42 
Proceedings of the Royal Society of Edinburgh. [Sess. 
fig. I.a when H= + 0'43 the “ons” and the “offs” decrease and increase the 
induction respectively by nearly equal amounts from the first, and either 
of these amounts corresponds to the difference between the “ on ” and “off” 
curves of fig. I. at this particular value of field, irrespective of whether the 
first or the seventh “ on ” curves be taken. 
When these experiments are repeated with permanently acting vibra- 
tions, fig. I.v shows the curves representing the fourth “on” and “oft 1 ” of 
load superposed on a loop without load, fig. II. v the curves representing the 
fourth “off” and “on” superposed upon a loop performed with permanent 
load. Under these conditions the first “ on ” differs very little from the 
fourth “on” (fig. I.v), and the first “off” very little from the fourth “off” 
(fig. II. v). These figures are the experimental results obtained for the same 
amplitude of cyclic field as in figs. I. and II., but the scale is three times 
closer. For approximately the same induction amplitude, and consequently 
lower field amplitude, the crossings of the curves remain essentially the 
same. 
In the above diagrams the curves representing the (practically) final 
“ ons ” or “ offs ” of load are obtained by the summation of .all the readings. 
In those now to be described, where “ ons ” and “ offs ” of load are super- 
posed forty times in succession, this method becomes wholly inapplicable. 
If the cyclic amplitude be sufficiently increased, the induction at cyclic 
extremes may be assumed to be independent of the “ ons ” and “ offs ” of 
load superposed during the cyclic. That this assumption is sufficiently 
correct is supported by the fact that there is no “ sagging ” in either 
direction when the field is reversed several times on the conclusion of any 
series of readings. The actual position of each final “off” of load may 
therefore readily be obtained by noting the induction change ivhen a 
single step is taken to the opposite cyclic extreme to that from which the 
observations started. This also fixes the position of the immediately 
preceding “ on ” of load. Fig. III. shows the curves, obtained in this manner, 
representing the fortieth “on” and the fortieth “off” of the 11 ozs. load 
(05 kilos per mm. 2 ) superposed under the A conditions upon the normal 
hysteresis loop, the values of field and induction at cyclic extremes being 
respectively H = 11T and B = 4200. The series of smaller diagrams 
(fig. Ill.a) show the instantaneous induction changes which occur between 
the first and fortieth “ ons ” and “ offs ” of load for various values of field 
between H = + 11 1 and H = — 11 1. 
In figs. IV. and IV.a the corresponding results are recorded when 
mechanical vibrations are permanently acting. 
Figs. III. and IV. eliminate not only possible errors very liable to occur 
