We don't have any photos of this building yet. Why don't you be the first to send us one?
Latitude: 51.4798 / 51°28'47"N
Longitude: -0.4503 / 0°27'0"W
OS Eastings: 507714
OS Northings: 176789
OS Grid: TQ077767
Mapcode National: GBR 23.K4Z
Mapcode Global: VHFTK.42TD
Plus Code: 9C3XFGHX+WV
Entry Name: Monument at North Western End of General Roys Survey Base
Listing Date: 15 December 1997
Grade: II
Source: Historic England
Source ID: 1119717
English Heritage Legacy ID: 469215
ID on this website: 101119717
Location: Hillingdon, London, TW6
County: London
District: Hillingdon
Electoral Ward/Division: Heathrow Villages
Parish: Non Civil Parish
Built-Up Area: Hillingdon
Traditional County: Middlesex
Lieutenancy Area (Ceremonial County): Greater London
Church of England Parish: St Mary the Virgin Harmondsworth
Church of England Diocese: London
TQ 07 NE
804/47/10049
NORTHERN PERIMETER ROAD
Heathrow Airport
Monument at north-western end of General Roy's survey base
II
Cast-iron cannon monument, installed 1791 to mark the north-western end of the baseline measured by General Roy in 1784 across Hounslow Heath, from King's Arbour to Hampton Poor House, which is now taken to be the origin of the Ordnance Survey. Roy originally marked his line by wooden posts, but in 1791 two guns were selected at Greenwich 'from amongst those which had been condemned as unfit for the public service'. The cannon is some nine feet long, the lower six feet of which are buried in the ground. Next to the cannon is a plaque which reads as follows:
'This tablet was affixed in 1926 to commemorate the 200th anniversary of the birth of Major General William Roy FRS, born 4th May 1726 - died 1st July 1790. He conceived the idea of carrying out the triangulation of this country and of constructing a complete and accurate map and thereby laid the foundation of the Ordnance Survey. This gun marks the NW terminal of the base which was measured in 1784, under the supervision of General Roy, as part of the operations for determining the relative positions of the Greenwich and Paris Observatories. This measurement was rendered possible by the munificence of HM King George III, who inspected the work on 21st August 1784. The base was measured again in 1791, by Captain Mudge, as the commencement of the principal triangulation of Great Britain. Length of base - reduced to MGL - as measured by Roy - 27404.01 feet, as measured by Mudge - 27404.24 feet, as determined by Clarke in 1858 in terms of the Ordnance Survey Standard 01 - 27406.19 feet.'
Source: Captain William Mudge and Isaac Dalby, An Account of the Operations Carried on for Accomplishing a Trigonometric Survey of England and Wales, vol. 1, 1799, p.223.
The monument at the south-east end of General Roy's baseline is listed under Roy Grove, Hampton, in the London Borough of Richmond.
Listing NGR: TQ0771476789
External links are from the relevant listing authority and, where applicable, Wikidata. Wikidata IDs may be related buildings as well as this specific building. If you want to add or update a link, you will need to do so by editing the Wikidata entry.
Other nearby listed buildings
