I shall
add, that if the Sun-beams be in a convenient manner trajected through a
Glass-prism, and thrown upon some well-shaded Object within a Room, the
Rain-bow thereby Painted on the Surface of the Body that Terminates the
Beams, may oftentimes last longer than Some Colours I have produc'd in
certain Bodies, which would justly, and without scruple be accounted
Genuine Colours, and yet suddenly Degenerate, and lose their Nature.
4. A greater Disparity betwixt Emphatical Colours, and others, may perhaps
be taken from this, that Genuine Colours seem to be produc'd in Opacous
Bodies by Reflection, but Apparent ones in Diaphanous Bodies, and
principally by Refraction, I say Principally rather than Solely, because in
some cases Reflection also may concurr, but still this seems not to
conclude these Latter Colours not to be True ones. Nor must what has been
newly said of the Differences of True and Apparent Colours, be interpreted
in too Unlimited a Sense, and therefore it may perhaps somewhat Assist you,
both to Reflect upon the two fore-going Objections, and to judge of some
other Passages which you'l meet with in this Tract, if I take this Occasion
to observe to you, that if Water be Agitated into Froth, it exhibits you
know a White colour, which soon after it Loses upon the Resolution of the
Bubbles into Air and Water, now in this case either the Whiteness of the
Froth is a True Colour or not, if it be, then True Colours, supposing the
Water pure and free from Mixtures of any thing Tenacious, may be as
Short-liv'd as those of the Rain-bow; also the Matter, wherein the
Whiteness did Reside, may in a few moments perfectly Lose all foot-steps or
remains of it.
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