The Second Instance was not less remarkable then the First; for I found,
when a Spark went out, nothing but a very small thin long sliver of Iron or
Steel, unmelted at either end. So that it seems, that some of these Sparks
are the slivers or chips of the Iron _vitrified_, Others are only the
slivers melted into Balls without vitrification, And the third kind are
only small slivers of the Iron, made red-hot with the violence of the
stroke given on the Steel by the Flint.
He that shall diligently examine the _Phaenomena_ of this Experiment, will,
I doubt not, find cause to believe, that the reason I have heretofore given
of it, is the true and genuine cause of it, namely, That _the Spark,
appearing so bright in the falling, is nothing else but a small piece of
the Steel or Flint, but most commonly of the Steel, which by the violence
of the stroke is at the same time sever'd and heat red-hot, and that
sometimes to such a degree, as to make it melt together into a small
Globule of Steel; and sometimes also is that heat so very intense, as
further to melt it and vitrifie it; but many times the heat is so gentle,
as to be able to make the sliver only red hot, which notwithstanding
falling upon the tinder_ (that is only a very curious small Coal made of
the small threads of Linnen burnt to coals and char'd) _it easily sets it
on fire_.
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