84 
ME88R8. (r. Y. C. SEARLE AND T. G. BEDFORD 
wliicli are placed on the ordinate corresponding to any number, .r, of complete 
revolutions, indicate the values found for Bq and AV when the wire was allowed to free 
itself from stress after the wheel had been turned through x revolutions. 
The curves (2a) show that, as in the case of specimen (]), the application of torsion 
causes a continued decrease of Ijoth and W. The decrease is at first very rapid, 
Bq falling from G520 to 4750 and W from 4380 to 3180 for the first half revolution 
of the wheel. The curves (26) show that after the first half revolution of the wheel 
both Bg and W diminish continually, but at first much less rapidly than is the case 
for the curves (2a). The initial parts of the curves (26) are an exception to the rest, 
for when the wire was allowed to untwist after the wlieel had been turned through 
the first half revolution both Bg and W were greater than before the wire was 
twisted at all, Bg rising from 6520 to 6720 and W from 4380 to 4590. 
Up to about 13 revolutions of the wheel, the relief of torsional stress was followed 
by an increase of both Bg and W, but beyond this point the relief caused a decrease 
of both Bg and W. 
The wire broke at 101 revolutions of the wheel, i.e., at practically the .same twist 
as wire (1); the length was very nearly the same, viz., 65‘7 centims. Just before 
fracture the values of Bg and W under the torsion due to 100 revolutions were 
Bg = 1050, AY = 383, and when the wire had freed itself from stress, Bg = 960, 
AY = 383. After fracture the values fell to Bg = 787, AA" = 302, the changes being 
much smaller than tliose for .specimen (1). It .seems probable that the diminution 
of Bg and AA' wiiich occurs on fracture is due to the violent jar which attends the 
fracture. 
The values of both Bg and AY in (2a) and ( 26 ) are for large twists very much 
smaller than the corresponding values in (l). It is true that the permeability of (2) 
l)efore it was strained, viz., /x = 1304 for Hg = 5, is much less than the value 
IX = 1694 for (1) under the same conditions. But the great difference between 
(1) and (2) in respect to Bg and AA^ for large twists can hardly be due to this fact. 
It is more likelv due to the untwistino; of the wire at the various .stao-es of the 
process. 
AA'hen the wire had been twisted we found just as for (l) that AA" dimiiiishes con¬ 
siderably even after 20 cycles of magnetisation. AYe took 20 cycles in each case 
before making the tests for Bg and AA^, but if AA^ is still diminishing with continued 
reversals, it is hardly possible to assign any very definite value to it. 
The wire, initially quite jDliable, was very stiff after it had been broken by 
twisting. Its length originally was 65'7 centims., and this was increased by the 
torsion to 66‘9 centims. The mean diameter diminished from '0796 to ‘0793 inch. 
Thus the volume of the wire increased by about 1 per cent. 
The smallest values reached by Bg and AA", viz., those found after fracture, are 
very small compared with those found before the wire was strained. Initially 
Bg = 6520, AA^ = 4380, and finallv Bg = 787, AA^ — 302. 
