New-York tribune., 1841-12-27

,..d, fon,d we shall obviously have the le"s'',
fro,, the ships zenith To The ceiesuai
e,,.,or But this Is concentric win 'iI SUI
90 of the Earth and BY knowing Its length We
Inv the number of degrees on A meridian between
| rho hin and the equator-whlch Is "hat we were
licking for-namey, its latitadc
Rnf his is not sufficient 10 determine the stnps
,s.ition; 70. it NAY be any where around the globe,
40 only the same distance from the equator be pre-
served In ORDER then, To determine it, position,
its longitude must also be known, by which we
mean its distance from the meridian Of any given
place the globe. If we suppose circle Of the
Earth to pass through the pole and any given
place, as for instance Newly ork, and another
through the pole and the place whose longitude
wish to hnd, the question really Is what u the
angle made the pole by these twe circles. Ihls
IS theoretically easily measured than the lsti-
Jude: for the Earth revolving lis axis through
circle of 800" in "a hours any place on its surface
Of course passes through 10 in single hour. Ii
,hen when it is l. clock AT New-l ork, We know
that it is at tue place whose longitude wish
to find, we know that there must be distance OF
l5C between the TWO meridlans--or the longitude
OF the place is l. if when 1t * II O'Clock at
New ork we know that il Is > O'Clock the other
gwen place, we Of course know that the longitude
u 30 sc. Thus if, when it Is : O'Clock at New
!
fidian OF London, we know that the Earth has
moved through seven hours Of time at the rate OF
| IS each hour seven times - then Will give us
the longitude of the place compared with the
other. The difference OF longitude then, is always
| known when we know what O'Clock it is at the
Two places whose longitude wish to determine.
| Ii i, be one clock Paris when II istwO at Dub
in We know AT once that the difference in ongi-
/ .ude is lj-; if when it Is Pan. il be five
o'clock at any other place. the difference of ongi-
! Jude is at once known TO be 60. These are astro-
aornical elements taught at school, and therefore |
take it for granted, familiar to you all.
! We sec, then, that this problem, famous for
us difficulty, resolves Itself to this 10 find what
clock it is, at the morcnt both At the place
whose longitude YOU wish to determine, and at that
from which it is to be reckoned As most books
refer to London or Greenwich us the meridian from
which the longitude is To be recksned shall as
sumo that as the starting point. Now suppose
snip at sea- lar from land the mariner wishes 10
determine his longitude, and, in order to it, there
arc things TO be known-lsl, what o'clock il
at his own pent aud ID, what Is the time
| Greenwich Now, hew are these two things To be
| discovered 1t is always easy by accurate
! chronometer. to determine the first point; since
the time may always be ascerIained when the sun
on the meridian, and these observations may be
repeated sufficiently often to keep the chronometcr
accurate. If there be no chronometer at hand
va'ious observations may be rcsorted to by which
the time may be determined; that the FIRST OF
the TWO things necessary to he knowR may readily
| be asccrtained. But tho grand difficulty is still
behind namely, to determine the time, at the same
moment at the meridian of Greenwich. You
would say at FIRST that nothing il more easy; fof
#, when tho mariner leaves Greenwich, he takes
with him good chronometer, properly set, md il
It be carried with suitable precaution against acct
dents and disturbing influences, he may always tell
! the time ut Greenwich. So he might if so perfect
chronomcter could be obtained, and if 1t neither
| gained nor lost any time on It's passage There
would then be difficulty in determining the time
and in solving the question of the longitude. But
is found that all chronometers are liable TO acct
Dent and that they will not go for any great length
Of time without varying much as, in such deli
cate calculations, seriously to affect the result. To
,cmedy this Two three chronometers have been
iaken, that if should fail, another might
serve in its stead and for long while the British
Government offered large rewards for the consIruc.
zion OF chronomeiers so perfect as to determine &C.
curately the longitude. But it at length became
apparent that all such cxpedlents, however per
feet they might be as works of art, were after ali
only expedients, and that the best of ,hsm was
liable To failure.
At length astronomers bethousht themselves
whether IA ctronometer might not be obtained
made by the hands ai Him who could not err. of II
mechanism 50 exact that it should never gain or
lose, Il clock which never required TO be wound
up, and was not liable to accident. clock wa.
found, on the face of which hands were placed that
could never err that clock was the iirmarnent-
the hands, whose motions ON Its face only required
The powers of the inIcllec; TO interpret them, are
the Sun and Moon. All that is necessary is to put
INTO thu hands of navlgatsrs ar instrument which
shall enable them TO determine accurately their
positions.
In the common clock there is a ,lial, upon the
face Of which are cut ecrtain fixed marks called
Rosr marks, which remain permanent aud mmoye
able. Over these marks travel the bands and by
observing their motions the time is readily known.
Now suppose that, instead of these regular marks
upon the dial there we're spread other fixed marks,
less regular Ia their arrangement and less easily
understood han the marks o; common clock
but whase position may still be understood and
from WHICH say that, If their position be
this that, the time will be thus or so. Now,
upon the face o the armament, the stars are these
hNed marks and the Moon is the hand which con-
unually changes It's position with regard to them.
The relative positions OF these stars are perfectly
known, and every change of place among them OF
the Moon can be marked and distinctly under
stood. This Is called the Lpner Method ef deter
mining the longitude, and a, the present day ii is
the one in common use. Mariners are provided
with Nautical Almanac. in which are registered
the various change. OF the Moons position; in
shat 1t is stated that when the Moon in certain
positions with respect 10 certain well known fixed
stars, the time is 81 and 80 at Greenwich and this
calculated and LAID down for certain short inter
.al, OF time. When 1t is | o'clock at Greenwich.
the Moon : many degrees from certain fxed
star &c. When the longitude Is to be obtained,
the distance OF the Moon from several conspicuous