In explanation of the physical phenomena involved in the induction of
the electric currents in the armature when the machine is in action as
a generator, Dr. Pacinotti makes the following remarks: Let us trace
the action of one of the coils in the various positions that it can
assume in one complete revolution; starting from the position marked
N, Fig. 2, and moving toward S, an electric current will be developed
in it in one direction while moving through the portion of the circle,
N a, and after passing the point, a, and while passing through the
arc, a S, the induced current will be in the opposite direction,
which direction will be maintained until the point, b, is reached,
after which the currents will be in the same direction as between N
and a; and as all the coils are connected together, all the currents
in a given direction will unite and give the combined current a
direction indicated by the arrows in Fig. 2, and in order to collect
it (so as to transmit it into the external circuit), the most eminent
position for the collectors will be at points on the commutator at
opposite ends of a diameter which is perpendicular to the magnetic
axis of the magnetic field. With reference to Fig. 2, we imagine
either that the two arrows to the right of the figure are incorrectly
placed by the engraver, or that Dr. Pacinotti intended this diagram to
express the direction of the current throughout the whole circuit, as
if it started from a, and after traversing the external circuit
entered again at b, thus completing the whole cycle made up of the
external and internal circuits.

Dr. Pacinotti calls attention to the fact that the direction of the
current generated by the machine is reversed by a reversal of the
direction of rotation, as well as by a shifting of the position of the
collectors from one side to the other of their neutral point, and