general statement takes the form of an effect, we want to know what the
causes are that produce such an effect. From the very nature of exposition
we may expect to find much of this kind of discourse relating to causes
and effects. (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. Exposition is that form of discourse the purpose of which is to
explain.

2. The essential characteristics of an exposition are--
_a._ That it possess unity because it contains only those facts
essential to its purpose.
_b._ That the facts used be arranged in a coherent order.

3. Exposition is concerned with (_a_) general terms or (_b_) general
propositions.

4. The steps in the exposition of a term are--
_a._ Definition. This may be--
(1) By synonym (inexact).
(2) By use of the logical definition (exact).
_b._ Division. This may be--
(1) Complete (classification).
(2) Incomplete (partition).
The same principle of division should be followed throug