and Retentiveness of Iron and Steel. 383 
instance, where the wire had been hardened by stretching, 
the maximum ratio of residual to total magnetism was 0*60, 
which was given by the application of a magnetizing force of 
about 10 C.Gr.S. units ; but after the application of a force of 
90 units the ratio fell to 0*33. In steel the maximum in this 
ratio is less sharp, but still distinct. Neither in hard iron nor 
in steel is the ratio, even at its maximum, so great as it is in 
soft iron, where (as has been said) it frequently reaches 0'9. 
During the magnetization of soft-iron wires the greatest 
ratio («) of Intensity of magnetization (I) to magnetizing 
force was generally about 200, sometimes nearly 300. And 
by gently tapping the wire during the application of magneti- 
zing force, this coefficient was on one occasion raised to the 
enormous value of 1590. In the case alluded to the magneti- 
zation went on so rapidly as the magnetizing force was in- 
creased, that a force of 1 C.Gr.S. unit gave an Induction of 
10,000. 
In this and other particulars the experiments have been 
strongly confirmatory of the idea that there is in soft iron a 
static frictional resistance to the rotation of the magnetic 
molecules, which is the principal cause of the remarkable re- 
tentiveness described above, and which is overcome by gentle 
mechanical agitation. 
Numerous measurements have been made of the energy 
expended in taking iron and steel through cyclic changes of 
magnetization. For example, in changing the magnetism of 
one specimen of annealed iron wire from I = 1250 to I = — 1240, 
and back, the amount of work done against magnetic friction 
(apart from any induction of currents) was 1670 centimetre- 
dynes per cubic centimetre of the metal. In hardened iron, 
and especially in steel, the work done is much greater. 
The effects of stress on existing magnetism and on' mag- 
netic susceptibility have been investigated at great length. 
The most remarkable effects occur in wires which have been 
hardened by stretching. In them the presence of a moderate 
longitudinal tensile stress increases the magnetic susceptibility 
immensely at low values of the magnetizing force, but dimi- 
nishes it at high values. It also increases very greatly the 
ratio of residual to temporary magnetization. Each of these 
effects passes a maximum when the stress is sufficiently in- 
creased. 
The whole subject is much complicated by the presence of 
the peculiar action which in previous papers the writer has 
named Hysteresis, the study of which, in reference both to 
magnetism and to thermoelectric quality, has formed a large 
part of his work. 
