1038 
PROFESSOR J. A. EWING AND MISS H. G. KLAASSEN 
Fig. 40. 
When a piece of previously unmagnetized, iron or steel is acted on by a magnetic 
force sufficiently strong to carry the metal to the stage of high permeability, but not 
strong enough to make it approach saturation, and this force is then caused to vary 
between equal positive and negative values, it is found that the first application induces 
more magnetism than is induced by subsequent applications, and that the changes of 
magnetism do not become cyclic until the force has been several times reversed. And 
during this gradual approach towards a cyclic regime the range through which the 
magnetism varies between its positive and negative extremes becomes reduced. These 
effects of hysteresis are wmll shown by fig. 38, which is copied from a former paper,’' 
aiid represents a test of a piece of annealed steel. 
The same phenomena occur in the model, provided the little magnets have been 
previously shaken up and allowed to settle in the absence of any directing field : a 
condition which may be supposed to correspond with the annealing of the solid metal. 
Fig. 39 is a characteristic instance. It represents a test of the same group of pivotted 
magnets as was used in figs. 36 and 37. After all effects of earlier deflecting fields 
had been eradicated by shaking up the group, a rather weak directing force was applied, 
first to the positive side, and then this was reversed three times. At the third 
reversal the changes of aggregate moment on the part of the group had become nearly 
cyclic, but with a range of variation which was decidedly less than that indicated by 
the first application of the field. Corresponding results were found in another 
^ ‘ Phil Trans.,’ 1885, Plate 61, fig. 28. See also fig. 26 on the same plate. 
