both that the Particles of white Metals have much
more Superficies, and so are smaller, than those of Gold and Copper, and
also that they are so opake as not to suffer the Particles of Gold or
Copper to shine through them. Now it is scarce to be doubted but that
the Colours of Gold and Copper are of the second and third order, and
therefore the Particles of white Metals cannot be much bigger than is
requisite to make them reflect the white of the first order. The
Volatility of Mercury argues that they are not much bigger, nor may they
be much less, lest they lose their Opacity, and become either
transparent as they do when attenuated by Vitrification, or by Solution
in Menstruums, or black as they do when ground smaller, by rubbing
Silver, or Tin, or Lead, upon other Substances to draw black Lines. The
first and only Colour which white Metals take by grinding their
Particles smaller, is black, and therefore their white ought to be that
which borders upon the black Spot in the Center of the Rings of Colours,
that is, the white of the first order. But, if you would hence gather
the Bigness of metallick Particles, you must allow for their Density.
For were Mercury transparent, its Density is such that the Sine of
Incidence upon it (by my Computation) would be to the Sine of its
Refraction, as 71 to 20, or 7 to 2. And therefore the Thickness of its
Particles, that they may exhibit the same Colours with those of Bubbles
of Water, ought to be less than the Thickness of the Skin of those
Bubbles in the Proportion of 2 to 7. Whence it's possible, that the
Particles of Mercury may be as little as the Particles of some
transparent and volatile Fluids, and yet reflect the white of the first
order.

Lastly, for the production of _black_, the Corpuscles must be less than
any of those which exhibit Colours. For at all greater sizes there is
too much Light reflected to constitute this Colour. But if they be
supposed a little less than is requisite to reflect the white and very
faint blue of the first order, they will, according to the 4th, 8th,
17th and 18th Observations, reflect so very little Light as to appear
intensely black, and yet may perhaps variously refract it to and fro
within themselves so long, until it happen to be stifled and lost, by
which means they will appear black in all positions of the Eye without
any transparency. And from hence may be understood why Fire, and the
more subtile dissolver Putrefaction, by dividing