or sifted at will, and led away by wires to an electric lamp, an
accumulator, or an electric motor, as desired. The character of
the electricity is precisely the same as that generated in the
voltaic battery.

The commutator may only collect the currents as they are
generated, and supply what is called an alternating current, that
is to say, a current which alternates or changes its direction
several hundred times a second, or it may sift the currents as
they are produced and supply what is termed a continuous current,
that is, a current always in the same direction, like that of a
voltaic battery. Some machines are made to supply alternating
currents, others continuous currents. Either class of current will
do for electric lamps, but only continuous currents are used for
electo-plating, or, in general, for electric motors.

In the "magneto-electric" machine the FIELD MAGNETS are simply
steel bars permanently magnetised, but in the ordinary dynamo the
field magnets are electro-magnets excited to a high pitch by means
of the current generated in the moving conductor or armature. In
the "series-wound" machine the whole of the current generated in
the armature also goes through the coils of the field magnets.
Such a machine is sketched in figure 40, where A is the armature,
consisting of an iron core surrounded by coils of wire and
rotating in the field of a powerful electro-magnet NS in the
direction of the arrows. For the sake of simplicity only twelve
coils are represented. They are all in circuit one with another,
and a wire connects the ends of each coil to corresponding metal
bars on the commutator C. These bars are insulated from each other
on the spindle X of the armature. Now, as each coil passes through