thereby I
found them to grow a little lighter, and the small Stems to be very easily
broken and snapt any where, without at all making the drop fly; whereas
before they were so exceeding hard, that they could not be broken without
much difficulty; and upon their breaking the whole drop would fly in pieces
with very great violence. The Reason of which last seems to be, that the
leisurely heating and cooling of the parts does not only wast some part of
the Glass it self, but ranges all the parts into a better order, and gives
each Particle an opportunity of _relaxing_ its self, and consequently
neither will the parts hold so strongly together as before, nor be so
difficult to be broken: The parts now more easily yielding, nor will the
other parts fly in pieces, because the parts have no bended Springs. The
_relaxation_ also in the temper of hardned Steel, and hammered Metals, by
nealing them in the fire, seems to proceed from much the same cause. For
both by quenching suddenly such Metals as have _vitrifed_ parts
interspers'd, as Steel has, and by hammering of other kinds that do not so
much abound with them, as Silver Brass, &c. the parts are put into and
detained in a bended posture, which by the agitation of Heat are shaken,
and loosened, and suffered to unbend themselves.

* * * * *

Observ. VIII. _Of the fiery Sparks struck from a Flint or Steel._

It is a very common Experiment, by striking with a Flint against a Steel,
to make certain fiery and shining Sparks to fly out from between those two
compressing Bodies. About eight years since, upon casually reading the
Explication of this odd _Phaenomenon_, by the most Ingenious _Des Cartes_,
I had a great desire to be satisfied, what that Substance was that gave
such a shining and bright Light: And to that end I spread a sheet of white
Paper, and on it, observing the place where several of these Sparks seemed
to vanish, I found certain very small, black, but glittering Spots of a
movable Substance, each of which examining with my _Microscope_, I found to
be a small round _Globule_; some of which, as they looked prety small, so
did they from their Surface yield a very bright and strong reflection on
that side which was next the Light; and each look'd almost like a prety
bright Iron-Ball, whose Surface was prety regular, such as is represented
by the Figure A. In this I could perceive the Image of the Window prety
well, or of a Stick, whi