RESEARCHES ON MAGNETOSTRICTION. 377 



dl [4xU(\ + d\ ( k-V \ k"lH* 



y Ji(l + 30)( ' . 4 4 



where E is Young's modulus and K the rigidity, being a constant 

 defined by the equation 



1 . 1 • 1 /minor axis V 



In the above formulae, the terms involving the ratio l - — . . J are 



\ nicijoi axis / 



not taken into account. 



Corresponding expressions for a long prismatic body placed in a 

 uniform magnetic field can be approximately calculated in the 

 following manner. 



Let the field strength in the coil be denoted by H ; then the 

 potential of the resultant magnetizing force would be 



where N is the demagnetizing factor, k the susceptibility and x the 

 direction of magnetization. Thus 

 <p=-Hx. 

 Supposing that the magnetization is uniform, the component of the 

 internai force would be (using Kirchhoff's notation) 



B=0, (7 = 0. 



The surface traction on the end-faces, which we consider to be 

 perpendicular to x axis, has components 



