Now, whilst Bodies become coloured by reflecting or transmitting this or
that sort of Rays more copiously than the rest, it is to be conceived
that they stop and stifle in themselves the Rays which they do not
reflect or transmit. For, if Gold be foliated and held between your Eye
and the Light, the Light looks of a greenish blue, and therefore massy
Gold lets into its Body the blue-making Rays to be reflected to and fro
within it till they be stopp'd and stifled, whilst it reflects the
yellow-making outwards, and thereby looks yellow. And much after the
same manner that Leaf Gold is yellow by reflected, and blue by
transmitted Light, and massy Gold is yellow in all Positions of the Eye;
there are some Liquors, as the Tincture of _Lignum Nephriticum_, and
some sorts of Glass which transmit one sort of Light most copiously, and
reflect another sort, and thereby look of several Colours, according to
the Position of the Eye to the Light. But, if these Liquors or Glasses
were so thick and massy that no Light could get through them, I question
not but they would like all other 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
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