peculiarities. It extends from the Isthmus of Darien to the Arctic
regions, and from the 65th to the 160th meridian of west longitude from
Greenwich, and has upon its surface a type of every climate in the world.
For the purpose of simplifying and illustrating the matter in hand, let us
divide it into five sections. Let the first section embrace Central
America and Southern Mexico, south of 28 deg.; the second, Northern Mexico and
Southern New Mexico, California, etc., between the parallels of 28 deg. and
32 deg.; the third, Northern California, Utah, Southern Oregon, and Western
New Mexico, north of the parallel of 32 deg.; the fourth, the entire
continent north of 42 deg.; and the fifth, the eastern United States, east of
the meridian of 100 deg.. These divisions are not intended to be entirely
accurate in their separation, but substantially so for the purpose of
illustrating the differences which exist in each.

The accompanying diagram shows approximately, by dotted lines, the
divisions.

[Illustration: Fig. 2.]

Now let us see in what a diverse manner, and to what a different extent,
they are severally supplied with moisture.

Central America and Southern Mexico lie within the tropics--their rains
are tropical rains. The season is divided into wet and dry, as are the
seasons of all tropical countries which are not rainless. During the rainy
season it rains a portion of nearly every day, and during the dry season
the sky is clear, the air is pure, and rain seldom falls.

All around the earth within the tropics, over the land and over the sea,
there is a belt of almost daily rains, varying in width, north and south,
in different sections, but averaging about five hundred miles. This belt
of daily rains is formed at and by the meeting of N. E. and S. E. trades,
and travels north and south with them, as they do with the sun,
_encircling the globe_. By this narrow belt a portion of the earth's
surface, an average of some 35 deg. of latitude, is supplied with moisture.
Wherever it is situated at any given period, the tropical rainy season
exists; and when it is absent in its northern or southern transit, the dry
season prevails. Southern Mexico is within the range of this moving belt,
and in its course to the northward with the sun, in our summer from May to
October, it arrives over, and covers that country with a rainy season.
When the sun returns to the south, taking with it the trades and this belt
of tropica