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The Principal Triangulation of Britain was a triangulation project carried out between 1784 and about 1853 at the instigation of senior surveyor General William Roy (1726–1790). ==History== In 1783 the French Academy of Sciences suggested it would be useful to astronomy to connect the royal observatories of London and Paris through the scientific method of triangulation. After the Royal Society agreed, General William Roy commissioned a new theodolite from leading instrument maker Jesse Ramsden. The baseline for the triangulation was established in 1784 between Hampton Poor House and King's Arbour on Hounslow Heath, a distance of just over 27,400 feet.〔(The French Connexion – Between English and French Map Surveys ) by Michael Knowles in Proceedings of the BRLSI Volume 7 2003.〕 The Hounslow endpoint is marked by a cannon embedded in the verge of the road over the Heathrow Airport access road tunnel.〔https://www.ordnancesurvey.co.uk/blog/2013/11/heathrow-airport-honours-the-work-of-major-general-william-roy/〕 This Ramsden theodolite, delivered in 1787, for the first time divided angular scales accurately to within a second of arc.〔Insley, J. (2008) (The Tale of the Great Theodolites ), retrieved 8 january 2014.〕 General Roy and his team used it to accurately triangulate the distance between the observatories to complete the Anglo-French Survey (1784–1790). The baseline derived during that work, together with the new theodolite, served as the basis for the planning and execution of the subsequent work on the Principal Triangulation. Around 1791, shortly after his death, Roy's team began the field work, using the specially built Ramsden theodolite. In 1794 a seven-mile-long baseline of verification was measured on Salisbury Plain. Eventually the triangulation extended to cover the whole of the British Isles, after it was decided in 1824 that a 6-inch-to-the-mile (1:10,560) map of Ireland was necessary for accurate land taxing. The Principal Triangulation was subsequently superseded by the Retriangulation of Great Britain some 150 years later. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Principal Triangulation of Great Britain」の詳細全文を読む スポンサード リンク
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