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clear significance — "the square root of 

 the mean square." The two things differ 

 by many per cent., depending on what 

 function the electromotive force was of 

 the time. The mean electromotive force 

 of an alternate-current and a direct-cur- 

 rent dynamo similarly constructed, must 

 be identical. Whether the wire was piled 

 up all at one place, or whether spread 

 uniformly round the armature, as in a 

 direct-current dynamo, the mean electro- 

 motive force must necessarily be the 

 same. The author spoke of " English 

 lines of force." There was no such thing 

 as an English line of force ; lines of force 

 were essentially cosmopolitan. One of 

 the great charms that the absolute 

 system of electrical and magnetic units 

 possessed was its perfect harmony, and 

 therefore any attempt to introduce new 

 units should be deprecated. Experi- 

 ments made at the Central Institution, 

 for finding the coefficient of self-induc- 

 tion of a transformer, showed that in no 

 case was there no lag between the im- 

 pressed electromotive force and the pri- 



