The democrat. [volume] (Weston, W. Va.) 1868-1874, 1873-05-19

reduced air.pressire over any particular
part OF the earth's surface which is
indicated by depression OF the NOR.
curyin the barometer within that region,
Hence the central district Of q storm is
technically called "nn area Of low bar.
ometer." Towards this region the sur.
rounding air rushes in to restore IN
equilibrium, and TINT rush OF mir is
known rs wind. The resulting circular
motion, around the central point, is due
to tho rotation Of the earth upon her
axis, from west to east.
It's easy to calculate that the velocity
OF rotation ut the equator, $4,000 miles
in "a hours, is 17.3 miles per minute,
whilo at the pole 1t is nothing. In the
latitude OF 40 degrees it is 1871 miles in
the latitude Of 45 degrees it Is 12l miles
per minute. The earth carries the at
mosphere along with 1t, and the velocity
OF the atmosphere at any point is the ye-
locityof tllatpoint, which decreases with
an increase in the latitude. tits evident
that, II mass OF air at any point be
moved northwnrd OF southwark, from
any cause, it will preserve for time the
eastward velocity OF hepointfrom which
1t started; Just as a stone thrown from
tho window Of q moving railroad car is
carried forward by the impetus OF the
train. Hence, mass OF air moving
soutliward, in this hemisphere, will lag
behind in therotation, while the relative
motion will be faster than that OF the
surface il it move northwarl, because
OF the change in velocity Of the surface
due to tho latitude.
Now suppose the top line Of our dia-
gram to represent the parallel Of 40 de-
grees Of latitude, and the length Of the
horizontal arrow indicate the motion per
minute on the parallel. Let the lower
line represent the parallel Of 10 degrees;
then the length fthe arrow near II will
indicate the velocity OF tho air there per
minute. In each case the surface, and
its superintendent air, moves in the
direction OF the arrow. II an area of
low barometer he at @, nearly midway
between these two parallels, the air will
move towards that area from every
point Of the compass; and the result
Is indicated in the diagram, where
the dotted lines show tho tendency,
and the full lines show the direction, Of
the actual movement. A mass Of mir
coming from the north ut N, moves
eastward with q velocity 12 miles per
minute, while the storm.Centre moves
12f miles per minute. Hence, the NOV
ing air drags behind at the rate OF !
mile per minute, or 80 miles per hour,
and takes the direction Of the arrow,
towards the circumference Of the small
circle, instead Of its centre at @. SINH
larly mass OF mir moving northward,
from s, has nn initial velocity Of 13t
miles per hour greater than that Of the
centre OF the storm; and moves in the
direction OF the arrow from s, instead
OF the dotted line. Similarly, we may
show that the same deviation occurs in
the case OF the air coming from every
direction towards o. and the conse-
quence is that the air moves round the
centre OF the area Of low barometer, in
a direction contrary to that Of the hands
Of watch that is laid with its face
upward.
The vertical motion resulting from
all directions towards q storm.center is
even more decided thnn indicated by
the diagram, which only represents the
secondary tendency. The central rush
Is opposed, or counteracted, by the
elasticity OF the several volumes Of air
as they approach each other and their
impetus carries them around in the
direction Of tho movement already
established, so that the wlirl extends
nearly as far from the center rs the
distance from which the winds blow.
All the air that tends towards the
storm.center moves round II in IN APP
proximNts circle /; in Just tic same way
that water courses round In funnel,
for a similar reason. and in the same
direction, the only difference being that
tile central column Of air moves up.
ward, while the central column OF water
in the funnel moves downward.
A knowledge Of these facts enables
us not only to tell the direction Of the
storm.conter, but often to know whether
II is approaching towards us, or re-
ceding, or Is passing IFS at q harmless
distance. II we face tho wind the
storm.center will always be on the
right hand or II we turn so that the
! wind blows from left to right we shall