To which may be added this other known Experiment, That if you gently let
fall a drop of _water_ upon small _sand_ or _dust_, you shall find, as it
were, an artificial _round stone_ quickly generated. I cannot upon this
occasion omit the mentioning of the strange kind of _Grain_, which I have
observed in a _stone_ brought from _Kettering_ in _Northamptonshire_, and
therefore called by Masons _Kettering-Stone_, of which see the Description.
Which brings into my mind what I long since observed in the fiery Sparks
that are struck out of a Steel. For having a great desire to see what was
left behind, after the Spark was gone out, I purposely struck fire over a
very white piece of Paper, and observing diligently where some conspicuous
sparks went out, I found a very little black spot no bigger then the point
of a Pin, which through a _Microscope_ appeared to be a perfectly round
Ball, looking much like a polisht ball of Steel, insomuch that I was able
to see the Image of the window reflected from it. I cannot here stay
(having done it more fully in another place) to examine the particular
Reasons of it, but shall only hint, that I imagine it to be some small
parcel of the Steel, which by the violence of the motion of the stroke
(most of which seems to be imprest upon those small parcels) is made so
glowing hot, that it is melted into a _Vitrum_, which by the ambient Air is
thrust into the form of a Ball.
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