d that the G.M.T. corresponding to
the time at which we measured the meridian altitude of the sun shows the
sun's declination to be 10 deg. N. Well, if you are 30 deg. North of the sun,
and the sun is 10 deg. North of the equator, you must be 40 deg. North of the
equator or in latitude 40 deg. N. For that is all latitude is, namely, the
distance in degrees, minutes and seconds you are due North or South of
the equator. That is the first and simplest case.

Another case is when you are somewhere in North latitude and the sun's
declination is South. Then the situation would, roughly, look like this:

[Illustration: BC = Altitude of the sun, AB = Zenith Distance and DB =
Sun's Declination.]

In this case, your distance North of the equator AD would be your zenith
distance AB minus the sun's declination DB. This diagram is not strictly
correct, for the observer's position on the earth 0 appears to be South
of the equator instead of North of the equator. That is because the
diagram is on a flat piece of paper instead of on a globe. So far as
illustrating the Zenith Distance minus the Declination, however, the
diagram is correct. The last case is where you are, say, 10 deg. N of the
sun (your zenith Distance is 10 deg.) and the sun is in 20 deg. S declination.
In that case you would have to subtract your zenith distance from the
sun's declination to get your latitude, for the sun's latitude (its
declination) is greater than yours.

Now from these three cases we deduce the following directions, which put
in your Note-Book:

Begin to measure the altitude of the sun shortly before noon. By
bringing its image down to the horizon, you can detect when its altitude
stops increasing and starts to decrease. At that instant the sun is on
your meridian, it is noon at the ship, and the angle you read from your
sextant is the meridian altitude of the sun. To work out your latitude,
name the meridian altitude S if the sun is south of you and N if north
of you.

Correct the observed altitude to a true altitude by Table 46. If the
altitude is S, the Zenith Distance is N or vice versa. (Note to
Instructor: If the sun is South of you, you are North of the sun and
vice versa.)

Correct the declination for the proper G.M.T. as shown by chronometer
(corrected). If zenith distance and declination are both North or both
South, add them and the sum will be the latitude, N or S as indicated.
If one is N, and the other S, subtract the less fro