ontal stripes.

3. Buoys indicating the fairway are marked with black and white vertical
stripes and should be passed close to.

4. Sunken wrecks are marked by red and black striped buoys described in
No. 2. In foreign countries green buoys are frequently used to mark
sunken wrecks.

5. Quarantine buoys are yellow.

6. As white buoys have no especial significance, they are frequently
used for special purposes not connected with Navigation.

7. Starboard and port buoys are numbered from the seaward end of the
channel, the black bearing the odd and red bearing the even numbers.

8. Perches with balls, cages, etc., will, when placed on buoys, be at
turning points, the color and number indicating on which side they shall
be passed.

9. Soundings in plain white are in fathoms; those on shaded parts are in
feet. On large ocean charts fathom curves, showing the range of
soundings of 10, 20, 30, 40, etc., fathoms are shown.

10. A light is indicated by a red and yellow spot. F. means fixed, Fl.,
flashing; Int., intermittent; Rev., revolving, etc.

11. An arrow indicates a current and its direction. The speed is always
given.

12. Rocks just under water are shown by a cross surrounded by a dotted
circle; rocks above water, by a dotted circle with dots inside it.

Practically all charts you will use will be called Mercator charts. Just
how they are constructed is a difficult mathematical affair but,
roughly, the idea of their construction is based upon the earth being a
cylinder, instead of a sphere. Hence, the meridians of longitude,
instead of converging at the poles, are parallel lines. This compels
the parallels of latitude to be adjusted correspondingly. Although such
a chart in any one locality is out of proportion compared with some
distant part of the earth's surface, it is nevertheless in proportion
for the distance you can travel in a day or possibly a week--and that is
all you desire. The Hydrographic Office publishes blank Mercator charts
for all latitudes in which they can be used for plotting your position.
It makes no difference what longitude you are in for, on a Mercator
chart, meridians of longitude are all marked parallel. It makes a great
difference, however, what latitude you are in, as in each a mile is of
different length on the chart. Hence, it will be impossible for you to
correctly plot your course and distance sailed unless you have a chart
which shows on it the degrees of latitude in which