(See Section 49.)
Notice the following example:--
The effect of the polar whirls may be seen in the rapid rotation of water
in a pan or bowl. The centrifugal force throws the water away from the
center, where the surface becomes depressed, and piles it up around the
sides, where the surface becomes elevated. The water being deeper at the
sides than at the center, its pressure upon the bottom is proportionately
greater. A similar effect is produced by the whirl of the air around the
polar regions. It is thrown away from the polar regions and piled up
around the circumference of the whirl. There is less air above the polar
regions than above latitude 30 deg.-40 deg., and the atmospheric pressure is
correspondingly low at one place and high at the other. Thus the
centrifugal force of the polar whirl makes the pressure low in spite of
the low temperature. The position of the tropical belts of high pressure
is a resultant of the high temperature of the equatorial regions on one
side and the polar whirls on the other.
--Dryer: _Lessons in Physical Geography_.
+Theme XCV.+--_Write an expository theme using cause or effect._
Suggested subjects:--
1. The causes of the French Revolution.
2. How ravines are formed.
3. Irrigation.
4. Effects of smoking.
5. Lack of exercise.
6. Volcanic eruptions.
(Did you find it necessary to make use of any other method of explanation?
Did you make use of description in any place?)
SUMMARY
1.
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