214 



Prof. J. A. Evvinff on the Molecular 



Again, a small repeated cyclic change of .0 superposed 

 upon a constant value of «£j produces small changes of aggre- 

 gate polarity, which are reversible if the change of <£j is very 



Fie-. 6. 



small. This, as Lord Rayleigh has shown*, is what happens 

 in a magnetic metal, and the susceptibility with respect to 

 small cyclic changes is small in the model, just as it is in the 

 actual solid. 



The chief facts of permeability and retentiveness, and 

 hysteresis generally, are therefore at once explicable by sup- 

 posing that Weber's molecular magnets are constrained by no 

 other forces than those due to their own mutual magnetic 

 attractions and repulsions. No arbitrary constraining forces 

 are required. In the model the centres of rotation are fixed; 

 in regard to the actual solid we may make an equivalent 

 supposition, namely, that the distances between the molecular 

 centres do not change (except in so far as they may bo 

 changed by strain). 



Hysteresis, then, is not the result of any quasi-frietional 



* Phil. Mag. March 1887. 



