Evening star. [volume] (Washington, D.C.) 1854-1972, 1881-04-25

Hol cOnCdlne0 IN the ordinary glass tube and
DulD. In the fluid Is q small glass index, which,
by fnclining the instrument, is brought I'D to
the end OF the fluid column. When the instru-
ment Is hung in horizontal position, and when
umn during its retraction carries the glass In.
dex With 1t and leaves 1t at the point which IN
dfcates che minimum temperature reached dur
Ing the period OF exposure. The maximum
registering thermometer IL a tube with a COR
traction near the bulb which allows the mer-
curry, with which It Is filled, to pass up With
SUFFICIENT freedom TO the greatest degree OF
heat, and when it recedes, the attraction Of CO.
hesion is not sufficient to overcome the stric-
lures In the tube The upper end of the column
above the construction marks the highest tenn
perature reached during the period of exposure.
To readjust this instrument the mercury Is sent
into the vacant space below the construction by
centrifugal force. The ''six's registering Their
mometer"i Is
MAXIMUM AND MINIMUM
instrument combined, and iJ il filled WITH both
spirits OF wine and mercury. The tube Is
U.shaped, so that two columns are presented
for marking the temperature. These two col
umns are partially filled with mercury. which
is brought into Intimate contact with the sur
face OF the spirit. AT either end OF the mercu-
rial column are small steel tndiceS inca 5ed in
glass, upon which is affixed a delicate spring OF
sufficient tension to keep each index IN Its place.
out not Offering sufficient resistance to It's being
readily adjusted by magnet. IL viii be apaar-
emit that when the spirit contracts, one END OF
the column of mercury moves up, Carrying the
index on one side Of the minimum temperature,
and when It expands the index In the other Is
carried In like manner to the maximum temper
allure.
Very few thermometers are positively accu-
rate, since no instrument made by man Is per-
feet, but good Instruments can be obtained II
Judgment Is used. Thermometers of q good
class can be obtained at prices ranging from
1925 to 500; but II one pays but 25, so or Is
cents he must not expect to get reliable in
strument.
BARoMETKRs.
BY means OF the barometer we are enabled to
estimate the pressure OF the atmosphere with
the same precision as IL we were actually
weighing 1t, and yet we can see nothing OF
what Is going on In the superior regions Of the
air: Placed upon the surface OF the earth one
feels the winds and hurricanes and distin-
cuisines those motions that are made evident
by the passage OF clouds at their ordinary ele.
walton, and no more. With the assistance OF
the barometer, however, and from the prOserty
which that instrument possesses of marking at
all times the weight OF The column OF air which
1t counterbalances, one can become aware OF
the changes in the whole OF the aerial ocean at
once. IL Ia easy to understand from this Cir
cumstance that the barometer will not remain
stationary for whole year, lor whole month,
or even for whole day. In every place. &C
barometer oseiliates between two two D po, f
above and below certain mean eleva-
ton. which Is peculiar to that place. though
sometimes, and apparently from a gen
suddenly depressed below, and at other
times suddenly forced above this mean point
IL has been found that Ia the ordinary condition
OF the atmosphere the barometer rises and falls
twice during twenty-fOur hours. The period
OF these regular changes, called the hourly or
diurnal variations OF the barometer occur at
stated hours, and the amplitudes OF the oscilla-
tons are very much the same In each given
. spot. Variations OF this kind are thus very
readily distinguished from the accidental va
riatlons, which are Irregular In their appear
seen.
The barometer was Invented by Torricelu
about the year 1913. but IL was many years
before It was applied to meteorological pur-
poses. Pascal and Perier, some time about the
year 165S, entered into the new and extensive
field OF inquiry that was opened by the expert.
ments OF Torricelli, and the world Is indebted
70 10th OF them as well as to TorricelH. For
more than two centuries the ingenuity Of
scientific men has been taxed to the utmost in
improving the construction of the barometer
have been contrived, those most approved TO-
day are but slightly varied from the straight,
inverted tube OF TOrr1celli, while mercury, the
liquid selected by him, is stu preferred to all
others, as the required weight OF 1t occupies but
little space, while 1t is not liable to be voiatil-
lied by slight elevations Of temperature, and
thus I'LL with its vapor the vacant space at the
top OF the tube. Particular attention Is required
In filling tube With mercury chemically pure.
The manner OF introducing it Is similar to that
employed In filling the tubes of Thermometers,
ana, indeed, there Is similarity between the
entire method OF manufacture so that 1t is not
necessary to repeat 1t In detail. When the
liquid rises and falls In the TUBE the level of
that In the bulb Or cistern must change. and
thus the absolute height OF the mercury is
asceTtained by rendering
THE SCALE MOVABLE,
and bringing its zero point always to the sur
face OF the mercury In the cistern; or by max
Ing the scale fixed and bringing the mercury to
its zero point by means OF a screw, which Is
made to press against flexible Dag that forms
the lower part OF the cylinder. A Sliding YER
nier enables the scale to be read to the 1,0oOth
OF an inch, and as yet no substitutes have been
found for these minute divisions and vernier
readings. common barometer has an index
which turns round upon a dial and points TO
figures which indicate the height OF the mer-
curry, and also points to the word descriptive OF
the weather, such as 'rainy." CLOUDY" "fair. I"
etc. Among the uninstructed however, an
erroneous impression prevails concerning the
barometer, conVeyed by the words on the dial
The Instrument does not designate By the aD-
solute height OF the mercury, but by its rising
or falling, the kind OF weather that Is to be
expected, and the index does not indicate q
change.
The barometer, like the thermometer, Is not
aperfect instrument, and, however well con-
structed and filled, is liable to vary after years
OF use by partial oxidation OF the mercury,
producing thin film, which attaches itself to,
and obscures, the inner surface of the tube, and
which can be removed only by cleaning and re-
filling with fresh mercury. After long usage
ar ar Is Liable s to creep In between the mercury
vacuum, producing In the best instruments
effects that are only perceived after q series of
years. Instruments used for long period show
less height In the latter part Of the period.
While little reliance can be placed upon the
barometer as indicating by any single obserVa-
ton the condition OF the weather, It's fiuctua-
tions caused by atmospheric pressure may
when carefully noticed, often serve to foreteli
the effects that must still ensue.
For instance, sudden and long. continued
fall Is sure sign OF an impending storm. The
barometer Is much valued In navigation, and
many instances are recorded OF vessels being
saved by the precautions taken In consequence
OF the warning OF the barometer at the 1mme-
date approach OF hurricanes, OF which no other
notice was given. Barometers are manufac.
tured at most establishments where good and
reliable thermometers are turned OUT. The ba.
roneter lot being an article in so universal
use, there are Rot so many inferior instruments
In the market Sc there are poor thermometers.
Mercury, the m6tGl that Is Indispensable In the
manufacture OF meteorological Instruments
was formerly obtained from Europe, but now
the bulk Of It comes from California Out of a
total consumption OF 1853 ,120 pounds in one
year, $4,000 pounds came from the land OF
gold.
Wedding FASHIONS.
! have never met, and never expect to meet.
the woman who can hear of wedding quite
unmOved. 1t Is rite that interests the whole
sex, young and old, pretty and plain, rich and
poor, gentle and simple. No matter how many
WpddfYSg they NAV have aeon. they never etra