Weston made the Deprez-D'Arsonval galvanometer portable by assembling the coil on two vertical pins, the points of which lie with no appreciable friction on two small agate capsules and by using very thin spiral springs of phosphorous bronze both to supply the antagonist moment of torsion and the deliver current to the coil.
The coil, wound on a very light aluminium frame which by induction rapidly dampens the oscillations, rotates between a cylindrical core of soft iron and the cylindrical polar expansions of a horseshoe magnet which lies on a plane orthogonal to the axis of the coil.
The relative position of magnet and coil, the large extension of the polar expansions and the presence of the soft iron cylinder confer great intensity and good cylindrical symmetry on the magnetic field in the gap, which make the deviations proportional to the intensity of the current for rotations up to about 70 degrees.
An aluminium index set on edge and joined to the coil allows readings on an rounded scale with a mirror to avoid parallax errors. ...continues