This pillar was erected in 1824 under the direction of the
Reverend John Pond M.A. Astronomer Royal. It was placed on
the Greenwich meridian and its purpose was to indicate the
direction of true north from the transit telescope of the Royal
Observatory. The Greenwich meridian as (sic) changed in 1850
& adopted by international agreement in 1884 as the line of zero
longitude, passes 19 feet to the east of this pillar.