Man's physical universe



vary because of seasonal changes and differ from place to place, but in

general they blow from westerly directions in the temperate zones

because of the effects of the rotation of the earth on the circulation of

the atmosphere.

Winds blowing toward the equator from higher latitudes are deflected

westward; these prevailing northeasterly and southeasterly winds of

the tropical regions are called the trade winds.

There are belts of comparative calm at about 30° latitude north

and south, between the trade winds and the prevailing westerlies.

Here the atmosphere forms high-pressure belts, particularly over the

North Pole

'/ / / NortKeaat'Trades / / / \


\\\ \\^ WW/


\ \ \ Southeast Trades \ \ \ /

Hi?h pressure

30° N. calm.

High pressure

"S. calm

South Pole

Fig. 75.

The most important prevailing winds on the earth.


These latitudes are called horse latitudes because sailing vessels

carrying horses from New England to the West Indies were obliged

to throw a part of their cargo overboard when water became scarce

because of slow progress due to the lack of winds. In these latitudes

one would expect to find the chief desert regions of the world.

The prevailing westerly winds are especially well developed in the

southern hemisphere, where, free to blow with great violence, they are

known as the roaring jorties.

The area of equatorial calm called the doldrums shifts north and

south with the seasons.

Near the poles the atmosphere is cooled and flows away from the


The prevailing winds tend to move the water at the surface of the

oceans by friction in the direction in which they are blowing. The

waters are thus blown toward the equator by the winds from the north.

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