CHAPTER VI.

Method of Obtaining Desired Speed of Motor orGenerator. ■

With the object of obtaining the desired speed in motorsoperated by means of alternating currents of differing phase,Mr. Tesla has devised various plans intended to meet the prac-tical requirements of the case, in adapting his system to types ofmultipolar alternating current machines yielding a large numberof current reversals for each revolution.

For example, Mr. Tesla has pointed out that to adapt a giventype of alternating current generator, you may couple rigidlytwo complete machines, securing them together in such a waythat the requisite difference in phase will be produced; or youmay fasten two armatures to the same shaft within the influenceof the same field and with the requisite angular displacement toyield the proper difference in phase between the two currents;or two armatures may be attached to the same shaft with theircoils symmetrically disposed, but subject to the influence of twosets of field magnets duly displaced; or the two sets of coilsmay be wound on the same armature alternately or in such man-ner that they will develop currents the phases of which differ intime sufficiently to produce the rotation of the motor.

Another method included in the scope of the same idea, where-by a single generator may run'a number of motors either at itsown rate of speed or all at different speeds, is to construct themotors with few'er poles than the generator, in which case theirspeed will be greater than that of the generator, the rate of speedbeing higher as the number of their poles is relatively less. Thismay be understood from an example, taking a generator that hastwo independent generating coils which revolve between twopole pieces oppositely magnetized; and a motor with energizingcoils that produce at any given time two magnetic poles in oneelement that tend to set up a rotation of the motor. A genera-tor thus constructed yields four reversals, or impulses, in each