The Universalist. [volume] (Chicago [Ill.]) 1884-1897, 1888-09-01
NAVIGATING THE MAIN.

To determine true time, the seaman
selects, not noon, as Is commonly sup
posed, but time when the sun is near
ly due east or due west. For, just as the
minute-hsnd of clock changes more
rapidly in height when it is near Ill
and TX. than when it is near XII, the
SUMS elevation or depression changes
most rapidly when nearly due east or
due west, and so gives the surest means of
determining the time. But the noon OBJ
servation would be- wanted to complete
the determination of the longitude, for,
until the latitude was known, the cap
tain would not be aware what apparent
path the sun was describing in the
heavens, and therefore would not know
the time corresponding to any solar OBJ
servation. The reader can now see that
the great point in finding the longitude
is to have the true time of some ref
erence station, in order that, by compar.
ing this time with ship time, the longi-
tude east or west of the reference station
may be ascertsined. Ship time can al
ways be determined by a morning or
afternoon observation Of the sun, or by
observing known star when toward the
east or west, at which time the diurnal
motion raises or depresses it most rapid
ly. The latitude being known, the time
of any given day at which the sun or
star should have any particular altitude
is known also; and therefore, conversely
when the altitude of the sun or a star has
been noted, the seaman has learned the
time of day. But to find Washington or
Greenwich time is another matter; and
without this reference time, ship time
teaches nothing as to the longitude. How,
then, is the voyager at sea or in desert
places to know the exact time at some
fixed station? Most readers know that
chronometers are used, under ordinary
conditions, for this purpose; but in long
voyages, even the best chronometers are
liable to go astray, from the continual
tossing and shaking to which they are
subjected, but especially from the great
charges of temperature which they en-
dure when ship passes from the tenn
perate ATTITUDES across the torrid zone
to the temperate zone again. And then
it is to be noted that very insight
ficsnt time error corresponds to differ
ence of longitude quite sufficient to
aonaai0v n oario11a amor in, the chiF1,.s
mated position. For this reason it is de-
sirsble to have some means of determin-
ing the time at fixed station indie pend
emily of chronometers. Any signal which
is recognizable, in whatever way, at both
stations-the reference station and the
station whose longitude is reauired-will
suffice to convey the time of one station
to the other. Evidently the only signals
available, when telegrsphic communics.
ton is impossible, are signals in the &C.
lestial spaces, for these alone can be dis
cerned simultaneously from widely dis
tant parts of the earth.
We know that all the planets, as well as
the sun and moon, traverse at various
rates and in different paths the sphere OF
the fixed stars. But the moon alone
moves with sufficient rspidity to act as
time indicator for terrestrial voyagers,
She completes the circuit OF the celestial
sphere in twenty-seven and one-third
days so that in one day she traverses
about thirteen degrees or her own diam
eter in about an hour. She thus acts as the
minute hand, SO to speak, of the celestial
clock; and as her rapid motion can be de
tected in a few seconds by telescope
comparison of the moons place with that
of some fixed star, it serves to show the