velocity of tidal currents, location, character,
height and radius of visibility of all beacon lights, location of rocks,
shoals, buoys, and nature of the bottom wherever soundings can be
obtained.

The top of the chart is North unless otherwise noted. When in doubt as
to where North is, consult the compass card printed somewhere on the
chart. On sea charts, such as those of the North Atlantic, only the true
compass is printed, with the amount and direction of Variation indicated
by lines on the chart.

Parallels of latitude are shown by straight lines running parallel to
each other across the chart. The degrees and minutes of these parallels
are given on the perpendicular border of the chart. Meridians of
longitude are shown by straight lines running up and down, perpendicular
to the parallels of latitude, and the degrees and minutes of these
meridians are given on the horizontal border of the chart.

Put in your Note-Book:

A minute of latitude is always a mile, because parallels of latitude are
equidistant at all places. A minute of longitude is a mile only on the
equator, for the meridians are coming closer to each other as they
converge toward either pole. They come together at the North and South
poles, and here there is no longitude.

* * * * *

I can explain this very easily by reference to the following
illustration:

[Illustration]

As every parallel of latitude is a circle of 360 deg. the distance from A to
B will be the same number of degrees, minutes and seconds whether
measured upon parallel AA' or EE', but it will not be the same number of
miles as the meridians of longitude are gradually converging toward the
poles. On the other hand, the distances from A to C, C to D, D to E,
etc., must be the same because the lines AA', CC', DD', EE' are all
parallel. That is why the distance is always measured on the latitude
scale (i.e. on the vertical border of the chart), and a minute of
latitude is always a mile on the chart, no matter in what locality your
ship happens to be.

You should be able to understand any kind of information given you on a
chart. For instance, what are the various kinds of buoys and how are
they marked?

Put in your Note-Book:

1. In coming from seaward, red buoys mark the starboard side of the
channel, and black buoys the port side.

2. Dangers and obstructions which may be passed on either hand are
marked by buoys with red and black horiz