The star. (Reynoldsville, Pa.) 1892-1946, 1907-04-24
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 Law of Mature
Called the DETECTING Force of the
Earth's Rotation.

Cdftn y nOtdtioH.
1t is a matter of common observa-
sion that when the window of warm
room is opened on still winter night
the cold air from without rushes into
the room. Nearer the ceiling the
warmeS 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 cRlled wind, would not
occur il 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 re-
verse Is true. Three examples will
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
one-half of the earth's surface and
blow with much steadness the year
round.
The monsoons, or 'seasona. 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 a consid-
erable height and then flows out to
sea, forming systematic circulation
between ocean and continent. In win
ter the ocean is warmer than the con
tinent, and the winds reverse their
direction.
The Gland 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 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 a stone,
presses against y 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.
1t 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 barome-
ter tube is always just balancing a
column Of air of the same diameter.
reaching from the barometer to the
tap 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 IL the air is rare the
mercury will stand low in the tube.
and we then use the term low pres
sure"
Over the United States. Canada and