timony, gold,
silver and copper, not only are non-magnetic, but they are actually
repelled by magnetism. They are called the diamagnetics.

NON-MAGNETIC MATERIALS.--Any non-magnetic body in the path of a magnetic
force does not screen or diminish its action, whereas a magnetic
substance will.

In Fig. 5 we show the simplest form of magnet, merely a bar of steel (A)
with the magnetic lines of force passing from end to end. It will be
understood that these lines extend out on all sides, and not only along
two sides, as shown in the drawing. The object is to explain clearly how
the lines run.

[Illustration: _Fig. 6._ SEVERED MAGNET]

ACTION OF A SEVERED MAGNET.--Now, let us suppose that we sever this bar
in the middle, as in Fig. 6, or at any other point between the ends. In
this case each part becomes a perfect magnet, and a new north pole (N)
and a new south pole (S) are made, so that the movement of the magnetic
lines of force are still in the same direction in each--that is, the
current flows from the north pole to the south pole.

WHAT NORTH AND SOUTH POLES MEAN.--If these two parts are placed close
together they will attract each other. But if, on the other hand, one of
the pieces is reversed, as in Fig. 7, they will repel each other. From
this comes the statement that likes repel and unlikes attract each
other.

REPULSION AND ATTRACTION.--This physical act of repulsion and attraction
is made use of in motors, as we shall see hereinafter.

It will be well to bear in mind that in treating of electricity the
north pole is always associated with the plus sign (+) and the south
pole with the minus sign (-). Or the N sign is positive and the S sign
negative electricity.

[Illustration: _Fig. 7._ REVERSED MAGNETS]

POSITIVES AND NEGATIVES.--There is really no difference between positive
and negative electricity, so called, but the foregoing method merely
serves as a means of identifying or classifying the opposite ends of a
magnet or of a wire.

MAGNETIC LINES OF FORCE.--It will be noticed that the magnetic lines of
force pass through the bar and then go from end to end through the
atmosphere. Air is a poor conductor of electricity, so that if we can
find a shorter way to conduct the current from the north pole to the
south pole, the efficiency of the magnet is increased.

This is accomplished by means of the well-known horseshoe magnet, where
the two ends (N, S) are brought close together, as in Fig. 8.