VARIATION OF MAGNETISATION WITH THE MAGNETISING FORCE. 633 



Weber* made a series of experiments with cylindrical bars and 

 by the method of deflections which have been calculated by 

 Kirchhoff.f For magnetising forces which first increase and then 

 decrease, they give the following values for the coefficient of mag- 

 netisation k : 



k 



29-6 25*0 



3'i 23-5 



82-3 i3'5 



n8'4 io'2 



151*2 8 '4 



208 'o 6 '4 



2397 57 



k 



248-4 5 '6 



197-5 6-7 



158-3 8-1 



1297 9-5 



96-7 I2'0 



61*2 i6'9 



29-2 25*0 



The values of k, or of the magnetisation /<, are a little greater 

 when the magnetising forces diminish; but the results agree in 

 both cases either with the formula of Lamont or with that of 

 Frohlich. 



ThalenJ determined by a method of induction and under the 

 mere action of the earth the magnetisation of cylindrical iron rods 

 2 cm. to 4 cm. in diameter and 40 cm. in length, which he placed 

 in a vertical position and then suddenly inverted. With various 

 specimens of annealed Swedish iron, the coefficient k varied from 

 27 to 45- 



Analogous experiments made by Riecke, with ellipsoids of 

 various eccentricities, and magnetising forces of 0*032 to 0*072, 

 gave values of 13-5 to 25*4 for the coefficient k. 



Quintus Icilius || used two ellipsoids the length of which was 

 101 or 165 times the diameter. He worked by the method of 

 deflection for rather large magnetising forces, and by induction 

 for feeble forces. The two series of observations were connected 

 by an experiment made in the same conditions and simultaneously 

 by the two methods. 



*. WEBER. Electrisische Maasbestimmungen, Diamagnetismus. Abhand. der 

 Konig. Gotting. Gesellschaft, Vol. I., p. 170. 1852. 



t KIRCHHOFF. CreWs Journal, Vol. XLViil. 1853. Gesamm. Abhand- 

 hingcn, p. 193. 



J R. THALEN. Nova Ada Reg. Soc. Upsal, 3rd Series, Vol. iv. 1863. 



RIECKE. Pogg. Ann., Vol. CXLI., p. 543. 1870. 



|i QUINTUS ICILIUS. Pogg. Ann., Vol. cxxi., p. 125. 1864. 



