and through Z drawing the Line OY, the Point Y falls upon the
circumference between E and F, something nearer to E than to F, and
thence I conclude, that the Colour compounded of these Ingredients will
be an orange, verging a little more to red than to yellow. Also I find
that OZ is a little less than one half of OY, and thence I conclude,
that this orange hath a little less than half the fulness or intenseness
of an uncompounded orange; that is to say, that it is such an orange as
may be made by mixing an homogeneal orange with a good white in the
proportion of the Line OZ to the Line ZY, this Proportion being not of
the quantities of mixed orange and white Powders, but of the quantities
of the Lights reflected from them.
This Rule I conceive accurate enough for practice, though not
mathematically accurate; and the truth of it may be sufficiently proved
to Sense, by stopping any of the Colours at the Lens in the tenth
Experiment of this Book. For the rest of the Colours which are not
stopp'd, but pass on to the Focus of the Lens, will there compound
either accurately or very nearly such a Colour, as by this Rule ought to
result from their Mixture.
_PROP._ VII. THEOR. V.
_All the Colours in the Universe which are made by Light, and depend not
on the Power of Imagination, are either the Colours of homogeneal
Lights, or compounded of these, and that either accurately or very
nearly, according to the Rule of the foregoing Problem._
For it has been proved (in _Prop. 1. Part 2._) that the changes of
Colours made by Refractions do not arise from any new Modifications of
the Rays impress'd by those Refractions, and by the various Terminations
of Light and Shadow, as has been the constant and general Opinion of
Philosophers. It has also been proved that the several Colours of the
homogeneal Rays do constantly answer to their degrees of Refrangibility,
(_Prop._ 1. _Part_ 1. and _Prop._ 2. _Part_ 2.) and that their degrees
of Refrangibility cannot be changed by Refractions and Reflexions
(_Prop._ 2. _Part_ 1.) and by consequence that those their Colours are
likewise immutable. It has also been proved directly by refracting and
reflecting homogeneal Lights apart, that their Colours cannot be
changed, (_Prop._ 2. _Part_ 2.) It has been proved also, that when the
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