The Redwood gazette. [volume] (Redwood Falls, Minn.) 1873-1940, 1877-10-04
Prof. LO0nlis' New Meteorological De.
auctions.

Prof. L0omis' New Meteorological De.
auctions.
PRoF. ELIAS LOOMS, of Yale College,
after examining the immense number of
weather observations collected by the
United States Signal Service, deduces the
following cancellations. The seven pa
pers wherein the detailed discussion has
embodied has appeared in the american
Journal of Science and Arts, whence the
conclusions below given are
extracted:
/. Areas of low barometer result from
q general movement of the atmosphere
toward q central area, and this movement
is accompanied by q detection of the
wind to the right, which causes tenden-
cy to circulate around the center with a
motion spirally inward.
2. This DETECTION to the right, which re-
suits from the earth's rotation, causes q
diminished pressure within the area of
this inward movement, and the pressure is
still further diminished by the cent? frugal
force reculting from the circulation about
center.
8. The amount of the barometric de-
preston depends upon the force of the
wind, and the geographical extent of the
revolving atmosphere. The effect Of GEN.
trifugal force is not considerable except
when the velocity of the wind approaches
that of q hurricane. With q velocity of
100 miles per hour, the depression due to
centrifugal force may amount to about
two inches; but in the winter storms of
the middle latitudes, with q velocity not
exceeding forty miles per hour, the de-
preston due to centrifugal force seldom
exceeds one or two.tenths of an inch. In
these storms, three-quarters of the OBJ
served depression of the barometer is usu-
ally the effect of tie earth's rotation; but
in order that the depression at the center
may amount to as much as one inch, it is
generally Necessary that this system of
circulating winds should prevail over an
area nearly 1900 miles in diameter.
A. In North America, south of latitude
IS deg, areas of low pressure are less fire.
quent. and generally exhibit less de-
preston than near latitude 45 deg, be-
cause the area over which a cyclonic
movement of the winds prevails is small
because, if cycloHic area could be
formed having radius of Zoo miles with
its center in latitude 80 deg, its circum-
ference must extend southwark to latitude
16 deg, where the trade winds are steady
and seldom interrupted. Such diver
sion of the winds toward the north, even
if it could be produced, could not be long
maintained; SO that large cyclonic area
with its center in latitude 80 deg. j. we'll
nigh impossible; and it is impossible that
there should be great depression of the
barometer in latitude 30 deg, except with
a wind having ahurricane velocity. This
is believed to be the reason why, in North
America, the centers of great storms are
generally found north Of latitude 40 deg.
5. The causes which may produce q
general movement of the atmosphere
toward q central area are (A) unequal
pressure as shown by the barometer; (B)
unequal temperature; and 60 unequal
amount of aqueous vapOr. OF these
three causes the effect of the first is gem
orally so decided that the influence of the
other two causes can only be detected by
careful observation; but when the pres
sure of the air is nearly uniform over .
large extent of country, the influence of
the other two causes is sometimes very
palpable, and their influence is generally
seen in slight DETECTION of the winds
from the direction they would have if
wholly controlled by the first cause.
6. A cyclonic mOvementOf large mass
of air is generally attended by an upward
motion in certain localities, chiefly ON the
eastern side of the center OF low pressure,
and this upward movement results in rain
fall. The rainfall is then not generally
the original cause of the Sarometric de-
preston, but rather an incident of the
cyclOidal movement of the atmosphere.
The fall of the barometer during a rain
storm cannot be ascribed to the simple
condensation of the vapor of the atmO-
sphere, as some have supposed, since q
rainfall of one or two inches prevailing
latitude 30 deg. produces scarcely an ap-
preciable effect upon the barometer.
z. The progress of areas of low barom-
eter in all ATTITUDES ia determined mainly
by the same causes which determine the
general system of circulation of the A.
mosphere; and their normal direction is
changed by whatever causes may change
the direction of the winds. i uEfs
8. The heat which is liberated in the
condensation of a large amount of aqueous
vapor must exert an influence upon the
movements of the air, 80 that while the
rain is generally to be regarded not as the
original cause but rather as one of the in
cidents of extensive cycloidal movement,
if the rain area has great geographical
extent, it may have . decided influence
upon the amount of the barometric de-
preston and upon the velocity with which
the storm advances; sometimes accelerat-
ing its motion, sometimes retarding it,
and sometimes holding it nearly stationary
in position for two or three days.