TEMPERATURE ON THE MAGNETIZATION OF STEELS, ETC. 11 



rather slowly, and we can follow it by the magnetometric method, 

 while the ballistic method «loos not allow us to trace the change 

 in its successive phases. 



Ordinary Steel. The curve (Fig. 9, PI. II.) shows the slight, 

 increase of magnetization with temperature rise. The fall of 

 magnetization takes place very rapidly after passing 700°, until 

 it finally vanishes at about 830°. A remarkable feature is revealed 

 on cooling. The return curve does not retrace the heating curve, 

 but the metal must be cooled about 40° below the critical tem- 

 perature, before the magnetization, which had disappeared in the 

 heating, again makes its appearance. The increase of magnetiza- 

 tion in cooling takes place slowly after reappearance, but eventually 

 the increase becomes very rapid, and attains such values that the 

 curve crosses the heating curve, and lies above it when the tem- 

 perature is below 650.° 



Further cooling results in a slight increase of magnetization. 

 The curve representing the variation of magnetization with tem- 

 perature is generally very smooth. 



Tungsten steel. The change in tungsten steel is of a complex 

 character. Before reaching the temperature of the sudden drop in 

 magnetization on heating and after passing that of the sudden 

 rise on cooling, we notice at least live corrugations in the curves 

 of magnetization in a constant field. In an experiment in £>' = 

 39.8, the corrugations lie at about 300°, 430°, 010°, 580° and 

 730°. The curve drops abruptly between the temperatures 830° 

 and 880°, showing evanessence of magnetization at about 910.° 

 The retardation in the reappearance of magnetization on cooling- 

 is very remarkable. When once the magnetization disappears it 

 can not be recovered until the temperature is lowered by about 

 240°, so that it reappears at about 570°, indicating a sudden 



