Description: Magnetic deflector.

Caption: Made by James White at Glasgow in about 1876. this instrument has a magnetic probe mounted on an adjustable pantograph. It was used to compensate for the horizontal errors in Kelvin's marine compass caused by magnetic deviations.

Introduction: The accuracy of a magnetic marine compass suffers from the effect of deviations, or non uniformity in the magnetic field, that surrounds it. There are two main components of these errors - the angle of dip in the Earth's magnetic field and the amount of iron in the vessel and its cargo.

Background: In 1870 Kelvin became the owner of a large sailing vessel, the 'Lalla Rookh', which he used as a holiday home and floating laboratory. In 1873 his favourite Nephew David Thomson King narrowly survived when the cable laying ship he was on ran aground off the coast of South America. In the following year he ran out of luck when another cable laying ship foundered in the Bay of Biscay. Kelvin's interest in navigation and marine safety became an obsession.

Reference: Green, George & Lloyd, John T.. "Kelvin's Instruments and the Kelvin Museum", 1970 p. 62

Reference: Holbrook, Mary. "Science Preserved A directory of scientific instruments in collections in the United Kingdom and Eire p. 132", 1992 p. 132

Historical Context: Design - 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 by Lord Kelvin - When: 1876

Historical Context: Design by Lord Kelvin, University of Glasgow - Where: Glasgow, Scotland

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 1876 - Where: Glasgow, Scotland - Who: James White & Company

Historical Context: Event - "Lord Kelvin: A life in science" exhibition, Hunterian Museum, University of Glasgow. Object on display in this exhibition.