o
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
more intense than before. And this also agrees with experience.

And if one look through a Prism upon a white Object encompassed with
blackness or darkness, the reason of the Colours arising on the edges is
much the same, as will appear to one that shall a little consider it. If
a black Object be encompassed with a white one, the Colours which appear
through the Prism are to be derived from the Light of the white one,
spreading into the Regions of the black, and therefore they appear in a
contrary order to that, when a white Object is surrounded with black.
And the same is to be understood when an Object is viewed, whose parts
are some of them less luminous than others. For in the borders of the
more and less luminous Parts, Colours ought always by the same
Principles to arise from the Excess of the Light of the more luminous,
and to be of the same kind as if the darker parts were black, but yet to
be more faint and dilute.

What is said of Colours made by Prisms may be easily applied to Colours
made by the Glasses of Telescopes or Microscopes, or by the Humours of
the Eye. For if the Object-glass of a Telescope be thicker on one side
than on the other, or if one half of the Glass, or one half of the Pupil
of the Eye be cover'd with any opake substance; the