Mechanical Vibrations upon Magnetization. 473 



The effect of permanently acting vibrations in reducing 

 residual magnetization at high inductions is greater in 

 annealed nickel than in annealed or quenched iron or steel. 

 In quenched nickel this effect, if it exists at all, is very 

 small *. 



A Conditions. 



When vibrations are superposed at all points of the normal 

 hysteresis loop, the induction change as the cyclic extremes 

 are departed from is first against, afterwards with, the field 

 change. The position of the neutral point depends upon 

 the intensity of the vibrations and of the cyclic field (in- 

 duction). The smaller the cyclic field and (so far as my 

 experiments go) the greater the vibrational intensity, the 

 closer is the neutral point thrust towards the vertical axis : the 

 higher the cyclic field and the less the vibrational intensity, 

 the closer is the neutral point thrust towards the cyclic 

 extreme. Thereafter the induction continues to follow the 

 field change until the other cyclic extreme is reached. 



Jn all cases the induction change is greater when vibra- 

 tions are superposed on the normal loop when the field is 

 increasing. For low fields the maximum change occurs at 

 or near cyclic extremes, where the slope of the curve is 

 greatest. But as the cyclic field is increased the maximum 

 induction change occurs at an earlier singe of the increasing 

 field, where in this case also the normal curve is steepest. 

 Vibrations of increasing intensity produce a progressive 

 collapse, by no means complete, of the two arms of the 

 loops. 



In quenched nickel the neutral point is not so well de- 

 fined as in the annealed condition of the three metals or 

 in quenched iron and steel. The residual magnetization 

 of quenched nickel is very little reduced by superposed 

 vibrations *. 



Magnetic Hysteresis. 



In ' Magnetic Induction in Iron ' Ewing states (§ 84, 

 3rd edition), the " influence of vibration and mechanical dis- 

 turbances generally" "may be succinctly described by saying 

 that vibrations lessen those differences of magnetic con- 

 dition to which hysteresis gives rise." Although E wing's 

 experimental methods, in which field change and tapping 

 alternated, almost certainly precluded the observation of the 



* Compare with " Note on Heusler's Magnetic Metal," by Prof. 

 A, Gray, Proc. Roy. Soc. vol. Ixxvii. Series A, p. 256. 



