Messrs. H. Nagaoka and K. Honda on Magnetostriction, 281 



The change in magnetization due to increase of volume by 

 hydrostatic pressure a is evidently 



8I=-H(i$/+J*"j<r, (e) 



and the change of susceptibility due to longitudinal stretching 

 X of a prismatic body 



»*={*' | -3(^+^0 }\. . . . in 



For the determination of the coefficients k' and h" the 

 combination of the experimental data in any two sets of the 

 experiments already described can be conveniently used. In 

 order to test Kirch hofPs theory we have calculated k' and k" 

 from experiments on the change of volume and of length by 

 magnetization, and compared them with values deduced from 

 experiments on the change of magnetization produced by 

 compression and by stretching. 



For an ovoid we obtain from (a) and (b) 



ry - Ki+2e)-g 



I 2(1 + 30) ' 



(A, L- -So- . 



(.* - 2(1 + 30) ' 

 and for a prismatic body we obtain from (c) and (d) 



* , =*+2UpP»-(l-l20) < r), 



(B) 

 where 



r=4rf-^ r2 C3X-<7); 



^ = _4K(l a +30) (r + 4rf + ^ 

 ?= _2E(l + 20 )x+ 8y (1 + @) + ^ 



From (e) and (/) we find 



k -\ bk <rHAE 



(C), , H 



As these coefficients depend on Young's modulus and 

 rigidity, it was necessary to determine the constants on the 

 specimens of ferromagnetics used in these experiments. 

 Young's modulus was determined in the usual way, from 

 flexure experiments on iron and nickel rods already examined. 

 The modulus of rigidity was found from measurement of 



