422 Intelligence and Miscellaneous Articles. 



There is a characteristic equation with coefficients independent of 

 the nature of the body ; consequently, the theorem of corresponding 

 states applies to magnetism. 



Let us imagine an ideal magnetic body for which the suscepti- 

 bility corresponding to an infinitely small field vanishes, and for 

 which the maximum intensity of magnetization l m is exactly equal 

 to three times the critical intensity I c . The curve representing 

 the intensity I as a function of K is a parabola, and by referring 

 the variables to their critical values I c and K c , the reduced equation 

 of the parabola may be written, as is readily seen, 



I K 



/I K\ 



(" = v y = ij 



*= 1 + 1(1-?/) ±f s/l-y. 



This is an ideal case, for : — 



I. The susceptibility has a finite value K when the field 

 vanishes : 



II. The value I of I corresponding to K is not equal to 3I e . 

 But to obtain the same conditions, let us measure the suscep- 



TT XT 



tibility, not from 0, but from K , and take the ratio — — ?■ 



If we construct curves for Eowland's experiments, it will be 



seen that -2. is very appreciably constant for all substances and is 



equal to 2*66. It follows from this by a simple calculation that 

 the characteristic equation is 



V~r y k c ~kJ 



a—1 + 0-33 (l-y) ± 1-3 s/T^[ f . 



The following are some examples showing the agreement of this 

 formula with experiments : — 



I. Soft Iron : 4ttK = 180 ; I c = 500 ; 4ttK c = 2460. - 



r. i". 



4ttK. 



Calc. 



Obs. 



Calc. 



Obs. 



650 



1211 



1230 



54 



50 



1500 



993 



985 



147-5 



150 



2000 



825 



810 



241-5 



250 



II. Soft Iron : 4ttK = 320 ; I c = 520 ; 4ttK c = 4700. 

 850 1300 1290 41 35 



2000 1151 1140 99 100-5 



3600 900 885 226 240 



4320 731 721 350 360 



