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however, good reason to believe that the 

 speed, at which the cyclic change of 

 magnetism is performed, has a consider- 

 able influence on the amount of energy- 

 dissipated in heat per cycle. It is prob- 

 ably due to the disadvantage of too great 

 a speed that most makers of alternators 

 find it advisable to work at a moderate 

 frequency. Another reason telling 

 against high frequency is that either the 

 speed of the machine, or the number 

 of field-poles, or both, must be incon- 

 veniently great. A very high speed is 

 mechanically objectionable, and the adop- 

 tion of a large number of field-poles 

 has the disadvantage of reducing the 

 pitch, and therefore of increasing the 

 magnetic leakage, whilst at the same 

 time lowering the coefficient k, all of 

 which tend to an increase in the weight, 

 bulk, and cost of the machine. On the 

 Other hand, too low a frequency would 

 also tend to increase the cost of the 

 machine, and there must therefore be, for 

 each type of alternator, a particular 

 frequency at which the best results are 



