This telescope at the Royal Observatory Greenwich became a crucial reference point for astronomers, navigators and cartographers alike.
In July 1816, Edward Troughton's 10-foot transit instrument telescope replaced an earlier one by the third Astronomer Royal, James Bradley, and also reconfirmed Bradley's meridian as the Prime Meridian for the Royal Observatory Greenwich until December 1850.
The telescope was commissioned by Astronomer Royal John Pond after the Mural Circle telescope, installed a few years earlier, had been found insufficiently stable for taking accurate transit observations. It was regularly calibrated by taking sightings off a number of distant markers.
On the centre of the telescope's axis the maker has inscribed: 'Designed and Executed for the Royal Observatory by Edward Troughton, London, 1816' on one side and on the other 'To the President of the Council of the Royal Society this and the Mural Circle, being his greatest and best works, are dedicated by the maker'.
The telescope now sits (and has done since 1967) on replica piers in the same site in which it sat in 1816.