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portion R E represents the electromotive 

 force actually available for doing work 

 through the resistance of the external 

 circuit ; and this will the more nearly 

 approach the induced electromotive force 

 the smaller the armature resistance, and 

 the smaller the self-induction of the 

 whole circuit. In order to obtain a 

 maximum of work in the external circuit 

 with an alternate-current plant, it is, 

 therefore, advantageous that the armature 

 of the alternator should have a minimum 

 of resistance, and that the total self- 

 induction of the circuit should be small. 

 The commercial value of a given type of 

 alternator depends, amongst other things, 

 upon the amount of work which can be 

 obtained from a given weight of materials 

 employed in the construction of that par- 

 ticular type of alternator. This value 

 will, therefore, be roughly indicated by 

 the ratio between the length of the lines 

 R E and O E ( ; and this ratio the author 

 proposes to call "plant-efficiency.'' It 

 must be borne in mind that the plant- 

 efficiency is not an indication of the more 



