1908-9.] Vibrational Neutral Points in Magnetised Iron. 31 
With field increasing towards a cyclic extreme, the molecular groups 
will tend to place themselves more and more in alignment with the 
direction of the field, so that when (say) the positive cyclic extreme is 
reached, the superposition of vibrations will assist the rotation of the 
molecules of very different degrees of stability, and the induction will be 
increased. This induction change will necessarily coincide in direction with 
that of the immediately preceding field change, and it will be independent 
of the intensity of the vibrations. When the field is decreased, the decre- 
ment may obviously be made so small that even the least stable molecular 
groups will remain unaffected, and the rotation of the molecules will, on the 
superposition of vibrations, remain unchanged in direction. But the 
induction change will now be against the immediately preceding field 
change, and this result also will be independent of the vibrational intensity. 
If, however, the field decrease had been a little greater than above indicated, 
by an amount sufficient to rotate negatively the more favourably placed 
molecules of the least stable groups, their rotation with the field change 
will also be assisted, and the induction change due to superposed vibrations 
will now be definitely reduced in amount. On a further field decrease the 
reduced positive induction change will more readily pass into negative 
induction change if the intensity of the vibrations is weak enough to leave 
uninfluenced the more stable molecular groups, the less stable molecules 
rotating negatively in response to the negative field change alone being- 
assisted. The induction change will now be with the field change, and 
once this has been established, will continue to be so for all greater decre- 
ments of field, provided the vibrational intensity be not unduly increased. 
But the decrease of field remaining as before, if the vibrations had been of 
a somewhat greater intensity to influence also a few of the more stable 
molecular groups not yet sensibly effected by the comparatively small field 
decrease, and whose last rotation was in the direction of the field (i.e. 
of the field change before the positive extreme was departed from), their 
tendency to rotate positively would also be assisted. Obviously the 
intensity of the vibrations could be adjusted so that their superposition at 
this particular value of decreasing field would produce no induction change 
whatever, the negative rotations of the less stable balancing the positive 
rotations of the more stable molecular groups. Further, if the vibrations 
had been of yet greater intensity, groups of yet greater stability, whose 
last rotation was positive, would have been brought into action, the 
molecular balancing would be upset, and the induction change would again 
be against the field change, a reversion to what took place at a smaller field 
reduction with weaker vibrational intensity. To re-establish a balance for 
