ith all their north-seeking poles
towards the one end of the bar, and their south-seeking poles towards
the other. If the bar is balanced freely on a pivot, it comes to rest
pointing north and south; for, the earth being a huge magnet, its north
pole attracts all the north-seeking poles of the molecules, and its
south poles the south-seeking poles. (The north-_seeking_ pole of a
magnet is marked N., though it is in reality the _south_ pole; for
unlike poles are mutually attractive, and like poles repellent.)

There are two forms of magnet--_permanent_ and _temporary_. If steel is
magnetized, it remains so; but soft iron loses practically all its
magnetism as soon as the cause of magnetization is withdrawn. This is
what we should expect; for steel is more closely compacted than iron,
and the molecules therefore would be able to turn about more easily.[12]
It is fortunate for us that this is so, since on the rapid magnetization
and demagnetization of soft iron depends the action of many of our
electrical mechanisms.

THE PERMANENT MAGNET.

Magnets are either (1) straight, in which case they are called bar
magnets; or (2) of horseshoe form, as in Figs. 50 and 51. By bending the
magnet the two poles are brought close together, and the attraction of
both may be exercised simultaneously on a bar of steel or iron.

LINES OF FORCE.

In Fig. 50 are seen a number of dotted lines. These are called _lines of
magnetic force_. If you lay a sheet of paper on a horseshoe magnet and
sprinkle it with iron dust, you will at once notice how the particles
arrange themselves in curves similar in shape to those shown in the
illustration. It is supposed (it cannot be _proved_) that magnetic force
streams away from the N. pole and describes a circular course through
the air back to the S. pole. The same remark applies to the bar magnet.

ELECTRICAL MAGNETS.

[Illustration: FIG. 50.--Permanent magnet, and the "lines of force"
emanating from it.]

If an insulated wire is wound round and round a steel or iron bar from
end to end, and has its ends connected to the terminals of an electric
battery, current rotates round the bar, and the bar is magnetized. By
increasing the strength and volume of the current, and multiplying the
number of turns of wire, the attractive force of the magnet is
increased. Now disconnect the wires from the battery. If of iron, the
magnet at once loses its attractive force; but if of steel, it retains
it in