1890.] Molecular Theory of Induced Magnetism. 



FIG. 8. 



355 



geneity, that is, variety in the distances, hence the rounded outlines 

 of the curves. We know that set teuds to develop, or at least to 

 emphasise, heterogeneity ; for instance, a bar of iron or steel pulled 

 in the testing machine stretches irregularly after the elastic limit is 

 passed. 



The effects of stress and consequent elastic strain on magnetic 

 quality are so complex and so various in iron, nickel, and cobalt that 

 it would be premature to attempt any full discussion of them from 

 the point of view of the theory now sketched. Only a few general 

 features need be referred to at present. Some of these can be traced 

 experimentally in the model by setting the supports of the magnets 

 upon a sheet of thin india-rubber, which may be stretched or dis- 

 torted to imitate the conditions of longitudinal or torsional strain. 



When pulling stress is applied, those rows of molecular magnets 

 which lie more or less along the direction of the stress have their 

 stability reduced by the lengthening of the lines of centres ; similarly, 

 rows which lie more or less normal to the stress have their stability 

 increased. The resulting effect on the general susceptibility of the 

 material will depend on which of these conflicting influences prepon- 

 derates. Let pull be applied before magnetisation begins while the 

 metal is still in a neutral state. The stretching of longitudinal lines 



