37 



current increases. It is obvious that the 

 line O A. can also be considered as the 

 resultant of E and E„ and the position 

 of these two electromotive forces becomes 

 thus at once defined. In order that the 

 machine may give off mechanical work, 

 the induced electromotive force must 



evidently be opposed to the current, that 

 is to say, it must lie to the right of the 

 vertical, whilst the terminal electromotive 

 force must lie to the^left. Under these 

 conditions only one parallelogram of 

 forces is possible, namely, that de- 

 termined by the points O B A C where 



