Diamonds; and as soon as the Continuance of their Motion had brought them
to an Inconvenient position in reference to the Light and the Eye, they
were only visible without Darting any lively Colours as before, which seems
to argue that these little Motes, or minute Fragments, of several sorts of
bodies reputed Opacous, and only crumbled as to their Exteriour and Looser
parts into Dust, did not barely Reflect the Beams that fell upon them, but
remit them to the Eye Refracted too. We may also observe, that several
Bodies, (as well some of a Vegetable, as others of an Animal nature) which
are wont to pass for Opacous, appear in great part Transparent, when they
are reduc'd into Thin parts, and held against a powerful Light. This I have
not only taken notice of in pieces of Ivory reduc'd but into Thick leaves,
as also in divers considerable Thick shells of Fishes, and in shaving of
Wood, but I have also found that a piece of Deal, far thicker than one
would easily imagine, being purposly interposed betwixt my Eye plac'd in a
Room, and the clear Daylight, was not only somewhat Transparent, but
(perhaps by reason of its Gummous nature) appear'd quite through of a
lovely Red. And in the Darkned Room above mention'd, Bodies held against
the hole at which the Light enter'd, appear'd far less Opacous then they
would elsewhere have done, insomuch that I could easily and plainly see
through the whole Thickness of my Hand, the Motions of a Body plac'd (at a
very near distance indeed, but yet) beyond it. And even in Minerals, the
Opacity is not always so great as many think, if the Body be made Thin, for
White Marble though of a pretty Thickness, being within a Due distance
plac'd betwixt the Eye and a Convenient Light, will Suffer the Motions of
ones Finger to be well discern'd through it, and so will pieces, Thick
enough, of many common Flints. But above all, that Instance is remarkable,
that is afforded us by _Muscovie_ glass, (which some call _Selenites_,
others _Lapis Specularis_) for though plates of this Mineral, though but of
a moderate Thickness, do often appear Opacous, yet if one of these be
Dextrously split into the thinnest Leaves 'tis made up of, it will yield