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PROFESSOR J. A. EWING ON EXPERIMENTAL 
§ 95. The same results are also exhibited graphically in Plate 65, fig. 48, in the 
manner explained in § 92, and this figure admits of immediate comparison with fig. 42, 
because both figures refer to the same piece of wire in the same physical condition. 
Fig. 48 shows very clearly how there is, for each value of the magnetising force, an 
amount of stress for which the susceptibility is a maximum, how this maximum occurs 
at a lower and lower value of the stress as the magnetisation is increased, and, finally, 
how the resultant effect which the greatest load (18'5 kilos.) exerts on the susceptibility 
passes from posit ive to negative as the state of saturation is approached. The magnetis¬ 
ing force to which each of the curves relates is given in the figure, and is in several 
values the same as that at which, in the previous group of observations, the effects of 
loading and unloading were investigated (§ 88). From what has been said in § 92 it 
will be at once seen that the curves of fig. 42 would agree with those of fig. 48 if the 
effects of hysteresis were absent. In that case it would be a matter of indifference 
whether stress were applied before magnetising force, or magnetising force before 
stress. Hysteresis affects both experiments, though quite differently, but by 
examining the two sets of curves together we can see the general relations of mag¬ 
netic susceptibility to stress in the features which are exhibited by both. From the 
two together we may confidently conclude that the influence of pull on magnetism 
is positive until the magnetisation is so much raised as to bring about the Yillapj 
reversal; that this positive effect is slight at low magnetisations, and increases greatly 
so as to pass a maximum before reversal; that the amount of this positive effect 
depends on the amount of stress applied, passing a maximum whose position varies in 
the way stated above; that the value of the magnetisation at which the Yillapj 
reversal occurs depends on the value of the stress, being lower the greater the stress. 
In fact, if we deal only with very small stresses it is doubtful whether any reversal 
of the positive effect of stress would be reached even at the highest attainable value of 
the magnetisation. 
§ 96. Residual Effects of Stress Changes occurring when the Wire is free from 
Magnetism. —During the progress of some experiments of the same type as those just 
recorded, but preliminary to them, a very curious phenomenon was noticed, which 
gave a fresh and interesting example of the presence of hysteresis in a somewhat 
occult form. 
If we take an iron wire which has already been stretched beyond its original limit of 
elasticity, and which has, therefore, reached a stable state as regards any subsequent 
applications of lesser pull, we may load and unload and magnetise it as we please, but 
provided we demagnetise it by the method of reversals after removing the load, we 
shall, on taking a new “ normal ” curve of magnetisation, always find its susceptibility 
sensibly the same. But suppose that after the wire has been completely demagnetised 
we apply a load and remove it. During this process there has been no magnetisation 
visible, and there has been no mechanical change of any ordinary kind. Nevertheless, 
a molecular change of a very decided character has occurred, which is at once detected 
