214 Dr. D. K. Morris on the Magnetic Properties 



researches of Ledeboer in 1888 *. and by those of Dr. Hop- 

 kinson, communicated to the Royal Society in 1889 f. In 

 the latter, a ring-magnet was used, furnished with primary 

 and secondary coils insulated with asbestos, and capable of 

 withstanding a red heat, which temperature was obtained by 

 means of a gas-furnace. Measurements could thus be made 

 of the permeability of the iron core by the ballistic method, 

 and the temperature was deduced from the resistance of the 

 copper secondary winding. 



M. Curie, in a more recent investigation J, used a method 

 by which the permeability could be obtained in intense 

 magnetic fields. He experimented on a sample of iron in 

 the interior of an electrically-heated porcelain furnace, and 

 deduced its magnetization from the forces acting on it when 

 placed in a non-uniform magnetic field. A thermo-electric 

 couple served to measure the temperature. 



The variations of magnetic hysteresis with temperature 

 have been studied by W. Kunz of Darmstadt §. 



The relation of the electrical resistance of iron to tempera- 

 ture has also received the attention of several experimenters; 

 curves expressing this relation, and extending to beyond the 

 critical temperature, having been given by Kohlrausch in 

 1887 ||, by Hopkinson in 1889% and by Le Chatelier in 

 1891**. 



General Description of the Method of Experiments. 



By the method used in the present work, measurements of 

 the electrical resistance and of the magnetization of the iron 

 could be made simultaneously. 



It consisted in the employment, as in Dr. Hopkinson's 

 experiments, of a ring-magnet, whose insulation was calculated 

 to withstand a white heat. The core of this ring-magnet was 

 formed of a length of insulated iron wire or strip, whose ends 

 projected out of the ring, so that the resistance of the iron in 

 the core could be measured ; and in this core was imbedded 

 an insulated platinum wire, from the resistance of which the 

 temperature of the iron could be deduced. 



* Ledehoer, Journal de Physique (2) vol. vii. p. 199. 



f Hopkinson, " Magnetic and other Physical Properties of Iron at a 

 High Temperature," Phil. Trans. Roy. Soc. 1889, A. p. 443. 



X P. Curie, "Propriety magnetiques des corps a di verses tempera- 

 tures," Ann. de Chim. et de Phys. July 1895, p. 289. 



§ W. Kunz, Elektroteehnische Zeitschrift, 1894, p. 194. 



|| W. Kohlrausch, Wied. Ann. vol. xxxiii. p. 42. 



^| Hopkinson, Proc. Poy. Soc. vol. xlv. p. 457. 

 ** Le Chatelier, Comptes Rendus, vol. ex. p. 283. 



