IRON AND STEEL IN A ROTATING MAGNETIC FIELD. 
725 
Hard Steel .—B ~ 2,720 
6,600 
9,800 
11,900 
14,400 
Hysteresis = 3,580 ergs. 
13,850 „ 
24,000 „ 
33,300 „ 
68,000 ,, 
These values are shown in the curves on Diagrams 4 and 5. 
Test of Variation of Hysteresis with Induction in Rotating Field. 
The following tests were taken to determine the nature of the variation of 
hysteresis as the induction is increased. Both hard cold-rolled steel, and soft 
charcoal iron were used. 
The machine was kept running continuously through the test, and the current was 
kept on continuously and gradually increased, except when very heavy currents were 
used. Some 10 or 15 secs, were allowed to pass before the reading was taken to give 
the deflection time to become steady. The effect of not complying with these con¬ 
ditions will be discussed later. 
The shape of the pole pieces was varied twice to obtain a stronger field, and the 
armature was reduced in length. The first change was to cut away the poles, making 
the length of the polar area 1‘8 centim. instead of 2‘5 centims., and later coned ends 
were fitted to give a stronger field, the latter shape being shown in the Diagram (1). 
The calibration curves for the three shapes are shown in Diagram 2. 
The hard steel armature was used. 
Headings were taken at 28 revolutions and at 56 revolutions per second, the agree¬ 
ment being fairly close. 
With a shortened armature and stronger field, a set was taken at 34 revolutions 
per second. 
With the shortened armature and cone-shaped pole pieces a set was taken at 
26 revolutions per second. This was the strongest field that could be obtained. 
The results are given in the adjoining table, and the curves are plotted in Diagram 4, 
together with the hysteresis curve, by the method of reversals for a piece of the same 
sample of steel. 
The whole curve is shown, from very low values of B up to nearly 20,000. It will 
be seen that all four sets of readings are very fairly concordant. A maximum value 
of 44,000 ergs is reached at an induction which varies between 14,000 and 15,000. 
At the beginning the curve rises very slowly and then turns up sharply along an 
almost straight line. Between 9,000 and 10,000 there is a slight flexure in all of 
them and another straight piece until the maximum is reached. Here there is an 
abrupt bend and a more rapid descent on the other side, again almost straight, the 
