506 MR JAMES RUSSELL ON THE SUPERPOSITION OF MECHANICAL VIBRATIONS 



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

 quenched iron and steel occur in the same descending order as in the annealed metals : 

 B v or B, R, R v . The field has not been carried high enough to show with certainty 

 whether this final relationship occurs in quenched nickel. 



Consider now the ratio of negative induction change (B v -R v /B — R) with and 

 without permanently acting vibrations. This ratio does not differ much from 1*2 to 

 1*4 for all the three metals in a quenched condition for all values of field; but 

 in the additional experiments referred to in the preceding page this ratio for quenched 

 nickel increased as the field was decreased below H = 3. 



Retentivity in Relation to Induction. — Permanently acting vibrations do not 

 decrease retentivity in all the quenched metals and at all values of induction, as is the 

 case, so far as observed, in the annealed condition of the same metals (see p. 500). 



In quenched nickel the residual magnetisation is decidedly greater with than with- 

 out vibrations for low values of induction. For inductions under 500 or 600 the 

 increase of retentivity with vibrations is relatively great. The cyclic curves of 

 fig. XVI. may also be referred to. The residual with vibrations (dotted curve when 

 H = 0) is substantially greater than the residual without vibrations (stronger full-line 

 curve when H = 0), the maximum induction before the field is withdrawn being 

 in both cases 180 C.G.S. units. 



For inductions ranging between 1000 and 3000 no certain conclusion was reached. 

 Fig. XVII. shows the residual with vibrations to be greater (by 20 magnetic lines) than 

 the residual without vibrations, the induction in both cases being 2400. On the other 

 hand, another experiment made at a different time, with an induction in both cases 

 of 2230, showed the residual to be less (by 6 magnetic lines) with than without 

 vibrations. 



In any case, no doubt exists that in quenched nickel the residual magnetisation is 

 greater with than without permanently acting vibrations when the field producing in 

 both cases the same induction of the order of hundreds is withdrawn ; further, that 

 at the highest inductions used (3000 to 4000) the decrease of residual magnetisation 

 with vibrations, if it exists, is very small. 



In quenched steel, on the other hand, permanently acting vibrations decrease the 

 residual magnetisation for all values of induction. 



For low values of induction, quenched iron takes an intermediate position. For 

 the same maximum induction, with and without vibrations, the residual magnetism 

 is the same. This is shown in fig. XV., where the maximum value of B = 85. But as 

 the induction is taken higher, permanently acting vibrations increasingly decrease 

 residual magnetisation. 



Cyclic Diagrams. — Figs. XVI. and XVII. show the effects both of permanently acting 

 and superposed vibrations for quenched nickel in low and higher cyclic fields respectively. 

 The continuous-line curves are the normal hysteresis loops for two values of field in 

 each figure. The dash-line curves measure the instantaneous induction change when 



