508 MR JAMES RUSSELL ON THE SUPERPOSITION OF MECHANICAL VIBRATIONS 



nickel. On the other hand, its increase for the same maximum value of low field is 

 greater in quenched than in annealed nickel. Compare figs. XVI. and VIII. 



Hysteresis Loss. — The same general conclusions applicable to the annealed condition 

 also apply to the quenched condition of the three metals. Iron and steel call for 

 no special remark. In quenched nickel the increase of hysteresis loss caused by 

 permanently acting vibrations for the same value of low field is (as in annealed 

 nickel) enormously greater than in iron and steel. On the other hand, for the 

 same value of induction, the reduction of hysteresis loss caused by vibrations is 

 very much less in quenched than in annealed nickel. In both cases figs. XVI. 

 and VIII. (annealed nickel) may be referred to. 



Quenched Metals, A Conditions. 



EXPERIMENTAL RESULTS. 



The superposition of vibrations at all stages of the normal hysteresis loop produces 

 the same general effects in the quenched as in the annealed condition of the three 

 metals. But in quenched nickel a striking peculiarity is found to exist. The neutral 

 point is not so well defined as in the annealed condition of the three metals, and in 

 quenched iron and steel. When this point is reached, the increase of induction has 

 disappeared, but the decrease of induction is very small until the field has passed 

 through zero and has changed sign. This is shown in figs. XVI. and XVII. It will 

 be observed that, when the increase of induction has disappeared, the dash-line curves 

 bend sharply towards the vertical axis, thus closely hugging the normal loop for some 

 distance. Fig. XVII. shows that, when the cyclic induction is considerable, the 

 decrease of induction due to superposed vibrations becomes almost immediately and 

 increasingly well marked after the field supporting the normal loop has changed sign. 

 On the other hand, when the cyclic induction is small (fig. XVI.) the dash-line curve 

 still hugs the normal loop for some distance after the field has been reversed. The 

 dash-line curves of fig. XVI. may be contrasted with fig. XI. for annealed nickel. 



Superposed vibrations, therefore, have relatively very little effect in reducing residual 

 magnetisation in quenched nickel. It is interesting to compare this result with that 

 recently obtained by Prof. Andrew Gray.* He found that vigorous tapping at the 

 temperature of the room had no effect in reducing the residual magnetisation of a rod of 

 a certain sample of Heusler's magnetic alloy, although previous tapping at the tem- 

 perature of 100° produced a considerable reduction in the residual magnetisation. 

 It is obvious that quenched nickel approximates closely to this magnetic alloy, in 

 resisting the usual effect of vibrations to lower residual magnetisation, whether 

 superposed under the A or under the B conditions. But in the latter case vibrations 

 increase residual magnetisation at low inductions (see p. 506). 



* " Note on Heusler's Magnetic Alloy," Proc. Roy. Soc, vol. lxxvii., Series A, p. 256. 



