450 Mr. J. H. Jeans on the 



If the solid is placed in a magnetic field, there will be a 

 couple acting on each such magnet, tending to turn its axis of 

 rotation parallel to the lines of magnetic force. Two effects 

 can be detected. 



I. The axes of rotation will turn towards the direction of 

 the lines of force. Hence, as in Weber's Theory (Maxwell, 

 § 443), if the axes be a ic set," in a particular direction giving 

 the phenomenon of induced magnetism. 



Other things being equal, this set will, for sufficiently small 

 values of H, be proportional to H ; it will also depend on the 

 rotation of the molecule being proportional to 1/w. 



It follows that the curve of induced magnetization will be 

 given by the superposition of a number of curves such as 

 that given by Weber. 



The discontinuities will occur at different points, so that 

 the resultant curve will be continuous. 



Fig. 1. 



MH 



When the magnetic force is removed, the molecules can 

 neither continue to rotate in their present condition, nor can 

 they return immediately to their original state. An inter- 

 mediate state will ensue, and the time required for the induced 

 magnetism to disappear will depend on the ease with which 

 energy passed between certain degrees of freedom in the solid. 

 The field of intermolecular force may be such that some 

 molecules retain their set for ever. For it may be that some 

 molecules cannot return to their old positions without passing 



