TOKSION AXD MAGNETIZATION. 273 



constant stream of water, tlie heating due to electric current 

 prevented the experiment from being pushed to the point where 

 the direction of the current is reversed. However, to judge from 

 the course of the curve, the tendency is such that there is a 

 reversal. In nickel, the direction of the induced current is 

 opposite to that in iron, and the total quantity of the current 

 attains a maximum, whence it continually diminishes, but not 

 to such an extent that the current ultimately changes its 

 direction. 



These experiments show that the twist produced by the 

 combined action of the longitudinal and circular magnetizations, 

 the circular magnetization produced by twisting a longitudinally 

 magnetized wire, and the longitudinal magnetization caused by 

 twisting a circularly magnetized wire are characterized by having 

 various peculiarities, which are common to all of them. This 

 can not be a mere chance coincidence ; we shall have to ascribe 

 these allied phenomena to the same common cause. 



In the experiments of this and the last paragraphs, we were 

 assisted by Mr. S. Shimizu, a post-graduate in physics, to whom 

 our best thanks are due. 



§4. Theory. 



As already remarked in our last paper on magnetostriction, 

 Kirchhoft^s theory can be extended to the study of the relation 

 between torsion and magnetization, exactly, in the same manner as 

 was done by Maxwell and Chrystal to explain the AViedemann 

 effect. There we found tliat the mean circular magnetization called 

 into play by twisting a ferromagnetic wire of radius R through 

 angle w amounts to 



