77 



common practice for an indication of 

 what the limit probably is. The present 

 types of alternators and transformers, it 

 must be remembered, are not mere 

 experimental machines, but the survival 

 of the fittest, and it would be futile to 

 ignore the lessons taught by practical 

 experience extending over several years. 

 The following is a list giving the average 

 frequencies adopted by several designers : 

 Ferranti, 67 ; Lowrie-Parker, 88 ; Mor- 

 dey, 100 ; Zipernowsky, 42 ; Kennedy, 

 60 ; Kapp, 80 ; Westinghouse, 133. 



Taking the average of European prac- 

 tice, the frequency is 73, or 8,750 reversals 

 per minute ; whilst the American practice 

 is 16,000 reversals per minute. This 

 large difference may, to a certain extent, 

 be accounted for by the general pre- 

 ference of European engineers for 

 machines running at moderate speeds: 

 but even when making due allowance for 

 this circumstance, it can hardly be as- 

 sumed that, had actual practice shown 

 the value of a very high frequency, elec- 

 trical engineers would not have found 



