1028 
PROFESSOR J. A. EWING AN’D MISS H. G. KLAASSEN 
a second—the commutator being driven uniformly by means of a small electric motor 
--and the exposure lasted during some twenty to thirty cycles. The curves, there¬ 
fore, give good evidence of the constancy with which the movement repeats itself 
In the last figure in the group of fig. 28 the commutator was slowly turned by hand, 
and two minor loops were superposed on the main cycle. 
Fig. 29 is another test made at the same time, and on the same metal as the tests 
of figs. 26 and 27. It shows a small loop superposed on a main cycle, and also a 
curve (drawn in broken line), which is the magnetization curve starting from zero, 
taken after the metal had been reduced to neutrality by the process commonly known 
as “ demagnetizing by reversals ”—namely by numerous reversals of a gradually 
Fig. 29. 
diminishing^ mag:netic force. Here is found a feature which was first remarked, we 
believe, by Dr. John Hopkinson, namely, that in magnetizing from the neutral state 
the curve crosses the rising limb of the cyclic curve. The same feature has been 
looked for, and always found, in many other curve-tracer tests. 
This crossing is in agreement wuth the fact already noticed, that the extremity of 
one cyclic curve projects beyond the rising limb of a higher cycle. For, after a piece 
has been put through the process of “ demagnetizing by reversals,” the magnetizing 
curve starting from zero passes, as nearly as we caji judge, through the projecting 
extremities of the cycles. Hence it lies outside of the upper part of the rising limb 
of any cyclic curve. 
Fig. 30 gives a further illustration of these remarks. It shows a magnetic curve- 
tracer test of moderately hard steel, the dotted curve being obtained by magnetizing 
