34:2 Dr. J. R. Ashworth on Magnetic Hysteresis 



this is the analogue of the straight line in the density- 

 pressure diagram of a fluid which represents the sudden 

 condensation from saturated vapour to liquid. Thus the 

 anhysteretic isothermal finds its place, according to theory, 

 side by side with the two branches o£ the hysteretic loop. 



This view naturally leads to the inquiry whether a latent 

 heat exists for magnetism as for fluids. If there is a latent 

 heat it is probably very small, for a reason which will be 

 given later in discussing the character of the intrinsic 

 field. 



9. For the stable parts of the isothermals there will be a 

 reduced field-coefficient of magnetic intensity (a), which 

 may be written 



1 dm 

 ai ~m~dl> 



.... (9) 



Z-27m 2 (l-2m) 



This is applicable to any ferromagnetic substance, and it 

 follows that equal reduced intensities ought to be found for 

 the same reduced fields at corresponding temperatures. 



Experiments on this subject are in progress. 



A corresponding proposition in the relations of magnetic 

 intensity to temperature has been shown to be true at least 

 for residual magnetism. 



10. We may add here that the ferromagnetic equation, 

 being a cubic in I, shows that there should be hysteresis in 

 the relation of intensity of magnetization to temperature as 

 there is hysteresis in the relation of intensity of magneti- 

 zation to field-strength. It is easy to demonstrate from the 

 reduced equation that when 1 = 1 and the temperature is 



the critical temperature, then ra= k , and that for values of n 



and of I less than unity there are on any isodynamic two stable 

 values of m, at two respective temperatures, between which 

 there is an unstable region where hysteresis effects are 

 possible. Experiments show that there is hysteresis with 

 temperature in general *, and it is usually prominent when 

 hysteresis in relation to field-strength is pronounced. 



* Honda & Takagi, Sci. Reports Tohoku Univ., Sendai, Japan, vol. i. 

 no. 4, p. 213 (1912). 



