| Transcript |
- LEFT PAGE
208 Latitude & [and] Longitude
presently to occupy the place which
its Easterly neighbor had before
occupied; while this last place
has gone further East yet.
Let us suppose that an hour is
the time required to carry a
westerly station to the position
which had been occupied by a
station to the East of it. Then
plainly every celestial phenomenon
depending on the Earths turning
will occur an hour later at the
westerly station. Sunrise and
Sunset are phenomenon of this
Kind. If I telegraph to a
friend at some station, far to
the west, but in the same latitude
"the sun is rising here" and he
finds that he has to wait Exactly
an hour before the sun rises there,
then he knows he is one hour
west of me, in longitude. As
thier are 24 hours in a day
while a complete circle running
through my station and his
is supposed to be divided into
360 degrees, he is 15 degrees,
that is a 24th part of a day
west of me, and if my station
is Washington, he is what we in
America call 15 degrees West
longitude
But what is true of
sunrise and sunset in the same
latitude but in differant
longitudes, is true of noon
whatever the latitude may be
only unfortunately one cannot
tell the Exact instant when the
sun is due South or at its
RIGHT PAGE
Latitude & [and] Longitude 209
highest above the horizon. Every
one wh makes a long sea voyage
must have noticed the importance
attached to noon observations;
and many are lead to suppose
that these observations are directly
intended for the determination of
the longitude, or which in Effect
is the same thing, for determining
true ships time. This however
is a mistake. A rough approxamation
to the local time can be
obtained, by noting when the
sun begins to dip after reaching
the highest point of his course
above the horizon. A determination
of time effected in this way
serves very well for the "ships
watches" and accordingly when
the sun, so observed, begins to
dip, they strike 8 Bells and
make it noon. But it would
be a serious matter for the
crew if that was made the
noon, for working the ships
place, for an Error of many
miles would be inevitable.
To determine true
time therefor, the seaman selects
non noon, as is commonly supposed,
but a time when the sun is nearly
due west or due East. For just
as the movements of a clock changes
more rapidly in height when it
near III [three] or IX [nine] than when it is
near tewlve, the suns elevation
or depression, changes most rapidly
when due East or due west, and
so gives the surest means of
determining the time. But
|
|---|
