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 hinder Bodies there from rising up and going
away from the Sun in the form of Vapours and Fumes, unless by means of a
far greater heat than that which on the Surface of our Earth would very
easily turn them into Vapours and Fumes. And the same great weight may
condense those Vapours and Exhalations as soon as they shall at any time
begin to ascend from the Sun, and make them presently fall back again
into him, and by that action increase his Heat much after the manner
that in our Earth the Air increases the Heat of a culinary Fire. And the
same weight may hinder the Globe of the Sun from being diminish'd,
unless by the Emission of Light, and a very small quantity of Vapours
and Exhalations.
_Qu._ 12. Do not the Rays of Light in falling upon the bottom of the Eye
excite Vibrations in the _Tunica Retina_? Which Vibrations, being
propagated along the solid Fibres of the optick Nerves into the Brain,
cause the Sense of seeing. For because dense Bodies conserve their Heat
a long time, and the densest Bodies conserve their Heat the longest, the
Vibrations of their parts are of a lasting nature, and therefore may be
propagated along solid Fibres of uniform dense Matter to a great
distance, for conveying into the Brain the impressions made upon all the
196