Description: Tangent galvanometer.

Caption: Galvanometers are instruments which measure voltage. This type of instrument has a small magnet free to rotate at the centre of a coil of fine copper wire. When the instrument is connected to an electrical circuit the magnet is affected by the flow of electricity in the coil which causes the needle of the instrument to deflect.

Introduction: This tangent galvanometer was part of an electrical testing set that was generally used for testing circuit continuity. It was designed for use in industrial engine rooms and power stations but was found useful in various situations. The instrument is called a tangent galvanometer because the voltage in the circuit under test is proportional to the tangent of the angle of deflection of the needle.

Background: This instrument is a development of a prototype test instrument see GLAHM 113329. Lord Kelvin designed it for the early electrical industry. In 1881 his official residence, at No 11 Professor's Square at the University of Glasgow, was the first house in the world to be entirely lit with incandescent electric lamps.

Historical Context: Design of the first galvanometer - Who: Schweigger, Johann Salomon Christoph (1779-1857) German physicist

Historical Context: Design of the first galvanometer by Schweigger - When: 1820 - Where: Halle, Germany

Historical Context: Design of the tangent galvanometer - Where: Paris, France - Who: Pouillet, Claude Servais Mathias (circa 1790-1868) French physicist

Historical Context: Design of the tangent galvanometer by Pouillet - When: 1837

Historical Context: Design of this form of tangent galvanometer - Who: Thomson, William, Professor (1824-1907) Sir William Thomson from 1866 and Ist Baron Kelvin of Largs from 1892 better known as Lord Kelvin

Historical Context: Design of this form of tangent galvanometer by William Thomson Lord Kelvin - When: circa 1890 - Where: Glasgow, Scotland

Historical Context: Discovery of the electromagnetic effect - Who: Oersted, Hans Christian (1777-1851) Danish Physicist

Historical Context: Discovery of the electromagnetic effect by Oersted - When: 1819 - Where: Copenhagen, Denmark

Historical Context: Donation by George Thomson to the Department of Natural Philosophy now Physics and Astronomy - When: 1974 - Who: Thomson, George

Historical Context: Donation by George Thomson to the Department of Natural Philosophy now Physics and Astronomy, Glasgow University - Where: University Avenue, Glasgow, Scotland

Historical Context: Historical collection - Who: Department of Natural Philosophy now called the Department of Physics and Astronomy, Glasgow University

Historical Context: Historical collection of the Department of Natural Philosophy now called the Department of Physics and Astronomy - When: circa 1980 - Where: University Avenue, Glasgow, Scotland

Historical Context: Manufacture - When: circa 1892 - Where: 16, 18, and 20 Cambridge Street, Glasgow, Scotland - Who: James White & Company

Historical Context: Owned by - Who: South of Scotland Electricity Board. The non nuclear division of this company is now Scottish Power

Historical Context: Owned by The South of Scotland Electricity Board - When: circa 1900 - Where: Scotland