Year: 1872

A vast amount of information is constantly !
being gathered and collated by the United
States Signal Service, out of which is being
gradually built up the true science of that
class of meteorological phenomena. Among
the general observations thus far noted may
be mentioned the following:


Storms are accompanied with a depression
Of the barometer near the central line of the
storm, and rise OF the barometer in the front
and rear.


This central line of minimum pressure is
generally Of a great length from north to
SOUTH and moves side foremost toward the
sea.


This line is sometimes nearly straight but
generally curved, aud most frequently with its
convex side toward the east.


The velocity of this line is such that it
travels from the Mississippi to the Connecticut
river in about twenty-four hours, and from the
Connecticut to St John, Newfounland, in
nearly the same time, or about thirtysix miles
an hour.


When the barometer falls suddenly in the
western part of New England, it rises at the
same time in the valley Of the Mississippi, and
also at ST. Johns, newfoundland.
In great storms the wind for several hundred
miles on both sides of the line of minimum
pressure blows toward that line directly or
obllquely.


! Inc IOrCc Ol the WlIlu IL Ill pTOpOTlluD ~ TIE
suddenness and greatness of the depression uf
the barometer.


In all great and sudden depressions OF the


barometer there is much rain or snow and in


all sudden great rains or SHOWS there is great
! deprC sSion of the barometer near the centre OF


the storm, and rise beyond its borders


Many storns are Of great and unknown


length froGI north to south, reaching beyond


our observers on the Cult Of Mexico and OH


the northern lakes, while their east and west


diameter is comparatively small. The storms
therefore more SIDE foremost.


Most storms commence in the ''far West,


beyond our most western observers, but some


commence in the United States


When a storm commences in the United


States the line of minimum pressure does not


come from the far West" but commence.


with the storm, and travels with it toward the


eastward.


There is generally lull of wind at the line
of minimum pressure, and sometimes q calm
When this line of minimum pressure passe:
: an observer toward the east, the wind generally


soon changes to the west, and the barometer


begins to rise.


There is generally but little wind near tht


line of maximum pressure; and on each side o
9 that line the winds are Irregular but tend out
ward from that line.
The fluctuations of the barometer are gener
, ally greater in the northern and the eastern
) than in the southern and the western parts o
e the United States.


d In the northern parts Of the United State
G the wind generally, in great storms, sets il
t from the north of east and terminates from tn
e north of west and in the southern parts tn
n wind generally sets in from the south of cas-
u and terminates from the south of west.
o During the passage of storms the wind genel
/ ally changes from the eastward to the westwar
|; by the south, especially in the southern part
h of the United States.
n The northern part of the storm general
'e travels more rapidly toward the east than tn
5. southern part.


RI During the high barometer of the day pre-
Is ceding the storm it is generally clear and mil
rs in temperature, especially if very cold.
as The temperature generally falls suddenly o
ot the passage of the centre of great storms an
~ sometimes, when storm is in the middle of ii
a United States, the lowest temperature of I'll
ns month will be in the west on the sanse day thu
Of the highest temperature is in the east.
)n The first of the principles upon which Il


Signal Corps proceeds is, that the invariab
ne course of ar-currents is such as will equals


the atmospheric pressure upon the earth
j. surface, and that wherever inequalities exi
nd the winds are set in motion, the air thus fin
p ing its level-!just az water Or any other visib
lr- fluid does.