, 1869-03-06

eltnef pole, measured In deg rees and paris n
degrees. Is called Latitude,
tae Latltude OF any place Is found yer
easily By the the aid Of a eextxnt. The a.,
Is known 70 be vertical to the Equator tvic
each year (March Goth and September ., :,
@nu nA angular departure from the yertica
possslon Tor any Instant Of time Is calculated
oy astronomers and published In thu alma
aaes: H. then. at noon on the day when th,
euo Is vertical to the Fquator, an obseryc
measure With his se1taut the angle besEer,
Tue sun and the horizon, that aucfe IA cxact
y equal to the distance OF the place OF oh
se1Vatton from the pole, and the angle sub
tfneted from 90 degrees will give the L,tI
tude. For any. Other day, the distance of III,
sun from the Equator, as ctreu Ia the nj
mahac. being added to, or subtrac,cd from
the difference. the sum or difference viii h,
equai 10 the Latitude.
The Longitude Of place Is the Angular dis
tahce cast or west from auy other place sc
'ected as the standard; The dis s,Aucc is meas.
ucd on the Equator, or parallel 10 that cir.
cle. II VIC SUPPOSE q great circle of the
sphere to pass through any place, aud also
through both poles. that circle Is the uerid-
ian OF the place. The difT.r-nce Of luu itnde
OF any two places NAV, therefore, be other
wise indicated a. the distance batxecn tbc
two meridians Of those places.
In England the Observat TT at Green xIrh
Is The place chosen ns that fran which the
longitude Of other place. I. reck yu.d. In
Inc untscd States, the Washington ub,ervato
~ Is nst.ly understood as being on the Ora:
lht 1'efion efthe Earth brings every part
ol ihe Equatorial circle under the Sun onca
caca daT' The 500 drssccs RI the circle are
mus DROUGHT round tI twenty.fouf hours. or
10 ocff fees per hour each degree, therefore.
occupying four miruscs OF time tn pa .siur
otder the Sun. That Is, there Ia a dlae1c zee
ol fcuf mil utcs In the actual tiue O. noon
between two places which differ one deerse
In Longitude.
Inc process Ct hcding thr Longitude Is also
very simple In theory, consl- thug ouls In flat-
lrg tho difference In the tune ofnoon b:twsco
Two mertdiaps. In practice, however, It Is
complicated operation, the tcadi1e t1oi.
Guilty tnct with lying in the fact taat Ii Is in.
possible 10 construct u time. piece which can
be depend. On to preserve exactly the same
''rase Of Eotnef white being carried from ono
place 10 Auotner.
Hence Fome other plan than that o. trans.
porting clocks has necessarily to b. rrsor,.d
to. The one most in use Is tho observa,,,,
o. tht ceInses Of fJupi.ct's uoons.
4ne SATELLITES Of Jupiter revo!se nronnd him
10 o1olts but little Inclined to the rlane Of
Inc tci'ptIc Hence they pass before md be-
n'ho the pla' ct, at esch revolution. The
s!mes at "hich these satellites appear to he In
eontaes with the edge Of the planet, being
calculated fer the meridian OF Grecnwieb. an
oostfEa'tcn at any her place will give tho
olHe1tnce OF time between the two plarcs.
Thus: The first satellite emerged from The
ooay OF the pla: It al hours 81 minutes I,
seconds past midnight At Greenwich on tho
morning OF March 4th, 1860. II 1t had bern
possible TO view the cmersion at Cbica,o. il
would have been fDuad 10 tuke place ut II
bours aud 10 seconds past uuo. on the Sd in-
SLANT showing that Chicago Is s hour, 10
minutes ~ seconds, or 81 degrees IS min.
utes, westot Greenwich.
These observations Involve the necessity Of
also dudiuE the instant when The sun c,o.~cs
the meridian Of the place uhoso LONGITUDE, !.
to be a<certaIncd, and the Opportunity Of
doing this may not OCCUR for several days
beiore or alter the observation OF the s,,t1.
li'c, owing to cloudy weather. During thu
lime the clock may vary several sccopds
from the true rate ol going, aud the Lonr,
tude, a. ccdueed by this process, will b 10
that ext. nj erroneous.
hincc the Introduction OF the clecttlc.,clc.
graph, the "wiscs" have been cx,custvcir
emp'oycd In comparing the time a, different
places. The passage oI the electric luld oyrr
the Wires Is practically Instantaue Jus, being
about 1000 mtles per second, 60 that all r.
qulEed ID good apparatus for observing and
comparing. The following Will give an idea
Of the process:
Cambridge Observatory Il selected a, the
point the Longitude OF which Is known, ard
san Ffarciseo is tho plac.tl Lor gitudc Of
Which ts to he determined. TIE TWO places
are CONNECTED ly telegraph, and comoar, On
made between the clocks Of the two 4,aiiors
BY striking the alcn.l key Al san Francisco
esnultsoe ously wt'h the beats o! the clock
there, the scas being recorded on register,
which record niso, the tn.tants ot tho Cam-
bridge clock beats. TIC clocks arc thus
compared, 10 small fraction OF u second
the current L ttel turred the other way, aud
the Cambrtdre clock beats arc recorded on a
register At Ban Francisco. A comparison o,
the two sets Of obs rvatlons will enable th-
operators to correct any difference due to
time lost in the tr2:sE,ssfop OF the sierals.
The clocks being thus compared, a number
Of stars. previously sslecsed, ase observed ut
each rlaee. The instant that tic etar crosses
the spider thread drawn acro,s
lhe Cambrldke telescope ia mark the line OF
drc south. Is recorded on the registers It
both tnds Of The line, and when A, lew hours
Afterwards, tee same star is eccn to cross the
meridian pt Fan Frunet>r,, h. ,n.+.,+ :. -