ROY, William.

An Account of the Trigonometrical Operation, whereby the distance between the meridians of the observatories of Greenwich and Paris has been determined. From the Philosophical Transactions.

No place, printer or date; London: 1790

4to, 162 pages, 1 leaf (blank), 11 folding engraved plates, 4 folding letterpress tables. Some dust-soiling in the outer corners of a few leaves, otherwise a fine copy. Modern boards, uncut.

OFFPRINT (first separate edition) of Major-General William Roy’s third and last paper on his triangulation connecting the Royal Greenwich Observatory with the Paris Observatory, which resolved the dispute over the difference in longitude between the Paris and Greenwich observatories, and resulted in the founding of the Ordnance Survey. “In the triangulation of the 1780s Roy quite consciously laid the foundations for such a survey by procuring from the foremost instrument maker the most advanced equipment yet produced; by establishing a base-line at Hounslow from which triangulation could be extended in all directions — not just towards France; by elaborating methods and procedures in his papers for the Philosophical Transactions which were suitable for both the particular Anglo-French scheme and a more general national triangulation; and, perhaps most importantly, by securing the backing of the duke of Richmond, the master-general of the ordnance, who had lent men and equipment for the triangulation. In his description of the work Roy made clear that he saw the Anglo-French triangulation as part of a larger future British project: in his 1790 paper in the Philosophical Transactions he recommends “that the trigonometrical operation, so successfully begun, should certainly be continued, and gradually extended over the whole island” (ODNB). The plates include the map of Kent and Sussex and the French coast, and show the instruments used in great detail, in particular Jesse Ramsden’s specially made theodolite.


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