POLYPHASE CURRENTS.

15

a direction always opposite to the supposed movement of thepoles. If a paper with tilings is put flat upon the ring and thecurrent turned on suddenly, the existence of a magnetic whirlmay easily be observed.

To demonstrate the complete analogy between the ring and arevolving magnet, a strongly energized electro-magnet was rota-ted by mechanical power, and phenomena identical in every par-ticular to those mentioned above were observed.

Obviously, the rotation of the poles produces correspondinginductive effects and may be utilized to generate currents in aclosed conductor placed within the influence of the poles. Forthis purpose it is convenient to wind a ring with two sets ofsuperimposed coils forming respectively the primary and second-ary circuits, as shown in Fig. 10. In order to secure the mosteconomical results the magnetic circuit should be completelyclosed, and with this object in view the construction may bemodified at will.

The inductive effect exerted upon the secondary coils will bemainly due to the shifting or movement of the magnetic action ;but there may also be currents set up in the circuits in conse-quence of the variations in the intensity of the poles. However,by properly designing the generator and determining the magneti-zing effect of the primary coils, the latter element may be madeto disappear. The intensity of the poles being maintained con-

tlr\

Fig. 8a.

Fig. 8.

stant, the action of the apparatus will be perfect, and the sameresult will be secured as though the shifting were effected bymeans of a commutator with an infinite number of bars. In suchcase the theoretical relation between the energizing effect of eachset of primarv coils and their resultant magnetizing effect maybe expressed by the equation of a circle having its centre coin-ciding with that of an orthogonal system of axes, and in whichthe radius represents the resultant and the co-ordinates both