And I further found it somewhat more evidently by
some attempts I made towards the making transparent Marble, for by heating
the Stone a little, and baking it in Oyl, Turpentine, Oyl of Turpentine,
&c., I found that I was able to see much deeper into the body of Marble
then before; and one trial, which was not with an unctuous substance,
succeeded better than the rest, of which, when I have a better opportunity,
I shall make further trial.
This also gives us a probable reason of the so much admired _Phaenomena_,
of 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 _Phaenomena_, 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.
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