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regard to the transformers, and it is 

 much to be desired that electrical engi- 

 neers should adopt a common standard. 

 Comparing two equal transformers, one 

 working with a frequency of, say, 65, and 

 the other with one of, say, 130, it is 

 evident that with the same pressure the 

 induction in the latter need only be half 

 that in the former ; and if the effect of 

 static hysteresis only had to be con- 

 sidered, the heat generated per cycle 

 would be something less than half; and 

 the total heat generated in a given time 

 would, with the high frequency, be some- 

 what less than with the low frequency. 

 But as there is every reason to believe in 

 the existence of viscous hysteresis, by 

 virtue of which the heat generated per 

 cycle increases with the speed at which 

 the cycle is performed, there must be a 

 limit to the frequency beyond which a 

 further increase becomes disadvantage- 

 ous. With the present imperfect knowl- 

 edge of this subject, it is not possible 

 to determine this limit on theoretical 

 grounds; but it is justifiable to look to 



