estrial substances can
be volatilised; and downrushes of the same photospheric matter take
place after it has parted with some of its stores of thermal energy.
Sun-spots of considerable magnitude have been observed to grow rapidly
and then disappear in a very short period of time; occasionally a spot
is seen to divide into two or more portions, the fragments flying
asunder with a velocity of not less than 1,000 miles an hour. It is by
these upheavals and convulsions of the solar atmosphere that the light
and heat are maintained which illumine and vivify the worlds that
gravitate round the Sun.

During total eclipses of the Sun, several phenomena become visible which
have enabled astronomers to gain some further knowledge of the nature of
the solar appendages. The most important of these is the CHROMOSPHERE,
which consists of layers of incandescent gases that envelop the
photosphere and completely surround the Sun. Its average depth is from
5,000 to 6,000 miles, and when seen during an eclipse is of a beautiful
rose colour, resembling a sheet of flame. As seen in profile at the edge
of the Sun's disc, it presents an irregular serrated appearance, an
effect created by the protuberance of luminous ridges and
processes--masses of flame which arise from over its entire surface. The
chromosphere consists chiefly of glowing hydrogen, and an element called
_helium_, which has been recently discovered in a terrestrial substance
called cleveite; there are also present the vapours of iron, calcium,
cerium, titanium, barium, and magnesium. From the surface of this ocean
of fire, jets and pointed spires of flaming hydrogen shoot up with
amazing velocity, and attain an altitude of ten, twenty, fifty, and even
one hundred thousand miles in a very short period of time. They are,
however, of an evanescent nature, change rapidly in form and appearance,
and often in the course of an hour or two die down so as not to be
recognisable. These _prominences_, as they are called, have been divided
into two classes. Some are in masses that float like clouds in the
atmosphere, which they resemble in form and appearance; they are
usually attached to the chromosphere by a single stem, or by slender
columns; occasionally they are entirely free. These are called
_quiescent_ prominences; they consist of clouds of hydrogen, and are of
more lasting duration than the other variety, called _eruptive_ or
metallic prominences. The latter are usually found in