ring violently
into the fix'd Body of the Nitre, sets loose the Spirit of the Nitre,
and excites a great Fermentation, whereby the Heat is farther augmented,
and the fix'd Body of the Nitre is also rarified into Fume, and the
Explosion is thereby made more vehement and quick. For if Salt of Tartar
be mix'd with Gun-powder, and that Mixture be warm'd till it takes fire,
the Explosion will be more violent and quick than that of Gun-powder
alone; which cannot proceed from any other cause than the action of the
Vapour of the Gun-powder upon the Salt of Tartar, whereby that Salt is
rarified. The Explosion of Gun-powder arises therefore from the violent
action whereby all the Mixture being quickly and vehemently heated, is
rarified and converted into Fume and Vapour: which Vapour, by the
violence of that action, becoming so hot as to shine, appears in the
form of Flame.

_Qu._ 11. Do not great Bodies conserve their heat the longest, their
parts heating one another, and may not great dense and fix'd Bodies,
when heated beyond a certain degree, emit Light so copiously, as by the
Emission and Re-action of its Light, and the Reflexions and Refractions
of its Rays within its Pores to grow still hotter, till it comes to a
certain period of heat, such as is that of the Sun? And are not the Sun
and fix'd Stars great Earths vehemently hot, whose heat is conserved by
the greatness of the Bodies, and the mutual Action and Reaction between
them, and the Light which they emit, and whose parts are kept from
fuming away, not only by their fixity, but also by the vast weight and
density of the Atmospheres incumbent upon them; and very strongly
compressing them, and condensing the Vapours and Exhalations which arise
from them? For if Water be made warm in any pellucid Vessel emptied of
Air, that Water in the _Vacuum_ will bubble and boil as vehemently as it
would in the open Air in a Vessel set upon the Fire till it conceives a
much greater heat. For the weight of the incumbent Atmosphere keeps down
the Vapours, and hinders the Water from boiling, until it grow much
hotter than is requisite to make it boil _in vacuo_. Also a mixture of
Tin and Lead being put upon a red hot Iron _in vacuo_ emits a Fume and
Flame, but the same Mixture in the open Air, by reason of the incumbent
Atmosphere, does not so much as emit any Fume which can be perceived by
Sight. In like manner the great weight of the Atmosphere which lies upon
the Globe of the Sun may