The true northerner. [volume] (Paw Paw, Mich.) 1855-1920, 1873-04-11

Inc StcOuuufN ctllSt VI u Stoiiii II 4"
reduced air-pressure over any particular
part of the earth's surface which is
indicated by n depression of the mer-
curry in the barometer within that region.
Hence the central district of n storm is
technically called "an area OF low bar
ometer." Towards this region the sur
rounding air rushes N to restore an equl-
librium, and that ush of air is known as
wind. The resulting circular motion,
around the central point, is due to the
rotation of the earth upon her axis, from
west to east.
1t is easy to calculate that the velocity
of rotation mt the equator, 2i,900 miles
in 81 hours, is 1913 miles per minute,
while ut the pole it is nothing. In the
latitude of 40 degrees it is l3! miles i'll
the latitude of 10 degrees it is 12t miles
per minute. The earth carries the at
mosphere along with it, and the velocity
of the atmosphere at any point is the We
locity of that point, which decreases with
an increase in the latitude. 1t is evident
that, if mass of air mt any point be
moved northward of southwark, from
any cause, it will preserve for time the
eastward velocityof the point from which
it started Just rs stone thrown from
the window of n moving railroad car is
carried forward by the impetus of the
train. Hence, II mass of air moving
southwark, in this hemisphere, will lag
behind in the rotation, while the relative
motion will be faster than that of the
surface if it move northward, because of
the change in velocity of the surface due
to the latitude
Now suppose the top line of our dia-
gram to represent the parallel of - de-
grees of latitude, and the length of the
horizontal arrow Indicate the motion per
minute on that parallel. Let the lower
line represent the parallel of 40 degrees
then the length of the arrow near it will
Indicate the velocity of the air there per
minute. In each case the surface, and
its superintendent air, moves in the di-
rection of the arrow. If an area of low
barometer be at &, nearly midway be-
tween these two parallels, the air will
move towards that area from every point
of the compass and the result is indi-
Gated i'll the diagram, where the dotted
lines show the tendency, and the full
lines show the direction, of the actual
movement. \ mass of air coming from
the north Mt y, moves eastward with Il
velocity l2i miles per minute, while the
storm-center moves II, miles per minute.
Hence, the moving air drags behind at
the rate of J 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 center at G..
Similarly mass OF air moving north.
ward, from :, has an initial velocity OF
III miles per hour greater than that OF
the center of the storm and moves III
the direction of the arrow from :, in.
stead of the dotted line. Similarly, We
may show that the same deviation oc-
ours In the case of the air coming from
every direction towards G. and the con
sequence is that the air moves round tin,
center of the area of low barometer, il
adirection contrary to that of the hand,
of n watch that is laid with its face up
ward.
The vertical motion resulting from
all directions towards storm-center il
even more decided than indicated by tin,
diagram, which only represents the
secondary tendency. The central rusl
is opposed, or counteracted, by the elias
ITCHY OF the several volumes of air nj
they approach each other; and theil
impetus carries them around in the di
rection of the movement already estab
lished, so that the whirl extends nearl,
as far from the center as the distanc,
from which the winds blow. All the al
that tends towards the storm center
moves round it, in an approximate circle
III just the same way that water courses
round in funnel, for similar reason
and IN the same direction, the only differ
ence being that the central column o
air moves upward, while the centra
column of water in the funnel moves
downward.
A knowledge Of these facts enables III
not only to tell the direction of the storm
center, but often to know whether it II
approaching towards us, or receding, o.
is passing us ut harmless distance. l
we face the wind the storm-center vii
J always be on the right hand or If W.
turn so that the wind blows from left t
: right we shall face the storm-center. III
, at the same time, the mercury in the bar
ometer continues to fall, we may be sur
that the vortex is approaching us
| while, if the barometer rises, w
, may count on its having passed by
The general direction of the movement