198 MAGNETISM 



to another will be gradual in the aggregate, for it will happen at 

 different values of H in different groups. Hence the curve will 

 assume a rounded outline in place of the sharp corners " of Fig. 

 150. As each group separately shows hysteresis the aggregate 

 will also show it. 



Figs. 151, 152, 153* show the imagined behaviour of a large 



FlQ. 151. 



FIG. 152. 



FIG. 153. 



group of square set molecules respectively under no torn. 1 , ;i force 

 which has pulled them nearly parallel, and a very large forcv. 



From E wing's model we see how retentiveness is accounted for 

 by the molecular poles holding each other more or less in their 

 displaced positions. 



We see, too, that as H increases in the later stage the mutual 

 action tending to hold the magnets in the nearly parallel position 

 increases. Hence if H is increased to a large value and then 

 decreased to a smaller value the magnets, being under a larger con- 

 trolling force due to their mutual action, do not return to the portion 



* Ewmj.', /inlucti'iii in Iron <tn<l <>lk< r JA {/.>. ord ud. j>. il.M, 



