Description: Voltmeter.

Caption: A typical power station consisted mainly of a single cylinder gas engine driving a dynamo that was connected to a large number of lead acid batteries. This instrument was designed for a system with an output of 215-235 volts. The operating current would have been determined by the number of batteries in the system.

Introduction: This instrument, of the sector pattern form of recording meter, was intended for use in direct current power station switch boards. In those days a power station was usually housed in a large room or basement because they were only intended for use as local street lighting systems, public buildings and a very few private houses.

Background: The reading is proportionate to the attractive force between a shaped piece of soft iron and a solenoid coil and is based on Faraday's discovery of electromagnetic induction. The instrument was mounted such that the axis of the solenoid was vertical and as the iron was pulled into the coil a lever arrangement transferred the deflection to the pen of a clockwork drum.

Reference: Green, George & Lloyd, John T.. "Kelvin's Instruments and the Kelvin Museum", 1970 p. 35-6, 61

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 moving iron instrument by Lord Kelvin - When: 1895 - Where: Glasgow, Scotland

Historical Context: Design of this form of moving magnet instrument - 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: Discovery of electromagnetic induction - Who: Faraday, Michael (1791-1867) English chemist and physicist

Historical Context: Discovery of electromagnetic induction by Faraday - When: 1831

Historical Context: Discovery of electromagnetic induction by Faraday at The Royal Institution of Great Britain - Where: 21 Albemarle Street, London, England

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 to the University of Glasgow - Who: Kelvin Hughes, a Division of Smith's Industries

Historical Context: Donation to the University of Glasgow by Kelvin Hughes, a Division of Smith's Industries - When: 1967 - Where: Glasgow, Scotland

Historical Context: Manufacture - When: circa 1906 - Where: 16, 18, and 20 Cambridge Street, Glasgow, Scotland - Who: Kelvin & James White Ltd Glasgow & London Successors to Jame White & Company