CHANGE OF RIGIDITY BY MAGNETIZATION. 



SOFT IRON. 



Here N denotes the moment of force expressed in C.G.S. units, O" 

 the angle of torsion per cm corresponding to the moment, as calculated 

 from the rigidity, and o>:f" the observed change of torsion due to 

 Diagnetization, given in seconds of arc. oä is taken positive when the 

 chano'e of twist indicates an increase of ri":idity and taken nesfative 

 when it indicates a decrease. H is the effective fjrce (=H^— IN). 



Thus, the untwisting of the rod always increases with magnetiza- 

 tion, its amount increasing in the same way that the intensity of 

 mao-netization is related to mao-netizin£'' force. As the moment of 

 force increases, the amount of untwisting increases proportionally, so, 

 that the change of rigidity is fairly independent of the twisting couple 

 for all magnetizing iields. The form of the curves is similar to that 

 of the curves of depression in the former experiment, except in very 

 weak fields. In the present case, the initial minute depression of the 

 curves was not observed. 



