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INVENTIONS OF NIKOLA TNSLA.

gize the disc and increase the attraction exerted upon the same bythe ring, and currents being generated in the coil as long as thespeed of the armature is inferior to that of the poles, consider-able work may be performed by such a motor even if the speedbe below normal. The intensity of the poles being constant, nocurrents will be generated in the coil when the motor is turningat its normal speed.

Instead of closing the coil upon itself, its ends may be connectedto two insulated sliding rings, and a continuous current suppliedto these from a suitable generator. The proper way to start sucha motor is to close the coil upon itself until the normal speed isreached, or nearly so, and then turn on the continuous cur-rent. If the disc be very strongly energized by a continuouscurrent the motor may not be able to start, but if it be weaklyenergized, or generally so that the magnetizing effect of the ring

is preponderating, it will start and reach the normal speed. Sucha motor will maintain absohrtely the same speed at all loads. Ithas also been found that if the motive power of the generator isnot excessive, by checking the motor the speed of the generator isdiminished in synchronism with that of the motor. It is charac-teristic of this form of motor that it cannot be reversed by revers-ing the continuous current through the coil.

The synchronism of these motors may be demonstrated experi-mentally in a variety of w r ays. For this purpose it is best toemploy a motor consisting of a stationary field magnet and anarmature arranged to rotate within the same, as indicated inFig. 13. In this case the shifting of the poles of the armatureproduces a rotation of the latter in the opposite direction. Itresults therefrom that wdien the normal speed is reached, thepoles of the armature assume fixed positions relatively to the