ld to traverse or
cut across the conductor with very high velocity.

It is a known fact that, in dynamos with large section armature
conductors, there are less eddy currents produced in the conductors
when they are provided with iron cores or wound upon iron cores than
when the conductors are made into flat bobbins moved in front of field
poles. Projections existing on the armature between which the
conductors are placed have a like effect, and enable us to employ
heavy bars or bundles of wire without much difficulty from local
currents. The reason is simple. In the armatures with coils without
iron in them, or without projections extending between the turns, the
conductor moves into and out of a very dense field at comparatively
low velocity, so that any differences of potential developed in the
parts of the section of conductor have full effect and abundant time
to act in setting up harmful local currents. In the cases in which
iron projects through the coil or conductor, the real action is that
the lines of the magnetic circuits move at high speeds across the
conductor, and the conductor is at all times in a field of very low
density. Figs. 8 and 9 will make this plain. In Fig. 8 we have shown a
smooth armature surface, having a heavy conductor laid thereon, and
which is at a just entering a dense field at the edge of the pole,
N, and at b leaving such field. It will be seen that when in such
position the conductor, if wide, is subjected to varying field
strength, and moves at a low speed for the generation of the working
potential as it passes through the field, thus giving rise to eddy
currents in the conductor.

[Illustration: Fig. 8.]

In Fig. 9 the conductors are set down between projections, in which
case both armature and field poles are laminated or subdivided. As
each projection leaves the edge of field pole, N, the lines which it
had concentrated on and through it snap backward at an enormous speed,
and cross the gap to the next succeeding projection on the armature,
cutting the whole section of the heavy armature conductor at
practically the same instant. This brisk transfer of lines goes on
from each projection to the succeeding one in front of the field pole,
leaving a very low density of field at any time between the
projections. The best results would be obtained when the armature
conductor does not project beyond or quite fill the depth of groove
between the projections. Of course there are other