122 



THE MAGNETIC CIRCUIT [ART. 42 



b c ' 



FIG. 33a. A four-pole revolving fieldstructure with non-salient poles. 



curve (Fig. 336) ; in reality, the corners are smoothed out by the 

 fringes. The total number of ampere-turns per pole must be such 



as to create the assumed 

 maximum flux density 

 B ma x in the air-gap 

 under the middle part 

 of the pole. The slots 

 are placed with due re- 

 gard to the mechanical 

 strength of the struc- 



FIG. 336. The flux-density distribution for ture > and SO as tO S et a 

 the field shown in Fig. 33a. flux-density ^ distribu- 



tion approaching a sine 

 wave. The middle part of the curve is left flat, because very little 



-Pole-pitch- 



