vertical sun appears to stop when it is midsummer
with us. As it moves southward, our
summer wanes; it crosses the equator, and
appears to travel on until it has reached
twenty-three and a half degrees on the other
side of the line—the tropic of Capricorn;*
then six months have passed, it is midwinter
with us and midsummer with people in the
southern hemisphere. The sun turns back—
(and the word tropic means the place of
turning)—retraces its course over the equator,
and at the expiration of a twelvemonth is at
our tropic again, bringing us summer. Now,
the rainy season is produced between, the
tropics, by the powerful action of the sun,
wherever it is nearly vertical, in sucking up
vast quantities of vapour, which become
condensed in the upper colder regions of the
atmosphere, and dash to earth again as
rain. The rainy season, therefore, follows the
sun. When the sun is at or near the tropic
of Cancer, both before and after turning, all
places near that tropic have their rainy season:
when the sun makes a larger angle with their
zenith, it has taken the rainy season with it
to another place. It is here obvious, that a
country between the tropics, and far from
each, is passed over by the sun, in its apparent
course, at two periods in the same year, with
a decided interval between them. It must
have, therefore, and does have, two rainy and
two dry seasons. The parts of Africa and
Asia bordering the northern half of the Indian
Ocean are an exception to this rule; and,
though in the region of the trade-winds, they
are independent of the trade-winds also. A
great expanse of water is there placed
between two continents, one of which, Asia,
stretching to the north-east, is heated during
our own summer, and the other, Africa, lies
south-west of the water, and is heated when the
sun is at the other tropic, and when our regions
are cold. The cool current flows over the water
into the space left by expanded air in Asia,
when that continent is warmed, from April
to October, making the south-west monsoon.
After October, southern Africa begins her turn
of summer, and the monsoon changes with a
little conflict in the way of storm and cloud,
and the air flows during the other six months
to the other continent, creating the north-
east monsoon. The end of March and the
beginning of April, the end of September
and the beginning of October, are the stormy
periods of monsoon changing. Water currents
are determined by these constant winds, and
each monsoon brings a rainy season to the
coast on which it blows. The monsoon region
extends beyond the coasts of Borneo and
Celebes, and on the coasts of China, northward
to Japan.

*The inclination of the earth's axis, to which, we have
before alluded, is twenty-three and a half degrees. The
apparent movement of the sun over the tropics, our long
days of summer and long nights of winter, and the whole
theory of polar nights and days, can be explained practically
with the greatest ease. In the evening let there be only
one lamp or candle, which you call the sun. Spit an orange
on a knitting needle; put some pins on it for men; hold the
needle, your earth's axis, not upright, but let it slant a little;
hold your earth, the orange, so that its equator is on the
same level with your sun.  Keep the axis inclined and
fixed always in the same postition relative to the walls of
the room, while you imitate the earth's yearly course, by a
revolution of your orange (always in the same level) round
the lamp. Make mimic days and nights, in the mean time,
by rolling your earth round upon its axis. Remember that
the sun is to men as the lamp might be to your pins, and
the rude experiment will be a little volume of astronomy.

Monsoon is a name drawn from an Arabic
word, implying season. Prevalent winds on
a smaller scale are determined in many other
portions of the globe by local peculiarities of
land and sea. Thus the great desert, the
Sahara, heated intensely by our summer sun,
pours up a current of ascending air, and sucks
cool air out of the Mediterranean; on that
sea, therefore, in the summer, a north wind
prevails, and for the same reason it is easier
to sail up than down the Nile.

Let us apply now some of the principles
we have discussed. The trade-winds blowing
equably, do not deposit much of their vapour
while still flowing over the Atlantic. Out at
sea it seldom rains within the trade-winds;
but when they strike the east coast of
America rain falls; and the rain-fall on that
coast, within the limits of the trade-winds,
is notoriously excessive. The chain of the
West India Islands stands ready to take (in
the due season) a full dose; the rain-fall
at St. Domingo is one hundred and fifty
inches. But the winds having traversed the
breadth of the continent, deposit their last
clouds on the western flanks of the Andes,
and there are portions, accordingly, of the
western coast on which no season will expend
a drop of rain. Thus in Peru it rains once,
perhaps, in a man's lifetime; and an old man
may tell how once, when he was quite a boy,
it thundered. Of the cold Antarctic current
slipping by the Peruvian shores, and yielding
the thick vapour called the Garua, which
serves instead of rain, we have already talked.
Upon the table-land of Mexico, in parts of
Guatemala and California, for the same
reason, rain is very rare. But the grandest
rainless districts are those occupied by the
great desert of Africa, extending westward
over portions of Arabia and Persia, to a desert
province of the Beloochees; districts presently
continued in the heart of Asia over the great
desert of Gobi, the table-land of Tibet and
part of Mongolia. In all these, are five or six
millions of square miles of land that never
taste a shower. Elsewhere the whole bulk
of water that falls annually in the shape of
rain, is calculated at seven hundred and sixty
millions of millions of tuns.

In equalising temperature, in wafting clouds
over the land, and causing them to break
and fall in fertilising showers, in creating and
fostering the art of navigation, by which
man is civilised, the winds perform good
service. Their pure current washes out the
stagnant exhalations from our homes, our
fields, our persons; breaks the ripe seed from
the tree, and sows it at a distance from its