Peninsula enterprise. [volume] (Accomac, Va.) 1881-1965, 1907-07-27
WHY THE WIND BLOWS
A Study Of the Circulation OF the
Worlds Atmosphere.
FORCES THAT MOVE THE AIR.

Contrasts In Temperature, High and
Low Pressure and a Law Of Nature
Called the DETECTING Force Of the
Earth's Rotation.
1t is matter of common observa
ton that when the window of warm
room is opened ON still winter night
the cold air from without PUSHES into
the room. Nearer the ceiling the
warmer air Is forced out Of the WIN
dow, thus completing general atmos'
pheric circulation on miniature scale.
These currents of air, which might
properly be called wind. would not
occur If the air within doors was not
warmer and consequently lighter than
the air without.
The range in temperature between
the equator and the north pole amounts
In winter to considerably more than
100 degrees F., and In summer the
contrast Is also great Moreover, in
summer the continents are warmer
than the oceans, but in winter the Ne
verse Is true. Three examples VIII
serve to illustrate how such contrasts
affect the winds of the world
At the equator the temperature aver
ages about so degrees throughout the
year. Consequently the lower air flows
in from regions Of high pressure on
each side, forming what are known as
the trades. These winds cover nearly
Ill 90 rfh
blow with much steadineSs the year
round.
The monsoons, or seasonal winds"
of India and the Indian ocean are the
most interesting Of their class. In
summer the cooler ocean air pushes In
toward the land, while the warmer air
over the continents rises to consid'
cradle height and then flows out to
sea. forming a systematic circulation
between ocean and continent. In win.
ter the ocean is warmer than the con-
tinent, and the winds reverse their
direction.
The land and sea breezeS" occur
with much regularity near large bodies
of water in some parts of the world.
The ocean Is cooler than the land dur
ing the day and warmer at night, caus-
ing on q small scale daily inter
change of air similar to that caused
by the monsoons.
A clear knowledge of the term "air
pressure" Is very helpful in studying
the causes Of wind. Air, like stone.
presses against the grOund-in other
words, it has weight, amounting to no
less than 2,117 pounds upon every
square foot Of the earth's surface at
sea level-but, unlike stone, the at
mosphere is elastic to a high degree
and also presses in all other directions.
On account Of this elasticity of the
air. certain forces which arise from
differences in temperature and the
earth's rotation cause 1t to become
dense or heavy in some regions and
rare or light in other regions.
It Is the effort of the atmosphere to
overcome these pressure differences
and resume a state Of equal density
that causes the winds to blow.
The column of mercury in a barome-
ter tube is always just balancing a
column of air Of the same diameter,
reaching from the barometer to the
top Of the atmosphere. II the air Is
dense the mercury will Of course stand
high in the tube, and to express this
condition we use the term high
pressure" but If the air Is rare the
mercury will stand low in the tube,
and we then use the term Glow pres
sure"
Over the United States, Canada and
other parts Of the world the pressure
is ascertained each day at numerous
stations. The barometer readings, eX-
pressed in inches Of mercury, are tele |
graphed to a central point and there
charted on a map. The exact regions |
where the pressure is high or low
may then be seen at glance. 1t has
been learned from such observations |
that these areas are constantly moving |
eastward at an average rate OF about |
900 miles per day.
Technically the low pressure areas |
are called cyclones and the high |
pressure areas "anticyclones." They |
are frequently 1000 or more miles IN
diameter. The little storms Of great
destructive force so often called cy-
clones are really tornadoes.
The higher the pressure In any par
ticular region relative to some other
region the greater will be the velocity |
Of the wind. The winds blow much |
faster In winter than In summer be-
cause the greater contrasts Of tempera-
ture cause more decided differences In |
pressure.
Observations demonstrate, however.
that the wind never blows In straight |
lines, because all bodies of air when
in motion are acted upon by law Of
nature called the DETECTING force Of
the earth's rotation" This force turns |
all wind to the right Of its course In
the northern hemisphere and to the
left In the southern.
Thus If wind in our hemisphere |
starts north 1t is soon turned slowly |
toward the northeast, or If 1t starts |
west II will soon turn toward the |
northwest When it is remembered |
that at the equator the earth is rotat-
ing at the enormous velocity of 1895
miles an hour one will not wonder that
such a DETECTING force could exist. All
areas Of high and low pressure, from
whatever cause, therefore become
whirling masses of air, and a little
thought Will show that they must turn
in opposite directions. In the north
ern hemisphere the low areas, or
slows" as ley are designated on th"
weather map, always rotate in a d.
rection contrary to that Of the hands
of a watch.-Youth's Companion.