106 Messrs. K. Honda and T. Terada on the 



approximation ; the third term in relation (10), which 

 becomes important in weak fields, is properly to be added. 



The relations for ^^ given by Heydweiller, Gans, and 



0-tL " -v 2 J 



Sano also agree with each other in the first term — ^^ 2 



Gans's differs principally from the others by a term not 

 generally small in weak fields. 



As regards the relation for ^-^ f Kolacek's and Sano's 



coincide with each other. Thomson's relation (6) also does 

 not differ from the others. If tc be independent of H, 

 Cantone's formula coincides with the others. 



Thus, the chief relations to be tested by experiments are 

 as follows : — 



BH~BT EBH' 



E 2 dH~ BT 2 ' 



Br _ JJdl _ BI 

 BH~?2R 2 Bt~ 5 BL' 



Our present experiments combined with the previous 

 investigations on the change of elastic property due to 

 magnetization furnish us with good materials for the testing 

 of these relations. 



Our results taken as a whole, give for the effect of tension 

 as well as of twist two different sets of experimental data 

 corresponding to the different orders of applying the magnetic 

 field and the stress. The mutual correspondence of the 

 results in the previous and the present experiments in this 

 respect is tabulated below : — 



Change of Strains by Change of Magnetization by 



Magnetization. Strain. 



1. Magnetic elongation under 1'. Magnetization under con- 



constant tension. stant tension. 



Elongation by tension under Change of magnetization by 



constant field. tension under constant 



2. Magnetic twisting under con- field. 



stant couple (Barus's 2'. Magnetization under con- 

 method), stant twist. 

 Change of rigidity under con- Change of magnetization by 

 stant field (oscillation twist under constant field, 

 method). 



