An additional note on the production of high permeability in iron

The observations recorded in this paper may be regarded as an Appendix to a former paper, elucidating a point which remained unsettled. It has been shown if stalloy in laminated ring form is subjected to a magnetising force due to a direct current, and ringing from 3 to 14 C. G. S. units, whilst it is cooling through the temperature at which it regains its magnetic properties, and is at the same time shielded from the influence of the earth's magnetism, the permeability recovered at atmospheric temperature has a maximum value of over 10,000 when the magnetic induction is of the order 6000-7000 C. G. S. units. It had been shown previously that high values of the permeability can be obtained without the use of a special magnetic shield, when the iron has impressed upon it a magnetising force due to an alternating current, during the time that it cools through the temperature at which it regains magnetic properties. The authors of this last mentioned paper, however, used an iron tube to inclose the specimen, and the tube itself was heated with the specimen. It seemed, therefore, desirable to discover whether these high values of the permeability can be obtained when there is no question of magnetic shielding.