window-panes, or on the grass, is
the moisture of the warm air cooled down and frozen, and is produced
when the cold at the surface is below the freezing-point. What we in
common parlance call the action of frost, and which in this climate is
well known to be very powerful, is not particularly injurious to
organized bodies.

Mists are the vapor near the ground rendered visible by the
temperature of the air falling below that of the vapor. When we see
our breath in a cold morning, we see a mist. Where the surface is
comparatively warm and damp, and the air is cooler, we have mists,
which, if dense, are called fogs. These are found plentifully on the
banks of Newfoundland; and with icebergs on the one hand and the Gulf
Stream on the other, we must always expect to have them.

The distribution of rain, which is one of the offices of the clouds,
is another of the more important features of Meteorology. The amount
of water taken up by evaporation into the atmosphere is almost
incredible. It is calculated by Lieutenant Maury that there is
annually taken up in the torrid zone a belt of water three thousand
miles in breadth and sixteen feet deep. Rain occurs regularly and
irregularly in different parts of the earth. In some places it may be
calculated upon to a day; in others it is quite unknown. Latitude and
longitude may indicate the points of distribution, but the causes are
dependent on temperature, winds, locality, and, what may seem a
strange assertion, upon the conduct of man himself. The greatest
quantity falls near the equator, diminishing towards the poles.
Much more falls on islands and coasts than in the interior of
continents,--more in the region of the variables and less in that of
the trades. There are, however, tropical countries of great extent
where rain is scarcely ever seen.

The influence of man upon rain is seen in the progress of
civilization, the destruction of forests, and the drying-up of meres,
swamps, and water-courses.

Forests undoubtedly affect the distribution of rain, and the supplies
of streams and springs. Their cooling influence precipitates the vapor
passing over them, and the ground beneath them not getting heated does
not readily evaporate moisture. Lands, on the contrary, which are
cleared of forests become sooner heated, give off larger quantities of
rarefied air, and the passing clouds are borne away to localities of
greater atmospheric density.

The Canary Islands, when first d