504 MR JAMES RUSSELL ON THE SUPERPOSITION OF MECHANICAL VIBRATIONS 



cyclic extremes (fig. X. for iron). Fig. I. shows an intermediate position at moderate 

 values of field and induction. 



But the position of the neutral point also depends, as we have seen (p. 497), upon 

 the intensity of the vibrations, and it is now apparent that the shift of the neutral 

 point depends upon the relative intensity of vibrations and cyclic field (induction). 

 Unless possibly when the normal cyclic induction is extreme, increase (decrease) of 

 cyclic field has the same effect as decrease (increase) of vibrational intensity in thrusting 

 the neutral point from (towards) the vertical axis. 



In all cases the induction change is greatest when mechanical vibrations are super- 

 posed on an increasing field. For low fields this occurs at or near cyclic extremes, 

 where the slope of the curves is greatest. But as the cyclic field maxima are increased, 

 the greatest induction change occurs at an earlier stage of the increasing field, where 

 in this case also the normal curves are steepest. 



Quenched Metals, B Conditions. 



Permeability and Retentivity Diagrams. — Figs. XII. , XIII., and XIV. show, for the 

 quenched condition of iron, steel, and nickel respectively, the usual permeability and 

 residual magnetisation curves with and without permanently acting vibrations, in the 

 same way as figs. III., IV., and V. show these curves for the annealed condition. The 

 corresponding ratio curves are also given. The scale of the horizontal ordinates of 

 fig. XIV. has been diminished three times as compared with fig. V., on account of the 

 lower permeability of quenched nickel. 



The effects of quenching the three metals in water from a red heat may be noted 

 by comparing the full (B) and faint (R) continuous-line curves of figs. XII. , XIII., and 

 XIV. with the corresponding curves of figs. III., IV., and V., for the annealed condition 

 of these metals. We are not, however, concerned with the effect of quenching, but 

 with the effect of mechanical vibrations upon the quenched condition. 



EXPERIMENTAL RESULTS. 



Permeability. — The effect of permanently acting vibrations in increasing per- 

 meability is very much reduced in quenched as compared with annealed iron and steel. 

 The reduction of the ratio B v /B is somewhat more marked in quenched steel than in 

 quenched iron (figs. XII. and XIII., full dash-line curves). 



In quenched nickel, on the other hand, the full dash-line curve B v /B (fig. XIV.) 

 shows the existence of two maxima, the second where dB Y /dH is a maximum. In another 

 series of experiments both maxima approximated to B v /B = 3, and in lower fields than 

 here shown the ratio fell as in the annealed metals. In quenched steel corresponding 

 maxima are just indicated. Quenched iron shows, like the annealed metals, one 

 maximum where approximately dB v /dii is greatest. 



Further, the increase of permeability with vibrations is very much greater in quenched 



