Earth current galvanometer. Steel stand. Wooden base, with central hole, mounted on the stand. On the wood is a brass plate, also pierced in the centre, carrying two coils, acting on a magnetic needle, and above them a 180 degree scale engraved on brass 90-0-90. Also rising from the brass plate is a brass arm for carrying the suspension thread supporting the pointer above the scale, needle and mirror (the latter being beneath the base) suspended through the centre of the instrument. The steel stand also carries a cylindrical lens for focusing the light on the mirror. Suspension thread defective.

Earth current galvanometer used at the Royal Observatory, Greenwich, from the 1860s to the 1890s. It was part of a collection of electrical apparatus built by James White of Glasgow and installed in the Observatory in 1864.

A galvanometer is an instrument used for measuring a very small electrical current. It uses the relationship between electricity, magnetism and movement. When a current passes through a coiled wire, it produces a magnetic field. If a magnetic needle is suspended in that coil, then it will move and this movement can be measured giving a value for the intensity of the electric current passing through the coil.

The first galvanometer dates from around 1820 following the work of Oested and Ampere on this relationship between electricity, magnetism and movement. This was the first galvanometer used at the Royal Observatory, introduced in 1864 and used continually within the Magnet House (roughly in the same site as the current Planetarium) until 1890 when it was discontinued due to the advent of electric trains.