METEORIC AND ARTIFICIAL NICKEL-IRON ALLOYS. 
61 
Fig. 18. Nickel steel. 
Curve showing relation between permeability and temperature during continuous cooling from about 
810° C. and continuous reheating to same temperature. 
The next experiments were made to find what happened on cooling from a 
temperature (705° C.) in the region (about 680° C. to 800° C.) in which the 
permeability is falling rapidly with increase in temperature. The results are shown 
in fig. 19 (observations 36 to 42). It is seen that the air temperature permeability is 
reduced by this treatment, as in the case of the meteorite (cf. 26 and 42). The ring 
was next reheated to 570° C., when it is seen that the permeability rose rapidly 
beyond 450° C. as before (cf fig. 18), and then allowed to cool to the air temperature. 
This procedure raised the air temperature permeability about 15 per cent. A subsequent 
reheating caused a further rise of 5 per cent. (cf. 45 to 49). Hence the effect of 
alternation of temperature between given limits is of the same character as in the case 
of the meteorite. 
Fig. 20 shows the effect upon the subsequent permeability of heating interrupted at 
a higher temperature than in fig. 19, but at which the permeability was still measurable, 
viz., 750° C. 
