Grassot has devised a galvanometer, or " fluxmeter," which greatly alleviates the tedious operation of taking ballistic readings.2 The instrument is of the d'Arsonval type; its coil turns in a strong uniform field, and is suspended in such a manner that torsion is practically negligible, the swings of the coil being limited by damping influences, chiefly electromagnetic. The index therefore remains almost stationary at the limit of its deflection, and the deflection is approximately the same whether the change of induction occurs suddenly or gradually.
In the Eschenhagen pattern instrument, in which a single quartz fibre is used for the suspension, two magnets are placed in the vicinity of the suspended magnet and are so arranged that their field partly neutralizes the earth's field; thus the torsion required to hold the magnet with its axis perpendicular to the earth's field is reduced, and the arrangement permits of the sensitiveness being altered by changing the position of the deflecting magnets.
At low temperatures, there is not enough thermal energy available to allow torsion angle changes, so the conformation becomes frozen in.
Soc., 1880, 30, p. 411, showing experiments on residual charge of condensers and a comparison between the behaviour of dielectrics and glass fibres under torsion.
In the bud of the screw-pine the leaves are arranged in three orthostichies with the phyllotaxis but by torsion the developed leaves become arranged in three strong spiral rows running round the stem.