see before launching into mid-ocean, by noting, as accurately as he
possibly can, its compass-bearing and distance from his ship at a
particular hour.

With these data he is enabled to lay down upon his chart the exact
position of his ship at that hour, and from this spot the _ship's
reckoning_ commences. The courses she steers, and the number of _knots_
or nautical miles (sixty of which are equal to sixty-nine and a half
English miles) she sails every hour, together with certain other items
of information, such as the direction of the wind, the direction and
speed of the currents, if any, which she passes through, and the state
of the weather, the _lee-way_ the ship makes, etcetera, etcetera, are
all entered in the log-book; and at noon every day, by means of certain
simple calculations, the ship's position is ascertained from these
particulars.

The entering of all these particulars in the log-book is termed _keeping
the dead reckoning_, and the working out of the calculations just
referred to is called _working up the days work_.

This, however, only gives the ship's position _approximately_, because
it is difficult to judge _accurately_ of the amount of lee-way which a
ship makes, and it is not at all times easy to detect the presence of
currents, both of which produce a certain amount of deviation from the
apparent course of the ship.

To correct, therefore, all errors of this kind, which are otherwise
impossible to detect when the ship is out of sight of land, various
observations of the sun, moon, or stars are taken, whereby the _exact_
latitude or longitude (or sometimes both together) of the ship at the
moment of observation is ascertained.

This short lesson in navigation over, we will now rejoin the _Water
Lily_, which we left at six p.m. off the Lizard, on the starboard tack.

It was my "eight hours out" that night, and when I took the tiller at
eight o'clock we were dashing along a good honest eight knots, under
whole canvas and a jib-headed gaff-topsail. The night was as fine as
the previous one, but with a little more wind, and we were just
beginning to get within the influence of the Atlantic swell. There was
no sea on, but the long, majestic, heaving swell was sweeping with
stately motion towards the Channel, rising like low hills on either side
of us as our little barkie sank between them, and gleaming coldly, like
polished steel, where the moon's rays fell upon their crests. But the
little