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Foot (Clarke's)

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In approximately 1795, Jean-Charles de Borda, in his capacity of Guardian of Standards, and on instruction by the French Academy of Sciences, constructed two length standards. One, designated the Mètre des Archives, which ultimately became the standard meter for the world, and another, called the Module, a bar two toises long, with the meter defined as a multiple of the toise. Until 1880, most of Europe, specifically including France, used this meter, defined in terms of Borda's Module, as a standard; however, England defined a legal metre (to use British spelling) in terms of a copy of the Mètre des Archives.[1]

In 1866, Colonel Alexander Ross Clarke used various copies of the toise to determine their relation to the British Imperial Standard Yard, and on the basis of this comparison, derived a value of the French legal meter of 39.370432 British Imperial inches = 3.28086933 British Imperial feet. Inverting this ratio, one obtains a foot of ≈ 0.3047972654 m[1].

Although Clarke's ratio was based on the French legal meter of the day, not the meter that became internationally accepted in 1883, a foot of 0.3047972654 m has become known as a Clarke's foot, and has been used in geodesy.

ReferencesEdit

  1. 1.0 1.1 Tomasz Zakiewicz, The Cape Geodetic Standards and Their Impact on Africa

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