cross the fields
near noon on warm summer days illustrate the movement of the air
in one of these great storms. The direction of the air in a cyclone
is opposite to that of the hands of a clock.

When the wind comes up from a southerly point, when high, thin
clouds, gradually growing thicken, spread over the sky, and the
barometer begins to fall, then it is known that a storm is corning.
If one will learn to watch the clouds and the winds carefully he
may become able to predict a storm with almost as much certainty
as if he had a barometer. This instrument registers the pressure of
the air, which is always less within the area of a storm, because
then the air is rising. So when the barometer falls we may always
know that a storm is approaching.

The greater number of the storms which occur in the central and
northern United States come in from the Pacific Ocean in the latitude
of Washington. Continuing east or southeast they reach the Mississippi
Valley, and then turn northeastward toward the St. Lawrence Valley.
In the summer months there are few storms, and they very rarely
reach as far south as California. As winter approaches the storms
become more frequent and severe, and move farther and farther south
until the whole land as far as Mexico receives a wetting.

Upon the Pacific coast there is often very little warning of the
coming of a storm, but in the Middle and Eastern States they may
frequently be predicted several days in advance. With the passing
of one of these storms the temperature falls rapidly, and this
lowering of temperature, together with the fierce wind, gives rise
upon the Great Plains to "blizzards" or "northers." These storms
endanger the lives of both men and animals.

At different times in the year, particularly in winter, spring,
and early summer, warm, dry winds occur. Those winds which sweep
down from the heights of the Rocky Mountains and quickly melt the
snows are known as "chinooks." The hot north and east winds of
California often do great damage to growing crops.

Now let us sum up briefly the factors which have together produced
the climatic features of the Pacific slope.

(1) Ordinarily the factor of the greatest importance is latitude.
We should expect that Seattle would have a much colder climate than
San Diego because it receives the sun's rays more slantingly.

(2) The influence of latitude is greatly modified by the temperate
winds blowing from the Pacific, so that places