350 Dr. J. R. Ash worth on Magnetic Hysteresis 



for instability (H gi( ) at air temperature can be calculated 



thus : — 



-Lieu. — '« x ri ee , 



H eM = —8*1 x 0*18= — 1*4 for iron, and 



H ett = -4-9 x 0-14= - 0-7 for nickel. 



If the magnetic intensity fell abruptly at the field for 

 instability this field would be the coercive field at the given 

 temperature. In well-annealed pure iron the magnetic 

 intensity falls very sharply as a nearly vertical line on a 

 hysteresis diagram of I = <£(H), and consequently, —1*4, the 

 external field for instability, is approximately the coercive 

 field as found by experiment. In nickel, however, the inten- 

 sity falls sluggishly, the magnetism behaving like a viscous 

 fluid, and therefore the field for instability cannot be com- 

 pared with the experimentally determined coercive field. 



5. In this and the previous paper on this subject * it has 

 been shown that Curie's paramagnetic law of magnetism may 

 be extended to include ferromagnetism in the same way as 

 the gas law may be extended to include the behaviour of a 

 liquid. The ferromagnetic equation which is analogous to 

 Van der Waals's equation to fluids recognizes two salient facts 

 in magnetism, namely, a limit to the magnetic intensity and 

 the existence of an intrinsic field. The existence of such a 

 field cannot be denied, but its calculated value is so large 

 that it calls for some remarks. 



The magnitude of the intrinsic field is derived mainly from 

 thermal considerations. It is based on the value of a', the 

 intrinsic constant, which has been obtained from the equation 

 to the critical temperature (TJ, where 



m _ ^ fl'Ip 



c ~ 21 R' ' 



Now T e and I are known with considerable accuracy, and 

 the experimental value assigned to R' cannot be seriously in 

 error. It may, indeed, be calculated from the gas constant 

 and the maximum intensity in the following way. 



The paramagnetic equation 



5=R'T or 4=R' T 

 I K 



is a susceptibility equation, but it may be converted into an 

 energy equation by multiplying both sides by il 2 - 



* Ash worth, he. cit. 



