610 
PROFESSOR J. A. EWING ON EXPERIMENTAL 
and 8 kilos. After demagnetising by reversals the load was put on, then magnetising 
force was gradually applied up to 18 c.g.s. units and gradually removed, while mag¬ 
netometer observations were taken. The results are shown in Plate 64, fig. 46, where, 
for the sake of comparison, a normal (no-load) curve, taken just before the wire was 
drawn by 15^ kilos., is also given. The effects of load, especially of 6 or 8 kilos., is 
enormous in increasing the susceptibility in the first part of the curve : the suscep¬ 
tibility is actually eight times greater with than without that load in the early part of 
the magnetisation. It is particularly interesting to notice that the wire after being 
stretched and then loaded with 4, 6, or 8 kilos, is actually more susceptible to mag¬ 
netisation by low fields (under <§=l) than it was when in the soft annealed state. 
The crossing of the 6 and 8-kilo, curves will be noticed. 
§ 94. Neither the range of loads nor the greatest magnetising force applied was 
sufficiently great to make this experiment exhaustive, and accordingly another series 
of similar observations was made (May 10, 1882) on the same wire after it had been 
further drawn by 18'5 kilos. Its state was then identical wuth that in which the 
experiment of § 88 was made, and the results given below are, therefore, directly 
comparable (allowance being made for the effects of hysteresis) wdtli those there 
described as obtained by the other method, and exhibited in fig. 42. Curves of the 
relation of 3 to <§ were taken under the following constant loads :—0, 1, 2, 4, 6, 8,10, 
12, 14, 16’2, 18'5 kilos., the highest magnetising force reached being 33'6 c.g.s. units. 
Before taking each curve the previous magnetisation was removed by the method of 
reversals before the previously applied load was removed. Then that load was 
removed, and the process of demagnetising by reversals was repeated. Then the 
desired load was put on, and the wire w T as magnetised, the relation of 3 to ,£) being ob¬ 
served. The results are given numerically below', and are shown in Plate 64, fig. 47, 
from which it will be seen that the curves taken with load, although lying much 
higher than the normal or no-load curve in the early part of their course, begin to 
cross it as the magnetisation becomes strong, the first to cross being the 18'5-kilo, 
curve—that of greatest stress. In other words, the magnetic susceptibility, although 
far greater in the stressed than the unstressed wire so long as the magnetisation 
is moderate, becomes less in the stressed wire as the region of saturation is reached. 
During nearly the wdiole of its length the 8-kilo, curve lies higher than any of the 
others. It is with this load that the maximum of susceptibility occurs, except at very 
low and again at very high values of the magnetisation. 
In the lower part of the same figure curves are given which show the relation of 
3 to during the gradual removal of <§. 
