1908-9.] Vibrational Neutral Points in Magnetised Iron. 3 
of a series of taps is first to cause the development of magnet ic poles in the 
sense of those produced by the magnetising current. The strength of the 
poles reaches a maximum and diminishes. I was not able to get this 
effect by tapping the iron after the magnetising current was broken, but 
only when the iron was at least approximately demagnetised. Fromme 
seems to have found this effect, though he says very little about it.” 
Eccles connects the magnitude of the spark effect “ at any point ” with 
the slope of the hysteresis loop ; Maurain, with the whole magnetic history 
of the iron. According to the latter, the direction of the induction change 
depends upon the position of the point where oscillations are superposed 
relative to “ la courbe d’ aimantation stable ” ; according to Garibaldi and 
Stradling, it must depend also on how that point had been reached. 
None of these apparently discordant results are, however, complete 
statements of the whole facts as observed by the author. All alike have 
failed to recognise the shift of the neutral points with the intensity either 
of the mechanical vibrations or electric oscillations, which implies that 
within the limits of the range of shift their intensity determines whether 
the induction will be increased or decreased. 
I shall endeavour to show that the introduction of this factor, which 
the present investigation fully confirms and extends, co-ordinates the 
apparently discordant results; is not only in harmony with the molecular 
theory of magnetism, but a necessary deduction from it. 
I. Mechanical Vibrations. 
Apparatus. 
The mild steel wire (100 cms. long and ’092 cms. diameter), one of the 
wires with which the former experiments had been made, was, after 
demagnetisation by decreasing reversals, reannealed by passing a bunsen 
flame along its entire length. It was wound with a few turns of soft 
woollen yarn and inserted in the axis of the horizontal magnetising coil, 
41 cms. long, placed at right angles to the earth’s magnetic field. One of 
its ends was soldered to the edge of the gong of the electric bell, the whole 
apparatus, as previously described, being suspended from the roof by means 
of india-rubber tubing to prevent as far as possible any external disturbances 
reaching the wire. The damped trains of mechanical vibrations were 
produced in the wire by a steel ball so arranged as to strike the gong once 
after rolling down the angle between two inclined planes. An exploring 
coil and ballistic galvanometer (11 seconds complete period), with com- 
