North and South Meridian Markers before restoration
Meridian Markers and Obelisk after restoration
J.A. Hamilton was responsible for the original marks. From the Observatory Minute Book for 6 Oct 1948, p.2: "South meridian mark repaired, substituted a massive iron ring for the former copper one. The north mark, a light arch, is singularly so chosen for a purpose where the utmost steadiness is required".
One, the northern mark, at Tullyards, just off the Armagh-Loughall Road, is an arch-shaped structure surmounted by two pinnacles. These served to provide the initial alignment of the transit instrument, with finer adjustment provided by a small copper disk with a triangular hole in its centre. A second meridian mark of similar design was built to the south of the Observatory at Corkley but was destroyed in the 19th century. Both of these marks were built in or around the early 1790's and were almost certainly the work of Francis Johnston. A second, southern, meridian mark which still survives was built at Ballyheridan, just beyond the southern extremity of the Palace Wall. It is a square neoclassical column and is probably also the work of Francis Johnston. Adjacent to the northern stone mark stands a cast iron obelisk in the Egyptian style. It is the work of Gardner's foundry at Armagh and was erected in 1864 when the Jones Mural Circle was converted by Robinson to serve as a meridian circle. With his modified instrument, Robinson was able to measure both coordinates of stars, (i.e. right ascension and declination), with the one instrument and a single observer, where previously he had required two. The fine adjustment of the instrument relied on an adjustable pointer which is hidden in the apex of the obelisk so that it was visible from the Observatory, but not to the vandals that so frequently tried Robinson's patience. Both of the northern markers have been recently restored by the Department of the Environment and may be visited by a short excursion from the City.
Last Revised: 2009 November 5th