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 remedies for the
eddy current difficulty, notably the stranding and twisting of the
conductor on the armatures so as to average the position of the parts
of the compound conductor.
[Illustration: Fig. 9.]
Perhaps the most extreme case of what may be called dilution of field
by projections and by closed magnetic circuits in transformers would
be that of a block of iron, B, Fig. 10, moved between poles, N and S,
and having a hole through it, into and through which a conductor is
carried. The path through the iron is so good that we can scarcely
consider that any lines cross the hole from N to S; yet as B moves
forward there is a continual snapping transfer of lines from the right
forward side of the hole to the left or backward side, cutting the
conductor as they fly across, and developing an electromotive force in
it. I have described this action more in detail because we have in it
whatever distinction in the manner of cutting the lines of the field
is to be found between wire on smooth armatures and on projection
armatures and modifications thereof; and also between flat, open coils
passing through a field and bobbins with cores of iron. The
considerations advanced also bring out the relation which exists
between closed iron circuit transformers and closed iron circuit
(projection) dynamos, as we may call them.
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