, that, for ought I have observ'd, are yet known; and a
single Leaf or Plate will be so far from being Opacous, that 'twill scarce
be so much as Visible. And multitudes of Bodies there are, whose Fragments
seem Opacous to the naked Eye, which yet, when I have included them in good
_Microscopes_, appear'd Transparent; but, _Pyrophilus_, on the other side I
am not yet sure that there are no Bodies, whose Minute Particles even in
such a _Microscope_ as that of mine, which I was lately mentioning, will
not appear Diaphanous. For having consider'd _Mercury_ Precipitated _per
se_, the little Granules that made up the powder, look'd like little
fragments of Coral beheld by the naked Eye at a Distance (for very Near at
hand Coral will sometimes, especially if it be Good, shew some
Transparency.) Filings likewise of Steel and Copper, though in an excellent
_Microscope_, and a fair Day, they show'd like pretty Big Fragments of
those Metalls, and had considerable Brightness on some of their Surfaces,
yet I was not satisfi'd, that I perceiv'd any Reflection from the Inner
parts of any of the Filings. Nay, having look'd in my best _Microscope_
upon the Red _Calx_ of Lead, (commonly call'd _Minium_) neither I, nor any
I shew'd it to, could discern it to be other than Opacous, though the Day
were Clear, and the Object strongly Enlightned. And the deeply Red Colour
of _Vitriol_ appear'd in the same _Microscope_ (notwithstanding the great
Comminution effected by the Fire) but like Grossy beaten Brick. So that,
_Pyrophilus_, I shall willingly resign you the care of making some further
Enquiries into the Subject we have now been considering; for I confess, as
I told you before, that I think that the Matter may need a further
Scrutiny, nor would I be forward to Determine how far or in what cases the
Transparency or Semi-diaphaniety of the Superficial Corpuscles of Bigger
Bodies, may have an Interest in the Production of their Colours, especially
because that even in divers White bodies, as Beaten Glass, Snow and Froth,
where it seems manifest that the Superficial parts are singly Diaphanous,
(being either Water, or Air, or Glass) we see not that such Variety of
Colours are produc'd as usually are by the Refraction of Light, even in
those Bodies, when by their Bigness, Shape, &c. they are conveniently
qualify'd to exhibit such Various and Lively Colours as those of the
Rain-bow, and of Prismatical Glasses.

28. By what has been hitherto disco