Arc measurement of Delambre and Méchain
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The arc measurement of Delambre and Méchain was a
Jean-Baptiste Delambre and Pierre Méchain in 1792–1798 to measure an arc section of the Paris meridian between Dunkirk and Barcelona. This arc measurement served as the basis for the original definition of the metre.[1]
In 1791, the
oblate spheroid, at the level of precision required for defining a standard of length. The irregular and particular shape of the Earth smoothed to sea level is represented by a mathematical model called a geoid, which literally means "Earth-shaped". Despite these issues, in 1793 France adopted this definition of the metre as its official unit of length based on provisional results from this expedition. However, it was later determined that the first prototype metre bar was short by about 200 micrometres because of miscalculation of the flattening of the Earth, making the prototype about 0.02% shorter than the original proposed definition of the metre. Regardless, this length became the French standard and was progressively adopted by other countries in Europe. This is why the polar circumference of the Earth is 40,008 km, instead of 40,000.[1]
See also
- Cartography of France
- Earth's circumference#Historical use in the definition of units of measurement
- Earth radius § History
- History of geodesy § Prime meridian and standard of length
- History of the metre § Meridional definition
- Meridian arc § 17th and 18th centuries
- Metre § Early adoption of the metre as a scientific unit of length: the forerunners
- Paris meridian#The West Europe-Africa Meridian-arc
References
- ^ ISBN 978-0-7432-1675-3. Retrieved 2020-08-02.