METEORIC AND ARTIFICIAL NICKEL-IRON ALLOYS. 
57 
a point on the rapidly descending part of the curve is accompanied by a lowering 
of permeability at ordinary temperature which a single reheating to 670° C. is not 
sufficient to remove (see, however, Section VI., § 8, p. 88 below). 
The experiments 111 to 119 (fig. 14) show the full effect of heating interrupted at 
about 620 c C. on the ordinary temperature permeability—-the point 111 having been 
obtained after uninterrupted cooling from beyond the critical point, and the point 115 
after heating interrupted at about 430 c C. 
The experiments 119 to 129 (fig. 14) show how the permeability now changes with 
rising temperature, 123 and 127 showing that the change is reversible, and 121, 122 
and 124 that there is apparently a minimum permeability in the neighbourhood of 
100° C. The experiments 130 to 132 corroborate the sudden fall and subsequent 
rise, with a minimum permeability at about 440° C., noticed after similar treatment in 
the case of the first winding (cf. fig. 9). 
Observation 133 shows that on cooling from 480° C. (132), after the permeability 
has begun to rise again, the air temperature permeability is practically the same as at 
the outset. The observations 134 to 136 were made to examine the effect of cooling 
from a point near 400° C., at- which temperature the permeability of the ring in its 
new condition was falling rapidly with rising temperature. These show that there is 
a well-marked temperature lag, the returning permeability at 300° C. being much 
below the permeability at the same temperature during heating, although the 
permeability eventually rises, at the air temperature, nearly to its original value. 
Experiments 137 to 140 show a similar effect, with a further slight decline in the 
ordinary temperature permeability. A subsequent heating to 625° C. (141) did not 
have much effect upon the air temperature permeability (144). The experiments 
144 to 153 corroborate those already made. 
The result of the experiments plotted in fig. 14 is, therefore, to show that reheating 
to 625° C. is followed by a large increase in the permeability at- ordinary temperature. 
The greater part of this increase takes place, irreversibly, below 100° C. The 
permeability remains high upon subsequent reheating until a temperature of about 
400° C. is reached ; but beyond 500° C. the permeability is the same as it was before 
the treatment which resulted in the relatively high permeabilities at lower tempera¬ 
tures. Further, the additional permeability produced as above is subject to 
approximately reversible variations, over temperatures between those of its appear¬ 
ance and disappearance, of the same kind as those observed at higher temperatures 
(cf figs. 11 and 15). 
An attempt was made next to determine whether the variation of permeability, as 
the temperature fell from between 700° C. and 800° C., was reversible in the meteorite, 
as it is stated to be by Guillaume in artificial alloys. The results of the experiments 
are difficult to represent in a single diagram (fig. 15); but the correct conclusion seems 
to be that in each case there is not strict reversibility and that the permeability 
is greater on reheating than it was at the corresponding temperature during cooling 
VOL, CCVIII.-A. 
I 
