510 MR JAMES RUSSELL ON THE SUPERPOSITION OF MECHANICAL VIBRATIONS 



The relative increase of coercive force is greater in annealed and quenched nickel 

 than in iron and steel. Increase passes into decrease earlier in the case of coercive 

 force than of residual magnetisation. 



The increase of hysteresis loss in low fields is relatively greater than its decrease in 

 high fields. In annealed and quenched nickel its relative increase is enormously great 

 in the lowest fields used. There is nothing corresponding to this when field is unduly 

 decreased in iron and steel. 



Coercive Force and Hysteresis Loss in Relation to Induction. — In all cases for 

 the same value of induction at cyclic extremes, coercive force and hysteresis loss 

 are decreased. At high inductions the decrease of energy loss is relatively smaller than 

 at lower inductions. At very low inductions the decrease of loss produced by 

 vibrations is a decided maximum in annealed nickel. 



Retentivity in Relation to Induction. — Vibrations do not in all cases decrease 

 residual magnetisation. In quenched nickel, when the field producing the same 

 induction of the order of hundreds in both cases is withdrawn, the residual magnetisa- 

 tion is greater with than without permanently acting vibrations. At low inductions 

 in quenched iron E v may equal E ; in all other cases R v is less than R. 



The effect of permanently acting vibrations in reducing residual magnetisation at 

 high inductions is greater in annealed nickel than in annealed or quenched iron and 

 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 relative 

 intensity of vibrations and cyclic field (induction). The smaller the cyclic field and 

 (so far as my experiments have gone) 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 change continues to follow the field change until 

 the other cyclic extreme is reached. 



In all cases the induction change is greater when vibrations 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 stage 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. The imperfect nature of this collapse is well 

 exhibited in quenched nickel in low fields. The curves cross at two points, three 

 loops being thus formed. This peculiarity is not confined to quenched metals. 



