226 
PROFESSOR fj. A. EWING AND MR. W. LOW ON THE 
turned down. The inner induction coil was wound in a single layer of ten turns with 
a mean diameter of 2'93 mm. The outer coil was a single layer of eight turns with a 
mean diameter of 4‘36 mm. With these conditions the induction was forced to the 
enormous value of 45,350 c.o’.s. units, thoimh the outside field between the two coils 
had a somewhat smaller value than before. This anomaly does not necessarily imply 
that the measurements were in error, for, as will appear from what follows, the 
relation of the outside field to the force within the metal is materially affected by the 
form of the conical ends, and that form had been altered, as has just been said, in 
the region close to the neck. The excessive smallness of the neck in this case, how¬ 
ever, made it more difficult than before to measure the outside field wdth precision. 
The following are mean results for the strongest magnetising currents :— 
Outside field. 
33. 
S — outside field 
© 
47r 
outside field' 
24,500 
45,350 
1660 
1-85 
§ 9. With regard to the quantity (ffii — outside field)/477, it will be noticed that, if 
we exclude the last (somewhat doubtful) case, there is a progressive decrease as the 
induction rises, within the I’ange covered by these experiments. With a field of 
5000 or 6000, the value of this quantity was 1700 in the Swedish sample and 1680 
in the Lowmoor sample, and it fell to 1430 as the field was raised to 25,000. This 
gives great interest to the question, whether the field as measured in the outside space 
has the same, or nearly the same, value as the magnetic face within the metal; for 
in that case we should have evidence that the intensity of magnetisation ^ passes a 
maximum and begins to decrease under the action of very strong fields, and this is a 
result which Weber’s molecular-current theory of diamagnetism, extended as Maxwell 
has extended it to a paramagnetic substance, would lead us to expect.^ After a 
careful examination of this important point, we have concluded, for reasons given 
below, that the apparent decrease of 3 in the experiments described above is in all 
probability wholly due to the outside field being greater than the field within the 
metal, and that, if there is any variation in the real value of 3 in strong fields, it is 
smaller than our method of experiment can detect. 
§ 10. An attempt to investigate the uniformity of the field (in a medial plane along 
lines radiating from the axis) was made by building up a bobbin over the neck of 
which four induction coils were wound, one above another, with small annular spaces 
between. The lowest coil was wound on the iron neck, and the other three on thin 
* See Maxwell’s ‘ Treatise on Electricity aucl Magnetism,’ vol. 2, cliap. 22:—“ If it should ever be 
experimentally proved that the temporary magnetisation of any substance first increases and then 
diminishes as the magi^etising force is continually increased, the evidence of the existence of these 
molecular currents woirld, I think, be raised almost to the rank of a demonsti’ation.” 
