The morning news. [volume] (Savannah, Ga.) 1887-1900, 1888-11-09

cHlel signal OFFICER 10 unub uIle lutcAAlSoi"
part of every community may utilize them
by making special predictions which will
supplement- the brief official forecasts, the
distribution will be as extensive as public
or private interest in the subject shall re-
qulre. With the assistance of the daily
weather map any intelligent person may
make predictions which will rarely fail of
veritication. it is not necessary TO have a
deep knowledge of meteorology, and a little
practice, together with an understanding;
of the general movements of storms, Will
insure fair degree of success at the outset.
The government, in the first place, con-
tracts with somebody to supply the signal
office with prepared sheets of paper, having
upon them the map of the Unitet States,
printed in light green. The names of all
the signal stations are given. with large
dot in front of each one to designate 1t as
station. * In placing upon them the daily
story of the weather the maps 60 through
two processes. On the bed of a large, old
fashioned hand press there is a heavy cop
per plate with oles in it to correspond with
the stations on the map. In these holes are
inserted symbols, which denote the direc-
ton of the wind and the general character
of the weather-clear, fair, cloudy, raining
or showing With these symbols, to which
there is key on every map, one soon be-
comes as familiar as with the letters of the
through the press they are passed over to
cyclostyle operator, by whom isobares, $50
therms and some general statistics are added.
These terms need not cause the aspiring
prophet to approach the subject with any
thing like feeling Of timidity, for they
represent facts which are easily mastered.
Storms are divided into two classes.
That in which deficiency of atmospheric
pressure occurs is commonly known as
lon - o,l in tho form
of an area of excessive pressure is briefly
known as high" Each map. therefore, is
divided into high and low areas, which be-
come readily defined as soon as the points,
or stations, having an equal atmospheric
pressure are connected by lines called is
bares, which are drawn for every tenth of
an inch of pressure. Each isobare shows
that the pressure over the earth along that
line is equal to that which would be exer-
cised by a layer of pure mercury to the
thickness Of the number OF inches printed
against tae isobare by the cyclostyle.
When the mercury of the barometer stands
at 80 inches in the tube it represents normal
atmospheric pressure, and an lsobare of
that mination-commonly spoken Of
as ''the line of 30'-usually defines the exact
boundary of a storm area.
The great storm of March II to March IA,
1888, Familiarity spoken of as the New York
y
these lines, because at the storm center the
mercury in the barometer fell below 20
inches, and, therefore. 10 or IL isobares
were required, one being drawn for each
tenth of an inch difference in the pressure.
At 10 o'clock D. M, March r. the center of
the storm was over Nantucket and Cape
Cod on the Massachusetts coast, and the
isobare Of 80 inches described a small and
perfect circle.
1.-THE line of thirty" ran from point in
Canada little west of Quebec city directly
south to Norfolk, Va, and there were nine
isobares between it and the small circle at
the center of the storm. This precipitous
decline in the atmosphere indicated very I'M
usual energy in the storm, and whenever on
any map the lines are noticed lying close
together they may be considered as presag-
ing winds of more than the average velo-
city. The shapes the lines form usually in
dictate tho rapidity of the storms movement.
A perfectly round storm moves slowly. and
a storm with flat front travels with great
speed. The shape also gives clew to the
probable course of the disturbance.
Low area storms travel across the United
States by divers paths, but the average
direction is little to the north of east and
the average velocity is about 500 miles in
twenty-four hours. In most cases the dir
ection can be predicted exactly after
careful observation of barometer readings
in advance of disturbance. A storm will
move naturally into an atmospheric valley !;
which may be explained by saying that if
the barometers at Chicago, Ill, and Nash
vile, Tenn, were high, while between those
cities the pressure was normal, or very
slightly under it, n storm travelling from
the Rocky mountain slope would not be
likely to go north of Chicago. but the center
would, in all probability, pass between Chi
cago and Nashville. The isobares in front of
the storm usually show tendency to bulge
out in the direction which the storm is TAX
ing, and this, also, is fact of much pre-
dictive value. The winds blow in toward
the storm centre from all sidas The direc-
ton is contrary to the movement of the
hands of a watch, spirally inward, and
their strength and violence are proportional
by the crowded condition of the isobares.
The low area is preceded by cloudy weather
and rain, which sometimes extends many
hundred miles to the eastward of the confer.
When heavy rains occur behind the center,
that is, west of it, which, however, they
rarely do, the movement of the storm is
usually retarded. The center is also pre-
coded by temperature quite high for the
season, except in very hot weather, when
the temperature, although higher by night,
is lower by day, owing to cloudiness. As a
general rule, easterly and southery winds
are observed in front Of low areas, and as
soon as the center has passed over they shift
to northerly or westerly, rain soon ceases,
and fair weather follows.
The high area generally comes with the
clearing weather. The high circulation of
winds in it is in reverse of the winds in the
low areas, the currents moving out spirally
from the center, or in the direction of the
hands of watch. With the areas advance
the temperature falls, and the weather is
usually clear and pleasant, especially in
summer, when high areas are not of suffi-
Gent force to be called storms. When,
however, a high area moves off the land,
with the center over the st. Lawrence val
ley orNNew England, it frequently occurs
that the northwesterly winds attendant upon
the area bring rain and cloudiness along
the New England and Middle Atlantic
coasts. In the winter time the advance Of
high areas is marked by very severe falls of
temperature, the changes amounting occa-
sionally to from 25' to 30' in twenty-four
hours. The areas then frequently advance
with sufficient force and persistency to
cause winter storms OF severity and VIC
lence. As high areas follow low ones their
paths are, OF course, easterly in general.
About one-half of them move eastward
from Minnesota to New England, either
directly or along the line of the st. Law
renee valley, affe ting the northern half of
the United States, and the others move first
southwark in the trans Mississippi country
to Texas. thence drifting eastward with the
general circulation Of the air, thus affecting
the whole country.
The isotherms are dotted lines which de-