62 
MR. S. W. J. SMITH ON THE THERMOMAGNETIC ANALYSIS OF 
Fig. 19. Nickel steel. 
Reheating to 810 C. interrupted at 705° C. 
Variation of /x during subsequent continuous cooling to the temperature of the air. 
Effect of two subsequent reheatings to 570° C. 
The air temperature permeability was again very low and, although slightly greater 
than that previously obtained (42), was about 28 per cent, lower than the value 
obtained after cooling from beyond the temperature at which the ferromagnetism 
becomes imperceptible. The ring was now reheated to about 600° C., as in the 
previous case, when the permeability seemed to vary reversibly below 400° C. (cf. 54 
and 58), as it did under similar circumstances in the previous experiments, and to rise 
rapidly between 400° C. and 600° C. [It will be seen (Section VI., § 10, p. 90) that 
the points 53 to 58 lie nearly in a straight line, as do the points 24 to 29, tig. 18, and 
41 to 43, fig. 19, and that these lines meet approximately at the same point on the 
axis of temperature produced.] The ring was next subjected to alternate heating 
and cooling between 400° 0. and 600° C. {cf. 59 to 62) with the result, as shown in 
fig. 20, that the permeability rose at first rapidly and then, during subsequent 
alternation, very slowly {cf. 58, 60, and 62). 
The ring was then allowed to cool to the air temperature, when its permeability 
