Clarke courier. [volume] (Berryville, Va.) 1869-1997, 1907-06-12
READING THE GLASS,
Use and Construction Of the Mer-
curiaI Barometer.
ITS VALUE ON BOARD SHIP.


The Significance of Fall of the Glass
Varies Considerably According to
Latitude -Fiuetuatsc of the Ba-
rometer In the Tropics.
How's the glassg This Is question
which is asked daily by thousands OF
people all over the world and frequent
ly for very trivial reasons. To the
navigator the fluctuations OF the Ia
rometer are always OF interest and not
infrequenly OF greaTmoment. Hence
( Il is customary I'm the navy TO record
/ the reading at least every four hours
and in stormy weather at much shorter
intervals. The style of barometer
which is supplied for use in the navy
is that known TO makers and T. = sicisls
as the "ciStern" barometer. Ii consists
of a glass tube about thirty-tbcee
inches in length and about one-third
inch internal diameter.
Any one who has seen a barometer
OF this type is aware that the glass
! tube contains a column of mercury
reaching within short distance OF the
top. b1t 1t is not as plainly apparent TO
the ordinary and uninStructed observer
! why this tall and narrow column thus
remains in the tube The two condi-
I tons essential to the construction of
Il mercurial barometer are, first. that
/ there shall be as perfect a vacuum rs
/ possible in the upper end OF the tube.
which is closed, and, secondly. that the
lower end. which is open. shall be kept
immersed in basin or cistern Of mer-
( curry.
These ends are accomplished in a
: simples fashion. first discovered by an
Italian scientist named .Torricelli. as
1 far back as the year 1913 The tube Is
+ held perpendicular. with the closed end
( downward, and mercury is poured in
i until il is quite full. Then the finger is
/ placed over the opening and the tube
/ IS turned over, end for end: the open
/ end is immersed in ciStern Of mer-
curry. and the finger or stopper Is re-
moved. The mercury then sinks a
\ short distance in the tube. leaving a
( space at the to9 which must obviously
be completely devoid of air. The pres
sure which the atmosphere exerts upon
+ the surface Of the mc~cury in the els
I tern maintains tho cc'-..,a I'm the tube
and any variations ia t,se air pressure.
will be acc0mrInicl rs 4 correspond
I ing rise or fail OF the mercury i'm the
f. tube.
The cistern must. OF course. be OF the
smallest dimensions possible Or the in.
strumeut would be too clur,sy. IN the
marine baroretC, IL consists OF cun
! about one anI olc-half inches In di.
ameter Tho noec- -Nry limitation OF
I the cistern causss ca.'t IN irregularities.
! which, howcve-, q no, practically af-
/ feet the eifiCicacr OF the instrument as
/ weather glGs; and in barometers
which are designed for more accurate
readings the difficulty is overcome by
an ingenious device which there Is not
/ space TO describe here.
1t shoull be no.ef that mercury is
used In the construction OF harometcrs
simply because :. i by Ear the lseavicst
OF liquids. = barometer can be made
equally we'll. for Instance. with water.
but this woull ca;ail having tube
nearly forty feet 81 len..l. Tor when
the mercury stan.,s n thirty inches the
water barometc~ VII stand - about
I thirty-four feet, cs,.,brous sccs OF in
strument for the navigator 20 carry
/ about with h;.N.
The glass tuhc s-l viS;cru thcs c.
bined are attac'ia 80 - Woo ,ea me-,
ing or place. "a q .1 ,lsc. w.tl
openings TO sloy' TIE go i.,rt o. ga.
tube. ana on l'i,. cas- "a SCI .lc Is CIT
showing inchss :~t ,eat>s aal .h,rn-
dredths OF an Inch, e.. ~ niartiag a
more 3ccu~atc g -c-.. .so.n a,l.~g
faA 49, t.ts q q.
Of an Inch. Rs-s.,ete7s are usually
scaled from tyven;y--cvca to thirS-one
inches. This lciH., !hc prae,ical Emit Of
the fluctuations DAG 10 weather. ana,
indeed. when the giasi gets down to
twenty-eight inches It is time to look
about you.
The Significance OF fall of the ba-
| rometer, however. varies considerabl
! according TO the latitude In Great
Britain. says writer In the Navy
and Army. it has fallen perhaps half
an inch or more during the night, and
yet there may be no very alarming
gale Of wind. but such n fall in the
tropics would be the signal for the
navigator to prepare for 4 cyclone, the
fluctuations of the glass in these lati-
tudes being usually confined to slight
and regular rise and fall az certain
hours. In q recent cyclone In Japan
the fall during one hour was three
tenths and the rise during the next
hour no less than six-tenths, or more
than half an inch.
1t Is indeed with regard &c these
terrific storms that the barometer Is
of the utmcst service to the navigator
The behavior Of the glass, in conianc-
ton with the shifting ~ the wind. win
Indicate to the cSne-ienccd seaman the
position CT the dreaded vortex and the
approximate cour~e upon which the
storm IS travelling
A Fi-eeo-
The nhi.n ~. -, l-,..,tAsnt fn-..r l,,.il.