On the susceptibility of feebly magnetic bodies as affected by compression

Abstract

This communication undertakes an investigation of the complex problem which is presented by the effects of mechanical stress upon the susceptibility, retentivity and other properties of magnetic substances. The present experiments are confined to compressive stress, and its effects upon the susceptibility of certain rock specimens. It was felt that an investigation into this part of the subject might possibly throw some light upon the susceptibility of the earth’s crust as affected by the enormous forces with which it has to contend, and their variations. It is unfortunate that, owing to the nature of rock specimens, the compressive stress has been limited to about 1200 kgrm. per square centimetre, but, nevertheless, some interesting results have been obtained, and these are recorded in the present paper. All the specimens are in the form of short bars about 4 cm. in length, whose cross-section is either square, being 1 cm. across each side, or 1 cm. in diameter; and, throughout the work, the compressive stress has been applied in the direction coinciding with the length of the bar. The susceptibility has been measured ( a ) in the direction of the stress and ( b ) at right angles thereto.