Messrs. H. Nagaoka and K. Honda on Magnetostriction. 285 



change of magnetization due to longitudinal pull (019 kg. 

 sq. mm.), we obtain the following numbers : — ■ 



H. 



SI 



(calculated). 



(51 (experiment). 



10 





-29 





-1-0 



20 





-40 





-53 



30 





-45 





-49 



40 





-4-9 





-4-2 



50 





-50 





-37 



90 





-50 





-33 



100 





-4-8 





-2-5 



The critical field given by theory is greater than that found 

 by experiment. 



We now use the numbers in Table II., and calculate the 



strains due to magnetization 



we thus obtain 



H. 



— (calculated 

 C 



— (experiment). 



^(cai.) 



— (experiment). 





from 7e 2 '). 







10 



- 3-1 Xl0" 7 



- 7'5xl0~ 7 



01x10 



-00x10 



15 



-18-9 



- 110 



o-i 



-00 



20 



-27-7 



- 205 



0-3 



-01 



1 30 



-37-5 



- 33-8 



05 



-01 



40 



-41-3 



- 500 



0-6 



-02 



50 



-46 



- 65-0 



0-7 



-0-3 



70 



-55-3 



- 930 



09 



-06 



i 90 



-58-1 



-115-5 



10 



-0-9 



i 100 



-60-2 



-124-0 



11 



-10 



The change of length in nickel, as calculated from the 

 stress- effect, agrees fairly with the observed values, except 

 in strong fields, where the deviation becomes apparent. Of 

 the two sets of k', the one derived from the effects of smaller 

 stress gives results which are more conformable to experiment, 

 at least in quality. The agreement between theory and 

 experiment would perhaps be closer, could we measure the 

 change in the intensity of magnetization by smaller loading, 

 or, better still, from the effects of small longitudinal com- 

 pression. Adopting the numbers obtained from the stress- 

 effect, the change of volume by magnetization ought to be 

 very small. The discrepancy between theory and experiment 

 lies in the sign ; theory gives increase of volume instead of 

 diminution as in the actual case. But considering the 

 minuteness of the change and the experimental errors which 

 enter in the determination of &', we cannot say that the 

 discrepancy is very great. 



