
surface; and no scientific explanation had been generally accepted.
Newton concludes his paper as follows:

"I might add more instances of this nature, but I shall conclude with
the general one that the colors of a