23

INVENTIONS OF NIKOLA TESLA.

abnormally diminished by producing in this circuit an additionalelectromotive force. Owing to these causes the reversal is in-stantaneous.

If it is desirable to secure a constant speed, and at the sametime a certain effort at the start, this result may be easily attainedin a variety of ways. For instance, two armatures, one for torqueand the other for synchronism, may be fastened on the same shaftand any desired preponderance may be given to either one, or anarmature may be wound for rotary effort, but a more or less pro-nounced tendency to synchronism may be given to it by properlyconstructing the iron core; and in many other ways.

As a means of obtaining the required phase of the currents inboth the circuits, the disposition of the two coils at right anglesis the simplest, securing the most uniform action ; but the phasemay be obtained in many other ways, varying with the machineemployed. Any of the dynamos at present in use may be easilyadapted for this purpose by making connections to proper pointsof the generating coils. In closed circuit armatures, such as usedin the continuous current systems, it is best to make four deriva-tions from equi-distant points or bars of the commutator, and toconnect the same to four insulated sliding rings on the shaft. Inthis case each of the motor circuits is connected to two diametri-cally opposite bars of the commutator. In such a disposition themotor may also be operated at half the potential and on the three-wire plan, by connecting the motor circuits in the proper order tothree of the contact rings.

In multipolar dynamo machines, such as used in the convertersystems, the phase is conveniently obtained by winding upon thearmature two series of coils in such a manner that while the coilsof one set or series are at their maximum production of current,the coils of the other will be at their neutral position, or nearlyso, whereby both sets of coils may be subjected simultaneouslyor successively to the inducing action of the field magnets.

Generally the circuits in the motor will be similarly disposed,and various arrangements may be made to fulfill the requirements;but the simplest and most practicable is to arrange primary cir-cuits on stationary parts of the motor, thereby obviating, at leastin certain forms, the employment of sliding contacts. In such acase the magnet coils are connected alternately in both the cir-cuits ; that is, 1, 3, 5.... in one, and 2, 4, 6.... in the other, andthe coils of each set of series may be connected all in the same