An EXPLANATION of the THIRD PLATE
FIG. I.
The Sparks of Fire struck from a Flint and Steel
IN the common Way of striking Fire with a Flint and Steel, fiery Sparks fly out at
every Blow ;
which Sparks are nothing more than small Pieces of the Flint or Steel,
(but usually of the Steel) broken off by the Violence of the Stroke, and either melted
instantaneously into Steel Globules, or made at least red-hot, and thereby capable of kind-
ling Tinder or Touch-wood. The Heat is likewise so intense sometimes as even to vitrify
the broken Particles.
As a Proof of this, Dr. HOOKE struck Fire over a Sheet of very white Paper, and ob-
serving diligently where the Sparks seemed to vanish, he discovered there certain very
small, black, but glittering and moveable Specks, which, when examined with his Mi-
croscope, appeared to be little round Globules ; some whereof did, from their Surface,
yield a very bright and strong Reflection on that Side next the Light, and resembled Iron-
Balls. One of which, whose Surface was pretty regular, is shewn by the Letter A.
He perceived in this the reflected Image of the Window, and also of a Stick, which he
moved up and down between the Light and it.
He found others almost regularly round, as to the Bulk of the Ball, but with rough
unpolished Surfaces ; which rendered the Reflection from them much more confused and
saint. Such are represented by the Letters B, C, D, E.
Some were cracked or cleft, as C ; others broken and quite hollow, as D ; which seemed
like half the hollow Shell of a Granado, broken irregularly in Pieces. There were other
different Shapes ; but that in particular, marked with the Letter E, was a larger Spark of
Fire than ordinary. It went out on one Side the Flint employed in striking it, and ad-
hered thereto by the Root F. On the Top of its Stem was fastned half an hollow Ball,
with the Mouth of it opening upwards ; so that it appeared somewhat like a Funnel, or a
Rummer-Glass without a Foot.
The melting of the Particles of Steel, instantaneously, upon the Collision, is very
wonderful, and comes up nearly to the Effects of Lightning : Indeed there seems to be in
Iron or Steel a sulphureous combustible Matter very easily put in Action ; for either ham-
mering, filing, or rubbing it with Violence, will presently make it so hot as to be able to
burn one's Finger : And if the Filings of Iron are only let drop through the Flame of a
Candle, (placing a Sheet of white Paper underneath, to catch them for Examination)
many of them will be found melted even by that sudden Transit, and appear remarkably
shining to the naked Eye ; and if we view them farther by the Microscope, we shall
soon be satisfied they are exactly such round Globules as are formed by striking Fire with
a Flint and Steel.
As obtaining such minute Globules as these, of Lead or Tin, and that even in Quan-
tity,
easily and quickly, may be desirable by some, we shall here subjoin the Way of
forming them, which Dr. HOOKE says a learned Physician taught him.
Reduce the Metal you would shape thus, into exceedingly fine Filings : for the smaller
your Filings are, the smaller will be your Globules. Strew some fine and well-dried
Powder of Quick-Lime at the Bottom of a Crucible, on which scatter some of your Fil-
ings very thinly ; then strew on more Powder, on that again more Filings, and so alter-
nately, Stratum super Stratum, till you have filled your Crucible, in such a manner, that,
as near as may be, no two Filings may touch each other. Place the Crucible in a gra-
dual Fire, and increase the Heat by Degrees, till it be sufficient to make all the Filings
mix'd with the Quick-Lime melt, and no more. For if the Fire be too hot, many of
the Filings will join and run together : But if the Heat be duly proportioned, upon
washing the Lime-Dust in Water, all those small Filings of the Metal will subside to
the Bottom, in a most curious Powder, consisting of Balls or Globules exactly round ;
which, if very fine, is excellent for Hour-Glasses.
One may, at any time, procure immediately minute Globules of Lead, by only
kindling a red Wafer,
such as Letters are sealed with, at a Candle ; for as it burns (and
it will not go out till it be wholly consumed) the red Lead employed in the Colour-
ing, melts, and falls down, in regular minute Globules ; which, if a Sheet of clean
