Description: Astatic mirror galvanometer.

Caption: The astatic galvanometer invented by Nobili had a pair of suspended magnets, which when mechanically coupled were "astatic"- unable to establish a fixed position. Unlike Kelvin's instrument Nobili's coils, of a relatively few turns of copper wire) were placed side by side. The addition of a lightweight mirror, by Kelvin, doubled the scale of the instrument without damping the action, and thus desensitizing this type of instrument.

Introduction: This low resistance moving magnet galvanometer has two coils placed one above the other. Two small magnets, which sit at the centres of the coils, are mechanically connected by a lightweight aluminium frame to improve the sensitivity of the instrument.

Background: The small glass mirrors for this type of instrument were constructed from microscope slide cover slips. This was an idea suggested to Kelvin by the instrument maker James White in 1858 when White was constructing the "Cable Galvanometer" (see GLAHM 113357).

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. 132

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 this form of 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 galvanometer by Lord Kelvin - When: 1858 - 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: First use of a mirror attached to a galvanometer suspension as a measuring device - Who: Poggendorff, Johann Christian (1796-1877) German physicist, chemist, and bibliographer

Historical Context: First use of a mirror attached to a galvanometer suspension as a measuring device by Poggendorff - When: 1826 - Where: Germany

Historical Context: Manufacture - When: circa 1910 - Where: 16, 18, and 20 Cambridge Street, Glasgow, Scotland - Who: Kelvin & James White Ltd Glasgow & London

Historical Context: Use of the astatic pair of magnets in a galvanometer - Who: Nobili, Leopoldo (1784-1835) Italian physicist

Historical Context: Use of the astatic pair of magnets in a galvanometer by Nobili - When: 1825 - Where: Florence, Italy

Historical Context: Used in lecture demonstrations - Who: Department of Natural Philosophy now called the Department of Physics and Astronomy, Glasgow University

Historical Context: Used in lecture demonstrations in the Department of Natural Philosophy now called the Department of Physics and Astronomy - When: circa 1940 - Where: Natural Philosophy Lecture Theatre, Gilbert Scott Building, University of Glasgow, University Avenue, Glasgow, Scotland