Theory of Induced Magnetism. 219 



The effects of stress and consequent elastic strain on mag- 

 netic quality are so complex and so various in iron, nickel, 



Ffc. 8. 



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 distorted 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 preponderates. Let 

 pull be applied before magnetization begins, while the metal 

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

 and the contraction of transverse lines will not only alter the 

 stability of those molecules which continue to lie in their 

 original rows, but will tend to make the members of those 



