METEORIC AND ARTIFICIAL NICKEL-IRON ALLOYS. 
65 
Effect of interrupted cooling and of subsequent alternation of temperature between 15° C. and 580° C. 
reversibly (in the time occupied by the experiments) over temperatures between those 
of the rising and falling permeability curves of fig. 18. This inference is seen to be 
correct from the results of the observations 89 to 92 and 94 to 96. It is noticeable 
(fig. 22) that, as in the case of the meteorite, but to a greater extent, alternation of 
temperature between the falling and rising permeability curves is followed by a 
relatively low permeability at the air temperature (see 93 and 97). (Cf Section VI., 
§ 11.) The effect of a single reheating to 580° C. upon the air temperature 
permeability is shown in the experiments 97 to 99, and the effect of subsequent 
alternation of temperature between 13° C. and 580° C. is shown in the observations 
99 to 107. x4.s in all previous cases, the permeability change produced by alternation 
diminishes rapidly from one alternation to the next, and, in the present case, after 
three alternations further change was imperceptible. The observations are also 
consistent with the inference from previous experiments that the irreversible increase 
of permeability does not begin until, on the first reheating, some temperature between 
400° C. and 500° C. is attained. 
The permeabilities finally obtained at 580° C. and 13° C., after five alternations 
VOL. CCVIII.—A. K 
