40 
MR. S. W. J. SMITH ON THE THERMOMAGNETIC ANALYSIS OF 
could be made without difficulty. The resulting data show that, in round numbers, 
for H = 0’35 the permeability before heating was 120, while after heating it was 
150 ; for H = 0'52 the corresponding numbers were 130 and 160. Hence there is no 
doubt that the permeability in weak fields was considerably higher after the thermal 
treatment than before. 
The preliminary experiments (first winding) over a considerable range of temperatures 
show that the permeability at ordinary temperature can vary between considerable 
limits depending upon the thermal history of the specimen. Thus the greatest 
permeability observed was about 50 per cent, greater than the lowest. The 
approximate values of these extreme permeabilities were calculated to be 300 and 200 
approximately (H = 0'48). 
In the later experiments (second winding) the highest permeability observed at 
ordinary temperatures (H = 0'433) was about 278 (= 1'73 x 160'5), while the lowest 
was about 129 (= 0‘8 x 160’5). Hence it is seen that the highest permeability at 
ordinary temperatures is more than double the lowest, and that the lowest corresponds 
approximately with the permeability of the meteorite in its original state. 
From the same experiments it is seen further that the average value of the 
permeability at ordinary temperatures, after cooling from about 850° C., lies between 
the above values and is about 167 (= 1'04 x 160’5). This number is seen to be 
approximately correct from the results of the final measurements after annealing at 
900° C., which gave p. = 154 for H = 0'36, and /x = 164 for H = 0'52. 
The final measurements, after annealing at 900° C. in the case of the nickel steel, 
show also that the constant 166'4, calculated for the approximate conversion into 
absolute values of the data obtained during measurements over a wide temperature 
range, is not seriously in error. Thus the final measurements give yu. = 179 for 
H = 0'37, and /a = 184 for H = 0*53, after annealing at 900° C. ; while the earlier 
experiments fix the limits between which the permeability may lie after heating to 
about 800° C. as 174 (= P05 x 166'4) and 208 (= P25 x 166'4) for H = 0M3. 
Section IY. —Permeability Measurements between 0° C. and 850° C. 
By S. W. J. Smith and J. Satterly, B.Sc. 
§ 1. In performing the experiments, of which the results are tabulated below, it 
was borne in mind that the permeability at a given temperature might not be free 
from a time effect. Hence, since in all probability the time rate of change of 
permeability at a given temperature would diminish fairly rapidly, and might become 
relatively small at the end of a comparatively short time, the ring was kept as long 
as was possible without prolonging the experiments unduly at a given temperature 
before the measurements were taken. Experience showed that consistent results 
