he question as to who first
discovered the fact that a magnetized needle points north and south,
and applied this discovery to navigation, has given rise to much
discussion. That the property was known to the Chinese about the
beginning of our era seems to be fairly well established, the
statements to that effect being of a kind that could not well have been
invented. Historical evidence of the use of the magnetic needle in
navigation dates from the twelfth century. The earliest compass
consisted simply of a splinter of wood or a piece of straw to which the
magnetized needle was attached, and which was floated in water. A
curious obstacle is said to have interfered with the first uses of this
instrument. Jack is a superstitious fellow, and we may be sure that he
was not less so in former times than he is today. From his point of
view there was something uncanny in so very simple a contrivance as a
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