32 Mr. R. L. Wills on, the Effects of Temperature 



With this specimen the maximum obtainable permeability 

 is reached at a temperature of about b'2b' C. with a magnetic 

 force of about 1*5 C.G.S. Increasing the temperature beyond 

 this point the magnetic susceptibility decreases, until at 

 about 700° 0. the metal is practically non-magnetic. 



The curve for a temperature of 637° C. is given in the 

 figure, from which it will be seen that the permeability at any 

 stage of the magnetizing process is less than that at the 

 corresponding stage when the temperature is 626° C. This 

 shows that with extremely weak fields the maximum per- 

 meability occurs at about 626° C, and that, unlike each of 

 the preceding specimens, the passage from the magnetic to 

 the non-magnetic state is gradual, even under the smallest 

 magnetizing force. 



It is interesting to notice that the successive stages of the 

 magnetizing process are quite distinguishable, even when the 

 temperature is such that the metal is passing from the 

 magnetic to the non-magnetic state. 



On cooling, the magnetic quality appears at. a temperature 

 of about 620° C. The general form of the curves obtained 

 by plotting permeability with respect to temperature for 

 different magnetizing forces agrees satisfactorily with those 

 given by Hopkinson *. 



Fig. 15 is drawn to show the change in the value of the 

 magnetic force giving the maximum permeability as the 



200° 300° 400° 500° 



Temperature in Degrees C. 



temperature is raised. It will be seen that this curve is very 

 similar to the corresponding curve for iron given in fig. 7 (p. 14) , 



* Proc. Roy. Soc. vol. xlviii. p. 7 (1890). 



