Harrisburg telegraph. [volume] (Harrisburg, Pa.) 1879-1948, 1919-03-29
A Delightful
instrument of Science

weather changes, etc, by measuring
the pressure of the atmosphere. 1
wish it were true, for. as "a. w"
says, the aneroid is n delightfully."-
interesting instrument, I know of few
mechanisms that L would rather put
into the hands of intelligent youth
than pocket aneroid barometer.
L commend it to the attention of
those who are puzzled in the sclec-
tion of Christmas or birthday pres
cnts. a bright boy will learn a lot
of science, and learn it so uncon-
sciously and pleasingly that its ac-
QUESTION will seem like play, IL he
carries shaped aneroid in
his pocket.
But as to substituting the anerold
for the standard mercurial barom-
eter. / am very doubtful il 1t can
ever be done. that is, for accurate
observations. For ordinary pur-
poses the substitution was made
long ago. The mercurial barometer
is cumbersome and frail instru-
ment. constantly in danger of be-
ing broken, and requiring many
precautions in its use, while the
aneroid. in its smaller forms, is just
as portable as a watch. Then, too,
it is sufficiectly accurate to be used
by aeronauts, mountain climbers, the
precaution being taken to compare
its indications as frequently as pos
sible with those of a standard mercu-
rial instrument.
1 have carried a watch aneroid"
to the top of the highest Alps and
found that it indicated the eleva-
tions accurately enough for ordi-
nary information. A similar in
of
to indicate changes of a few feet
will most interestingly show. by
the movements of its needle, the
floors in an office building or a
house.
l have thus measured the depths
of caves and of complicated cavi-
ties, formerly the cisterns of active
geysers, or boiling springs. in the
Yellowstone National Park. Few
things can add more to the interest
and profit of a country vacation. es-
pecially in a hilly or mountainous
region, than the possession of a small
aneroid. AS to reading the coming
weather changes on its face, that is
not so simple, because the relations
of the atmospheric pressure to the
local weather are not always clear
Nevertheless. with practice, much
may be learned in this respect from
the indications of an aneroid. For
that purpose a "clock aneroid" is
preferable to a smaller instrument.
In the form of the "weather-glass"
this instrument is commonly used on
ships.
But it is as an instrument of
popular education that the aneroid
barometer ought to be better known
and more widely distributed. Its con-
struction in itself is full of informa-
tion not generally comprehended.
Who ever thinks of the almost con-
tinuous changes in the pressure of
the air. which play like the touches
of fingers upon our bodies? These
changes are sometimes concerned in
the torments of neualgic pains, al
though the sufferers may never ina
gine where the enemy is concealed.
We are weighed by q mass of air
many miles in height, gradually thin
ming above and becoming denser be-
low, and the total average pressure
of the air at the bottom, /. e., at
the earth's surface, is sufficient to
push a column of mercury to a height
of about thirty inches in a vertical
tube from which the air has been
exhausted. Such n tube constitutes
q mercurical barometer.
The average air pressure, which
keeps the mercury at height of
thirty inches, amounts to about
fifteen pounds per square inch on
all surfaces exposed to 1t. But
even at sea-level, the pressure of
the air, owing to alterations of
temperature, moisture, etc, may be-
come so diminished that the mercury
will rise only 27 or % inches, and
then the force of compression on
our bodies falls to ii or 1914 pounds
per square inch, and the nerves may
become aware of it, just as they
may when the pressure rises SO that
the mercury goes up to 80 or 33
inches, increasing the compression
per square inch to 1874 or IL pounds.
In a general way low atmospheric
pressure accompanies stormy wealth
er, and high pressure fair weather.
So, in a sense, the weather follows
the barometer IS the tides follow the
moon.
But, If you rise above the sea
level the mercury descends just as
it would have done If an area of
low pressure had come over 1t while
it was at sea level. but in this case
there are no attendant weather
changes. For ordinary, rough meas
urement it may be said that the
barometer. falls one inch for each
900 feet of ascent, in climbing a
mountain, after you have got up a
few thousand feet you may become
partially deaf owing to the difference
in pressure on the two sides of your
ear drums. They are swelled out by
the denser air within. The aneroid
barometer, instead of carrying a long
tube of mercury, is furnished with a
little metallic box made with very
thin elastic sides, and then perma-
nently exhausted of air.
The changing pressure on the out
side of the box easily causes the sides
to sink in or swell out, and this
slight motion is magnified by ingen-
ious levers, and then transferred to
a needle. or hand, moving around
to a graduated dial, which shows
just how much the pressure has in
creased or decreased.
CITIZEN TNO RETURN