44 ART. 6. — K. HONDA AND S. SHIMIZU. 



constant field plotted against the temperature were thus obtained, 

 and are given in Fig. 6 a. 



The change of magnetization of Swedish iron by temperature 

 rise was found to agree well with the results obtained by previous 

 investigators*. The weak magnetization beyond the critical point, 

 as first observed by Curie, was also noticed. Here the magnetiza- 

 tion at different temperatures ranging from 800°C to 1200°C 

 diminishes very slightly as the temperature rises. Thus the 

 meaning of the critical point becomes vague ; H. Du Bois de- 

 fines this temperature to be a point of inflexion in the curve of 

 magnetization to temperature ; but it is more convenient to define 

 the temperature as the point of the maximum curvature. The 

 critical temperature so defined is, in the case of Swedish iron, 

 780°C for H =400 C.G.S. It is also to be observed that the 

 critical temperatures for ferromagnetic metals and alloys depend 

 more or less upon the strength of the field. 



The magnetization in a stage of descending temperatures falls 

 a little short of the magnetization in ascending temperatures for 

 the same field and temperature. But at ordinary temperatures, 

 they coincide with each other. Combining the above results 

 with those of the magnetizations at the liquid air temperature, 

 we obtain a hysteresis curve with regard to temperature, whose 

 lower range is considerably extended by the present experiment. 



Annealed Cobalt. As in the case of Swedish iron, the curves 

 of magnetization to temperature were obtained, and are given in 

 Fig. 6 b. 



*) J. HoPKiNSON, Phil. Trans. CLXXX, p. 443, 1889; Proc. Roy. Soc. XLIV, p. ;517, 

 1888. LYDALLand Pocklington, Proc. Roy. Soc. LIT, p. 228, 1893. D. K. Moekis, Phil. 

 Mag. XLIV, p. 213, 1897. Ledeboer, C.R. CVI, p. 129, 1888. TomlinsOxV, Proc. Phys. 

 Soc, IX, p. 181, 1888. CuKiE, C.R. CXV, p. 805, 1892; CXVIII, p. 796 and 859. Wilde, 

 Proc. Roy. Soc. L, p. 109, 1891. Kunz, Elekt. Zeits., XV, p. 194, 1894. Wills, Phil. 

 Mag. L, p. 1, 1900. Xagaoka and Kusakaee, Jour. Coll. Sei., XIX, Art. 9., 1904. 



