as often as those parts are sufficiently agitated; whether that
agitation be made by Heat, or by Friction, or Percussion, or
Putrefaction, or by any vital Motion, or any other Cause? As for
instance; Sea-Water in a raging Storm; Quick-silver agitated in _vacuo_;
the Back of a Cat, or Neck of a Horse, obliquely struck or rubbed in a
dark place; Wood, Flesh and Fish while they putrefy; Vapours arising
from putrefy'd Waters, usually call'd _Ignes Fatui_; Stacks of moist Hay
or Corn growing hot by fermentation; Glow-worms and the Eyes of some
Animals by vital Motions; the vulgar _Phosphorus_ agitated by the
attrition of any Body, or by the acid Particles of the Air; Amber and
some Diamonds by striking, pressing or rubbing them; Scrapings of Steel
struck off with a Flint; Iron hammer'd very nimbly till it become so hot
as to kindle Sulphur thrown upon it; the Axletrees of Chariots taking
fire by the rapid rotation of the Wheels; and some Liquors mix'd with
one another whose Particles come together with an Impetus, as Oil of
Vitriol distilled from its weight of Nitre, and then mix'd with twice
its weight of Oil of Anniseeds. So also a Globe of Glass about 8 or 10
Inches in diameter, being put into a Frame where it may be swiftly
turn'd round its Axis, will in turning shine where it rubs against the
palm of ones Hand apply'd to it: And if at the same time a piece of
white Paper or white Cloth, or the end of ones Finger be held at the
distance of about a quarter of an Inch or half an Inch from that part of
the Glass where it is most in motion, the electrick Vapour which is
excited by the friction of the Glass against the Hand, will by dashing
against the white Paper, Cloth or Finger, be put into such an agitation
as to emit Light, and make the white Paper, Cloth or Finger, appear
lucid like a Glowworm; and in rushing out of the Glass will sometimes
push against the finger so as to be felt. And the same things have been
found by rubbing a long and large Cylinder or Glass or Amber with a
Paper held in ones hand, and continuing the friction till the Glass grew
warm.
_Qu._ 9. Is not Fire a Body heated so hot as to emit Light copiously?
For what else is a red hot Iron than Fire? And what else is a burning
Coal than red hot Wood?
_Qu._ 10. Is not Flame a Vapour, Fume or Exhalation heated red hot, that
is, so hot as to shine? For Bodies do not flame without emitting a
copious Fume, and this Fume burns in the Flame. The _Ignis Fatuus_ is a
Vapour shining without heat, and is there not the same difference
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