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BELL SYSTEM TECHNICAL JOURNAL 



and the maximum permeabilities for this composition. The scale for 

 maximum permeability is on the left and for initial permeability on the 

 right. The cooling rate is in degrees centigrade per second. It is 

 interesting to note that the highest initial permeability was obtained 



100000 



90000 



2000 4000 6000 8000 10000 12000 14000 

 H 



Fig. 15 — Permeability curves for 78.5 permalloy and for Armco iron. 



when the cooling rate was approximately 20° C. per second, while a 

 rate four times as rapid gave the highest maximum permeability. 

 Ten thousand and 120,000 were the highest initial and maximum 

 permeabilities, respectively, for these particular samples. These 

 values are not the highest we have obtained for this composition. 

 Test samples from other castings have given as high as 13,000 for 

 initial permeability and upwards of 400,000 for maximum. 



