That will give you an East
and West line, for then the sun bears true North and South. An East and
West line is your correct latitude. Now you have an 8 A.M. observation
which is nearly correct for longitude and a noon position which is
correct for latitude. How can you combine the two so as to get
accurately both your latitude and longitude? Put in your Note-Book:

Through the 8 A.M. position, draw a line on the chart at right angles to
the sun's true bearing. Suppose the sun bore true E 1/2 S. Then your
line of position would run N 1/2 E. Mark it 1st Position Line.

[Illustration]

Now draw a line running due East and West at right angles to the N-S
noon bearing of the sun and mark this line Second Position Line. Advance
your First Position Line the true course and distance sailed from 8 A.M.
to noon, and through the extremity draw a third line exactly parallel to
the first line of position. Where a third line (the First Position Line
advanced) intersects the Second Position Line, will be your position at
noon. It cannot be any other if your calculations are correct. You knew
you were somewhere on your 8 A.M. line, you know you are somewhere on
your noon line, and the only spot where you can be on both at once is
the point where they intersect. You don't necessarily have to wait until
noon to work two lines. You can do it at any time if a sufficient
interval of time between sights is allowed. The whole matter simply
resolves itself into getting your two lines of position, having them
intersect and taking the point of intersection as the position of your
ship.

There is one other way to get two lines to intersect and it is one of
the best of all for fixing your position accurately. It is by getting
lines of position by observation of two stars. If, for instance, you can
get two stars, one East and the other West of you, you can take
observations of both so closely together as to be practically
simultaneous. Then your Easterly star would give you a line like AA' and
the westerly star the line BB' and you would be at the intersection S.

[Illustration]

Assign for reading: Articles in Bowditch 321-322-323-324. Spend the rest
of the period in getting times from the N. A., getting true altitudes
from observed altitudes, working examples in Mercator sailing, etc.

WEDNESDAY LECTURE

LATITUDE BY MERIDIAN ALTITUDE

A meridian altitude is an altitude taken when the sun or other celestial
body observed bears