you are. For
instance, if your Mercator chart shows parallels of latitude from 30 deg. to
40 deg. that chart must be used when you are in one of those latitudes. When
you move into 41 deg. or 29 deg., you must be sure to change your plotting chart
accordingly. In very high latitudes and near the North pole, the
Mercator chart is worthless. How can you steer for the North pole when
the meridians of your chart never come together at any pole? For the
same reason, bearings of distant objects may be slightly off when laid
down on this chart in a straight line. On the whole, however, the
Mercator chart answers the mariner's needs so far as all practical
purposes are concerned.

The instruments used in consulting a chart, i.e., parallel rulers,
dividers, etc. have already been described. The only way to lay down a
course and read it is by practice.

The one important thing to remember in laying down a course, is that
what you lay down is a true course. To steam this course yourself, you
must make the proper correction for your compass error.

Assign for Night Work in Bowditch, Arts.
9-239-240-241-243-244-245-246-247-248-249-251-252-253-254-255-256-257-258.

If any time in class room is left, spend it in laying down courses on
the chart and reading them; also in answering such questions as these:

1. I desire to sail a true course of NE. My compass error is 2 points
Westerly Variation and 1 point Easterly Deviation. What compass course
shall I sail?

2. I desire to sail a true course of SW x W. My Variation is 11 deg. W,
Deviation 2 pts. W and Leeway 1 pt. starboard. What compass course shall
I sail?

3. I desire to sail a true course of 235 deg.. My compass error is 4 pts. E
Variation, 27 deg. W Deviation, Leeway 1 pt. port. What compass course shall
I sail?

4. I desire to sail a true course of S 65 deg. W. My compass error is 10 deg. E
Variation, 3 deg. E Deviation, Leeway 1/4 point starboard. What compass
course shall I sail?

FRIDAY LECTURE

THE PROTRACTOR AND SEXTANT

The protractor is an instrument used to shape long courses. There are
many kinds. The simplest and the one most in use is merely a piece of
transparent celluloid with a compass card printed on it and a string
attached to the center of the compass card. To find your course by
protractor, put the protractor down on the chart so that the North and
South line on the compass card of the protractor will be immediately
over a meridian of lo