THE INDUCTION MOTOR. 343 



A similar effect may be produced by means of three 

 coils, situated at aii angle of 120 apart, and supplied each 

 with current from one phase of a three-phase system. In 

 this case also, the current in the several coils will attain 

 its maximum value successively, and the magnet would 

 be attracted into a position normal to each coil in turn. 

 The magnetic field in this case also makes one revolution 

 in the time of one complete cycle of the current. 



The rotating field is employed in the case of all 

 induction motors, and the principle of its production is 

 the same as that just described. The method of winding 

 the wire upon the iron magnetic circuit of a motor is 

 necessarily somewhat different from that shown in 

 Fig. 170. 



In an actual induction motor a laminated ring-shaped 

 core is employed as typified by the ring in Fig. 170. 

 In place of the pivoted magnet, however, a cylindrical 

 iron core is used with conductors embedded in slots in 

 its circumference. The nature of the magnetic field 

 produced in the ring and inner core is illustrated by 

 Fig. 171, where a single winding only is shown carrying 



FIG. 171. FIELD IN INDUCTION MOTOR. 



current. Exactly the same magnetic field would be pro- 

 duced by applying the winding to the ring in any other 

 position, so long as the winding embraces the lines 

 forming the magnetic flux. Thus, in Fig. 172, the winding 

 is shown as embracing the magnetic flux at the point 

 where it comes to the air gap and passes from the ring to 

 the inner core. 



