examples and other things, that we shall hereafter have occasion to take
notice off in this Tract, will sufficiently declare, till when, it may
suffice to put you in mind, that of two Flat-sides of the same piece of,
for example, red Marble, the one being diligently Polished, and the other
left to its former Roughness, the differing degrees or sorts of Asperity,
for the side that is smooth to the Touch wants not its Roughness, will so
diversifie the Light reflected from the several Plains to the Eye, that a
Painter would employ two differing Colours to represent them.

[3] _See the Discourse of the Nature of Whiteness and Blackness._

7. And I hope, _Pyrophilus_, you will not think it strange or impertinent,
that I employ in divers passages of these Papers, examples drawn from
Bodies and Shadows far more Gross, than those minute Protuberances and
shady Pores on which in most cases the Colour of a Body as 'tis an Inherent
Quality or Disposition of its Surface, seems to depend. For sometimes I
employ such Examples, rather to declare my Meaning, than prove my
Conjecture; things, whom their Smallness makes Insensible, being better
represented to the Imagination by such familiar Objects, as being like them
enough in other respects, are of a Visible bulk. And next, though the Beams
of Light are such subtil Bodies, that in respect of them, even Surfaces
that are sensibly Smooth, are not exactly so, but have their own degree of
Roughness, consisting of little Protuberances and Depressions; and though
consequently such Inequalities may suffice to give Bodies differing
Colours, as we see in Marble that appears White or Black, or Red or Blew,
even when the most carefully Polish'd, yet 'tis plain by the late Instance
of Red Marble, and many others, that even bigger Protuberances and greater
Shades may likewise so Diversifie the Roughness of a Bodies Superficies, as
manifestly to concurr to the varying of its Colour, whereby such Examples
appear to be proper enough to be employ'd in such a Subject as we have now