49 



will then occupy the position E/" 

 Under these conditions the machine will 

 work as a generator, and much more 

 advantageously than formerly, though 

 not yet with the best plant efficiency. 

 To obtain the best result the field must 

 further be strengthened, until the in- 

 duced electromotive force occupies the 

 position E, and the terminal electromo- 

 tive force the position E ft when the maxi- 

 mum output is reached, and the machine 

 is in exactly the same condition as the 

 other machines. The safe limits, within 

 which the strength of the field may be 

 varied, are given by the length of the 

 lines OE and OE', and the ratio of the 

 corresponding exciting currents must 

 obviously be still greater than that be- 

 tween these two lines. It is instructive 

 to observe what part armature resistance 

 and self-induction take in determining 

 this ratio. As regards the armature re- 

 sistance, the lower this can be made the 

 better; in modern machines the resist- 

 ance is generally so small that the loss of 

 pressure is limited to from 2 to 5 per 



