Springfield globe-republic. (Springfield, Ohio) 1884-1887, 1886-02-08
THE WORK OF "OLD PROPS"
HOW THE SIGNAL SERVICE GETS
ITS METEOROLOGICAL FACTS.
Making Up = Forecast from Reports
Received in Cipher-AtmosPheric Mois-
tur.-The Barometer-what L. Meant
by an Area of Low Depression"

The weather bureau, as now organized,
Is q military institution, or an appendage
Of the regular army. Throughout the
United States there are 376 signal stations,
in charge of nineteen officers and 500 men
of the signal corps of the army. Zach
station is provided with the best instru-
ments, including the latest inventions
for observing and accurately recording
the constant variations of the weather.
From l39 Of these stations telegrephic
reports are sent daily to Washington; the
others report by mail.
Reports are received from the trained
observers at important stations three
times every twenty four hours. These re-
ports contain full particulars of the
weather in the different districts. Seven
teen stations in Canada, one in st Johns,
Newfoundland, and one In the north
western part of British America send
reports, and there are over 800 outside
or volunteer observers in different
sections who also send reports
by mail The telegraphic reports
are transmitted to Washington by
means of a secret code, few figures con-
veying a large amount OF information.
These reports are received from all the
stations In the United States, Canada, and
the West Indies inside of thirty minutes.
A translator" takes the kilograms in
hand and reads them of to eight clerks,
each of whom has a special weather map
before him on which he marks the par
ticular readings he has been instructed to
take. These eight maps are sfterward
combined in one general map, which then
fully represents all phases of the weather
throughout the territory covered. This
map is closely studied by an expert signal
officer, the storm center" located, the
probable course of coming storms deter
mined, and the complete indications"
made up for the several districts.
SYSTEM AND INSTRUMENTS USED.
Some account of the system and instru.
ments used may be interesting to the
majority of readers. The bureau passes
its forecasts upon observations as to bar.
ometer, thermometer, hygrometer, anemo-
nafer, weather vans, and rain gauge,
made at the same instant three times a
day at all the stations Each observer
inspects his instruments at 7:35 q. m, 4:Ss
p. m. and ll:35 p. m, Washington time,
where the bulletins are made up and pub
lished in each case one hour and twenty
five minutes after the observations are
made-at . a. m, q p. m, and a. m, re
spectively. Reliable weather prophecy re-
anires that at least four things be known
respecting the condition of the atmosphe.
over a wide area-its weight as indicated
by the barometer; its temperature, Us
shown by the thermometer; its degree OF
humidity, as shown by the hygrometer
and the direction and velocity of its cur
rents, as recorded by the weather ,vans
and thermometer
The barometer used in our service Is the
common mercurial barometer, in which
the yaring weight of the atmosphere at
any given place is balanced against the
weight of column of mercury contained
in a glass tube about thirty-three inches
in length. At the sea-level in fair weather
a column of air one inch square and ex
tending to the upper limit of the atmos
phere weighs fifteen pounds; a column Ol
mercury of the same section and thirty
inches high weighs the same; hence the
power of the air under the condition:
mentioned to sustain in tube containir s
vacuum in its upper end column
mercury of the height named. II follows
of course, that the height Of the mercuria
column will vary with the variation.
in the weight of the atmosphere, falling
when the air is rendered light by reasor
of the presence of watery vapor, by exces
sive heat, or other cause, and rising whe,
the air is cold and dry, or dense from
other causes not necessary at present Il
enumerate. IL must not be supposed thai
q falling barometer Is an invariable pre-
cursor of storm; the indications Of thu
instrument are to be relied on only in con
lection with those of other Instruments
AN AREA OF Low BARoMETER-
Suppose all the data In at the Washing
ton Office at ABS p. m, and II is found tha
at Nashville, Tenn, and hundred mile
around it in every direction there is al
@area Of depression, an area Of low baron
eter, say 292, while around Nashville as
center we may draw q line showing ,
high barometer, say 3O.02, at Cincinnati
Indianapolis, st. Louis, Memphis, Atlanta
Abingdon, Va, and Wheeling. What i
the forecast. There will be flow of air
winds-inward from all points named to
ward Nashville. So far as practical effec
Is concerned, low barometer Is equivalen
to q depression of the upper surface of tn,
sea of air in which we live, and higf
barometer is equivalent TO an elevation
or wave, which will naturally flow dowI
and fill up the depression. There will
therefore, be an inflow toward Nashvill,
from all points of the compass.
Like water flowing toward hole in tn,
bottom OF a tub. the current Of air viii
take on q whirling motion, and thin
cyclonic movement, which, in the north
ern hemisphere, under the influence o
the earth's rotation, is always from righI
to left, will go on increasing in intensity
Violent winds whirling about Nashville
at distance of about seventy-flve miles
but dead calm perhaps at the city itself
In an ordinary water whirlpool there j,
suction downward, but in our whirlwinC
the suction is upward, with, Of course, .
lower barometer. The warm, damp all
about Nashville being thus varied by the
cyclonic movement into the upper. colder
and less dense regions of the atmosphere
becomes expanded and chilled so as to bs
incapable OF sustaining longer its burdens
of moisture, which fails as rain or snow.
Washington Cor Globe be-Democrat.