88 TERRESTRLAL ADAP'l‘A'l‘l0NS.

nance of the vapoury state, some 0f the steam
will be condensed and will become Water. It is
in this manner that the curl of steam from the
spout of a boiling tea-kettle becomes visible,
being cooled down as it rushes to the air. The
steam condenses into a fine Watery powder,
which is carried about by the little aerial cur-
rents. Clouds are of the same nature with such
curls, the condensation being generally produced
When air, charged with aqueous vapour, is mixed
with a colder current, or has its temperature
diminished in any other manner.

Clouds, while they retain that shape, are of
the most essential use to vegetable and animal
life. They moderate the fervour of the sun, in
a manner agreeable, to a greater or less degree,
in all climates, and grateful no less to vegetables
than to animals. Duhamel says that plants
grow more during a week of cloudy weather
than a month of dry and hot. It has been ob-
served that vegetables are far more refreshed by
being watered in cloudy than in clear weather.
In the latter case, probably the supply of fluid
is too rapidly carried off by evaporation. Clouds
also moderate the alternations of temperature,
by checking the radiation from the earth. The
coldest nights are those which occur under a
cloudless winter sky.

The uses of clouds, therefore, in this stage of
their history, are by no means inconsiderable,