Tungsten Wire Suspensions for Magnetometers

Abstract

OWING to the troublesome changes of zero and torsion constant of the silk suspensions of magnetometers, experiments have been made at the Royal Observatory, Greenwich, with the view of finding a satisfactory substitute. Quartz fibres were first tried, but were too rigid in proportion to their tensile strength. Success has, however, been obtained with tungsten wires such as are used in metallic filament electric lamps. These were suggested to us by Mr. F. Jacob, of Messrs. Siemens Bros., who kindly obtained various samples of wire for us; of these a tungsten wire of circular section, and diameter 20 microns, has been adopted as the suspension for our declination magnet, which is of the ordinary Elliott pattern, weighing about 50 grams. This wire, about 25. cm. in length, has now been in use for five months, during which time its zero has not changed within the limits of measurement, i.e. certainly less than 10°; the effect of 90° torsion on the wire is to turn the magnet through 4′ (it may be noted that a thicker wire, of diameter 51 microns, which was also tried, gave a deflection of the magnet of more than 2° for 90° torsion).