90

INVENTIONS OF NIKOLA TESLA,

hut the continued weakening of a is attended by a subsequentweakening of b. Assuming the current to be an alternating one,a will now be reversed, while b still continues of the first impartedpolarity. This action continues the magnetic condition of b, fol-lowing that of a in the manner above described. If an armature—for instance, a simple disc f, mounted to rotate freely on anaxis—be brought into proximity to the core, a movement of rota-tion will be imparted to the disc, the direction depending uponits position relatively to the core, the tendency being to turn theportion of the disc nearest to the core from a to b, as indicatedin Fig. 72.

This action or principle of operation has been embodied in apracticable form of motor, which is illustrated in Fig. 73. Let a

Fig. 74.

Mm.

in that figure represent a circular frame of iron, from diametric-ally opposite points of the interior of which the cores project.Each core is composed of three main parts b, b and c, and theyare similarly formed with a straight portion or body e, aroundwhich the energizing coil is wound, a curved arm or extension c,and an inwardly projecting pole or end d. Each core is made upof two parts b b, with their polar extensions reaching in onedirection, and a part c between the other two, and with its polarextension reaching in the opposite direction. In order to lessenin the cores the circulation of currents induced therein, the severalsections are insulated from one another in the manner usuallv