equently, a region of refrigeration. In an
atmosphere of metallic gases rising from a molten surface, and presently
reaching a limit at which condensation takes place, the molecular state,
especially toward its upper part, must be such that a moderate
diminution of density, and fall of temperature, will cause
precipitation. That is to say, the rarefied interior of a solar cyclone
will be filled with cloud: condensation, instead of taking place only
at the level of the photosphere, will here extend to a great depth below
it, and over a wide area. What will be the characters of a cloud thus
occupying the interior of a cyclone? It will have a rotatory motion; and
this it has been seen to have. Being funnel-shaped, as analogy warrants
us in assuming, its central parts will be much deeper than its
peripheral parts, and therefore more opaque. This, too, corresponds with
observation. Mr. Dawes has discovered that in the middle of the spot
there is a blacker spot: just where there would exist a funnel-shaped
prolongation of the cyclonic cloud down toward the Sun's body, the
darkness is greater than elsewhere. Moreover, there is furnished an
adequate reason for the depression which one of these dark spaces
exhibits. In a whirlwind, as in a whirlpool, the vortex will be below
the general level, and all around, the surface of the medium will
descend toward it. Hence a spot seen obliquely, as when carried toward
the Sun's limb, will have its umbra more and more hidden, while its
penumbra still remains visible. Nor are we without some interpretation
of the penumbra. If, as is implied by what has been said, the so-called
"willow-leaves," or "rice-grains," are the tops of the currents
ascending from the Sun's body, what changes of appearance are they
likely to undergo in the neighbourhood of a cyclone? For some distance
round a cyclone there will be a drawing in of the superficial gases
toward the vortex. All the luminous spaces of more transparent cloud
forming the adjacent photosphere, will be changed in shape by these
centripetal currents. They will be greatly elongated; and there will so
be produced that "thatch"-like aspect which the penumbra presents.

* * * * *

[The explanation of the solar spots above suggested, which was
originally propounded in opposition to that of M. Faye, was eventually
adopted by him in place of his own. In the _Comptes Rendus_ for 1867,
Vol. LXIV., p. 404, he refers to t