ON THE MEASUREMENT OF MAGNETIC HYSTERESIS. 
73 
H = 20’54, the changes in W being roughly the same as those for the iron wire, 
demagnetised by annealing, under approximately the same magnetic forces. 
Ho = 7-29. 
H„ = 20-54. 
Bo. 
W. 
Bo. 
W. 
1 
1275 
853 
11430 
32840 
2 
1255 
838 
11370 
32670 
3 
1275 
838 
11370 
32530 
4 
11370 
32580 
11 
1240 
787 
11310 
32110 
21 
1275 
779 
11340 
32110 
41 
1275 
768 
11280 
32040 
W — Bq Curves for Zero Stress. 
§ 50. The energy dissipated through hysteresis can be varied in many ways. We 
describe, in the sequel, many experiments in which the hysteresis loss for constant 
values of Hq was caused to vary by varying the stress applied to the specimen ; Mr. 
Wills has varied the hysteresis loss for constant values of Hq by varying the 
temperature of the specimen. But perhaps the most natural, and certainly the most 
usual, way of varying W is to vary Hq, while the stress is kept at a constant zero 
value. The curve representing W as a function of Bq under these conditions is the 
curve which is useful to engineers when designing transformers. To distinguish it 
from the curves, which represent W as a function of Bq, when Hq is kept constant 
and Bq is varied by varying the stress, we call it a W — Bq curve for zero stress. It 
is the curve for which Mr. C. P. Steinmetz has proposed the formula W = -17 Bq' *’. 
Effects of Stress. 
§ 51. We now pass on to describe a number of experiments in which we studied 
the effects of tension and torsion upon the mean maximum magnetic induction, and 
upon the energy dissipated by hysteresis when the magnetic force ranged between 
definite limits -E Hq. In each case the same series of stresses was applied to the 
specimen for each value taken for Hq. 
Effect of Tension on Soft Iron Wire. 
§ 52. The first systematic experiments on the effect of stress upon the energy 
dissipated in hysteresis were made in 1898 upon a soft iron wire. 
VOL. CXCVIII.-A. L 
