West Virginia Democrat. [volume] (Charles Town, W. Va.) 1885-1890, 1888-06-29

ian THAT is, a certain circle through
the poles, from which distances east
and west are measured ;Sor techni.
cally he changes his latitude and
his longitude.
Changes of the first kind are read
ily measured, because the elevation
of the pole of the heavens increases
while the elevation of the celestial
EQUATOR due south diminishes as the
equator is left and vice versa. The
stars, of course. partake in these
changes. But the sun is the best
object to observe for its determine
ton. His distance from the equa-
tor ON any day throughout the year,
and at any hour, is known. Ifthen,
he be observed at solar noon, when
he is due south and moving parallel
to the horizon, has observed height
at oncelgives the means of deducing
the height of the celestial equator
whence the latitude is determined.
(For whatever the height of the
equator at any place, the latitude of
the place is ninety degrees dimin.
ished by that angular height.
Changes of longitude are by no
maans determined so readily as
changes of latitude. To an observ-
'er in the same latitude in North
America as that of Greenwich in
England, the star skies present abb
solutely the same appearance. The
sun, moon and planets are in slight
ly different positions when southing
or in any other definite directions
with respect to the cardinal points,
simply because they reach these ap-
parent directions some five or six
hours later, by which time they are
in slightly different directions with
regard to the earth. But'the differ
ences thus existing are far too small
to be available for determining lon
gitude at sea, except in the case of
the moon, whose movements are
rapid enough to be measurable fnot
merely recognizable jim short periods
of time. Even in observing the
moon in this way, which is one of
the methods actually employed for
determining the longitude, it is
found that results less satisfactory
are deduced than can be obtained
by the simpler method Of keeping
Greenwich (or other known meridi-
nal time on board ship and asccr-
tanning local time from observations
of the sun. Suppose, for instance "a
captain could ascertain that the sun
was due south when his chronome-
ter showing Greenwich time, point
ed to III. 81 IN. Up. IN. This would
show that solar time ut the ships
place was 5 h. 81 IN. later than
mean solar time at Greenwich. Cor
recting from true solar into mean
solar time from the column "c.ock
before sun" or "clock after sum-" in
the almanac, our captain could,
let us say, correct the difference of
5 h. 81 m. into 5 h. 20 NJ This
would show him that the ships
place was f.3 twenty-fourths of
360 degrees, or 80 degrees west Of
Greenwich.
AS matter of fact, though, it is
not at noon that navigator tries to
determine solar time, though many
ocean travellers imagine that noon
is the time, noting that at that time
ship noon is determined. Ship-noon
is only noon for fixing the watch
es," not for purposes Of navigation.
1t will easily be seen how unsuita-
bic is noon for timing at sea, il it
be remembered that the only avail
able way Of determining when It is
solar noon is by noting when the
sun is atits highest, and as at noon
he is moving parallel to the horizon
at the change of height this time
takes place at the lowest. On land
solar noon can be readily and neat
ly determined by observing when
the sun souths-as by sun dial;
but Mt sea there is no means of de-
termining the South except from the
rough indication of the magnetic
compass. The proper hour for de-
termining solar time at the sea in
order to compare it with frst-merid-
time, is somewhere about nine in
the morning or three in the after
noon, when the suns elevation
changes more quickly than at other
times, so that the observer can read
ilv determine the moment when the
moment when the sun is at a deter
inmate height, or (Which is equally
effectively can readily determine the
height of the sun at a particular
moment. 1t takes two persons to
make the observation properly, one
noting the time the otherwith sex
tant measures the suns elevation
above the horizon. The sextant is
so planned that an observer looking
through telescope at the horizon
below the sun can, by means OF O
reflector. bring the SUMS image in
to the telescopes field of view SO as
lust to touch the horizon. Agrad.
uated arc enables him then to as.
certain what is at the moment the
SUMS elevation ADORE the horizon,
Other objects can in like manner
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