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



The coefficients k' and k n are very large in low fields and 

 diminish rapidly as the field is increased. The values of 

 'dk' + k" calculated from the strains caused by magnetization 

 show that it is generally very small compared with k' or k" 

 and the condition 



Zk'=-k" 

 is nearly fulfilled. Since the change of magnetization due to 



k y ■{- ^)(t, we see that if 

 k' + — >0, there is increase of magnetization by compression. 



Thus, if we accept Kirchhoff's theory, the smallness 

 of the volume-change by magnetization is necessarily ac- 

 companied by the smallness of the effect of hydrostatic 

 pressure, and the strains produced in nickel by magnetization 

 lead to the conclusion that the pressure must increase the 

 magnetization. 



Using the experimental results for the change of mag- 

 netization by longitudinal pull, we find the following numbers 

 for V :— 



Table II. 



H. 



61, (for 

 0-38 kg. sq. mm.). 



£I 2 (for - 

 O^kg.sq.inm.). 



k' (from olj). 



Jc' (from 5I 3 ). 



10 



-2-95 



-125 



—6130 



- 5200 



15 



-7-20 



-4-84 



-9980 



-13390 



20 



-8-27 



-5-32 



-8610 



-11060 



30 



-816 



-4-85 



-5650 



- 6740 



40 



-680 



-4-05 



-3530 



- 4200 



50 



-552 



-362 



-2290 



- 3010 



70 



-397 



-303 



-1180 



- 1860 



90 



-280 



-2-57 



- 646 



- 1190 



100 



-2-37 



-241 



- 493 



- 1000 



k" 



The numbers for k! — rr calculated from the stress-effect 



o 



on the magnetization of nickel is in rough agreement with 



those deduced from the strains caused by magnetization, the 



coincidence becoming closer with smaller loading. 



Let us now calculate the strain which should be produced 

 by magnetization, according to Kirchhoff's theory, from the 

 effects of stress, and the stress-effect from the strains pro- 

 duced by magnetization. 



If we adopt the numbers in Table 1., and calculate the 



