Description: Tangent galvanometer.

Caption: The magnet carries a very light aluminium pointer and when a current passes through the coil the magnet is deflected by the electromagnetic field of the coil. The voltage of the current is proportional to the tangent of the angle of the deflection.

Introduction: This is a simple galvanometer which measures in the millivolt range. It was used with a combination of shunts (resistances) as a testing device and is a prototype for GLAHM 105012. It has a small magnet suspended in a brass frame that is positioned so that magnet is at the center of a coil with a large number of turns of fine copper wire.

Background: The instrument is a version of Pouillet's tangent galvanometer but the coil has 7,281 turns and a resistance of 18,492 ohms. Because of this great care has to be used when operating this instrument since even a modest current applied across the terminals would destroy the coil.

Reference: Green, George & Lloyd, John T.. "Kelvin's Instruments and the Kelvin Museum", 1970 pp. 31 & 60

Reference: Holbrook, Mary. "Science Preserved A directory of scientific instruments in collections in the United Kingdom and Eire", 1992 p. 131

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 Lord Kelvin - When: circa 1890

Historical Context: Design of this form of tangent galvanometer by William Thomson Lord Kelvin - 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: Manufacture - Who: James White & Company

Historical Context: Manufacture by James White - When: circa 1890 - Where: 16, 18, and 20 Cambridge Street, Glasgow, Scotland

Historical Context: Used at the Gilbert Scott Buildings in research and lecture demonstrations in the Department of Natural Philosophy - 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: Used in research in lecture demonstrations in the Department of Natural Philosophy now called the Department of Physics and Astronomy - Where: Natural Philosophy Lecture Theatre, Gilbert Scott Building, University of Glasgow, University Avenue, Glasgow, Scotland

Historical Context: Used in the Gilbert Scott B'lding by Prof. William Thomson in the Department of Natural Philosophy now called the Department of Physics and Astronomy - When: circa 1890