68

INVENTIONS OF NIKOLA TESLA.

of one sign, and the corresponding end of pole-piece o' Mali beof the opposite sign. The armature also exhibits two poles atright angles to the coils f f, like poles to those in the pole-pieces being on the same side of the coils. While the currentis flowing there is no appreciable tendency to rotation devel-oped ; but after each current impulse ceases or begins to fall,the magnetism in the armature and in the ends of the pole-pieces c o' lags or continues to manifest itself, which produces arotation of the armature by the repellent force between themore closely approximating points of maximum magnetic effect.This effect is continued by the reversal of current, the polari-ties of field and armature being simply reversed. One or bothof the elements—the armature or field—may be wound with

WlSlk f©

Fro. 54. Ftg. 55.

closed induced coils to intensify this effect. Although in theillustrations but one of the fields is shown, each element of themotor really constitutes a field, wound with the closed coils,the currents being induced mainly in those convolutions or coilswhich are parallel to the coils f k.

A modified form of this motor is shown in Fig. 5(i. In thisform Or is one of two standards that support the bearings forthe armature-shaft, h n are uprights or sides of a frame, prefer-ably magnetic, the ends o c' of which are bent in the mannerindicated, to conform to the shape of the armature i> and formfield-magnet poles. The construction of the armature may bethe same as in the previous figure, or it may be simply a mag-netic disc or cylinder, as shown, and a coil or coils f f are se-