Rock Island Argus. (Rock Island, Ill.) 1893-1920, 1912-10-24

air on the western side of the low has
| a greater capacity for moisture as
its temperature is raised during its
/ journey southwark. Fair and cooler
weather is. therefore, to be expected
after the passage of the storm center,
I when the wind shifts to a westerly or
a nOrthwesterly direction
| After the low must come the area
of high pressure, just as the spot over
which an eddy in the water is passing
Will be covered to a greater depth an
instant later. The circulation within
the high" or anti-storm, is just the
( opposite of that already described in
the low, or storm; that is. the move
ment Of the air is downward and out
ward. Thus, on the eastern side of
the high We find that bracing. invigor-
ating air of the higher levels. the on
rush of which we first notice when,
after a period of warm, oppressive
weather, with its enervating influences,
the wind changes to the west and the
temperature begins to fall.
AS the autumn season advances, the
lows become more energetic; that is,
the enormous atmospheric whirls are
more violent, and the pressure in the
succeeding highs is greater. The warm,
rainy weather that goes with the east
eriy TO southerly winds in the front
of the low is then succeeded by the
sharp fall in temperature, usually
amounting to a cold wave, attending
the westerly winds that indicate the
passage Of the low and the coming of
the hiGh. The onward or eastward,
movement of the low is at about ex-
in winter, we find a decided storm CEN
ter ever Colorado, and the extreme
upper Missouri valley and the Cana
dian northwest occupied by a high of
corresponding intensity, in which the
temperatures are below zero, we will
naturally expect rain or snow in east
ern Iowa and northwestern Illinois for
/ about q TO SO hours, followed by clear
ing conditions ard a cold wave. The
severity and duration of the cold wave
will generally depend upon the 0arom-
etric pressure within, and the extent
of territory covered by the high.
Should any school boy be asked to
draw a picture of an eddy in the wa
ter. il is likely he would use a series
OF concentric lines to depict the whirl.
Exactly such lines are used by the
1 meteorOlogist in his effort to show to
4 the public the whiTl in the atmosphere.
i The heavy. solid lines are used to in
4 GiCate the height of the barometer at
every point in the territory through
which they pass, and the closer the
4 lines are together the more energetic
is the storm, just as the lines to in
dictate a deep eddy in the flowing
stream of water would be separated
by very narrow spaces. The average
height of the barometer when it is
4 corrected to read the same as it would
If it were lowered to sea level from
] he point OF observation and exposed
( in a freezing temperature. is about
1 300 inches. In other words, the weight
Of the air from sea level to the outer
! most limits of the atmosphere is equal
: to the weight of a layer of mercury
about go inches thick If there were
4 no storm eddies in the atmosphere,
4 the barometers over the entire obser-
I walton field should read about the
q same To detect the presence of the
a lows, or storms, the forecaster draws
Z the isobar through all places of the
4 same barometer reading. He may start
q with the isobaT 10 indicate an air pres
\ sure of 800 inches: then draw another
line for the pressure of 299 inches,
another for 29.S inches, and so on. until
7 the point of lowest pressure OF the
4 center Of the storm is reached. the com.
\ pleted system isobars in a well de.
4 velOped winter storm often having the
4 appearance Of a spiders web or a
s target. Sometimes the barometer at
4 the center of an unusually energetic
4 storm eddy falls to 290 inches. and
j occasionally, il is even lower than that
q reading. To gain an idea OF what thfs
9 means, imagine a vortex so violent that
q the layer Of air thrown on from its
s center would be equal in weight TO {
layer OF mercury one inch thick.
q In addition TO the isobars, isotherms
d or dotted-iiines, are drawn upon the
8 maps issued 10 the public to inclose
y the areas in which the temperature is
b below the freezing point and below
8 zero.
AT the bottom Of the weather mar
4 will be found explanatory notes TO in
s dictate just what information is to be
q found entered at every station from
s which reports are received. II one :;
) interested in the ea-her il some dis