2S8 Messrs. H. Nagaoka and K. Honda on Magnetostriction. 



The numbers found above are widely different from those 

 calculated from the strains due to magnetization, but the 

 general character of the coefficient k 1 is similar. Using the 

 values of k 1 in Table IV. we find that the change of length 

 (3rd column) agrees fairly with the experimental determina- 

 tion (4th column). The field of maximum elongation given 

 by calculation coincides pretty well with the actual result. 

 According to calculation, there is always increase of volume 

 with increasing field, but the calculated result is about 15 

 times greater than the experimental numbers. The theoretical 

 conclusion as regards the change of volume by magnetization 

 agrees only in quality. 



The values of the coefficients k 1 and k" for iron and nickel 

 agree in sign with Cantone's determinations from the strains 

 produced by magnetization, but are far behind thern in actual 

 numbers. Drude * found from the effect of twist on a circu- 

 larly magnetized iron that fi" = 4:7rk"= -400000 in weak 

 fields. In the present case k"=— 30000 in H = 10, if it be 

 calculated from the stress-effect ; thus ///'= —380000, which 

 is very near to Drude's observation. 



Summary. 



The principal results obtained in the present research are 

 given in the following summary. 



1. Magnetization produces minute increase of volume in 



iron. 



2. Diminution of volume by hydrostatic pressure produces 



minute decrease of magnetization in iron. 



3. Magnetization produces minute diminution of volume in 



nickel. 



4. Diminution of volume by hydrostatic pressure produces 



minute increase of magnetization in nickel. 



5. Positive transverse stress produces increase of magneti- 



zation in an iron tube, which reaches a maximum in 

 a certain critical field. 



Kirchhoff's theory of magnetostriction leads to the following 

 conclusions : 



I. Effects of stress deduced from the strains due to 

 magnetization. 



(a) (Theory). — Hydrostatic pressure produces increase 

 of magnetization in iron. 

 (Experiment). — Hydrostatic pressure produces de- 

 crease of magnetization in iron. 

 * Drude, Wied. Ann. vol. lxiii. p. 9 (1897). 





