Grant County herald. [volume] (Lancaster, Wis.) 1850-1968, 1883-01-25
How To Read Thermometers.

1t is not surprising that those own
ing thermometers should think that all
thermometers are graded alike, and
that all should read alike. The ther-
mometers costing from so cents to a
dollar, are tested only at the freezing
point, to-wit: 80 degrees. This is either
done by pounded ice, or melted snow;
and only one test is made, hence, they
may read at 80 degrees correctly, and
all agree, and when they read 5, 10 or
20 degrees below, zero, disagree very
much indeed. These instruments are
blown hollow, of course, by the glass
blower, and afterwards by the maker
tested at the freezing point only. Now
should there be an ~unevenness in this
hollow tube, no matter how slight,
there will be a p~erceptible difference
in the reading with a U. S. standard
instrument; and should all instruments
read alike at a given or stated time.
say Z a. m. there will also be a diff
erence in the reading. This is caused
by local attractions, and by the descend
ing of the cold wave, but would not
in any locality like Galena make a diff
erence of from 4 to 6 degrees.
To read a thermometer correctly re-
quires some little care, us the eye must
be exactly at the level of the reading,
and in all cases it must be so situated
that a line drawn from the eye to the
top of the column, would be perpen-
dicular to the reading. If the eye is
above the top of the column, however
little, the reading will be too low, and
vice versa. This a matter frequently
neglected by careless observers, and,
besides do not depend for accuracy on
the first reading, but compare with
second reading.
Again, the thermometer must be read
quickly, and the face and hands must
not be near it, otherwise it will be af-
fected. 1t is best always to have the
instrument facing the north, and never
be allowed, for accuracy, to be in the
sun, or where it will be affected by re-
Election. 1t should be suspended in the
open air, and wherever practicable an
instrument shelter should be built.
This is done by lattice work, so that
while there is access of air to the inside,
the radiant heat and rain or snow, are
effectually excluded. Many people
think that the thermometer is affected
by wind. From careful observation
this will be found to be an error.
Alcoholic thermometers have a ten.
dency to read lower by age. owing to
the relative nature of the fluid, allowing.
particles in the form of vapor to rise
and fall in the tube. Every person
owning a thermometer should know the
index error, and so correct that reading.
and by no means jerk or shake the in
strument.
All thermometers for accuracy should
be Of known reliability and standard
make, and never make the assertion
that the instrument is correct, when you
havenot tested it, or have not the means of
knowing whether it is 50 or not. A COM
nor thermometer may be accurate at
the freezing point, and very much out
of the way at or below zero; and BY all
means do not try to get ahead of your
neighbor IN an intense cold morning oy
making it colder than it is. 1t is very
true, that you can on a cold morning
get up a feeling of ill-will, quicker on
the thermometer subject than either on
religion o polities. GEO. w. GIRDoS,
Vol. Obs. U. S. Signal Service.