26 
MR. S. W. J. SMITH ON THE THERMOMAGNETIC ANALYSIS OF 
is even more regular than appears from the photographs. At the same time, the 
want of symmetry in the numbers given, showing an apparent anomaly in the 
positions of the layers parallel to 11, is, I think, too great to be accounted for as 
arising from unavoidable errors of observation. 
The chief importance, for the present purpose, of the numbers and description just 
given lies in the fact that they serve to define the geometrical distribution of the 
alloys of different composition in the ring of which the permeability was examined. 
It was proved directly by polishing and etching the ring at the conclusion of the 
experiments that the regularity of distribution observed in the core extended to the 
portion of the material of which the ring was composed. 
§ 6. The micro-structure of the meteorite is shown in the four photographs (Plate 2), 
for three of which I am indebted to Mr. Wraight. 
The photographs a and b represent different portions of the etched surface 
magnified about 50 diameters. The duller portion of the surface (crossed by sets of 
fine parallel “ Neumann ” lines) is in each case the easily etched constituent “ kamacite.” 
The brighter less easily etched constituent is “ taenite.” In the photograph a the 
thin bands of taenite are almost rectilinear, and there are numerous subsidiary, 
discontinuous bands. The centre of fig. b shows that there is sometimes no taenite 
c5 
between contiguous layers of kamacite. Lower in the figure there is an unbroken 
band of taenite separating two layers of kamacite, while in the upper part of the 
figure more nickeliferous material occurs in the gaps between layers of kamacite. 
Fig. c shows a portion of the surface magnified about 80 times. It suggests, like b, 
that the crystallisation of the taenite is subsequent to that of the kamacite, and also 
that the former is not in reality homogeneous, since the comparatively thick band of 
taenite in the middle of the figure has obviously been unequally etched by the reagent 
(cf Cohen, “ Meteoritenkunde,” I., p. 80 et sec/.). Similar inequalities of etching- 
are shown in the lower band of taenite in the negative from which fig. b was 
obtained. 
In obtaining these three photographs the degree of etching was very slight—the 
minimum amount necessary to bring out the structure represented. 
In the photograph d (magnification roughly 500 diameters), which 1 took later, the 
degree of etching was much greater. The surface of the meteorite was no longer 
approximately plane, and the different parts could not be simultaneously focussed. 
The dark parts of the field are the deeply etched and unfocussed kamacite. The 
regions partly dark and partly bright represent highly magnified portions of the bands 
of etched taenite, in one of which there are distinct traces of lamination. 
§ 7. The nickel-iron alloy, of which the magnetic properties were compared with 
those of the meteorite, was kindly supplied to me by Mr. R. A. Hadfield, M.Inst.C.E., 
and was a sample of the 5 '81 per cent, nickel steel described by him in the ‘ Proceedings, 
Institute Civil Engineers,’ vol. 138, p. 114, 1899, where its composition is given as 
follows :— 
