opake Bodies appear of one and the
same Colour in all Positions of the Eye, though this I cannot yet affirm
by Experience. For all colour'd Bodies, so far as my Observation
reaches, may be seen through if made sufficiently thin, and therefore
are in some measure transparent, and differ only in degrees of
Transparency from tinged transparent Liquors; these Liquors, as well as
those Bodies, by a sufficient Thickness becoming opake. A transparent
Body which looks of any Colour by transmitted Light, may also look of
the same Colour by reflected Light, the Light of that Colour being
reflected by the farther Surface of the Body, or by the Air beyond it.
And then the reflected Colour will be diminished, and perhaps cease, by
making the Body very thick, and pitching it on the backside to diminish
the Reflexion of its farther Surface, so that the Light reflected from
the tinging Particles may predominate. In such Cases, the Colour of the
reflected Light will be apt to vary from that of the Light transmitted.
But whence it is that tinged Bodies and Liquors reflect some sort of
Rays, and intromit or transmit other sorts, shall be said in the next
Book. In this Proposition I content my self to have put it past dispute,
that Bodies have such Properties, and thence appear colour'd.

_PROP._ XI. PROB. VI.

_By mixing colour'd Lights to compound a beam of Light of the same
Colour and Nature with a beam of the Sun's direct Light, and therein to
experience the Truth of the foregoing Propositions._

[Illustration: FIG. 16.]

Let ABC _abc_ [in _Fig._ 16.] represent a Prism, by which the Sun's
Light let into a dark Chamber through the Hole F, may be refracted
towards the Lens MN, and paint upon it at _p_, _q_, _r_, _s_, and _t_,
the usual Colours violet, blue, green, yellow, and red, and let the
diverging Rays by the Refraction of this Lens converge again towards X,
and there, by the mixture of all those their Colours, compound a white
according to what was shewn above. Then let another Prism DEG _deg_,
parallel to the former, be placed at X, to refract that white Light
upwards towards Y. Let the refracting Angles of the Prisms, and their
distances from the Lens be equal, so that the Rays which converged from
the Lens towards X, and without Refraction, would there have crossed and
diverged again, may by the Refraction of the second Prism be reduced
into Parallelism and diverge no more. For then those Rays will recompose
a beam of whit