Newlyn tidal observatory and part of the south pier


Heritage Category:
Listed Building
List Entry Number:
Date first listed:
Location Description:
National Grid Reference SW4676128559, South Pier, Newlyn, Cornwall


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The building or site itself may lie within the boundary of more than one authority.

Location Description:
National Grid Reference SW4676128559, South Pier, Newlyn, Cornwall
Cornwall (Unitary Authority)
National Grid Reference:


Tidal observatory built for the Ordnance Survey, and part of the south pier, constructed between 1913 and 1915.

Reasons for Designation

Newlyn tidal observatory and part of the south pier are listed at Grade II, for the following principal reasons:

Historic interest: *as the location of the establishment of Mean Sea Level by the Ordnance Survey between 1915 and 1921; *for the contribution of more than 100 years of tidal data to studies in oceanography, geology and climate change.

Architectural interest: *for the use of local materials and contractors, including Harvey & Co of Hayle, in the construction of the pier and observatory; *for the survival of the tidal observatory and the stilling well within the south pier extension, as specified by the Ordnance Survey in 1914.


Originating as a small medieval fishing village with a tiny quay, Newlyn flourished from the 1880s when a large harbour and two piers were built. As a port of refuge and call the harbour welcomed the town’s own fishing fleet alongside other British and foreign fishing fleets. A new road system in the early C20 also encouraged the large-scale export of granite from nearby quarries, which was transported by tracks along the south pier to waiting ships.

The south pier at Newlyn was completed in 1887 with a lighthouse at its northern end. Historic images (including a painting of 1893 by Stanhope Forbes) show this lighthouse with a small single-storey building adjacent to it. In common with other harbours and coastal locations, during the C19 Newlyn had three wooden rod tidal gauges and one was probably located on this pier. Tidal information was essential for ports and harbours, especially as C19 advances in technology resulted in the construction of larger ships which needed bigger draughts. At the same time the Ordnance Survey were contemplating problems with the heights of features shown on their maps; a baseline from which heights all over the country could be measured was needed. Mean Sea Level (MSL) provided the answer, and Liverpool was initially chosen in 1844 as the place to establish this during the First Geodetic Levelling between 1840 and 1860. This levelling was used for the first edition of Ordnance Survey maps. Other coastal towns took their own tidal measurements and, on comparison, it soon became clear that MSL was variable. A report on the poor state of repair of Newlyn’s tidal rod gauges coincided with the Ordnance Survey’s Second Geodetic Levelling of England and Wales from 1912, implemented to establish a reliable MSL. Alongside the creation of 86 fundamental bench marks within the established levelling network, Newlyn was included as one of three locations for a national tidal observatory to deliver the Second Geodetic Levelling. An extension to the south pier was planned on the advice of the consulting engineer to the Harbour Commissioners, WT Douglass, to ensure more efficient cover and shelter for the harbour and, on request from the Ordnance Survey, a building to house the automatic tidal recording machines was included in its plans in 1913. The pier extension was built in five sections: a new lighthouse (a secondary light to almost the same design as the C19 one) was completed in 1914 and by April 1915 the pier was completed. Adjacent to the lighthouse on the landward side was a small concrete building: the tidal observatory. The tidal observatory had cost £470. The C19 lighthouse was used as a lookout for pilots, but this and the single-storey building were demolished in 1918.

The 100ft long pier extension was built from concrete blocks on the rock foundation of the seabed. The tidal observatory was from its inception designed to be functional and constructed from concrete, with special blocks made for quoins, copings and the shaft into the pier, built to the Ordnance Survey’s specifications. Incorporated in the pier extension on its harbour side was a foot-long inlet nine inches in diameter which allowed water in and out of a stilling well, 5ft square in section and approximately 23ft deep, equipped with a float connected to a chart-recording gauge within the observatory. The first tidal gauge was provided by the Cary & Porter Company. A steel tape was hung from above the tidal gauge from which soundings could be taken to the water surface in the well as the tide fluctuated. Every Monday morning the clockwork-driven instruments had to be rewound by a tidal observer; all except the last observer were employed by the Ordnance Survey and until the 1980s they were responsible for collecting and replacing the charts and sending them to the headquarters.

Newlyn was eventually chosen as the principal place to determine MSL due to the tide coming in unimpeded from the Atlantic; as the granite geology was stable; and its proximity to the continental shelf so that changes in the ocean depth could be read. The first tidal measurements took place on 21 April 1915, but the hourly automatic measurements taken between 1 May 1915 and 30 April 1921 determined and fixed MSL for the country, resulting in what is now known as Ordnance Datum Newlyn. A brass bolt placed in the floor of the observatory is the bench mark for the whole of mainland England and Wales, and all heights are referenced to this point, 4.75m above MSL. Since 1956 height information on Ordnance Survey maps is based on Newlyn datum and the Third Geodetic Levelling (1950-68).

In 1937 heating and lighting was installed in the observatory and a lobby was added in the late 1970s. In 1953 the observatory became part of the newly-established UK Tide Gauge Network. From the beginning, meteorological measurements were also made manually at the observatory but as technology developed new systems were installed. In 1983 the Cary Porter gauge was replaced with a Munro tide gauge, on the original metal stand bolted to the floor; and a bubbler pressure gauge installed. At the end of 1983 the role of the observatory for supplying tidal data to the Ordnance Survey ceased, and its responsibility passed to the Natural Environment Research Council, who in turn delegated responsibility for tidal observations to the Proudman Oceanographic Laboratory (now part of the National Oceanographic Centre). Manual checks of the equipment were no longer required, and computer generated readings were sent by telephone line to various institutions (including the Met Office) for use in flood defence systems and scientific studies. The last tidal observer’s work was part-time compared with her predecessors who worked 365 days a year, sometimes taking manual readings every 10 minutes for 24 hours. The last observer retired in 2015.

In the 1980s much of the original equipment in the observatory was transferred to the Ordnance Survey store. In 1991 a plaque was mounted on the outside wall of the observatory to commemorate the bicentenary of the Ordnance Survey.

Having fulfilled its original purpose of providing the a base for establishing Mean Sea Level in 1921, the observatory continues to provide a facility for scientific tidal measurements, particularly for guiding climate change and coastal management studies.


Tidal observatory for the Ordnance Survey, and part of the south pier, constructed between 1913 and 1915.

Constructed of concrete blocks with a flat felt-covered roof, the tidal observatory is rectangular in plan. It is single storey and comprises a single room with a small lobby on the south side set back from the west elevation. The original structure has canted corners and there is a shallow cornice to the roof. On the west and north elevations are large, square timber-framed windows with steel double-shutters; the window to the north has small top-hung brass-framed casements. The building is accessed through sheet-steel doors on the west elevation of the lobby, within which is mounted a plaque to commemorate the bicentenary of the Ordnance Survey. The rear (east) wall of the observatory is the pier parapet.

The internal door to the observatory is simply boarded and set within an iron frame. The stilling well trap-door is roughly central inside the observatory and comprises sheets of timber, with various holes for the float in the stilling well shaft, situated within the south pier. A Munro tidal gauge is positioned at an angle above the trapdoor, on a cast iron base bolted to the floor. Attached to the ceiling above is a pully/hook (originally for the steel dipping tape). Set into the floor adjacent to the well shaft is the square, brass Observatory Bench Mark.

The pier extension is concrete faced in granite blocks tied together with steel bars, on a concrete raft on the rock foundation, two feet below the sea bed. All of the concrete blocks were made by Harvey & Co of Hayle at a yard on the nearby beach, using Portland cement and ingredients supplied by the St Ives and Penlee Stone Company.

Pursuant to s1 (5A) of the Planning (Listed Buildings and Conservation Areas) Act 1990 (‘the Act’) it is declared that the south pier lighthouse is not of special architectural or historic interest, however any works which have the potential to affect the character of the listed building as a building of special architectural or historic interest may still require LBC and this is a matter for the LPA to determine.


Books and journals
Beacham, P, Pevsner, N, The Buildings of England: Cornwall, (2014), 373
Cockram, R, Holmes, L, Hogg, R, Iddiols, F, Newlyn Tidal Observatory, (2018)
Hewitt, R, Map of a Nation: a biography of the Ordnance Survey , (2010)
British Oceanographic Data Centre – Newlyn (Cornwall) Site History , accessed 04/10/2018 from
Heritage Gateway: south pier lighthouse, accessed 09/10/2018 from
Mr Mycetes – England & Wales Lighthouse Compendium – Forgotten Lighthouses – Newlyn Lighthouse , accessed 04/10/2018 from
National Tidal and Sea Level Facility – The UK National Tide Gauge Network – Newlyn Tidal Observatory , accessed 04/10/2018 from
Ordnance Survey – Exploring our surveying antiquities , accessed 04/10/2018 from
Penwith Local History Group – Newlyn Tidal Observatory , accessed 04/10/2018 from
The Second Geodetic Levelling of England & Wales 1912-1921 published by Order of the Ministry of Agriculture and Fisheries (1921) , accessed 04/10/2018 from
Drawing, concrete blocks, tidal gauge shaft, south pier, Newlyn harbour, 1912 [Cornwall Record Office, X1428/3/9]
Drawing, new position for lighthouse and tidal gauge, south pier Newlyn harbour, 1912 [Cornwall Record Office, X1428/3/8]
E Bradshaw, PL Woodworth, A Hibbert, LJ Bradley, DT Pugh, C Fane & RM Bingley: A Century of Sea Level Measurements at Newlyn, Southwest England (2015)
Ordnance Survey (Cornwall) (1908) (1:2500)
Ordnance Survey (Cornwall) (1936) (1:2500)
The Cornish Telegraph ‘Newlyn Harbour: completion of extensive improvements’ Thursday 14 January 1915.
The Cornishman ‘Newlyn Pier Extension: new lighthouse to be built: the site of a tidal observatory’ Thursday 12 June 1913, p2.


This building is listed under the Planning (Listed Buildings and Conservation Areas) Act 1990 as amended for its special architectural or historic interest.

The listed building(s) is/are shown coloured blue on the attached map. Pursuant to s1 (5A) of the Planning (Listed Buildings and Conservation Areas) Act 1990 (‘the Act’) structures attached to or within the curtilage of the listed building but not coloured blue on the map, are not to be treated as part of the listed building for the purposes of the Act. However, any works to these structures which have the potential to affect the character of the listed building as a building of special architectural or historic interest may still require Listed Building Consent (LBC) and this is a matter for the Local Planning Authority (LPA) to determine.

End of official listing

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