Clouds are continually varying in their form and appearance, but may be
classed under the four principal heads of the cirrus, the cumulus, the
stratus, and the nimbus.
The cirrus is a light, fleecy cloud resembling a lock of hair or a
feather.
The cumulus or summer cloud is generally massive and of a round form;
sometimes of small size, and sometimes covering nearly the whole sky,
and occasionally appearing in the horizon like mountains capped with
snow.
The stratus is a horizontal, misty cloud sometimes observed on fine
summer evenings comparatively near the ground, and often crossing the
middle regions of mountainous or hilly districts.
The nimbus or rain cloud has a uniform gray tint; it is fringed at the
edges when these are displayed, but usually covers the whole sky. The
region of clouds is a zone extending in the atmosphere from about one to
four miles above the Earth. The most elevated clouds, which are light
and fleecy, are those comprehended under the name of cirrus, and the
lowest are those which are called stratus.
The cirro-cumulus, cirro-stratus, and cumulo-stratus are only
modifications and combinations of the above-named principal classes.