1908-9.] Load and Vibrations upon Magnetism in Nickel. 51 
irreversible vibrational effect observed upon the first superposition of load. 
The increase of induction due to this cause is not so completely eliminated 
with permanently acting vibrations as the increase due to the first super- 
position (figs. IX. and VII.). Permanently acting vibrations, while increasing 
the induction change due to load, decrease the area of the loops formed 
during a cyclic load process, and observed in these figures when loading 
and unloading is performed in steps. A comparison of fig. VIII. with, say, 
fig. 108 given on p. 218 of Ewing’s Magnetic Induction, 3rd ed., shows 
that the irreversible vibrational effect of cyclic loading does not differ from 
the same effect in iron, except that it is the first increment of load that 
in general gives rise to induction increase, and not successive increments 
as in iron. This is due to the fact that in nickel the irreversible 
vibrational and the reversible effects of load oppose each other, while 
in iron they assist each other. Nevertheless, the vibrational effect of 
repeated loading and unloading tends towards induction increase in nickel 
as in iron. 
This latter effect is especially marked in low fields (fig. X., dash line 
curves). The final “off” curve is for all values of field the higher of the 
two, but lower than that obtained under the B conditions with permanently 
acting vibrations of sufficient intensity. The final “ on ” curve (A conditions) 
and the permanent load curve (0*5 kilos per mm. 2 — B conditions) with vibra- 
tions fall above or below the normal BH curve as the fields are low or 
high respectively. The permanent load curve without vibrations (B 
conditions) is the lowest throughout of the six curves compared, that with 
permanently acting vibrations of sufficient intensity without load (B con- 
ditions) the highest; the load curves therefore fall below the corre- 
sponding curves without load. This almost universally recognised result 
is irrespective of whether mechanical vibrations are or are not acting. 
Permanently acting vibrations, however, eliminate in fields increasing 
from zero the irreversible first effects of loading and unloading to a 
greater extent that at some stages of cyclic field (fig. XII. and figs. Ill.a, 
IV.a respectively). 
But the load effect, i.e. the ordinate differences between each pair of curves, 
is at all values of induction decidedly less under the A conditions without 
vibrations than under the B conditions irrespective of whether vibrations 
are or are not acting. It may be noted that the approximation of the load 
effect under the A conditions with vibrations to the load effect under the 
B conditions will depend upon their intensity. 
