1 905 - 6 .] Electric Oscillations and Magnetic Properties of Iron. 37 
at or near cyclic extremes , where the slope of the curves is greatest. 
But as the cyclic field maximum is increased, the greatest 
induction change occurs at an earlier stage of the increasing field, 
where in this case also the curves are steepest. 
To so great an extent is this the case for co-directional 
oscillations, that the usual order of things is reversed and the 
up curve (increasing field) actually reaches higher induction 
values than the down curve (decreasing field). The curves for the 
complete cycle thus cross (forming three loops) where co-directional 
oscillations give rise to an induction the same in value and sign 
whether they are superposed on the decreasing or increasing 
field. 
It may be worth noting that at some maximum value of field 
between those given in figs. 1 and 2, these crossing points may 
coincide with the neutral point when the field is decreasing where 
superposed co-directional oscillations produce no induction change. 
The curves for transverse and co-directional oscillations given in 
figs. 2 and 3 must not he confounded with the usual hysteresis 
loops in the sense that the areas they enclose measure the energy 
loss during one complete cycle. They do not do so. 
They measure for any given value of field the instantaneous 
change of induction which takes place when oscillations — co- 
directional and transverse — are superposed at any and all stages 
of the normal hysteresis loop. 
Now suppose that after any instantaneous induction change has 
been measured, the field is made to vary by some small amount — 
say, by a decrement if the field had previously been decreasing — 
the induction change which now takes place is entirely different 
(see dotted arrow). Hysteresis or lag in the usual sense comes 
into full play, and one naturally passes to the conditions of field 
superposition where a cyclic field change may he regarded as 
superposed upon permanently acting oscillations. 
Experimental Methods under B conditions. 
First. After demagnetisation and twenty reversals of a fixed 
maximum field, the normal B - H hysteresis loop is determined by 
Ewing’s method of single steps from the fixed maximum to a 
sufficient number of points all round the loop. 
