English: General Roy monument, Hampton Hill. 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 TQ0776 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.