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206 Latitude & [and] Longitude
into ninety Equal parts, Each
of which is a degree. Longitude
is the distance East or West of
Greenwich in English maps, of
Washington in American usage,
but other nations Employ a
differant starting point for
measuring longitude from. Longitude
too, is measured in degrees, and
a place which is half round the
world from the starting point is,
as Every school boy should Know,
Exactly 180 degrees East or West
of this point, as the case may be.
Now it is Easy Enough for a
sea captain, in fine weather, to
determine his latitude. This can
be done in several ways, but
commonly the seaman trusts to
observation of the sun at noon,
when the sun is highest above
the horizon. The actual height is
determined by means of the
instrument called the sextant,
which is so devised thtat the
observer can see two objects at
once; one directly and the other
after reflection of its light, and
the amount by which he has to
move a certain bar carrying the
reflecting instrument, in order
to bring the two objects into
view in the same direction,
shows him the real divergement
of lines drawn from his eye to
the two objects. To take the
suns altitude then with this
instrument, the observer takes
the sun as one object, and the
horizon directly below the sun,
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Longitude & [and] Latitude 207
as the other; he brings them into
view together, and then looking
at the sextant, to see how much
he has had to move the swinging
arm which carries the reflecting
glasses, he learns how high the
sun is This being done at noon,
with proper arrangements to
insure that the greatest height
then reached by the sun is observed
at once indicates the latitude
of the observer. Suppose for
Example he finds the sun to be
forty degrees above the horizon
and the Nautical Almanac tells
him that, at the time, the sun
is ten degrees north of the celestial
Equator, then he Knows that the
celestial Equator is thirty degrees
above the southern horizon. The
pole of the heavens is therefore
sixty degrees above the Northern
horizon and the voyager is in 60
degrees North latitude.
The longitude
or distance East or West from some
fixed station, is not so Easily
determined. But we Know that
the Earch, by turning round on
her axis, causes the changes which
we call day and night, and
therefor these must happen at differant
times, in places set differant distances
round. For Example, it if [inserted] is clear
that if [inserted] it is noon at one station,
it must be midnight at a station
half way round from the former.
The Earth too, turns from West to
East, that is, a place lying due
west of another, is so carried as
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