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to complain of the combination of differ- 

 ent kinds of units, C. G. S. and English. 

 He was sorry to find the same practice in 

 the present paper, and he wished to 

 enter his protest against it. The author 

 spoke of the mean value of the electro- 

 motive force of an alternating current 

 as the electromotive force of a direct 

 current, which will, in a given re- 

 sistance free from self-induction (say, 

 for instance, the wire of a Cardew 

 voltmeter), produce the same amount of 

 heating. That was not a definition of 

 the mean value of the electromotive 

 force of the alternating current. He 

 would beg the author to withdraw the 

 expression " mean value," and substitute 

 " virtual or equivalent value." Until a 

 few years ago, electricians thought that 

 a continuous current was the proper one 

 to use for distribution, and that the 

 alternate current was objectionable for 

 many reasons. But now they were quite 

 agreed that the alternate current was in 

 many of its adaptations far more beauti- 

 ful and more readily adapted than the 



