the windings develop magnetization in the opposite direction from that
of the other, so that the two will neutralize each other, or at least
exert different and opposite influences. The principle of the
differential electromagnet may be illustrated in connection with Fig.
96. Here two wires _1_ and _2_ are shown wrapped in the same direction
about an iron core, the ends of the wire being joined together at _3_.
Obviously, if one of these windings only is employed and a current
sent through it, as by connecting the terminals of a battery with the
points _4_ and _3_, for instance, the core will be magnetized as in an
ordinary magnet. Likewise, the core will be energized if a current be
sent from _5_ to _3_. Assuming that the two windings are of equal
resistance and number of turns, the effects so produced, when either
the coil _1_ or the coil _2_ is energized, will be equal. If the
battery be connected between the terminals _4_ and _5_ with the
positive pole, say, at _5_, then the current will proceed through the
winding _2_ and tend to generate magnetism in the core in the
direction of the arrow. After traversing the winding _2_, however, it
will then begin to traverse the other winding _1_ and will pass around
the core in the opposite direction throughout the length of that
winding. This will tend to set up magnetism in the core in the
opposite direction to that indicated by the arrow. Since the two
currents are equal and also the number of turns in each winding, it is
obvious that the two magnetizing influences will be exactly equal and
opposite and no magnetic effect will be produced. Such a winding, as
is shown in Fig. 96, where the two wires are laid on side by side, is
called a _parallel differential winding_.

Another way of winding magnets differentially is to put one winding on
one end of the core and the other winding on the other end of the core
and connect these so as to cause the currents through them to flow