74 MR. S. BUTTER,WORTH ON EDDY-CURRENT LOSSES 
The wire used was copper of diameter 1-168 cm., and the frequencies employed 
ranged from 60 to 5,000 cycles per second, so that the range of z in formula (48) is from 
0• 84 to 7 • 7. The spacing (D — d) varied from 0 • 03 cm. to 60 cm., so that the observa¬ 
tions afford a very complete check on the adequacy of the formula. 
The resistance of the loop, which for direct currents was of the order 0-01 ohm. was 
measured by an alternating current bridge. In this method variation of contact 
resistance would probably be the chief source of trouble. As to whether this effect is 
appreciable, may be judged by a comparison of the tabulated direct current resistances 
after allowing for temperature variations. In fig. 5 this is done by plotting the 
resistances on a resistance-temperature diagram. Of the five groups of observations at 
spacings 60 cm., 20 cm., 6-4 cm., 0-8 cm., 0-03 cm., four show to within half a per 
