20

INVENTIONS OF NIKOLA TESLA.

the quantity of the shifting magnetism constant, especially if themagnets are not properly subdivided.

To obtain a rotary effort in these motors was the subject oflong thought. In order to secure this result it was necessary tomake such a disposition that while the poles of one element ofthe motor are shifted by the alternate currents of the source, thepoles produced upon the other elements should always be main-tained in the proper relation to the former, irrespective of thespeed of the motor. Such a condition exists in a continuouscurrent motor; but in a synchronous motor, such as described,this condition is fulfilled only when the speed is normal.

The object has been attained by placing within the ring a prop-erly subdivided cylindrical iron core wound with several indepen-dent coils closed upon themselves. Two coils at right angles as

■Q ri 6

in Fig. 14, are sufficient, but a greater number may be advan-tageously employed. It results from this disposition that whenthe poles of the ring are shifted, currents are generated in theclosed armature coils. These currents are the most intense at ornear the points of the greatest density of the lines of force, andtheir effect is to produce poles upon the armature at right anglesto those of the ring, at least theoretically so; and since this actionis entirely independent of the speed—that is, as far as the locationof the poles is concerned—a continuous pull is exerted upon theperiphery of the armature. In many respects these motors aresimilar to the continuous current motors. If load is put on, thespeed, and also the resistance of the motor, is diminished andmore current is made to pass through the energizing coils, thus