46 
Proceedings of Royal Society of Edinburgh. [sess. 
the magnetic circuit was completed wholly in the iron, and 
consequently the maximum induction at cyclic extremes depended 
entirely on the increased permeability due to the oscillations. It 
is just possible that in the earlier Ewing- Walter instrument, the 
induction in the iron rings depended upon their geometrical form 
and very little upon their permeability. If this were the case, 
the energy dissipated per cycle would be reduced. 
The later result, however — an increase of energy loss, due to 
oscillations — is fully in harmony with my experimental results. 
Messrs Ewing and Walter state ( Proc . P.S., vol. lxxii. p. 120) 
that the unexpected augmentation of hysteresis (loss) is probably 
to be ascribed to the oscillatory circular magnetisation increasing 
the range of longitudinal induction (permeability), and so indirectly 
increasing the energy loss in the iron or steel. 
This explanation, however, is not, taken by itself, altogether 
adequate. In the first place, it seems to imply that transverse 
(circular in this case) oscillations facilitate the magnetising 
process in some unexplained way not possessed by co-direction al 
oscillations. It affords no explanation why the first form of 
apparatus did not show increased hysteresis loss with co-direc- 
tional oscillations with low fields. In the second place, induction 
change due to oscillations (or even to mechanical vibrations) has 
generally been ascribed to a greater freedom on the part of the 
molecules to follow a changing field. If the field be increased, 
the induction will be increased (increased permeability); if the 
field be decreased, the induction will be decreased (decreased 
retentivity). Increased range of induction, therefore, due to 
oscillations, by no means implies, on the usually accepted views, 
increased energy loss per cycle. 
As a matter of fact, however, we have seen that all the more 
important magnetic properties of hard iron are modified by 
oscillations. For low fields increased permeability is associated 
with increased retentivity and also with increased coercive force ; 
for medium field, with increased retentivity but decreased coercive 
force; while for high fields increased permeability is relatively 
reduced and is associated both with decreased retentivity and 
decreased coercive force. 
But as these are precisely those factors which determine energy 
