500 MR JAMES RUSSELL ON THE SUPERPOSITION OF MECHANICAL VIBRATIONS 



B v — B is not a maximum until, on the further increase of H, the maximum value of 

 clB/clH is more nearly approached. 



In the former case the increase is much greater in nickel than in either iron or 

 steel. In nickel, the maximum value of B v /B= 10, while in iron and steel it is only 

 about 3 and 4 respectively. As H passes beyond these values, B v /B rapidly falls, 

 and in sufficiently strong fields approximates to unity (strong dash-line curves). 



In the latter case the actual maximum difference (B v — B) is greatest in steel 

 (4500), less in iron (2300), least in nickel (1250). It should be noted that the steel is 

 more permeable than the iron wire used. 



Residual Magnetisation in Relation to Field. — Permanently acting vibrations 

 increase or decrease residual magnetisation as the fields are low or high. Both these 

 effects are greatest in annealed nickel. 



When the field is sufficiently increased, the induction and retentivity curves are 

 always in the following descending order : B v or B, B, R v . This final relationship is 

 very marked in annealed nickel, much less so in iron, least in steel. 



It is instructive to consider, not merely the residual magnetisation, but the ratio 

 of the negative induction changes with and without vibrations when the field is 

 withdrawn (B v — R v /B — R). In this way a ready comparison may be made with 

 relative positive induction change with and without vibrations when the field is 

 acting (B v /B). 



The effect of vibrations in increasing the negative induction change in low fields 

 when H is withdrawn is much greater in annealed nickel than in either iron or 

 steel. In nickel (faint dash-line curves), the maximum value of B v — R v /B — R = 5'8, 

 while in iron and steel it is only 2*2 and 2 '6 respectively. These maxima occur 

 at or near the lowest field values used. As H is somewhat increased these ratios 

 rapidly fall in all the three metals. In nickel, as H is further increased this 

 fall takes place slowly, and continues to do so at the maximum value of field used, 

 viz. H=15. 



In iron and steel, on the other hand, these ratios increase in value when the field 

 is higher than about 2 C.G.S. units. 



Consequently, in annealed nickel, B v — R v /B — R is much greater in low than in high 

 fields. In iron and steel, on the other hand, this difference is comparatively small. 



The faint dash-line curves show the comparative results fully. 



Residual Magnetisation in Relation to Induction. — If R and R v be plotted 

 against B and B v respectively, it is seen that the residual magnetisation is less with 

 than without permanently acting vibrations, when the field supporting the same 

 induction in both cases is withdrawn. This decrease is greatest in annealed nickel. 



See results under the same conditions for quenched nickel (p. 506). 



Cyclic Diagrams. — Figs. VI., VII., and VIII. , taken in conjunction with fig. II. for 

 iron (curve 3 having the same intensity of vibrations as now used), show the changes in 

 the hysteresis loops when a cyclic field is superposed upon permanently acting vibrations 



