th cooler currents of air; and sometimes, again, by being
driven in winds toward a higher, and, consequently, cooler latitude. If,
on the other hand, air moves from cold mountains toward warm and sunny
plains, or from higher latitudes to lower, or if, among the various
currents into which it falls, it becomes mixed with air warmer than
itself, its capacity for containing vapor in solution is increased, and,
consequently, instead of releasing its hold upon the waters which it has
already in possession, it becomes thirsty for more. It moves over a
country, under these circumstances, as a warm and drying wind. Under a
reverse of circumstances it would have formed drifting mists, or,
perhaps, even copious showers of rain.

It will be evident, from these considerations, that the frequency of the
showers, and the quantity of the rain which will fall, in the various
regions respectively which the surface of the earth presents, must
depend on the combined influence of many causes, such as the warmth of
the climate, the proximity and the direction of mountains and of seas,
the character of the prevailing winds, and the reflecting qualities of
the soil. These and other similar causes, it is found, do, in fact,
produce a vast difference in the quantity of rain which falls in
different regions. In the northern part of South America, where the land
is bordered on every hand by vast tropical seas, which load the hot and
thirsty air with vapor, and where the mighty Cordillera of the Andes
rears its icy summits to chill and precipitate the vapors again, a
quantity of rain amounting to more than ten feet in perpendicular height
falls in a year. At St. Petersburg, on the other hand, the quantity thus
falling in a year is but little more than one foot. The immense deluge
which pours down from the clouds in South America would, if the water
were to remain where it fell, wholly submerge and inundate the country.
As it is, in flowing off through the valleys to the sea, the united
torrents form the greatest river on the globe--the Amazon; and the
vegetation, stimulated by the heat, and nourished by the abundant and
incessant supplies of moisture, becomes so rank, and loads the earth
with such an entangled and matted mass of trunks, and stems, and twining
wreaths and vines, that man is almost excluded from the scene. The
boundless forests become a vast and almost impenetrable jungle,
abandoned to wild beasts, noxious reptiles, and huge and fero