96 
MR. S. W. J. SMITH ON THE THERMO MAGNETIC ANALYSIS OF 
results are clearly in accord with the hypothesis of a conversion of the nickel-rich 
and nickel-poor constituents of the taenite into a mixture which becomes non-magnetic 
at a temperature below that at which the permeability of one of the original 
constituents is a maximum. Similarly, if the maximum permeability observed during 
cooling is compared with the value observed at the corresponding temperature during 
heating it will be seen that it is relatively less in the second winding than in the first. 
Thus in the one case the ratio (at 540° C.) is about 1 : 2 and, in the other about 3 : 5. 
It is possible that part of this difference is due to the more gradual cooling in the 
first experiments; but part of it is possibly also due to decrease in the total amount 
of the nickel-poor alloy. 
§ 5. If the values of permeability obtained below 500° C. during the 1st winding 
(when the meteorite had been heated only a few times to a high temperature) are 
compared with those of fig. 14 (representing the behaviour of the material after a large 
number of heatings), it will be seen that there are notable differences. 
The field strengths (‘48 and ’43 respectively) are different in the two cases; but the 
data already referred to show that the permeability variation with the field strength 
is not rapid enough to make this difference very important (cf. Section IV., § 2, p. 41). 
It is seen from the curves, however, that the percentage differences between the greater 
permeabilities at temperatures below 400° C. and those obtained at corresponding 
temperatures after continuous cooling from 800° C. are much less in the earlier than 
in the later experiments. The maximum value at the air temperature (assuming that 
the calculated constants of the two windings are substantially correct) is about the 
same at the end as at the beginning of the experiments, viz., about 280 and 270 
respectively. But, in accordance with the statement above, the permeability at the 
air temperature after continuous cooling from 800° C. (about 220 C.G.S.) is 
considerably greater in the earlier than in the later experiments (about 170 C.G.S.). 
These results agree with the interpretation (see below) that, after continuous 
cooling from 800° C., the gaps in the magnetic circuit at 15° C. (due to the taenite) 
are less at first when the taenite contains an appreciable amount of nickel-poor alloy 
and of nickel-rich alloy, separately magnetic at that temperature, than later, when 
practically the whole of the taenite may be non-magnetic. 
§ 6. Upon heating from 15° C. the permeability decreases continuously in the 
earlier experiments until a temperature of about 300° C. is reached—the decrease 
being especially marked in the curves of greatest permeability (see fig. 9, 1st 
winding)—while in the later experiments the decrease is scarcely perceptible in the 
lowest curve and ceases below 100° C. in the curve of greatest permeability (see 
fig. 14, 2nd winding). 
Thus in the first case the maximum decrease between 15° C. and 160° C. is about 
12 per cent, and the minimum about 5 per cent. ; in the second the maximum 
decrease (between 15° C. and 90° C.) is about 2‘5 per cent, and the minimum is less 
than 0'5 per cent. 
