The Bradley Meridian
The first British National Meridian
The Greenwich Meridian was set according to the
location of the telescope used by the Astronomer
Royal to establish time. Between 1750 and 1850, the
Greenwich Meridian was marked by the north-south line
running through the Transit Instrument first used
by James Bradley, the 3rd Astronomer Royal (1742-62).
The Bradley Meridian served as Longitude 0° for all of
the earliest Ordnance Survey maps of England.
When the Airy Transit Circle Telescope was erected in
1850, the Greenwich Meridian was moved
approximately 19 ft east to its present location. This
move equals only 1/50th of a second of time - a
quantity too small for ninteenth-century astronomers
Meridian Building - Royal Observatory Greenwich, London, United Kingdom