IMAGES TAKEN NEAR TO
Hanworth Road, HAMPTON, TW12 3DL

In the centre of the photo is the cannon marking the south eastern end of the original OS base line Image

This cannon embedded in the ground in Roy Grove marks the south eastern end of General Roy's original base line for setting out the Ordnance Survey triangulation of Great Britain in 1784. The white plaque in the background was put in place in 1926 to mark the 200th anniversary of General Roy's birth. The north western end of the base line is at Heathrow, on the other side of what was at the time Hounslow Heath Image

This is a very significant picture for the Geograph Project. The cannon was erected in 1926 to commemorate the 200th anniversary of Major General William Roy, who conceived the idea of using triangulation to produce a map of the whole country, thus laying the foundations for the Ordnance Survey. The monument was placed at the south-eastern end of the very first base-line for the Ordnance Survey, which was at the time part of Hounslow Heath. The other end is marked by a similar monument on the north side of Heathrow Airport (which has been rendered rather pointless by it having been moved to allow development there). The area was chosen because at the time it was flat and unobstructed, allowing a long, straight baseline to be measured. This was done using accurately measured rods which were used almost like a huge pair of rulers to measure the length of the line. Modern surveys have shown that this was just a couple of inches out - a remarkable achievement. The cannon is today on the corner of a fairly ordinary pre-war housing estate, but the significance is also recalled in the street names - Cannon Close and Roy Grove.

The inscription on the plaque reads: "THIS TABLET WAS AFFIXED IN 1926 TO COMMEMORATE THE 200TH ANNIVERSARY OF THE BIRTH OF MAJOR GENERAL WILLIAM ROY F.R.S., 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 S.E. TERMINAL OF THE BASE WHICH WAS MEASURED IN 1784 UNDER THE SUPERVISION OF GENERAL ROY, AS PART OF THE OBSERVATIONS FOR DETERMINING THE RELATIVE POSITIONS OF THE GREENWICH AND PARIS OBSERVATORIES – THIS MEASUREMENT WAS RENDERED POSSIBLE BY THE MUNIFICENCE OF H.M. 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 M.S.L. • AS MEASURED BY ROY – 27404.01 FEET • AS MEASURED BY MUDGE – 27404.24 FEET • DETERMINED BY CLARKE IN 1858 IN TERMS OF THE ORDNANCE SURVEY STANDARD 01 – 27406.19 FEET" This is really quite a significant picture for Geograph, as this is the very point where the triangulation of Great Britain started, leading ultimately to the Ordnance Survey and the National Grid system. The other end of the baseline is on the north side of Heathrow Airport in square Image and is marked with another cannon, but due to airport development this is no longer in its original position. I originally photographed this monument some years ago, when the plaque was fixed to the top of the cannon. It has now been moved to the nearby railings, where it sits on a rickety wooden stand and is held in place by plastic cable-ties. It is an easy target for vandals, although somehow it has survived this long. Where it was previously fixed to the cannon there is now a crude wooden bung. I don't know whether the site is cared for by Richmond Council, or the OS or by Crown Estates, but it really should be better cared for.

The location is Roy Grove, a small cul-de-sac off Hanworth Road, Hampton named after Major General William Roy. Behind the railings can be glimpsed some of the buildings of the Lady Eleanor Holles school. The cannon set into the ground marks one end of the original Ordnance Survey baseline - I am also submitting a supplemental picture to this square which will carry full details of this monument.

A multitude of wooden posts have been placed lest any vehicle ventures onto the verge via the crossing driveways.

View NNW from near the junction with Hanworth Road. The name itself is interesting - this was the main road to Uxbridge in days when west Middlesex was still largely rural - and Uxbridge the next place of any consequence as you headed north-west. These days much of the intervening terrain is residential suburbs, and a stretch of the old road that crossed the Heathrow site (at its eastern end) has disappeared.

Modern 1960s style town houses

Now apparently flats, the building still displays 'Isleworth Fine Ales' on its pediment.