1908- 9.] Load and Vibrations upon Magnetism in Nickel. 45 
cally equal amounts from the first to the linal “on” and “off” of load. 
These points occur with small induction amplitudes, as in fig. I., when 
H^O'43 (fig. I.a) ; at higher amplitudes, as in fig. III., not quite at but near 
the cyclic extreme (fig. Ill.a). They are thrust towards or from the cyclic 
extremes as the amplitude is greater or less, and in this respect are subject 
to the same laws which govern the superposition of mechanical vibrations 
and other forms of disturbances superposed under the A conditions. || The 
positions where the initial irreversible effects of repeated loading and 
unloading vanish are therefore vibrational (but not load) neutral points. 
It may be observed that in figs. II. and Il.a the vibrational neutral points, 
as above defined, are not quite so perfectly marked, and occur much closer 
to the vertical axis, just as is the case with the actual neutral point already 
referred to when “off” is first superposed upon the loop performed with 
permanent load, the reason in each case being the same. 
Passing now from these irreversible changes essentially vibrational in 
relation to the loops upon which loading and unloading are superposed, the 
curves representing the final effects in relation to each other may now 
be considered. Load “on” invariably decreases, load “off” invariably 
increases, not only the induction at cyclic extremes, but the residual 
magnetisation. At points in the second and fourth quadrants, where 
induction and field oppose each other, loading and unloading produce (after 
the initial vibrational effects, which may be considerable, are over) no 
induction change whatever. Thereafter, until zero induction is reached, 
loads “ on ” and “ off” increase and decrease induction respectively. There 
thus exist in cyclic fields well-marked Villari reversals in nickel. 
Fig. III. may more especially be referred to. Fig. Ill.a shows how 
the Villari critical point is reached. It occurs at some definite field value 
between H = 0'78 and H^O’95. The curves, after forty “ons” and “offs” 
of load, have practically reached asymptotic values. With a field of 
H=— 078 (the induction being positive) it is evident that the Villari 
critical point will not be reached however often the loading and unloading 
be repeated. With a larger negative field of H = — 0*95 the critical point has 
been passed, but it may be observed that the crossing of these curves does 
not, strictly speaking, constitute a Villari neutral point, as, in the immediate 
neighbourhood of this point, “ ons ” and “ offs ” are both producing negative 
induction change. It must therefore occur at some intermediate value of 
field for which, after the irreversible vibrational effects are over, repeated 
“ ons ” and “ offs ’ would give rise to no induction change whatever. With 
lower cyclic amplitudes the Villari reversal occurs closer to the vertical 
|| Reference p. 38. 
