indigo-making Rays are mixed, it must be a violet inclining much to
indigo. At R where the violet-making, indigo-making, blue-making, and
one half of the green-making Rays are mixed, their Colours must (by the
construction of the second Problem) compound a middle Colour between
indigo and blue. At S where all the Rays are mixed, except the
red-making and orange-making, their Colours ought by the same Rule to
compound a faint blue, verging more to green than indigo. And in the
progress from S to T, this blue will grow more and more faint and
dilute, till at T, where all the Colours begin to be mixed, it ends in
whiteness.
[Illustration: FIG. 12.]
So again, on the other side of the white at [Greek: t], where the least
refrangible or utmost red-making Rays are alone, the Colour must be the
deepest red. At [Greek: s] the mixture of red and orange will compound a
red inclining to orange. At [Greek: r] the mixture of red, orange,
yellow, and one half of the green must compound a middle Colour between
orange and yellow. At [Greek: ch] the mixture of all Colours but violet
and indigo will compound a faint yellow, verging more to green than to
orange. And this yellow will grow more faint and dilute continually in
its progress from [Greek: ch] to [Greek: p], where by a mixture of all
sorts of Rays it will become white.
These Colours ought to appear were the Sun's Light perfectly white: But
because it inclines to yellow, the Excess of the yellow-making Rays
whereby 'tis tinged with that Colour, being mixed with the faint blue
between S and T, will draw it to a faint green. And so the Colours in
order from P to [Greek: t] ought to be violet, indigo, blue, very faint
green, white, faint yellow, orange, red. Thus it is by the computation:
And they that please to view the Colours made by a Prism will find it so
in Nature.
These are the Colours on both sides the white when the Paper is held
between the Prism and the Point X where the Colours meet, and the
interjacent white vanishes. For if the Paper be held still farther off
from the Prism, the most refrangible and least refrangible Rays will be
wanting in the middle of the Light, and the rest of the Rays which are
found there, will by mixture produce a fuller green than before. Also
the yellow and blue will now become less compounded, and by consequence
91