On the susceptibility of feebly magnetic bodies as affected by tension

A previous communication recorded an investigation of the effects of compressive stress upon the susceptibility, retentivity and other properties of certain feebly magnetic substances. The present communication is confined to tensile stress, and its effects upon the susceptibility of certain rock specimens, including some of those previously tested under compression. Great difficulty was experienced in the finding of such perfect specimens as are necessary for successful tests of this kind, and even in the best cases the maximum specific loading has been limited to values ranging from about 50 to 130 kgrm. per square centimetre. Throughout the work the susceptibility has been measured in the direction of the stress.Instrumentation . The apparatus employed in the application of tensile stress consisted of a horizontal lever, which was pivoted at one end and weighted at the other. The effective length of the lever was 90 cm. At a point 30 cm. distant from the fulcrum the pull was applied to the specimen, which was supported by a massive iron tripod. The specimen had a length preferably of about 6 cm., and its cross-section was square (1 cm. x 1 cm.). The ends were V-shaped, and accurately fitted into similar gaps in two stout phosphor-bronze rings. The upper ring was attached to a shackle provided with right- and left-hand threaded bolts, the upper bolt being fixed to the tripod, and the lower ring was fixed to the horizontal lever. By these means the loading could be varied and the shackle allowed of a vertical adjustment.