If the most refrangible Rays coming from the superior Prism take up all
the Space from M to P, the Rays of the same sort which come from the
inferior Prism ought to begin at P, and take up all the rest of the
Space from thence towards N. If the least refrangible Rays coming from
the superior Prism take up the Space MT, the Rays of the same kind which
come from the other Prism ought to begin at T, and take up the
remaining Space TN. If one sort of the Rays which have intermediate
Degrees of Refrangibility, and come from the superior Prism be extended
through the Space MQ, and another sort of those Rays through the Space
MR, and a third sort of them through the Space MS, the same sorts of
Rays coming from the lower Prism, ought to illuminate the remaining
Spaces QN, RN, SN, respectively. And the same is to be understood of all
the other sorts of Rays. For thus the Rays of every sort will be
scattered uniformly and evenly through the whole Space MN, and so being
every where mix'd in the same Proportion, they must every where produce
the same Colour. And therefore, since by this Mixture they produce white
in the Exterior Spaces MP and TN, they must also produce white in the
Interior Space PT. This is the reason of the Composition by which
Whiteness was produced in this Experiment, and by what other way soever
I made the like Composition, the Result was Whiteness.
Lastly, If with the Teeth of a Comb of a due Size, the coloured Lights
of the two Prisms which fall upon the Space PT be alternately
intercepted, that Space PT, when the Motion of the Comb is slow, will
always appear coloured, but by accelerating the Motion of the Comb so
much that the successive Colours cannot be distinguished from one
another, it will appear white.
_Exper._ 14. Hitherto I have produced Whiteness by mixing the Colours of
Prisms. If now the Colours of natural Bodies are to be mingled, let
Water a little thicken'd with Soap be agitated to raise a Froth, and
after that Froth has stood a little, there will appear to one that shall
view it intently various Colours every where in the Surfaces of the
several Bubbles; but to one that shall go so far off, that he cannot
distinguish the Colours from one another, the whole Froth will grow
white with a perfect Whiteness.
_Exper._ 15. Lastly, In attempting to compound a white, by mixing the
coloured Powders which Painters use, I consider'd that all colour'd
Powders do suppress and stop in them a very considerable Part of the
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