Memphis daily appeal. [volume] (Memphis, Tenn.) 1847-1886, 1870-07-18
THE RARoMETER.
What Il Is and How to Use lt.--Rules for
ForsteIllng the Weather.

A lady correspondent writes us as fol-
lows; '"Whst do you mean when you say
that the barometer stands at so many
taehesS / always thought that the bar
ometer and Thermometer were marked by
degreesP" Thermometers, being con-
structed on the principle Of the expansion
Of metals or fluids by heat. are marked
by degrees, but barometers being con-
structed on a totally different principle,
viz: the pressure of the atmosphere, are
marked by inches and fractions Of inches,
the marks showing the height to which a
column of mercury Tor other fiuid) Is
forced In an exhausted tube by b pres
sure of the atmosphere. There are sew
eral barometers in use, but nearly,
if not all of them are made on the
principle first discovered by TorFiceIli,
a pupil of Calico, who first began the
experiments which led to the solution Of
the vexed question why water would not
raise in a vacuum over thirty-twO feet.
Torricslli, in pursuance of Galileo's dis
coveries, made the famous experiment
which has gone after his name, and was
the immediate precursor OF the mercury
barometer as now known to Us. The in
strument in general use is the syphon
barometer of Gay Lussac, improved by
Bunten-the name syphon being APP
piled to all barometers of which the
lower End is turned up to form
a short arm, which constitutes a
~cistern, and may be left open for the air
to press directly upon the mercury.
Those used mostly at sea are made by
Carry, of london. But little reliance can
be placed upon the barometer, as indicat-
ing at any single observation the condi-
ton of the weather, and it requires a
careful notation Of fluctuations, and the
weather at the time 70 be able with any
accuracy to foretell the effects which must
ensue. Without making this reply" too
long, we cannot explain the various
causes which produce ~insccuraey. The
best rules for prognostieatiDg tbs weather
from the barometer are those quoted by
DR.. Brande, from the Saturday Magazine,
which are as follows:
First-After a continuance Of dry
weather, If the barometer continues 30
fall slowly and steadily, rain will GER
tainly ensue. But if the dry spell has
been of long duration the mercury may
fall two or three days before any per-
ceptible change takes place, and the
longer the time hat elapses before rain
does fall, the longer the wet weather is
likely to continue.
Second-ConverseIy, if after a great
deal of wet weather, the barometer be-
gin to rise, fine weather may be expected
though two or three days may elapse be-
fore the "elear up"
Third-On either of the two foregoing
suggestions, if the change immediately
ensues the motion of the mercury, the
change will not be permanent.
Fourth-If. the barometer rise slowly
and steadily for two days OF more, fine
weather will come, though those two
days it should rain necessarily, and rice
versa.
Fifth-If the barometer rise for two
DAYS or more during rain and then on the
appearance of fine weather again begins
to fall, the fine weather be transient,
and Uice UerSG.
Sixth-A sudden fall of the barometer
in the spring or autumn Indicates wind;
in the summer during very hot weather,
a thunder storm may be expected; in
winter a sudden fall after a frost of any
continuance indicates a change of wind,
with thaW and rain; in a continued frost
a rise of the mercury indicates snow
Seventh-No rapid fluctuations Of the
barometer are to be interpreted as indi-
eating either wet or dry weather of any
continuance; it is only the slow, steady,
continued rise or fall that needs to be at
tended to in this respect.
Eighth-A rise in the mercury late in
the autumn. after q long continuance of
wet and windy weather, generally indi-
Gates a change of wind to h northern
and the approach of frost.
After all, however, no general set of
rules can have a general application.
Each region or place has its own peculiar
atmospheric conditions, which can only
be learned by continued observations, and
not until they are learned, can the varia-
lions of the barometer be Observed with
any degree of confidence.
The other kinds of barometer in use,
besides the mercury N to which we
have alluded, are, the "AnerOid " and
the +" Freezing and Boiling Point" Their
The former is in very extern
sive use among b~alloOnists, travellers and
The latter is used in measuring
the hight of mountains, etc, and almost
altogether by scientific men.