45 



much on the capacity of the machine 

 which is . being switched on, as on the 

 consideration as to how much current 

 may be temporarily taken from the other 

 machines at work. A new machine is 

 only added, if the limit of output of 

 these machines is in danger of being 

 overtaken by the demand for current in 

 the whole system ; and since the avail- 

 able margin will therefore necessarily be 

 small, the machine about to be coupled 

 up must not be allowed to act as a heavy 

 drain upon the other machines. . This 

 limits the amount of current at disposal 

 for bringing the new machine into step. 

 Let this maximum current be represented 

 by the line O A. Before switching on, 

 the engine is started and run up to the 

 proper speed, in which case the only 

 work done by the engine is that of over- 

 coming its own friction, and the fric- 

 tional resistance of the machine. If, at 

 the moment of switching on, the in- 

 duced electromotive force occupies a 

 position to the left of the line Oy, there 

 will be a momentary increase of current, 



