h the Perception of White, then they could never lose their
Whiteness by such Reflexions. I inclined therefore the Paper to the Rays
very obliquely, as in the second Experiment of this second Part of the
first Book, that the most refrangible Rays, might be more copiously
reflected than the rest, and the Whiteness at Length changed
successively into blue, indigo, and violet. Then I inclined it the
contrary Way, that the least refrangible Rays might be more copious in
the reflected Light than the rest, and the Whiteness turned successively
to yellow, orange, and red.

Lastly, I made an Instrument XY in fashion of a Comb, whose Teeth being
in number sixteen, were about an Inch and a half broad, and the
Intervals of the Teeth about two Inches wide. Then by interposing
successively the Teeth of this Instrument near the Lens, I intercepted
Part of the Colours by the interposed Tooth, whilst the rest of them
went on through the Interval of the Teeth to the Paper DE, and there
painted a round Solar Image. But the Paper I had first placed so, that
the Image might appear white as often as the Comb was taken away; and
then the Comb being as was said interposed, that Whiteness by reason of
the intercepted Part of the Colours at the Lens did always change into
the Colour compounded of those Colours which were not intercepted, and
that Colour was by the Motion of the Comb perpetually varied so, that in
the passing of every Tooth over the Lens all these Colours, red, yellow,
green, blue, and purple, did always succeed one another. I caused
therefore all the Teeth to pass successively over the Lens, and when the
Motion was slow, there appeared a perpetual Succession of the Colours
upon the Paper: But if I so much accelerated the Motion, that the
Colours by reason of their quick Succession could not be distinguished
from one another, the Appearance of the single Colours ceased. There was
no red, no yellow, no green, no blue, nor purple to be seen any longer,
but from a Confusion of them all there arose one uniform white Colour.
Of the Light which now by the Mixture of all the Colours appeared white,
there was no Part really white. One Part was red, another yellow, a
third green, a fourth blue, a fifth purple, and every Part retains its
proper Colour till it strike the Sensorium. If the Impressions follow
one another slowly, so that they may be severally perceived, there is
made a distinct Sensation of all the Colours one after another in