UPON MAGNETISATION, AND CONVERSELY, IN IRON, STEEL, AND NICKEL. 509 



Summary of Experimental Results. 



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Vibrations may be superposed upon constant field (A conditions), or change of field 

 may be superposed upon permanently acting vibrations (B conditions). 



A and B Conditions. 



Permeability. — In all cases vibrations increase induction. In high fields B v /B 

 approximates to unity. The relative magnitude of this effect under the A and under 

 the B conditions depends upon the magnetic metal and possibly on the field intensity. 

 In nickel, the induction reached is greater (if field be not unduly increased) when 

 vibrations are superposed [A conditions) than one-half the induction change on reversals 

 when vibrations are permanently acting (B conditions). The reverse is the case for 

 iron and steel. 



B Conditions. 



Permeability. — In all cases B v /B is approximately a maximum when dB y /dH is a 

 maximum. In annealed nickel the maximum value of B y /B=10; in annealed iron 

 and quenched nickel, about 3 ; in annealed steel, 4 ; and in quenched iron and steel, 

 a decided minimum. In quenched nickel the B v /B curve shows two well-marked 

 maxima : the second when dBy/dH is a maximum, the first at a lower value of field. 

 Two corresponding maxima are merely indicated in quenched steel. In no other case 

 are they observable. 



On H being further increased, maximum values of B v — B oc°.ur, so far as observed, 

 a little earlier than maximum values of c/B/rfH. In annealed steel the maximum 

 value of B v — B = 4500; in annealed iron, 2300; in annealed nickel, 1250; but in 

 quenched iron and steel rather less (700) than in quenched nickel (1000). 



Negative Induction Change. — The ratio of the negative induction change when field 

 is withdrawn, with and without vibrations (B v — R v /B - R), distinguishes the quenched 

 from the annealed condition. In the quenched metals this ratio does not differ greatly 

 from 1 -3 for all values of field other than the lowest. In the annealed metals, on the 

 other hand, it varies largely with field, reaching a maximum in annealed nickel (5*8), 

 and minimum values (l'6) in annealed iron and steel, when H is approximately =2. 

 (In quenched iron a corresponding minimum is merely indicated.) In nickel 

 B v — R v /B — R is much greater in low than in high fields. In annealed iron and steel 

 this difference is less marked. In all cases and in the lowest fields used B v - R v /B - R 

 approximates to B v /B. 



Coercive Force, Retentivity, and Hysteresis Loss in Relation to Field. — These are 

 increased or decreased as the field is low or high, but in quenched nickel the decrease 

 of residual magnetisation, if it exists at all, is very small. 



