sea, but had observed this one of its
well-known peculiarities--namely, the tendency of the needle to point in
a _very slight degree_ away from the true north.

In the thirteenth century, too, we find mention made of the needle by a
poet and by two other writers; so that whatever Flavio Gioia may have
done (and it is probable he did much) in the way of pushing the compass
into notice in Europe, he cannot be said to be the inventor of it. That
honour doubtless belongs to the Chinese. Be this as it may, the compass
was invented; and in the fourteenth century it began that revolution in
maritime affairs to which we have alluded.

The first compasses were curiously formed. The Chinese used a
magnetised needle, which they placed in a bit of rush or pith, which was
floated in a basin of water, and thus allowed to move freely and turn
towards the poles. They also made needles in the form of iron fish. An
Arabian author of the thirteenth century thus writes:--"I heard it said
that the captains in the Indian seas substitute for the needle and reed
a hollow iron fish magnetised, so that, when placed in the water, it
points to the north with its head and to the south with its tail. The
reason that the iron fish does not sink, is that metallic bodies, even
the heaviest, float when hollow and when they displace a quantity of
water greater than their own weight."

The use of the compass at sea is so simple, that, after what has been
said, it scarcely requires explanation. When a ship sets sail for any
port, she knows, first of all, the position of the port from which she
sets sail, as well as that to which she is bound. A straight line drawn
from the one to the other is her true course, supposing that there is
deep, unobstructed water all the way; and if the compass be placed upon
that line, the point of the compass through which it passes is the point
by which she ought to steer. Suppose that her course ran through the
east point of the compass: the ship's head would at once be turned in
that direction, and she would continue her voyage with the needle of the
compass pointing straight _across_ the deck, and the east and west
points straight _along_ it.

But various causes arise in the actual practice of navigation to prevent
a ship keeping her true course. Winds may be contrary, and currents may
drive her either to the one side or the other of it; while land--
promontories, islands, and shallows--compel her to deviate f