r_, which will manifestly
rise a sixth or eighth part higher in the Pot, whilst it is boyling, then
it will remain at, both before and after it be boyled. The reason of which
odd _Phaenomenon_ (to hint it here only by the way) is this, that there is
in the curious powder of Alabaster, and other calcining Stones, a certain
watery substance, which is so fixt and included with the solid Particles,
that till the heat be very considerable they will not fly away; but after
the heat is increased to such a degree, they break out every way in
vapours, and thereby so shake and loosen the small corpusles of the Powder
from each other, that they become perfectly of the nature of a fluid body,
and one may move a stick to and fro through it, and stir it as easily as
water, and the vapours burst and break out in bubbles just as in boyling
water, and the like; whereas, both before those watery parts are flying
away, and after they are quite gone; that is, before and after it have done
boyling, all those effects cease, and a stick is as difficultly moved to
and fro in it as in sand, or the like. Which Explication I could easily
prove, had I time; but this is not a fit place for it.

To proceed therefore, I say, that the dropping of this expanded Body into
cold Water, does make the parts of the Glass suffer a double contraction:
The first is, of those parts which are neer the Surface of the Drop. For
Cold, as I said before, contracting Bodies, that is, _by the abatement of
the agitating faculty the parts falling neerer together_; the parts next
adjoyning to the Water must needs lose much of their motion, and impart it
to the Ambient-water (which the Ebullition and commotion of it manifests)
and thereby become a solid and hard crust, whilst the innermost parts
remain yet fluid and expanded; whence, as they grow cold also by degrees,
their parts must necessarily be left at liberty to be condensed, but
because of the hardness of the outward crust, the contraction cannot be
admitted that way; but there being many very small, and before
inconspicuous, bubbles in the substance of the Glass, upon the subsiding of
the parts of the Glass, the agil substance contained in them has liberty of
expanding it self a little, and thereby those bubbles grow much bigger,
which is the second Contraction. And both these are confirmed from the
appearance of the Drop it self: for as for the outward parts, we see,
first, that it is irregular and shrunk, as it were