CHANGE OF ELASTIC CONSTANTS OE FERROMAGNETICS. 



43 



In general features, the change of rigidity is similar for the 

 three specimens. Magnetization generally increases the rigidity ; 

 the change increases rapidly with the field and soon tends to 

 asymptotic values. Tlie effect of tension is invariably to diminish 

 the change of rigidity. The last two specimens, which in weak 

 fields, display a slight decrease of rigidity, resemble each other 

 not only in their general behaviour, but also in the amount of 

 their change. In !28.74 ?o Ni., the amount of the change is much 

 less than that for the others. It is to be noticed that the general 

 aspect of the change of rigidity resembles that of the change of 

 elasticity. 



Q>) IVleasurement of the change of rigidity by 

 Barus's method. 



The same specimens, on the other hand, were tested by the 

 differential method used by Barus,'-' in which the wires were first 



* Barus, loc. cit. 



