The magnetic properties of iron when shielded from the Earth's magnetism

The primary object of the experiments described in this paper is to examine the magnetic properties of iron under small magnetic forces when shielded from the earth’s magnetism. In a previous paper* experiments were described in which these magnetic properties were examined at low forces, and hysteresis loops obtained at maximum values of the magnetic induction as low as 0·937. The specimen, which was of the same material as used in the present experiments, was exposed to the influence of the earth’s magnetism, and it is this influence which has now been removed as far as possible. The specimen is of ring form and is built up to an axial length of 38·8 cm. of stampings of an alloy of iron known as “Stalloy,” containing 3 per cent. Of silicon. The internal and external diameters of each stamping are 7·6 and 12·75 cm. Respectively, and the thickness varies from 0·34 to 0·14 cm. The secondary winding is next to the stampings and has 177 turns of copper wire 0·81 mm. Diameter insulated by cotton impregnated with paraffin. The primary or magnetising winding has 10 turns of copper strip 19mm. Wide and 0·13 mm. Thick covered with insulating tape.