47 



quarter period. This circumstance tends 

 greatly to minimize the disturbing in- 

 fluence of the machine, which absorbs 

 current upon the other machines supply- 

 ing current to the mains. Thud the idle 

 machine takes most current at a time 

 when the mains take hardly any, and 

 when the mains take maximum current 

 that passing through the machine is 

 nearly zero. This automatic process of 

 compensation is valuable, as it allows the 

 permissible current, for bringing the new 

 machine into step, to be fixed consider- 

 ably higher than would otherwise be safe. 

 If, without increasing the field, more 

 steam be given to the engine, causing it 

 to push the armature into a more 

 advanced phase, the point E' will move 

 to the left of the vertical, and E'< will 

 move to the right, whilst the current will 

 increase. As soon as E' f has passed the 

 vertical it opposes the current, and the 

 machine ceases to act as a motor, but 

 acts as a generator supplying current to 

 the mains. It is thus possible to run the 

 machine as a generator in parallel with 



