METEORIC AND ARTIFICIAL NICKEL-IRON ALLOYS. 
63 
Fig. 20. Nickel steel. 
Reheating to 810 C. interrupted at 750 C. 
Variation of /x during subsequent cooling. 
Effect of reheating to 600° C. and of subsequent alternation of temperature between 400° C. and 600 C. 
Effect of subsequent alternation between 15° C. and 650 C. 
was found to be practically the same as it was under corresponding circumstances 
previously (cf 45 and 63). 
The ring was next subjected to alternation of temperature between 15° C. and 
600° C. and finally between 15° C. and about 650° C., the permeability being measured 
at various intermediate temperatures as shown. It is seen that, as a result, the 
permeability acquires a practically steady state at all temperatures below that of 
maximum permeability. This state is represented by the curve passing through the 
points 63 to 73, fig. 20, and shown by dotted lines in the other figures. (It is 
noticeable that, if the ring is heated nearly to its temperature of maximum 
permeability, the subsequent air temperature permeability is slightly less than when 
the temperature is not raised beyond 600° C.—compare 63, 67, and 70 with 73. A 
possible interpretation of this will be found later, see Section VI., § 8, p. 88.) 
The ring was now heated to a temperature (690° 0.) not far beyond the maximum 
