High-Frequency Alternator. 301 



the motor-shaft as the driving-wheel ; the other, which was 

 carried in an ordinary front-fork and hub with ball-bearings, 

 acting as a tension-pulley to balance the pall on the alter- 

 nator-spindle. 



The pulleys on the alternator-spindle were of steel, having 

 a diameter of only 10 mms. at the bottom of the V-grooves 

 in them. The ratio of the belt-drive, that is the number 

 of turns of the alternator-spindle for each revolution of the 

 motor, was found experimentally to be 42'5. 



To measure the frequency, a Young's speed-indicator was 

 used geared down from the inductor-spindle by means of 

 worm and wheel, having a ratio of 20 : 1. Although the 

 spindle was constantly run at speeds of between 30,000 and 

 40.000 revolutions per minute, no trouble was experienced 

 with this gear. 



Curves I. — Characteristics of High-Frequency Alternator 

 on Open Circuit. Inductor with 30 teeth. 



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With this method of driving, frequencies up to 18,000^- 

 per second could be obtained. Curves 1. are characteristic 



