floating straw persistently showing him the direction in which he
must sail. It made him very uncomfortable to go to sea under the
guidance of an invisible power. But with him, as with the rest of
us, familiarity breeds contempt, and it did not take more than a
generation to show that much good and no harm came to those who
used the magic pointer.

The modern compass, as made in the most approved form for naval
and other large ships, is the liquid one. This does not mean that
the card bearing the needle floats on the liquid, but only that a
part of the force is taken off from the pivot on which it turns,
so as to make the friction as small as possible, and to prevent
the oscillation back and forth which would continually go on if
the card were perfectly free to turn. The compass-card is marked
not only with the thirty-two familiar points of the compass, but
is also divided into degrees. In the most accurate navigation it
is probable that very little use of the points is made, the ship
being directed according to the degrees.

A single needle is not relied upon to secure the direction of the
card, the latter being attached to a system of four or even more
magnets, all pointing in the same direction. The compass must have
no iron in its construction or support, because the attraction of
that substance on the needle would be fatal to its performance.

From this cause the use of iron as ship-building material
introduced a difficulty which it was feared would prove very
serious. The thousands of tons of iron in a ship must exert a
strong attraction on the magnetic needle. Another complication is
introduced by the fact that the iron of the ship will always