33 
METEORIC AND ARTIFICIAL NICKEL-IRON ALLOYS. 
assuming proportionality between induction throws and corresponding fields, the field 
due to the heating coil when the steady current was 2 amperes would be roughly y- 5 - 
of that used in the permeability observations. 
§ 6. To find how far effects arising from either of the causes enumerated above 
were likely to influence the measurements, subsidiary experiments were made upon a 
wrought-iron ring of the same dimensions as the meteoric ring. These experiments 
showed that neither the influence of the Earth’s field nor want of bifilarity in the 
heating coil would produce appreciable effect upon the form of the temperature- 
permeability curves, for a constant field, determined in the way described in the 
paper. A primary, a secondary, and a tertiary—the latter to represent a unifilar 
heating coil—were wound upon the wrought-iron ring. The ring was then placed at 
the centre of a large solenoid, so that its axis of figure coincided with the axis of the 
solenoid. By means of this “ axial solenoid” a field of any desired magnitude could 
be produced in the direction of the axis of the ring. 
The ring was taken through a succession of cycles under different conditions of 
steady current in the axial solenoid and in the tertiary coil. The demagnetisation of 
the ring previous to the determination of each cycle was performed in the ordinary 
way by the method of continuous reversal and diminution of a current in the ring 
primary. 
The ordinary permeability-hysteresis cycle, with no current in the axial solenoid or 
in the ring tertiary, was first obtained. Cycles were then performed with currents 
of different magnitude in the axial solenoid. The axial field with the greatest current 
used was about 25 C.G.S. units. It was found that if this field was established before 
the demagnetisation process was performed, the permeability and hysteresis curves 
subsequently obtained were practically identical (for both directions of the axial 
solenoid field) with those of the “ ordinary cycle.” It was only when the axial field 
was established after demagnetisation that a perceptible difference in the forms of the 
curves could be noted. 
Similar results were obtained with a steady current in the tertiary coil, the current 
in the axial solenoid being zero, and also with the axial solenoid and tertiary fields 
acting simultaneously. 
Section III.—Arrangement of the Apparatus for Measurements of 
Permeability over a Wide Range of Temperatures. 
§ 1. The method of carrying out the permeability measurements over a wide range 
of temperatures differed little from well-known methods, and needs only a very brief 
description. The current in the heating circuit was observed by means of a Weston 
ammeter reading to 5 amperes, and was derived from the main supply—of which the 
voltage (continuous) was about 100 ; it was regulated by means of incandescent lamps, 
of variable number, arranged in parallel, and by bare wire resistance boards of the 
VOL. CCVIII.-A. F 
