p. 73

53

Log page 17.

"The Equinoctial Line"

Where the days and nights are equal, and the
Latitude of a place is its distance north or south
of the equator reckoned in degrees, minutes and seconds.
As far as 90 degrees either sides, and the Longitude
of a place is the distance East or west from the
Meridian running through [[Greenwich]]. The [[Nautical Almanac]]
gives the position of the sun every day of the year
and by observations, every day at noon from the vessel's
deck, and calculations, her actual position is ascertained.

The following extract will perhaps make the matter
better understood-

"The navigator requires to determine his Latitude
at sea daily. He finds by means of a sextant, the
sun's altitude at the instant it pass the meridian.
From this he deduces his zenith distance. The [[Nautical
Alamanac]] tells him the sun's declination, or distance
from the equator on the day of observation. The
sum or difference of these is his Latitude, according
as the sun and the ship are on the same or different
sides of the equator. Suppose for instance that he
is north of the equator when the Almanac tells him
that the sun's declination is 20o north.

Let him find the Sun's altitude at noon to be- 59o 0 0
He will subtract that from - - - - - - 90o 0 0
Which gives him the zenith distance - - - - - 31o 0 0
He then adds the declination - - - - - - 20o 0 0
And finds his Latitude to be, north - - - - 51o 0 0

It is possible that the 'observation' may require to be made
when the star or sun is north of the zenith. This would be the
case if the vessel were within the Tropics and the sun at
its greatest northern declination of 23 1/2o.

"