GO 
MR. S. W. J. SMITH ON THE THERMOMAGNETIC ANALYSIS OF 
Too 5 200° 300 ° 400 ° 500 ° " 600° 700 ° 8O0°C 
0 
Fig. 17. Nickel steel. 
Field intensity = O'43, C.G.S. values of p. — ordinates x 166*4 (approximate). 
Effect of cooling from 770° C. and of subsequent reheating to 640° C. 
ferromagnetism had completely disappeared. The temperature of reappearance and 
the subsequent variation of permeability during cooling were again observed (see 
fig. 18, 21 to 26) and the variation of permeability during subsequent reheating to 
600° C. is shown by the observations 27 to 31. 
It is seen from the observations 21 to 31 that the rising and falling permeability 
curves are practically superposable (below about 550° C.) as in the curves given by 
Hopkinson, which, as already described, differ from those for the meteoric iron. 
The permeability at air temperature resulting from heating interrupted at 600° C. 
is shown in 32, and the value upon subsequent heating to 490° C. is shown in 33. 
The air temperature permeability is seen to be raised comparatively little by treatment 
identical with that which produced a large increase in the case of the meteorite; but 
the permeability at 490° C. (33) is notably larger than the values obtained previously 
at about the same temperature (cf. 23 and 29). A second cooling from about 600° C. 
produced a slight further rise in the air temperature permeability (cf. 32 and 35). 
The other data shown in fig. 18 will be referred to later (see Section VI., § 10, p. 90). 
