108 
MR. S. W. J. SMITH ON THE THERMO MAGNETIC ANALYSIS OF 
( i.e ., between 250° C. and 300° 0.), but that of the nickel-poor constituent persists and 
does not disappear until about 500 C. Hence at 400° 0. the nickel-rich crystals have 
become converted into a non-magnetic solid solution, but the nickel-poor crystals still 
remain. 
If the heating is continued until the solution of the nickel-poor crystals has begun, 
but interrupted before it is complete, there will be a partial re-growth of these 
crystals as the temperature falls. At the air temperature, however, a considerable 
portion of the nickel-poor alloy will be still in the non-crystalline (non-magnetic) 
condition (cf. Section VI., § 10, p. 88). 
But below 300° C. during cooling the nickel-rich component of the eutectic (which, 
on account of insufficient heating, has not become incorporated with the nickel-poor 
crystals to form a homogeneous solid solution) will begin to regain its magnetism. 
Its permeability will increase rapidly as the temperature falls (cf the curves for the 
36 per cent, alloy). 
At the air temperature the permeability of the material as a whole will be less than 
before heating began, because some of the nickel-poor alloy is still non-magnetic, but 
the material will be magnetically softer, because it now contains a relatively greater 
proportion of nickel-rich alloy. For this last reason also, during subsequent rise of 
temperature, the permeability will decrease much more rapidly than during the first 
heating. 
Each of these conclusions is in accord with experimental data (cf Honda and 
Shimizu, loc. cit., pp. 657, 658, and fig. 7, j, Plate XII.). 
§ 10. A study of the thermomagnetic properties of alloys containing lower percent¬ 
ages of nickel than 24 and higher percentages than 29 will reveal more, and may show 
that the percentages of nickel to be ascribed to the two constituents of the eutectic 
are not quite as I have stated them. Meanwhile the evidence already obtained, and 
indicated above, seems sufficient to establish the coexistence of two constituents (in 
different proportions) in alloys containing between 24 and 30 per cent. Ni. The 
general accuracy of the interpretation given seems also assured. 
§ 11. In the preceding Section VII., discussing the f) curves for a meteoric iron 
under the influence of weak fields, 1 have attempted to show that the taenite consists 
originally of (in round numbers) 6 per cent, and 40 per cent, nickel-iron alloys 
intimately mixed, but sufficiently segregated to be distinguishable thermomagnetic- 
ally. I have interpreted the curves on the assumption that a succession of heatings 
to a temperature of about 800° C. converts the material into a more intimate, i.e., 
finer-grained, mixture possessing the properties of the artificial 27 per cent, alloy. 
The initial decrease of permeability, observed after treatment described in the paper, 
between 15° C. and 300° C., has been explained by assuming that it is due to the 
presence of alloys containing between 40 per cent, and 27 per cent, of nickel in a 
relatively coarse mixture while the destruction of “meteoric” segregation in the 
eutectic is still incomplete. I have since confirmed this interpretation by observing 
