Cannon

From TrigpointingUK
Jump to: navigation, search

Cannon

In 1784, Major-General William Roy undertook the measurement of a triangulation base on Hounslow Heath. The work was carried out with glass tubes approximately 18 feet in length [1]. This was followed, in 1794, by the measurement of a base on Salisbury Plain, this time using steel chains [2]. The ends of these base lines were marked by cannons.

These cannons are not recorded in OSGB36 but are of historical importance.

The four trig stations in TP:UK corresponding to these are:

Three of the cannons are easily accessible, with the Salisbury Plain Baseline North marked on T:UK as 'inaccessible'. It is co-located with the Beacon Hill trig pillar and is assumed to be buried. The Hounslow Heath NW cannon has been moved a short distance to accommodate Heathrow Airport boundary fencing.

References

  1. The History of the Retriangulation of Great Britain, Section 1.02
  2. The History of the Retriangulation of Great Britain, Section 4.00