like may be said of the shining _Bellies of Gloworms_; since 'tis evident
they can at pleasure either increase or extinguish that Radiation.

It would be somewhat too long a work for this place _Zetetically_ to
examine, and positively to prove, what particular kind of motion it is that
must be the efficient of Light; for though it be a motion, yet 'tis not
every motion that produces it, since we find there are many bodies very
violently mov'd, which yet afford not such an effect; and there are other
bodies, which to our other senses, seem not mov'd so much, which yet shine.
Thus Water and quick-silver, and most other liquors heated, shine not; and
several hard bodies, as Iron, Silver, Brass, Copper, Wood, &c. though very
often struck with a hammer, shine not presently, though they will all of
them grow exceeding hot; whereas rotten Wood, rotten Fish, Sea water,
Gloworms, &c. have nothing of tangible heat in them, and yet (where there
is no stronger light to affect the Sensory) they shine some of them so
Vividly, that one may make a shift to read by them.

It would be too long, I say, here to insert the discursive progress by
which I inquir'd after the proprieties of the motion of Light, and
therefore I shall only add the result.

And, First, I found it ought to be exceeding _quick_, such as those motions
of _fermentation_ and _putrefaction_, whereby, certainly, the parts are
exceeding nimbly and violently mov'd; and that, because we find those
motions are able more minutely to shatter and divide the body, then the
most violent heats _menstruums_ we yet know. And that fire is nothing else
but such a _dissolution_ of the Burning body, made by the most _universal
menstruum_ of all _sulphureous bodies_, namely, the Air, we shall in an
other place of this Tractate endeavour to make probable. And that, in all
extreamly hot shining bodies, there is a very quick motion that causes