POLYPHASE CURRENTS.

11

shifting of the poles of one of its elements, and the questionpresented itself—How to perform this operation by the directaction of alternate currents 't I will now proceed to show howthis result was accomplished.

In the first experiment a drum-armature was provided with

Fig. U

N

Fig. la.

two coils at right angles to each other, and the ends of these coilswere connected to two pairs of insulated contact-rings as usual.A. ring was then made of thin insulated plates of sheet-iron andwound with four coils, each two opposite coils being connectedtogether so as to produce free poles on diametrically oppositesides of the ring. The remaining free ends of the coils were thenconnected to the contact-rings of the generator armature so asto form two independent circuits, as indicated in Fig. 9. Itmay now be seen what results were secured in this combination,and with this view I would refer to the diagrams, Figs. 1 to 8a.The field of the generator being independently excited, the rota-tion of the armature sets up currents in the coils c c l5 varying in

Fig. 2a.

Fig. 2.

strength and direction in the well-known manner. In the posi-tion shown in Fig. 1, the current in coil c is nil, while coil cq istraversed by its maximum current, and the connections may besuch that the ring is magnetized by the coils e t c 1} as indicated bythe letters n s in Fig. la, the magnetizing effect of the coils