630 



CONSTANTS OF MAGNETISATION. 



by a curve (Fig. 244), composed of a right line OA and another 

 part concave towards the axis of the abscissae having as asymptote 

 a horizontal line CD which would correspond to an intensity of 

 magnetisation of 1700 or 1800. 



Numbers of the same order have been obtained by different 

 observers for the maximum of magnetisation : 



1670 

 1400 



Von Waltenhofen* . 



Stefanf 



Frommet 



The maximum of magnetisation is a direct consequence of the 

 hypothesis of Ampere, which consists in regarding particular cur- 



Fig. 244. 



rents as pre-existing in soft iron, and the act of magnetisation 

 as a simple direction of the primitive currents. 



This hypothesis is confirmed by an ingenious experiment of 

 Beetz. || A silver wire, which is coated with varnish except along 

 a very fine line parallel to the axis, is taken as negative electrode 

 in a bath of iron in a magnetic field parallel to its length. The 

 thin film of iron obtained in these conditions has a very considerable 

 permanent magnetisation, which is greater as the wire is finer, and 

 therefore the reaction of the contiguous particles is less felt. 



* Von WALTENHOFEN. Pogg. Ann., Vol. cxxvu., p. 518. 1869. 

 t STEFAN. Wiener Berichte [2], Vol. LXIX., p. 200. 1874. 

 % FROMME. Wied. Ann., Vol. xin., p. 695. 1881. 



AMPERE. Reponse a Van Beck. 1822. Collect, de Mem. de la Societe 

 Fran^aise de Phys., Vol. II., p. 214. 



|| BEETZ. Pogg. Ann., Vol. cxi., p. 107. 1860. 



