UPON MAGNETISATION, AND CONVERSELY, IN IRON, STEEL, AND NICKEL. 513 



only would residual magnetisation be increased with permanently acting vibrations (as 

 in quenched nickel), but also coercive force and hysteresis loss, relative to the same 

 value of induction. Such a result may be highly improbable, but its possibility does 

 not appear to be excluded by these general theoretical considerations, and in the 

 case of quenched nickel the experimental results are certainly converging in this 

 direction. 



Observe further that, however much the cyclic amplitudes be increased, the full 

 and dotted line curves of diagrams a and b might still be used to illustrate the 

 possibilities under deduction (2) ; but as the limiting value of magnetisation is 

 approached, the vertices of both cycles would coincide, and the slope of the curves at 

 high inductions would be less with than without vibrations, if the reverse held at low 

 inductions. 



Hence, when saturation values are departed from, the rate of magnetic change 

 with field change would be less with than without permanently acting vibrations. 

 Diagram c may be referred to, illustrating a position as regards the crossing points 

 midway between the extremes shown in diagrams a and b. 



Electric Oscillations. 



The similarity between the effects of electric oscillations and mechanical vibrations 

 was, as stated at the outset, anticipated. It has long been recognised that disturbances 

 other than mechanical produce effects upon magnetisation essentially vibratory. A rise 

 or a fall of temperature increases induction, decreases residual magnetisation.* 

 Similarly, transverse magnetisation (which contributes nothing to the result) supplies 

 the first molecular tap, which, if superposed at a cyclic extreme, produces increase 

 of induction, or, if superposed when the field is withdrawn, a decrease of residual 

 magnetisation. The experiments of Gerosa and Finzi and others of a similar nature 

 are well known. 



But in these latter cases the purely vibrational effects are materially altered by 

 the direct magnetic effects of the subordinate unidirectional or alternating currents, 

 and sooner or later the analogy becomes imperfect. Permeability is lowered in high 

 fields, and direct hysteresis effects are unavoidable. On the other hand, as the direct 

 magnetising action of high-frequency currents is very greatly reduced, it appeared 

 reasonable to suppose that the vibrational effects due to high frequency would be 

 increased, and consequently that the analogy between the magnetic effects of electric 

 oscillations and mechanical vibrations would be more complete. 



It became immediately apparent, as soon as this investigation was commenced, that 

 the effects of mechanical vibrations upon magnetisation were essentially the same as 

 those produced by electric oscillations in coils surrounding the iron previously dealt 



* Magnetic Induction in Iron, 3rd ed., p. 181 (Wiedemann). 



