The motor is of such a size that when supplied with a continuous current of proper strength the induced electrical effect in the shunt circuit will light one incandescent lamp. If, however, it is supplied with an alternating current of the same power, it will light eight lamps, and the mechanical power given off is even more than with a continuous current, provided that the alternations from the dynamo do not exceed 6,000 a minute. At first I was considerably puzzled by this great difference, because in both cases it is impossible for the lamp circuit to be acted upon by the main current. It occurred to me, however, that the rapid alternations of the exciting current from the dynamo, and the consequent speed of magnetic molecular rotation, gave the latter a certain momentum, and that by widening the insulating strips of the first or main current commutator, and proportionately increasing the width of conducting surface in the shunt commutator up to certain limits, this effect would be increased. I found such to be the case, from which I inferred that the increase of induced current in the shunt circuit was on account of its longer duration, by reason of the acquired momentum of the magnetic molecular rotations _after_ the alternating exciting current had ceased. [Illustration] Those who have facilities for carrying out experiments may prove it in the following manner: E, in the inclosed drawing, is an electro-magnet whose brushes press on two metallic bands, B and B¹, fixed to but insulated from the spindle, A. The band, B, is in electrical circuit with the shunt commutator, S, and the main commutator, M; while the band, B¹, is in contact with shunt commutator, S¹, and main commutator, M¹. This contact is made by conducting rods, as indicated. The commutators, as regards their brushes, are so arranged that when M and M¹ are in action, S and S¹ are out of action, and _vice versa_. The spindle and commutators are rotated by the pulley, P. L is an incandescent lamp in the shunt circuit. Let us now suppose the apparatus at rest, and the brushes in electrical contact with the main commutators, M and M¹. The current from an alternating dynamo passes into the magnet, E, and rapidly reverses its polarity. By actuating the pulley, P, the commutators are rotated, when M and M¹ go out of, and the shunt commutators, S and S¹, come into action, enabling the _after_ current set up in the magnet to light the lamp, L, in the shunt circuit.