CHANGE OF ELASTIC CONSTANTS OF FERROMAGNETICS. 3 



dS ~ 31 ' 



where c is a constant (lepcnding on the dimensions of the speci- 

 men. Hence we have finally 



J L _ _L 'X>-//-^-o) 



3Jjr Mo ~ c US 



9(c//-Co) 

 tiS 



^0^ 



or Mh-Mq _d3I dS . 



Mn Mu ' iî^ ' 



dS 

 Thus the change of elasticity may be calculated from the 

 effect of tension on the magnetic elongation ; and that of rigidity, 

 from the change of twist caused by magnetization, provided rela- 

 tion (1) holds. 



The validity of (3) depends upon relation (1), which . is 

 usually employed in the theory of magnetostriction. It was 

 thought, therefore, that it would be interesting to test experi- 

 mentally how far the relation actually holds. Accordingly the 

 present investigation was carried out in the following order : — 

 I. Experiments on the change of elasticity : 



(a) Measurement of the change of elasticity by the 



elongation method. 

 {b) Measurement of the modulus of elasticity, 

 (c) Comparison of the results with those of the 

 flexure method. 

 II. Experiments on the change of rigidity : 



(a) Measurements of the change of rigidity l)y the 

 oscillation method. 



