282 Messrs. H. Nagaoka and K. Honda on Magnetostriction. 



the torsion of the rods by a known twisting couple ; for 

 calculating the rigidity the following formula, due to Saint 

 Venant *, was used : 



-** i -, » . . ,., 6 twisting couple 



Modulus or rigidity = oK ; % — -£ : — - 



8435 x angle or torsion x cross-section - 



The following are the results : — 





E(Young's modulus). 



K (Rigidity). 



Bulk modulus. 



e. 



Iron 



2-JOx 1CP 

 2-07 Xl0 12 



0-800 xlO 12 

 0-771 XlO 12 



l-83xl0 12 0-844 



Nickel 



2-16 xlO 12 



1-082 



The constants for nickel are in fair agreement with 

 Prof. Voigt'sj determination, who gives E = 2*03xl0 12 , 

 K = 0-7 82 xlO 12 . 



We now possess sufficient experimental data to calculate 

 the coefficients k' and k" . In finding k' and k" from ex- 

 periments on the effects of stress on magnetization we shall 

 combine the measurement of the changes produced by pull 

 and by hydrostatic pressure. Taking into account the 

 minuteness of the effect of pressure compared with that of 

 pull, we can greatly simplify the calculation. ., 



From § 2 we know that -y^— is very small compared with 



— ; we therefore conclude from (<?) that in the combination 



A* 



above mentioned 



w=—u 



whence (/) gives for the change of susceptibility due to 

 longitudinal pull j$ 



OK == -fr K • 



We can thus find k' and k" without further experiment 

 from measurement of the effect of longitudinal pull only. 



The difference in the value of k' caused by neglecting ex- 

 iles within the experimental error as will be immediately 

 shown by actual calculation. 



k' and k" for Nickel — As the nature of these coefficients is 

 simpler in nickel than in iron, we shall first give the result of 

 calculation for the former metal. 



J The following table contains the numbers obtained from 

 the experimental curves and used in the calculation of k' and 

 k" from the strains produced by magnetization. 



* Saint Venant, Torsion des Prismes, p. 376 (1855). 



t Voigr, Wied. Ann. vol. xlix. p. 396 (1893). 



