e Sun's border, and the appearances during a total
eclipse, alike show this. What now must be the constitution of this
atmosphere? At a temperature approaching a thousand times that of molten
iron, which is the calculated temperature of the solar surface, very
many, if not all, of the substances we know as solid, would become
gaseous; and though the Sun's enormous attractive force must be a
powerful check on this tendency to assume the form of vapour, yet it
cannot be questioned that if the body of the Sun consists of molten
substances, some of them must be constantly undergoing evaporation. That
the dense gases thus continually being generated will form the entire
mass of the solar atmosphere, is not probable. If anything is to be
inferred, either from the Nebular Hypothesis, or from the analogies
supplied by the planets, it must be concluded that the outermost part of
the solar atmosphere consists of what are called permanent gases--gases
that are not condensible into fluid even at low temperatures. If we
consider what must have been the state of things here, when the surface
of the Earth was molten, we shall see that round the still molten
surface of the Sun, there probably exists a stratum of dense aeriform
matter, made up of sublimed metals and metallic compounds, and above
this a stratum of comparatively rare medium analogous to air. What now
will happen with these two strata? Did they both consist of permanent
gases, they could not remain separate: according to a well-known law,
they would eventually form a homogeneous mixture. But this will by no
means happen when the lower stratum consists of matters that are gaseous
only at excessively high temperatures. Given off from a molten surface,
ascending, expanding, and cooling, these will presently reach a limit of
elevation above which they cannot exist as vapour, but must condense and
precipitate. Meanwhile the upper stratum, habitually charged with its
quantum of these denser matters, as our air with its quantum of water,
and ready to deposit them on any depression of temperature, must be
habitually unable to take up any more of the lower stratum; and
therefore this lower stratum will remain quite distinct from it.[20]

* * * * *

Considered in their _ensemble_, the several groups of evidences assigned
amount almost to proof. We have seen that, when critically examined,
the speculations of late years current respecting the nature of