ELECTROMOTIVE FORCE AND CURRENT. 



25 



forces in a circuit may be obtained by representing the two 

 quantities in magnitude and phase by two vectors drawn 

 from a common point and both directed away from this 

 point. The vector of the resultant quantity is the diagonal of a 

 parallelogram of which the two vectors form the sides. Its direc- 

 tion will also be away from the common point. This form of 

 the rule is illustrated by Fig. 9. The method shown in Fig. 10 

 for obtaining the resultant may be put into words as follows : 



Draw the vectors of the two quantities with the fixed 

 end of one upon the rotating end of the other, i.e., with the 

 arrows of both directed towards the same end of the completed 

 bent line. The vector of the resultant is the line joining 

 the free ends of the bent line thus obtained. Its direction 

 will be such that its arrow points in the opposite direction 

 round the closed figure formed by the vectors to the arrows 

 of the component quantities. 



This construction may be extended to any number of 

 component quantities. The resultant of them all is always 

 the line joining the free ends of the figure obtained by drawing 

 all the quantities in regular sequence, the fixed end of one 

 vector coinciding with the rotating end of the previous one. 

 The angle which the resultant line makes with the components 

 represents its phase relative to them. 



The application of the construction just given may be 

 illustrated by the following experiment: 



EXPERIMENT I. DETERMINATION OF THE RESULTANT 

 ELECTROMOTIVE FORCE OF TWO ALTERNATORS COUPLED 

 TOGETHER. 



DIAGRAM OF CONNECTIONS. 



FlQ. U, 



