RESEARCHES IN MAGNETISM. 
595 
fall outside the field of the operations, namely, to the left of the origin. If we could 
extend the experiment by applying ‘push we should expect to find a continuation of 
the curve such as that sketched in a dotted line, with a maximum point between E 
and F. But of course on reapplying the load from zero the curve followed is E G C, 
and any succeeding repetition of the cycle gives a loop like EGCD. On the other 
hand, if at the beginning we had loaded with 1 kilo, only, on would have given rise 
and off would have given fall of magnetism in any repetition of the cycle, since in 
that case the whole action would have been confined to the ascending branch of the 
curve, namely, between A and B. 
In this way, then, hysteresis causes the maximum which would otherwise occur at or 
near a load of 1 kilo, to disappear when cyclic loading is continued with greater loads. 
It also raises the value of the magnetism found with load =0 to a value which may 
fairly be called abnormal (as at E in the figure above), so that subsequent tapping 
under no load causes a fall of magnetism. 
§ 79. If this explanation of the apparently anomalous actions which occur during the 
loading and unloading of an annealed wire be correct, the principal difference between 
the curves before and after stretching is in the position of the maximum point. 
Before stretching the maximum lies so near the origin as to disappear in the manner 
just described when the loading is repeated more than once. As the range of load is 
increased it shifts towards the right, and becomes prominently visible when and after 
the limit of elasticity is reached. It continues to shift towards the right as the wire 
is drawn out by successive increments in the range of stress. We thus find on 
careful examination not only continuity between the results obtained before and after 
stretching, but an essential similarity. 
At the same time, experiments both with this and with other specimens of iron 
have shown that, when loaded and unloaded until the action becomes cyclic, a piece 
which has not been strained beyond its elastic limit since annealing behaves after the 
type of curve No. 1 below, and one which has received permanent set behaves after 
the type of No. 2. 
