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



the magnetization must to some extent be reciprocal to the 

 change of magnetization wrought by compression. 



Unfortunately our knowledge of the volume-change by 

 magnetization is very scanty and discordant, so that we had to 

 undertake; fresh experiments on the specimens of ferro- 

 magnetics used in our research. The question regarding 

 the effect of hydrostatic pressure on the magnetization is 

 intimately connected with the thermodynamics of elastic 

 bodies. From this standpoint, the problem was for the first 

 time attacked by Wassmuth*, whose experimental results are 

 in rough agreement with his theory. His experiments were 

 rather of a qualitative nature, no absolute measurement of 

 pressure as well as that of magnetization being undertaken. 

 H. Tomlinson f, in his series of experiments on the effect of 

 stress on the properties of matter, has examined this point, 

 and was led to the following conclusion : — " Fluid pressure 

 does not temporarily affect either the temporary magnetic 

 susceptibility of annealed iron, or the permanent magnetization 

 of hard steel, except, it may be, to a degree which is not 

 comparable with that of the effect of stress in any one 

 direction." 



Although experiments on the effect of hydrostatic pressure 

 are very scanty, the effect of one-sided pressure was a subject 

 of investigation by several physicists ; the effect of trans- 

 verse stress on the magnetization of iron was examined by 

 Lord Kelvin t, and that of longitudinal compression by 

 Ewing § and Chree ||. Unlike all these effects, the change 

 wrought by hydrostatic pressure is of different order of 

 magnitude, as remarked by Tomlinson. Without special 

 arrangements for detecting a minute change in magnetization, 

 we cannot well measure the change produced by all-sided 

 pressure. 



In a paper on the effect of magnetic stress in magneto- 

 striction, Mr. E. T. Jones and one of us If have pointed out 

 the importance of investigating the relation of magnetization 

 to hydrostatic pressure in deciding the intricate question of 

 magnetostriction. Mr. Jones ** has, however, found out that 

 it is unnecessary to take up experiments on hydrostatic 

 pressure, inasmuch as the quantity which is required to settle 



* Wassmuth, Sitzber. d. Akad. d. Wiss. zu Wien, vol. lxxxvi. 2, p. 539 

 (1882). 

 f H. Tomlinson, Proc. Rov. Soc. vol. xlii. p. 230, art. 49 (1887). 

 % Lord Kelvin, Phil. Trans, vol. clii. 1878, p. 64. 

 § Ewing, Phil. Trans, vol. clxxix. 1888, p. 333. 

 || Chree, Phil. Trans, vol. clxxxi. A, 1890, p. 329. 

 f Nagaoka and Jones, Phil. Mag. May 1896. 

 ** E. T. Jones, Phil. Trans, vol. clxxxix. A, 1897, p. 189. 



