[ 336 ] 

 XXX. Intelligence and Miscellaneous Articles. 



ON THE MAGNETIZATION OF SOFT IRON. BY M. P. JOUBIN. 



rpHE phenomena of magnetization have as yet only been re- 

 -*- presented by empirical and approximate expressions ; thus, for 

 instance, the well-known formula of Frohlich which is so frequently 

 used does not show that the magnetic susceptibility passes through 

 a maximum, a fact which is very important. 



1. Let I be the intensity of magnetization, H the field, K the 

 susceptibility, defined by the equation I = KH. In order to find 

 another relation between these three magnitudes we may, with 

 Rowland, trace a curve by taking for coordiuates not I and H, 

 but I as ordinate, and K or AirK. as abscissae. To each value of K 

 two values of I correspond, and the centre of each chord is on a 

 right line very slightly inclined to the axis of abscissae, and the 

 angular coefficient of which is negative. This curve is exactly a 

 parabola (except near the axis of the ordinates) as Rowland 

 has shown, who, however, represents it by a sinusoidal function. 

 Thus it is that the equation 



1=660-0-078 4ttK + 14-53 V 2336 - 4ttK 



represents exactly the magnetic condition of an iron investigated 

 by Bosanquet, as shown in the following table. This example is 

 taken at random among many others. 



I. 



H. 4ttK. 



0-2 629 



0-5 753 



1 1448 



2 2281 

 5 1979 



10 1301 

 20 744-5 



50 323-3 



100 170-5 



2. The general aspect of these curves recalls in a striking 

 manner the curves which give the densities of saturated fluids 

 as a function of the temperature (MM. Cailletet and Mathias). 

 To each value of the susceptibility (which replaces the tem- 

 perature) correspond two values of the intensity of magnetization 

 (or superficial density) which approach each other as K. is increased, 

 and merge into each other at the critical 'point. The maximum 



Calculated. 



Observe 



12 



10 



25 



30 



115 



115 



375 



363 



779 



788 



1028 



1035 



1183 



1183 



1287 



1286 



1322 



1356 



