rom the
direct line. A vessel also makes what is called "leeway;" which means
that, when the wind blows on her side, she not only advances forward,
but also slides through the water sidewise. Thus, in the course of a
day, she may get a considerable distance off her true course--in sea
parlance, "make a good deal of leeway."

To perform the voyage correctly and safely in the face of these
obstacles and hindrances is the aim and end of navigation; and the
manner of proceeding is as follows:--

The hour is carefully noted on setting sail, and from that moment, night
and day, to the end of the voyage, certain observations are made and
entered in the ship's journal, called the log. Every hour the rate at
which the ship is going is ascertained and carefully noted. The point
of the compass towards which the ship is to be steered is given by the
captain or officer in command to the steersman, who stands at the wheel
with a compass always before him in a box called the "_binnacle_." The
course is never changed except by distinct orders from those in command;
and when it is changed, the hour when the change is made and the new
course to be steered are carefully noted down. Thus, at the end of the
day, or at any other time if desired, the position of the ship can be
ascertained by her course being drawn upon a chart of the ocean over
which she is sailing,--correct charts, or maps, being provided by the
captain before starting.

The estimate thus made is, however, not absolutely correct. It is
called the "_dead-reckoning_," and is only an approximation to the
truth, because allowance has to be made for leeway, which can only be
guessed at. Allowance has also to be made for variations in the rate of
sailing in each hour, for the winds do not always blow with exactly the
same force during any hour of the day. On the contrary, they may vary
several times within an hour, both in force and in direction. Those
variations have to be watched and allowed for; but such allowance may be
erroneous in a greater or less degree. Currents, too, may have exerted
an unseen influence on the ship, thus rendering the calculation still
less correct. Nevertheless, dead-reckoning is often the only guide the
sailor has to depend upon for days at a time, when storms and cloudy
skies prevent him from ascertaining his true position by other means, of
which we shall speak presently.

Of course, in the early days of navigation there were no char