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conditions, it will easily be seen, can only 

 be fulfilled if the machines are capable of 

 working in parallel, and it is, therefore, 

 of considerable practical importance to 

 investigate the conditions under which 

 alternators may be expected to work 

 safely in parallel. This subject is closely 

 allied with that of working alternators as 

 motors, and it is, therefore, convenient 

 to consider the two problems jointly. 

 The analytical treatment of an alternate- 

 current motor is even more difficult than 

 that of an alternate- current generator; 

 but by an extension of the graphic 

 method, the question can be treated in a 

 very simple and easily understood man- 

 ner. It is well known that an alternator 

 will not start without mechanical assist- 

 ance, but that, having been started at a 

 speed approximately corresponding to 

 the frequency of the supply current, it 

 is kept in motion when this current is 

 switched on to its terminals, and it may 

 under certain conditions even give off 

 mechanical energy. The problem in- 

 volved may therefore be stated somewhat 



