treated according to Van der WaaWs Equation. 339 



equation (see fig. 2). For example, when ?? = then m = l, 

 and the intensity has its maximum value ; when 1 = the 

 equation is a quadratic in m, and 



1 + 



/i 32 



V l -2i n 



(3) 



L- when T= ffTc 

 K = I when T= Tc 



Reduced hysteretic and anhysteretic magnetic isothermals. 



The upper of the two values for m is a stable one, and is 

 that of the reduced residual magnetic intensity (m r ) ; the 

 lower value is on the unstable part of the curve. 



The point where the curve changes from a stable to an 



unstable stage is where —rr is equal to infinity. 



