1908-9.] Vibrational Neutral Points in Magnetised Iron. 29 
to the cyclic extremes, the direction of the induction change coincides 
with that of the immediately preceding field change throughout a very 
much wider range of cyclic field. Consequently a greater opportunity 
is. afforded for at least a general correspondence between the magni- 
tude of the “spark effect” and the slope of the hysteresis loop which 
Eccles sought to establish. Between the upper limiting value of the 
neutral point and the cyclic extreme this correspondence is impossible, 
because the direction of the “ spark effect ” according to my results is 
opposed to that of the field change. 
The direction of the induction changes due to superposed oscillations 
is, however, according to Maurain, wholly independent of their intensity, 
and is determined by “ la consideration de la distance D a la courbe 
d’aimantation stabled These differences therefore appear to be more 
fundamental than those between Eccles’ results and my own. In the 
series of experiments above referred to, Maurain starts with oscillations 
sufficiently strong to completely annul the hysteresis. Curve 1 is thus 
obtained. Curve 2 results from oscillations rather less strong;. Curve 3 
is obtained with oscillations described as “ plus faibles ,” and curve 4 with 
oscillations “ tres faibles d 
On the other hand, my experiments begin with the weakest intensity, 
producing in the case of mechanical vibrations and electric oscillations an 
induction change of B = 10 and 25 respectively at the cyclic extremes. 
In the latter case the maximum induction change obtained where approxi- 
mately the slope of the loop is steepest (and consequently not given in the 
tables) was B=1Q0. Maurain’s maximum induction change under the 
same conditions appears to have been of the order of B — several thousands 
for the weakest intensity of oscillations (curve iv. fig. 2, Maurain). My 
experiments end with the strongest vibrational or oscillational intensity used, 
which appears to have reduced the residual magnetisation to a rather less 
extent than the induction obtained with the intensity of oscillations 
described as “ plus faibles ” (curve iii. fig. 2, Maurain). Curve iv., obtained 
with the weakest oscillation with which Maurain experimented, is therefore 
the only curve which may probably fall within my range of intensities, 
either for mechanical vibrations or electric oscillations. 
I found it impossible, however, to show with accuracy, or even to show 
at all, the gradual shift of the neutral points towards the cyclic extremes in 
a diagram which also exhibits, as in Maurain’s case, the normal hysteresis 
loop. The angles which the curves make with the horizontal axis become 
much too small as the intensities of the oscillations are reduced. In 
fig. VIII. (present paper), for instance, the ordinate scale has been 
