144 



TREATISE ON ALTERNATING CURRENTS. 



simple alternator, it is tapped at four equidistant points that is, 

 each 90 from the next and that each tapping is carried to a 

 separate collecting-ring on the shaft of the machine, as is shown 

 diagrammatically in Fig. 47. 



It is then evident that each pair of connections 180 apart will 



FIG. 47. 



give rise to a simple alternating current ; but the current in one 

 pair of leads will be 90, or a quarter of a period, behind the other, 

 according to the direction of rotation of the armature. 



In Fig. 47, if the direction of rotation is clockwise, the current 

 in coils a, a' will lag behind that in coils I, I' by a quarter of a 

 period. 



If the current in coils a, a' is represented by i sin pt, that in 



coils 6, &' will be represented by i Q sin (pt + | j 



If these two currents were transmitted along the same wire, 

 the resulting current would be given by 



i = sin pt 



i sin (pt 



(1) 



These are represented graphically in Fig. 48 ; the dotted line 



FIG. 48. 



