307. The Influence of Magnets upon Each Other. If while our
suspended magnetic needle is at rest in its characteristic
north-and-south direction another magnet is brought near, the
suspended magnet is turned; that is, motion is produced (Fig. 225). If
the north pole of the free magnet is brought toward the south pole of
the suspended magnet, the latter moves in such a way that the two
poles _N_ and _S_ are as close together as possible. If the north pole
of the free magnet is brought toward the north pole of the suspended
magnet, the latter moves in such a way that the two poles _N_ and _N_
are as far apart as possible. In every case that can be tested, it is
found that a north pole repels a north pole, and a south pole repels a
south pole; but that a north and a south pole always attract each
other.

[Illustration: FIG. 225.--A south pole attracts a north pole.]

The main facts relative to magnets may be summed up as follows:--

_a_. A magnet points nearly north and south if it is allowed to swing
freely.

_b_. A magnet contains two unlike poles, one of which persistently
points north, and the other of which as persistently points south, if
allowed to swing freely.

_c_. Poles of the same name repel each other; poles of unlike name
attract each other.

_d_. A magnet possesses the power of attracting certain substances,