N._

The homogeneal Light and Rays which appear red, or rather make Objects
appear so, I call Rubrifick or Red-making; those which make Objects
appear yellow, green, blue, and violet, I call Yellow-making,
Green-making, Blue-making, Violet-making, and so of the rest. And if at
any time I speak of Light and Rays as coloured or endued with Colours, I
would be understood to speak not philosophically and properly, but
grossly, and accordingly to such Conceptions as vulgar People in seeing
all these Experiments would be apt to frame. For the Rays to speak
properly are not coloured. In them there is nothing else than a certain
Power and Disposition to stir up a Sensation of this or that Colour.
For as Sound in a Bell or musical String, or other sounding Body, is
nothing but a trembling Motion, and in the Air nothing but that Motion
propagated from the Object, and in the Sensorium 'tis a Sense of that
Motion under the Form of Sound; so Colours in the Object are nothing but
a Disposition to reflect this or that sort of Rays more copiously than
the rest; in the Rays they are nothing but their Dispositions to
propagate this or that Motion into the Sensorium, and in the Sensorium
they are Sensations of those Motions under the Forms of Colours.

_PROP._ III. PROB. I.

_To define the Refrangibility of the several sorts of homogeneal Light
answering to the several Colours._

For determining this Problem I made the following Experiment.[J]

_Exper._ 7. When I had caused the Rectilinear Sides AF, GM, [in _Fig._
4.] of the Spectrum of Colours made by the Prism to be distinctly
defined, as in the fifth Experiment of the first Part of this Book is
described, there were found in it all the homogeneal Colours in the same
Order and Situation one among another as in the Spectrum of simple
Light, described in the fourth Proposition of that Part. For the Circles
of which the Spectrum of compound Light PT is composed, and which in
the middle Parts of the Spectrum interfere, and are intermix'd with one
another, are not intermix'd in their outmost Parts where they touch
those Rectilinear Sides AF and GM. And therefore, in those Rectilinear
Sides when distinctly defined, there is no new Colour generated by
Refraction. I observed also, that if any where between the two outmost
Circles TMF and PGA a Right Line, as [Greek: gd], was cross to the
Spectrum, so as both Ends to fall perpendicularly upon its Rectilinear
Sides, there appeared one and