The Bradley Meridian and James Bradley black plaque in London
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
James Bradley FRS (March 1693 – 13 July 1762) was an English astronomer and served as Astronomer Royal from 1742, succeeding Edmund Halley. He is best known for two fundamental discoveries in astronomy, the aberration of light (1725–1728), and the nutation of the Earth's axis (1728–1748). These discoveries were called "the most brilliant and useful of the century" by Jean Baptiste Joseph Delambre, historian of astronomy, mathematical astronomer and director of the Paris Observatory, in his history of astronomy in the 18th century (1821), because "It is to these two discoveries by Bradley that we owe the exactness of modern astronomy. .... This double service assures to their discoverer the most distinguished place (after Hipparchus and Kepler) above the greatest astronomers of all ages and all countries."