354 H - NAGAOKA AND K. HONDA ; 



these facts was given by J. J. Thomson ;° by applying similar reason- 

 ing to the effect of hydrostatic pressure on magnetization, we can 

 show that the change of volume accompanying the magnetization 

 must to some extent be reciprocal to the change of magnetization 

 wrought out by compression. 



Unfortunately our knowledge of the volume change by magneti- 

 zation is so very scanty and discordant that we have had to 

 undertake fresh experiments on the samples of ferro-magnetics used in 

 our experiments. 



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, 2) whose experimental results are in 

 rough agreement with his theory. His experiments are of rather a 

 qualitative nature, no absolute measurement of pressure as well as 

 that of magnetization having been undertaken. H. Tomlinson, 3) in his 

 series of experiments on the effects of stress on the properties of matter 

 has examined this point ; he concludes " Fluid pressure does not 

 temporarily affect either the temporary magnetic susceptibility of an- 

 nealed 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 has been a subject of inves- 

 tigation by several physicists ; the effect of transverse stress on the 

 magnetization of iron was examined by Lord Kelvin, 1 ' and that of 



11 J. J. Thomson, Application of Dynamics to Physics awl Chemistry, chapter 4 (IS83). 



■l). Wassmuth, Sitzber <1. Akad. </. Wissensch. zu Wien. 33, 2, 539, 1832. 



3). H. ToLuliuson, Proc. Roy. Soc. 42, 230, art, 49, 183". . 



1). Kelvin, Phil. Tram. Ig3, (2), (593, 1877. 



