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bout 150 currents (300 positive and 

 egative) per second, but by practice he 

 ad come down to the figure given by 

 tie author, 78. He had omitted to men- 

 !on that throughout Europe the alter- 

 ate-current machines were being con- 

 tracted principally by the firm of Ganz, 

 f Budapest. The Zipernowsky system 

 ad been introduced, first in Italy, and 

 here worked out thoroughly by a dis- 

 nguished electrician, Professor Ferraris, 

 n the Zipernowsky system the frequency 

 ad been brought down from 150 cur- 

 ents to 42. Mr. Parker had brought it 

 own to 100. That was one of the most 

 nportant questions to be decided, and it 

 ould only be done by actual practice, 

 lir William Thomson had shown, by 

 lathematical reasoning, that if currents 

 fere sent with high frequency, they had 

 ot time to penetrate into the interior of 

 conductor. With a solid conductor, 

 ay between Deptford and London, one 

 rich thick, at a high frequency, the cur- 

 ent would not enter more than about 3 

 lillimeters inside the surface ; thus the 



