Temperature on M<? Villari Critical Point of Iron. 147 



It will be seen from Table I. and from figs. I.-IV. that the 

 magnetizing forces 2*84, 3*70, 4*83, and of course all inter- 

 mediate forces, are Villari critical values. If we regard only 

 the first point where each curve cuts the line of loads, we see 

 that at all temperatures the Villari value increases as the load 

 decreases and, for a given load, increases with the temperature. 

 If, on the contrary, we consider the second point of cutting 

 the line of load, we find the critical value increases both with the 

 load and with the temperature*. 



It will be seen from fig. I. that as the temperature rises the 

 two points of cutting the load-line creep nearer and nearer 

 together until for a temperature a little below 285° C. they 

 coincide, and the curve osculates the load-line ; whilst for 

 285° C. and for higher temperatures the magnetizing force 

 2*84 ceases to be a Villari point for any load. When the 

 magnetizing force reaches the value 7*69 (fig. IV.) both points 

 of cutting the load-line vanish, at any rate when the loading 

 is not carried beyond 12 kilos f, and for magnetizing forces 

 beyond 7*69 (figs. V.-VI.) Villari critical values become 

 impossible. 



In all cases rise of temperature increases the alteration of 

 the permeability in the positive direction and diminishes it in 

 the negative direction ; but the diminution in the latter case 

 is greater than the increment in the former, so that the 

 summits of the two bends in the curves become more and 

 more nearly on the same level. 



The percentage alteration of permeability was calculated as 

 follows : — 



If P and P n represent the permeability with no load and a 

 load of n kilogrammes respectively, the percentage alteration 

 is 



loo (p.-p„) nr 100 (P n -P.) 



Po Po 



according as the loading produces increase or decrease of 

 permeability. Table II. gives the values of P for the various 

 magnetizing forces. 



* The effect of change of temperature on the critical value is there- 

 fore in the same direction for both points of cutting the line of loads, i. e. 

 in both cases the Villari value is increased by rise of temperature. 



t The second point could, however, be probably reached by taking the 

 load to higher values. 



L2 



