been shwn.

These are some of the most striking uses of What has the atmosphere. It is the food of animal life, and the instrument given to the insignificant fly to enable it to crawl from one place to another.

It wafts over the deep our monster ships, What else. and conveys to our delicate ears the halfinaudible whisper.

It is the great scavenger of the earth, bearing Continue. away into regions unknown its pestilential exhalations, and administers to the delight of the eye, the ear, and the organ of smell.

er uses.

It is so powerful that gigantic forest oaks Name othcannot stand against it, yet so elastic that the puny strength of the tiniest insect can displace it. So transparent is it that it hides nothing What else from our view, and yet is it sufficiently dense to screen the earth by day, and wrap it up warm in the cold night.

performed,

It has ten thousand offices to perform at the How is all same moment, yet never makes mistakes or fails in any.

What can more plainly bespeak the wisdom what this and goodness of that Being, who knew all teaches us. this, contrived all this, and endowed man with faculties to understand and powers to enjoy it?

character,

In the temperate zones the wind is so What their changeable that it has become proverbial for fickleness; but it is far otherwise in the equatorial seas.

How so.

What is it called.

Where al

so certain.

How these are called.

How in

our zone.

There it blows invariably from east to west, driving the merchant's sail with a gentle breeze from the Old World to the New.

This is called the trade wind; not because it aids the navigation of trading ships, but because it always treads in the same course.

In the Indian Ocean the wind is also certain; blowing for six months of the year from the north-east, and for the other six months from the south-west.

These winds are called monsoons, an. Arabic word, meaning a "set time” or “season.”

Even in the temperate zones, by the seacoast, there is a constant breeze from land to sea at sunset, and a sea-breeze blowing inland at sunrise.

How caused

Explain,

produces.

SECTION I.

THE CONSTANT WINDS.

§ 1.-TRADE-WINDS.

The trade-winds are caused by the difference of temperature between the polar regions and the torrid zone.

The cold air from the poles, being dense and heavy, presses upon the thin warm air of the equator, and drives it upward.

What this By this means are established two lower currents, flowing from the poles to the equator; and two upper currents, flowing from the equator to the poles.

What their

If there were no disturbing influence, the direction. direction of these currents would be due north and south; but they are turned aside by the daily rotation of the earth from west to east.

ed thereby.

This rotatory movement, being communicated How affectto the air, ought to give it a similar direction, whereas the polar currents are deflected one way and the equatorial another.

This is owing to the ball-like shape of the Why so. earth. As its girth at the equator is much larger than it is nearer the poles, the rotatory motion of any spot in the torrid zone is more rapid than that of any similar spot in the frigid. For example: the velocity of the earth from Exemplify. west to east, in the 60th degree of latitude, is 700 feet in a second, but at the equator it is double that speed.

Suppose now a volume of air turning from Continue. west to east, at the rate of 14,000 feet in a second, were transported to the 60th degree of latitude, it would be rushing eastward twice as fast as the earth, and the earth would seem to lag behind.

contrary.

If, again, a volume of air turning from west How if the to east, at the rate of 700 feet in a second, were transported to the equator, it would go eastward only half as fast as the earth, and would consequently fall in the rear.

they flow.

In the former case, the volume of air would How would go from west to east with the earth, only much more rapidly; in the latter it would keep falling back, and therefore go in an opposite direction.

their route.

The swift revolving air of the equator, when What then it journeys towards the poles, outstrips the motion of the earth, and hence becomes a northwest and south-west wind.

the other.

While the slow-revolving air of the polar What of circles, when it journeys towards the equator,

At the e

falls gradually in the rear, and therefore becomes a north-east and south-east wind.

At the equator the two polar currents clash, quator how and mingle together. The northern direction of the one neutralizes the southern direction of the other, while that from west to east is confirmed and perpetuated.

The tradewind what

Whre they

meet what

takes place

The trade-wind, therefore, is the air from the polar regions, with its original direction nort! and south neutralized; but its deflected motion corroborated by the mutual tendency of the air from both poles to the same direction.

At the point of collision is the region of calms and the hottest belt of the earth. When a balance is exactly equal it is very easily disturbed, and the slightest influence suffices to disturb the calm which reaches two degrees north and south of the equator.

What here Some slight disturbing force breaking the equilibrium produces those dreadful whirlwinds called tornadoes; and scarcely a day passes without some violent thunder-storm.

Where blw

§2.-MONSOONS.

The trade-winds blow through two belts of trde winds the globe, beginning two degrees each side of the equator, and extending to the tropics. Interrupt- These belts suffer an interruption in the ed where. Indian Ocean, where they are changed into what are termed monsoons, or season winds.

What their

The northern and western boundaries of the

boundaries monsoons are formed by the coasts of Africa

and Asia; the southern boundary would be a

line drawn through the north extremity of Madagascar to the north coast of New Holland. From April to October the wind in this vast How do basin blows uniformly from the south-west, and from October to April from the north-east.

The reason of these winds is simply the change of seasons. When the sun is south of the equator, all that part of Africa which lies in southern hemisphere is greatly heated, whereas the northern hemisphere is proportionably deprived of the sun.

they blow.

What cau

ses them.

ter what.

December, January, and February are the our winsummer months to the southern hemisphere, but the winter months to the northern.

What hap

pens then.

While the sun is south of the equator, Arabia, Persia, India, and China, pass their coldest months, and the cold air from these parts flows towards the warmer regions of Southern Africa, producing a north-east wind. When the sun has crossed the line at the S. Africa end of March, then Southern Africa gets colder in the same proportion as the northern hemisphere gets warmer.

cools when,

pens then.

It is then that the lands of Arabia, Persia, What hapIndia, and China, are hotter than Southern Africa; and the colder air from the south presses towards those shores of Asia, producing a south-west wind.

lows hence.

Hence the north-east monsoon continues What folwhile the sun is south of the equator, and the south-west monsoon while he remains in the northern hemisphere.

The transition from one monsoon to another takes a few days, during which time the winds are variable, and furious tempests, whirlwinds, and hurricanes prevail.