Magnetic Qualities of Nickel (Supplementary Paper)

摘要: The present paper is a supplement to one with the same title, by author and Mr. G. C. Cowan, which was read before Royal Society on May 17 (p. 325, Supra ). In that experiments were described in effects of stress, consisting longitudinal pull, magnetic permeability retentiveness nickel had been examined, it shown pull an immense influence reducing both induced residual magnetism nickel. It was, therefore, be expected (as Sir William Thomson pointed out his first discussion stress quality) compression would make more susceptible magnetisation, ready retain polarity. Experiments magnetisation under have now carried author’s directions two students, W. Low D. Low, results are below. Further also made investigate nickel, very strong fields, method already used for iron these given at end this paper. dealing tensile quality, convenient test metal form long wire, enough prevent ends from materially affecting field throughout main part length. But approximating condition endlessness impracticable. Dr. Hopkinson has short bar may brought endlessness, suitable measurement its susceptibility, sinking massive yoke iron, affords easy path return lines induction end, outside bar, he use plan determining curves various samples steel. This lends itself well compressive fix lower apply weights directly, or lever, upper end. arrangement adopted fig. 11. sample supplied Messrs. Johnson Matthey (which found analysis contain 0·75 per cent, iron). 10 cms. long, turned diameter 0·656 soft wrought cross-section either side 67 square supported resting screw-bolt; plunger pressed, through desired applied means lever (fig. 11). clear length sample, within yoke, 5 Over there wound magnetising solenoid 250 turns, inside small coil close metal. determined reversing current while connected ballistic galvanometer. To find broken after reversal, effect break subtracted half reversal. every case several reversals taken; process demagnetising resorted whenever necessary get rid previous magnetisation.