J3527 : Slieve Donard Triangulation Pillar

taken 1 year ago, 3 km from Widows Row, Northern Ireland

Slieve Donard Triangulation Pillar
Slieve Donard Triangulation Pillar
Trig pillar at the summit of Slieve Donard. The pillar is situated on the top of the stone tower as seen in J3527 : The Mourne Wall, Slieve Donard. Donard was first triangulated in 1826 but this pillar was built for the re-triangulation of Northern Ireland c1950. It is officially called Slieve Donard (New) as readings couldn't be taken from the original station as the Mourne Wall (built c1910) blocked the cross-channel rays; therefore the new station had to be constructed on top of the tower to overcome this problem. Donard is one of the 12 Primary Stations established by the Ordnance Survey Northern Ireland for their re-triangulation. From here connections were made to other primary stations in Ireland - Divis, Trostan, Knocklayd, Sawel, Carrigatuke, Loughan Leigh, Castlecoe, Hill of Howth and Kippure; Donard is also a cross channel station and connections were made with Cairn Pat and Inshanks in Scotland, South Barrule on the Isle of Man and Holyhead in Wales. See J3527 : Flush Bracket, Slieve Donard Triangulation Pillar for a closer view of the flush bracket; a keen climber has added a rock to the top of the pillar but I wouldn't risk it!
Bench Mark

Bench marks were historically used to record the height above sea level of a location as surveyed against the Mean Sea Level data (taken at Clarendon Dock, Belfast, for Northern Ireland data, Newlyn in Cornwall for data in Great Britain and Portmoor Pier, Malin Head, for data relating to the Republic of Ireland). They were used as part of a greater surveying network by the UK Ordnance Survey, Ordnance Survey Northern Ireland (OSNI) and the Ordnance Survey Ireland (OSI). If the exact height of one bench mark is known then the exact height of the next can be found by measuring the difference in heights, through a process of spirit levelling. In this way hundreds of thousands of bench marks were sited all around the UK & Ireland from the mid 19th to late 20th centuries. There are several distinct types of bench mark:

- Fundamental bench marks have been constructed at selected sites where foundations can be set on stable strata such as bedrock. Each FBM consists of a buried chamber with a brass bolt set in the top of a granite pillar. See NG8825 : Dornie fundamental bench mark for an example. FBMs were used in Ireland as well as GB but those in Ireland do not have any surface markers, nor are they marked on standard maps.
- Flush brackets consist of metal plates about 90 mm wide and 175 mm long. Each bracket has a unique serial number. They are most commonly found on most Triangulation Pillars, some churches or on other important civic buildings. See J3270 : Flush Bracket, Belfast for an example.
- Cut bench marks are the commonest form of mark. They consist of a horizontal bar cut into a wall or brickwork and are found just about anywhere. A broad arrow is cut immediately below the centre of the horizontal bar. See J3372 : Bench Mark, Belfast for an example. The horizontal mark may be replaced by or contain a bolt - see J1486 : Bench Mark, Antrim.
Other marks include:
- Projecting bench marks such as SD8072 : Projecting Bracket Benchmark on St Oswald's Tower
- Bolt bench marks such as SJ1888 : OSBM bolt on Hilbre Island
- Rivet bench marks such as J3978 : Bench Mark, Holywood
- Pivot bench marks such as SJ2661 : Pivot bench mark on Leeswood Bridge

Bench marks are commonly found on older buildings or other semi-permanent features such as stone bridges or walls. Due to updated mapping techniques and technological advances such as GPS, bench marks are no longer maintained. Many are still in existence and the markers will probably remain until they are eventually destroyed by redevelopment or erosion.

The Mourne Wall

The Mourne Wall is a 22 mile long wall in the Mourne Mountains. It was built between 1904 and 1922 by the Belfast Water Commissioners to enclose their water catchment areas in the Mournes and protect the area from the effects of cattle and sheep on the water course. The wall is predominately constructed from local granite stone using traditional dry stone walling techniques; on average the wall is about 1.5 metres high and 0.8 to 0.9 metres thick. It is not uniform in construction along the entire length - the 'classic' granite wall is only to be found north of Carn mountain and Long Seefin with particularly impressive sections on Slieve Commedagh and Slieve Donard; elsewhere the wall largely resembles dry stone walls found elsewhere in the Mournes and south County Down. In places, such as Slieve Muck, the wall is not constructed of granite at all.

OSNI Triangulation Stations

The re-triangulation of Northern Ireland by the Ordnance Survey Northern Ireland began in 1950. This was the first complete survey of Northern Ireland which included observations with the new primary triangulation of the country, its connection with the Republic of Ireland and the cross-channel connection between Ireland and Great Britain. This began by OSNI establishing a series of triangulation stations throughout the country. Almost all of these stations were topped by trig pillars and 80, mainly primary and secondary pillars, had been constructed by October 1949. Measurements between primary stations began in 1950 and measurements for these and the secondary stations were completed by July 1956. The construction and measurements for tertiary stations were completed later (probably no later than the mid 1960s). Only two stations are not topped by pillars - Lighthouse Island, marked by a brass rivet, and Ardglass, which utilised the top of a high stone folly. The older triangulation stations on the Lough Foyle Base Line were also re-surveyed as part of this process. A majority of the stations are still extant today but a few have been removed or destroyed.

Creative Commons Licence [Some Rights Reserved]   © Copyright Rossographer and licensed for reuse under this Creative Commons Licence.
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J3527, 97 images   (more nearby search)
Photographer
  (find more nearby)
Date Taken
Sunday, 31 May, 2020   (more nearby)
Submitted
Monday, 1 June, 2020
Geographical Context
Uplands  Historic sites and artefacts  Boundary, Barrier 
Primary Subject of Photo
Summit  Trig Point 
Place (from Tags)
Mourne Mountains  Slieve Donard  Mourne Wall  Triangulation Station 
Subject Location
Irish: geotagged! J 357 276 [100m precision]
WGS84: 54:10.8121N 5:55.2596W
Camera Location
Irish: geotagged! J 357 276
View Direction
North-northeast (about 22 degrees)
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Image Type (about): close look 
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