, 1892-03-09
WEATHER GAUGERS.
Thermometers ARE MANuFAc-
TuRED WITH GREAT CARE.

They Are Made Very Accurately, and.
Though Quickly, Pass Through Nine
teen Pairs of Hands-The Different
Processes of the Instruments.
The making of Thermometer may be
either a delicate scientific operation, or
one of the simplest tasks of the skilled
mechanic, according to the sort of Their
molneter made. With the extremely
sensitive and infinitely accurate instru-
ments designed for scientific uses great
care is taken, and they are kept in stock
for months, sometimes for years, to be
compared and recompared with instru-
ments that are known to be trustworthy.
But so much time cannot be spent over
the comparatively cheap thermometers
in common use, and these are made rap
idly, though always carefully. The
method of manufacture has been SO sys-
tematized within a few years that the
very cheapest thermometer should not
vary more than a fraction of a degree
from the correct point.
Whether the thermometer is 10 be
charged with mercury or alcohol; wheth-
Or it is to be mounted in a frame of
wood, pressed tin or brass, the process
Is substantially the same. Mercury is
generally used for scientific instruments,
but most makers prefer alcohol, because
1t is cheaper. The alcohol is colored
red with al aniline dye which does not
fade.
The thermometer maker buys his glass
tubes in long strips from the glass fac
tories. The glassblower on the premises
cuts these tubes to the proper lengths,
and with his gas jet and 0lowpipe makes
the bulb on the lower end. The bulbs
are then filled with colored alcohol, and
the tubes stand for twenty-four hours.
On the following day another work
man holds each bulb in turn over a gas
jet until the colored fluid, by its expan-
sion, entirely fills the tube. 1t then
goes back into the hands of the glass
blower. He closes the upper end and
turns the tip backward to make the lit
tie glass hook which will help keep the
tub in place in the frame.
MARKING THE TUBES.
The tubes now rest until some hun-
dreds of them, perhaps thousands, are
ready. Then the process of gauging be-
gins. There are no marks whatever on
the tube, and the first guide mark to be
made is the freezing point, 80 dogs.
Fahrenheit. This is found by plunging
the bulbs into melting snow. No other
thermometer is needed for a guide, for
melting snow gives invariably the exact
freezing point. This is an unfailing test
for any thermometer whose accuracy
may be suspected. But melting snow is
not always to be had, and a little ma
chine resembling a sausage grinder is
brought into use. This machine shaves
q block of ice into PARTICLES, which an
swer the purpose as well as snow.
When the bulbs have been long enough
in the melting snow a workman takes
them one by one from their icy bath,
seizing each so that his thumb nail
marks the exact spot to which tho fluid
has fallen. Here he makes a scarcely
perceptible mark upon the glass with a
fine file, and goes on to the next.
The tubes, with the freezing point
marked on each, now go into the hands
of another workman, who plunges them,
bulb down, into a vessel filled with
water kept constantly at "a dogs.
A standard Thermometer attached to
the inside of this vessel shows that the
temperature of the water is. correct.
Another tiny file scratch is put at "a.
Then a third workman plunges the
bulbs into another vessel of water kept
constantly at 96. This is marked
like the others, and the tube is now sup
piled with these guide marks, each
90 dogs. from the next. A small tab
is then attached to each tube, on which
its number is written-for, owing to un-
avoidable variations in the bore of the
tube, each one varies slightly from the
others.
THE CASES.
With its individuality thus established
the tube goes into the hands of a mark