The PROOF by Experiments.
_Exper._ 9. The Sun shining into a dark Chamber through a little round
hole in the Window-shut, and his Light being there refracted by a Prism
to cast his coloured Image PT [in _Fig._ 5.] upon the opposite Wall: I
held a white Paper V to that image in such manner that it might be
illuminated by the colour'd Light reflected from thence, and yet not
intercept any part of that Light in its passage from the Prism to the
Spectrum. And I found that when the Paper was held nearer to any Colour
than to the rest, it appeared of that Colour to which it approached
nearest; but when it was equally or almost equally distant from all the
Colours, so that it might be equally illuminated by them all it appeared
white. And in this last situation of the Paper, if some Colours were
intercepted, the Paper lost its white Colour, and appeared of the Colour
of the rest of the Light which was not intercepted. So then the Paper
was illuminated with Lights of various Colours, namely, red, yellow,
green, blue and violet, and every part of the Light retained its proper
Colour, until it was incident on the Paper, and became reflected thence
to the Eye; so that if it had been either alone (the rest of the Light
being intercepted) or if it had abounded most, and been predominant in
the Light reflected from the Paper, it would have tinged the Paper with
its own Colour; and yet being mixed with the rest of the Colours in a
due proportion, it made the Paper look white, and therefore by a
Composition with the rest produced that Colour. The several parts of the
coloured Light reflected from the Spectrum, whilst they are propagated
from thence through the Air, do perpetually retain their proper Colours,
because wherever they fall upon the Eyes of any Spectator, they make the
several parts of the Spectrum to appear under their proper Colours. They
retain therefore their proper Colours when they fall upon the Paper V,
and so by the confusion and perfect mixture of those Colours compound
the whiteness of the Light reflected from thence.
_Exper._ 10. Let that Spectrum or solar Image PT [in _Fig._ 6.] fall now
upon the Lens MN above four Inches broad, and about six Feet distant
from the Prism ABC and so figured that it may cause the coloured Light
which divergeth from the Prism to converge and meet again at its Focus
G, about six or eight Feet distant from the Lens, and there to fall
perpendicularly upon a white Paper DE. And if you move this Paper to and
fro, you will perceive that near the Lens, as at _de_, the whole solar
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