Magnetic Properties of Iron and Nickel. 19 



permanent magnetism until just below visible ignition in the 

 dark (this would be somewhere about 500° 0.), but lost their 

 susceptibility at a much lower temperature than the steel. 

 Nickel was found to lose its susceptibility about 330° 0. to 

 340° C. (according to Becquerel about 400° C. ; according to 

 Pouillet 350° C.) . Gore has published accounts of experiments 

 relating to the sudden loss of magnetic properties of both 

 iron and nickel at certain temperatures*. Chrystalf, in the 

 course of some experiments on the magnetic sounds in iron, 

 nickel, and cobalt when traversed by an interrupted current of 

 electricity, found evidence of sudden changes in the magnetic 

 susceptibility of iron and nickel at certain temperatures, and 

 gives some curves which enable us to trace the connexion 

 between these changes and the equally curious changes of 

 thermoelectrical power observed by Tait in iron and nickel at 

 certain temperatures %. Baur § and Wassmuth || have also 

 taken up the matter. According to the former, for small 

 magnetizing forces the susceptibility of iron at first increases 

 rapidly as the temperature increases, reaches a maximum at 

 red- heat, and then falls suddenly to zero. For large forces 

 the susceptibility decreases gradually up to red-heat, and then 

 falls suddenly to a very small value. According to him, if a 

 bar be cooled from a white heat the first traces of susceptibility 

 are observed at a very bright red, the brighter the greater the 

 magnetizing force. BersonH has published a curve showing 

 the relation between the magnetic induction of nickel and the 

 temperature right up to the point at which the susceptibility 

 practically vanishes, namely, 336° C. The author** has also 

 quite recently published similar curves for nickel, and finds 

 that the susceptibility practically vanishes at temperatures 

 ranging from 333° C. to 412° C. according to the strength of 

 the magnetizing force, the greater the force the higher the 

 temperature. The author, like Berson, finds the temperature 

 at which the nickel begins to rapidly lose its temporary sus- 

 ceptibility to be 300° 0. Ledeboerft nas published similar 

 curves for iron. He makes the susceptibility of iron to vanish 



* Proc. E. Soc. vol. xvii. p. 261 (1868-1869) ; Phil Mag. vol. xxxviii. 

 p. 60 (1869); Phil. Mag. vol. xl. p. 175 (1870). For extracts see 

 1 Electrician,' vol. xx. Nos. 505, 506. 

 f < Xature,' vol. xxii. (1880). 

 % Heat, pp. 176-178; Trans. R.S.E. (1873). 

 § WiedL Ann. xi. (1880). 

 |j Wien. Btr. (1680, 1861, 1882). 

 % Ann. de Phys. et de Chim. vol. vii. (1886). 

 ** Phil. Mag. vol. xxv. Xo. 156 ( 1888). 

 tt La Lumi'ere Elect rique, tome xxvii. no. 2. 



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