340 Dr. J. R. Ash worth on Magnetic Hysteresis 



dm _ 

 Hi ~ I 



xt dm 1 — m , AX 



m 



— 27wi(l — 2m) 

 and this is infinity when the denominator is zero. Hence 



l=27m„*(l-2m u ), (5) 



l u and m u being values where instability begins. This value 

 of l u is negative when m u is greater than 0*5 or n less 

 than 27/32. 



From this equation l u can be determined when m u is 

 known. Now m u is known when the temperature is chosen, 

 for, by substituting 27m tt 2 (l — 2m tt ) for I in the reduced 

 equation (2), we get 



4 

 m u( 1 - m u y=27^ ( 6 ) 



a relation which allows m u to be calculated for any assigned 

 reduced temperature n. 



6. The curve is traced in fig. 2 for n = 0*283, which is 

 equivalent to 300° A. or 27° C. when the critical temperature 

 is that for iron, namely 785° C. The residual magnetic 

 intensity (m r ) is then 0*905 of the maximum intensity (I ) v 

 and instability begins when ?n = 0*76. 



The maximum reduced field for instability (l tl ) is —8*1. 

 Below m u = 0'16 the intensity is in an unstable state as far 

 as m = 0*05 (I being then +0*061), when instability again 

 passes to stability and the curve finally descends to the 

 origin. The unstable part of the curve crosses the axis at 

 m = 0*092. 



The curve is traced in the figure in a similar manner for 

 negative values of the intensity. 



Suppose we follow the path of stable values of the reduced 

 magnetic intensity (m), and begin by applying a strong 

 positive magnetic field so that m is very large ; then, as the 

 field diminishes to zero, m falls slowly to the point D, where 

 it has the residual value ; and after that, when the field 

 becomes negative, the curve droops more and more rapidly 

 to the initial point of instability C. The magnetic intensity 

 must then very rapidly pass to the next stable position, if it 

 has not done so before, consistent with the existing negative 

 field, and this is the point F' on the negative side of the 

 axis of intensity. 



As the negative field is brought back through zero to its 



