of insulated copper wire, r r r, in a similar manner to that adopted
in winding the Brush armature, and between them are fixed as many
wooden wedges, m m, by which the helices are firmly held in their
place. All the coils are wound round the ring in the same direction,
and the terminating end of each coil is connected to the commencing
end of the next or succeeding helix, and the junctions so made are
attached to conducting wires which are gathered together close to the
vertical shaft on which the armature ring is fixed, passing through
holes at equal distances apart in a wooden collar fixed to the same
shaft, and being attached at their lower extremities to the metallic
contact pieces of the commutator, c, shown at the lower part of Fig.
3, which is an elevation of the machine, while Fig. 4 is a plan of the
same apparatus.

The commutator consists of a small boxwood cylinder, carrying around
its cylindrical surface two rows of eight holes, one above the other,
in which are fitted sixteen contact pieces of brass which slightly
project above the surface of the wood, the positions of those in the
upper circle alternating or "breaking joint" with those in the lower,
and each contact piece is in metallic connection with its
corresponding conducting wire, and, therefore, with the junction of
two of the helices on the armature. Against the edge of the commutator
are pressed by means of adjustable levers two small brass contact
rollers, k k, which are respectively connected with the positive and
negative poles of the voltaic battery (either through or independent
of the coils of a fixed electro-magnet, to which we shall presently
refer), and the magnetic axis of the ring will lie in the same plane
as the line joining the points of contact of the battery and rotating
helix, this axis remaining nearly fixed notwithstanding the rotation
of the iron ring in which the magnetism is induced.