als of fish. Sometimes the whole sky is
so mottled with them, as to obtain for it the name of the _mackerel-back
sky_, from its great resemblance to the back of that fish. Sometimes
they assume an arrangement like discs piled obliquely on each other. But
in this, as in other instances, the structure must be attended to rather
than the form, for this varies much, presenting, at times, the appearance
of parallel bars or interwoven streaks, like the grain of polished wood.
It is thick in the middle and thinned off towards the edge.

[Picture: The Cirro-Stratus, or wane-cloud]

These clouds precede wind and rain. The near or distant approach of a
storm may often be judged of from their greater or less abundance and
duration. They are almost always to be seen in the intervals of storms.
Sometimes the cirro-stratus, and the cirro-cumulus, appear together in
the sky, and even alternate with each other in the same cloud, presenting
many curious changes; and a judgment may be formed of the weather likely
to ensue, by observing which prevails at last.

The cirro-stratus most frequently forms the solar and lunar halo. Hence
the reason of the prognostics of bad weather commonly drawn from the
appearance of halos.

THE CUMULO-STRATUS, OR TWAIN-CLOUD.

[Picture: The Cumulo-Stratus, or twain-cloud]

This is a blending of two kinds of cloud (hence the name of
_twain-cloud_,) and it often presents a grand and beautiful appearance,
being a collection of large fleecy clouds overhanging a flat stratum or
base. When a cumulus increases rapidly a cumulo-stratus frequently forms
around its summit, resting thereon as on a mountain, while the former
cloud continues to be seen, in some degree, through it. This state of
things does not continue long. The cumulo-stratus speedily becomes
denser and spreads, while the upper part of the cumulus extends likewise,
and passes into it, the base continuing as it was. A large, lofty, dense
cloud is thus formed which may be compared to a mushroom with a very
thick, short stem. The cumulo-stratus, when well formed and seen singly,
and in profile, is quite as beautiful an object as the cumulus. Mr.
Howard has occasionally seen specimens constructed almost as finely as a
Corinthian capital; the summit throwing a well-defined shadow upon the
parts beneath. It is sometimes built up to a great height. The finest
examples occur between the first appearance of t