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The Wood That Built London: Greenwich

In 1783, as President of the Royal Society, [Joseph Banks] received a memorandum from Jean-Dominique de Cassini, Director of the Paris Observatory, whose father, grandfather and great-grandfather had pioneered the triangulation of France. Cassini suggested that a joint trigonometric survey be conducted to resolve discrepancies between measurements taken by the Greenwich and Paris observatories. The following year, Banks commissioned the military engineer Major-General William Roy to take charge of the operation, and in 1784 Roy measured out a five-mile baseline on flat ground on Hounslow Heath (now under Heathrow Airport), using a steel chain precision-engineered by Jesse Ramsden, the leading instrument maker of the day.

From there, with the aid of a large theodolite also made by Ramsden, mounted on a portable scaffold and transported in its own carriage, he constructed a series of triangles across Surrey and Kent to Dungeness, and – using white lights – over the Channel to Dunkirk. One of Roy’s triangulation stations was at Norwood, ‘towards the Croydon end of the heights’; on his map, it corresponds to the present site of the transmitting station on Beaulieu Heights. From this one-hundred-metre elevation, he could take sightings over the swaying canopy of the North Wood to Hanger Hill in Ealing, Hundred Acres on Banstead Downs, the Royal Observatory at Greenwich and Severndroog Castle on Shooters Hill.

From The Wood That Built London by C.J. Schüler

Back to the map.

C.J. Schüler

C.J. Schüler