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be about 1 per cent, of the output, and 

 the loss in resistance of the armature 

 about 1£ per cent. This machine (Fig. 

 31) was not yet completed, but one of 30 

 units had been made and carefully tested. 

 With regard to the question of hysteresis, 

 he had made experiments upon the loss 

 in the armature. A cylindrical armature - 

 core, 5 inches in diameter, composed of 

 one hundred iron plates to the circle, 

 insulated from each other by thin paper, 

 but not insulated from the spindle, was 

 rotated in a bi-polar field. The energy 

 required to rotate the core when sub- 

 jected to different intensities of field, and 

 at different speeds of rotation, was meas- 

 ured by independent means. In one 

 experiment the same core was rotated, 

 first at 8,500 revolutions per minute, and, 

 secondly, at 6,500, the strengths of field 

 being maintained in the two cases in- 

 versely proportional to the speeds ; or, 

 in other words, the electromotive force, 

 had the core been wound with conduct- 

 ing wire, would have been identical in the 

 two cases. It was found that the power 



