the _Oculus Mundi_, an _Oval_ stone, which commonly looks like white
Alabaster, but being laid a certain time in Water, it grows _pellucid_, and
transparent, and being suffer'd to lie again dry, it by degrees loses that
transparency, and becomes white as before. For the Stone being of a hollow
spongie nature, has in the first and last of these appearances, all those
pores fill'd with the obtunding and reflecting air; whereas in the second,
all those pores are fill'd with a _medium_ that has much the same
refraction with the particles of the Stone, and therefore those two being
_contiguous_, make, as 'twere, one _continued medium_, of which more is
said in the 15. _Observation_.

There are a multitude of other _Phænomena_, that are produc'd from this
same Principle, which as it has not been taken notice of by any yet that I
know, so I think, upon more diligent observation, will it not be found the
least considerable. But I have here onely time to hint _Hypotheses_, and
not to prosecute them so fully as I could wish; many of them having a vast
extent in the production of a multitude of _Phænomena_, which have been by
others, either not attempted to be explain'd, or else attributed to some
other cause than what I have assign'd, and perhaps than the right; and
therefore I shall leave this to the prosecution of such as have more
leisure: onely before I leave it, I must not pretermit to hint, that by
this Principle, multitudes of the _Phænomena_ of the air, as about _Mists_,
_Clouds_, _Meteors_, _Haloes_, &c. are most plainly and (perhaps) truly
explicable; multitudes also of the _Phænomena_ in colour'd bodies, as
liquors, &c. are deducible from it.

And from this I shall proceed to a second considerable _Phænomenon_ which
these Diamants exhibit, and that is the regularity of their _Figure_, which
is a propriety not less general than the former, It comprising within its
extent, all kinds of _Metals_, all kinds of _Minerals_, most _Precious