The National tribune., 1890-12-25
THE WEATHER.
By LIEUT.. J. P. FINLEY, U. $. SIGNAL SERVICE

By LIEUT.. j. P. FINLEY, U. s. SIGNAL SERVICE.
Correspondence invited suggestions desired
and information eheerfully furnished. Every eff
fort employed TO make this Bureau Of practical use
to the readers Of The NATIONAL TRIBUNE. All
communications should be addressed Weather,
THE NATIONAL TRIBUNE Office, Washington u. O.
4 Thermometer is an instrument for measur-
ing the temperature or warmth of the air or
other medium, by means Of the expansion of a
fluid inelosed IN a glass bulb Nearly all fluids
expand and occupy a greater space when
warmed, but that used for thermometers is
usually either mercury or spirits of wine. 1t
quite fills the bulb and extends some distance
up fine tube opening into it, and as the bore
of the tube is very small, a very small change
in the volume or bulk Of the fluid is made per-
ceptible by its extension or repression iIsthe
tube.
The popular conception Of temperature is
based on the different sensations produced by
bodies when termed hot, warm, or cold the
hotter body being said 20 have the higher tenn
perature. Thus, the temperature of body is
the degree OF its sensible heat and thermOmetry
the art of its measurement. In arranging for
the graduation Of thermometers there are two
fixed points Of temperature Obtainable without
much difficulty, and with great accuracy, viz,
that at which ice melts and that of the steam
given of by boiling water. The difference be-
tween these temperatures is represented on the
Fahrenheit scale (the standard in the United
States and Englandl by leo equal parts, called
degrees. The lowest or freezing point is
marked 30, and the highest or boiling point, is
marked 2I2.
In graduating standard thermometers, the
tubes when filed arc immersed first i'm melt
ing ice aud then in the steam Of boiling water
and marks are made on the tube to Indicate
the points at which the fluid stands in the two
trials respectively. The interval Is divided into
$50 equal parts. A number of similar equal
a., Ill
ing point aud the 32d is termed zero.
Thus it will be understood that degrees are
purely conventional divisions and not only
might the interval between the melting point
of ice and the boiling point Of water be sub
divided into any other number Of parts than
$50, but two such other systems of subdivision
are very widely employed.
Reference is here made 10 the scale of Reau-
muir, aud the scale OF Centigrade. In the
former the freezing point is marked zero, and
the boiling point 50 In the latter the freezing
point is marked zero and the boiling point
100.
Five degrees on tie Centigrade scale are
equal 10 four degrees on Reaumur therefore the
reduction of temperatures from one scale TO
the other can be effected by multiplying by
the fraction fOur-ifth5 or by i've lourths. The
relation Of these scales 10 Fahrenheit is rather
more complicated, because the latters zero is
not at the freezing point, but 30 points below
it. A comparison of scales reveals the fact that
81 OF Fahrenheit are equal to 81 of Centigrade,
or A. of Reaumur.
The tube bulb and scale are the essentials of
every thermometer, yet the scale is often en-
grayed on the tube, and sometimes no other
scale is attached. Generally a scale is of use
only for that particular tube for which it has
been engraved.
Although there has been a great improve
ment in the manufacture of Thermometers of
late years, yet very few instruments are free
from error, and none can be accepted as abso-
lutely correct.