, and thereby their
tenacity spoiled, the springiness of the more outward parts quickly makes a
divulsion, and the broken pieces will, if the concave Surface of them be
further scratcht with a Diamond, fly again into smaller pieces.

From which preceding considerations it will follow Sixthly, That the sudden
flying asunder of the parts as soon as this Arch is any where disordered or
broken, proceeds from the springing of the parts; which, indeavouring to
_extricate_ themselves as soon as they get the liberty, they perform it
with such a quickness, that they throw one another away with very great
violence: for the Particles that compose the Crust have a _Conatus_ to lye
further from one another, and therefore as soon as the external parts are
loosened they dart themselves outward with great violence, just as so many
Springs would do, if they were detained and fastened to the body, as soon
as they should be suddenly loosened; and the internal parts drawing inward,
they contract so violently; that they rebound back again and fly into
multitude of small shivers or sands. Now though they appear not, either to
the naked Eye, or the _Microscope_, yet I am very apt to think there may be
abundance of small flaws or cracks, which, by reason the strong reflecting
Air is not got between the _contiguous_ parts, appear not. And that this
may be so, I argue from this, that I have very often been able to make a
crack or flaw, in some convenient pieces of Glass, to appear and disappear
at pleasure, according as by pressing together, or pulling asunder the
contiguous parts, I excluded or admitted the strong reflecting Air between
the parts: And it is very probable, that there may be some Body, that is
either very rarified Air, or something _analogous_ to it, which fills the
bubbles of these drops; which I argue, first, from the roundness of them,
and next, from the vivid reflection of Light which they exhibite: Now
though I doubt not, but that the Air in them is very much rarified, yet
that there is some in them, to such as well consider this Experiment of the
disappearing of a crack upon the _extruding_ of the Air, I suppose it will
seem more then probable.

The Seventh and last therefore that I shall prove, is, _That the gradual
heating and cooling of these so extended bodies does reduce the parts of
the Glass to a looser and softer temper_. And this I found by heating them,
and keeping them for a prety while very red hot in a fire; for