Evening capital. (Annapolis, Md.) 1884-1910, 1884-06-05
ALL ABOUT THE WEATHER.
T1ae United State Signal Service and
How 10 IL Managed.

NAA@h AfeA1 eASCOnili&EAGh 30 HluGll. WIS
organized by General Myer, a man whose
sobriquet, "Old Probs," is as familiar as
household wordsin every American home.
The service was established in 1870 by
Joint resolution in both houses of Con
gress, and to-day it's the most efficient
organization of the kind ever known. 1t
is bureau Of the war department, and is
composed Of force of five hundred men.
Although essentially military organiza
ton, the duties Of its members are not
strictly OF military character. All the
grades Of rank that obtain in the army
obtain in the signal service.
Applications for appointment to the
service are made to the chief signal Off
Der, and the candidates selected are re-
quired to prove the possession of strong
mind, healthy body, and, above all,
good moral character
When the candidate has fully estab-
lished that he is healthy and sound and
moral he is formally enrolled as one Of
General HaZen's assistants. Before being
put to work. however, the successful
candidate spends some time ut the school
of instruction near Washington, where he
is taught few military evolutions and a
good deal that pertains TO meteorological
observation, and upon finishing his sci
entitic education he is generally assigned
to a station as assistant Sometimes. If
sufficiently qualified, he is given charge
Of small station at the outset
The object of the signal service is to
warn the people of coming changes of
temperature and approaching storms, and
all that these meteorological variations
aud pnnvnloiano ppVfan1 Tho ftra1in-
tons which astonish the world by their
accuracy are made from a comparison at
Washington of local records sent in from
stations scattered all over the country.
In this way at Washington the authori
ties have practically bird's-eye view of
the meteorological conditions prevailing
all over the continent. The data upon
which they make their predictions are the
pressure of the air measured by the
barometer, the temperature of the air as
measured by the hygrometer, the velocity
of the air as measured by the anemome-
ter, and the direction of the wind as
measured by the ordinary wind vane.
In addition to these recording instru-
ments are the rain and snow gauge and
the spectroscope. The conditions re-
corded by these instruments, together
with the appearance of the clouds, are
the means by which the weather likely
to prevail in any locality is determined
Among the recording instruments the
uses of the thermometer and barometer
are generally known, and with their aid
every man, to a certain extent, is his own
weather prophet. The hygrometer con-
sists of pair of thermometers. The
bulb of one is enveloped in piece of
muslin that connects with vessel con-
tanning cold water. The muslin cover
ing the bulb Is thus kept damp, and as a
given amount of heat is required to pro-
duce given amount of evaporation, the
thermometer having its bulb covered
with damp muslin will record lower
temperature than the thermometer having
its bulb intact. The difference between
the two thermometers indicates the
amount of moisture there is in the air.
If one OF the thermometers records forty
five degrees and the other fifty degrees,
it demonstrates that the atmosphere is
very dry, and that it retains but twenty
five per cent. of the moisture it is capable
of holding.
The thermometer is an instrument with
four hemispherical cups at the extreme
ends of two rods which cross each other
at right angles. This continuance is
placed on the top of a spindle, at the
base of which are graduated cogwheels
The cups, turned by the wind, impart
their motion through the spindle by
means of an endless screw TO series of
cog-wheels, the revolutions of which are
taken as the measure of the winds force
Five hundred revolutions of the cups
equal one mile. There is an ingeniously
contrived electrical apparatus connected
with this, by means of which a complete
record of the winds variations is trans
ferred to paper. For every mile of the
winds velocity an electric circuit is COM
pleted, and this fact is Immediately
mechanically telegraphed to the officer
below
The spectroscope has proved useful
adjunct to the other instruments. 1t is
used particularly in the prediction of
local rain storms, especially those of the
summer months. When tae spectrum
shows a strong rain aud for the upper
atmosphere, and the hygrometer demon
strates that the lower atmosphere is sat
urated with moisture, there is strong
probability of rain. The advantages of
the spectroscope as a meteorological in
strument lies in the fact that it affords a
means of examining the condition of the
upper atmosphere, which is altogether
out of the range of the other instruments.
The rain gauge is a simple instrument
of funnel shape. The superficial area of
the bell shaped top is ten times greater