The History

The elegant Georgian building at 10 Argyll Street has a disinguished history, and played a vital part in one of the great British innovations of the Georgian era: the establishment of Ordnance Survey and the accurate mapping of the British Isles.


Drawn by the high achievers of the residents of Argyll Street, the eminent Scottish military Engineer, surveyor and Antiquarian, Major-General William Roy FRS FSA FRSE lived at The Observatory until his death in 1790. It was while he lived here that he established the baseline at Hounslow Heath and conducted the Anglo/French triangulation survey of 1784 “to measure the distance between the Royal Observatories of Greenwich and Paris”.  Roy was awarded the Copley medal from the Royal Society for this achievement and was the founder of the British Governments national mapping agency “Ordnance Survey”.


Roy’s technical drawings, accurately predicting the course of the Battle of Minden bring him to the notice of Duke Ferdinand of Brunswick, commander-in-chief of the Allied forces. A rapid series of promotions follow.


Recognising Britain’s vulnerability to invasion, Roy makes his first proposal for a survey to accurately map the country.
With public finances stretched, the project is deemed too expensive.


Roy, now Chief Engineer of the British Army, is promoted to the rank of Major-General.


As part of the London-Paris project, Roy measures a base-line across five miles of uncultivated Hounslow Heath, using first deal rods, then glass tubes, and finally a steel chain. The curious spectacle attracts numerous distinguished visitors, including King George III. This base-line becomes the foundation for all subsequent surveys of the United Kingdom.


Using the specially commissioned Ramsden theodolite, a large-scale, high-precision instrument weighing 200lb and requiring its own carriage, Roy makes his topographical survey of Middlesex, Surrey, Kent and Sussex. This survey, determining the longitude and latitude of points across the region, forms the start of the Principal Triangulation of Great Britain, 1791-1822.


The relative position of Roy’s Observatory at Argyll Street is tabulated in his submission to the Royal Society 1790. Roy leaves the house, his savings, gold watch and Copley Medal from the Royal Society to Thomas Reynolds, who had worked with him since 1784, and a substantial sum to Reynolds’ mother, who lived nearby in Poland Street.


Following Roy’s recommendations and methods, the Duke of Richmond establishes the Trigonometrical Survey of the Board of Ordnance – later known as Ordnance Survey – to map the entire country.


The Observatory has become one of the historic landmarks of London’s West End and now a prestigious business premises.

Argyll Street Connections - film project

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