In 1969 Bidston Observatory became a component body of the Natural Environment Research Council and was renamed the Institute of Coastal Oceanography and Tides (ICOT) with an expansion of its oceanographic work. In the ICOT Annual Report for 1969/70 it states:–
“An essential component of any environmental research effort is the acquisition of relevant observations against which theories can be tested. In the marine sciences such fieldwork is invariably expensive both in capital equipment and operating costs; data acquisition systems should therefore be designed for maximum efficiency and minimum maintenance. It follows that such a system will provide a basis for the long-term monitoring of oceanographic variables, the analysis of which can be expected to yield a bonus in the same way that barometers and thermometers have contributed to both synoptic meteorology and climatology.”
This short film, by Andy Lane, Andy Heath and Craig Corbett, is part of the Tide and Time exhibition at the National Oceanography Centre, Liverpool. The exhibition showcases two tidal prediction machines – the Roberts-Légé and the Doodson-Légé. The film also explores the history of tidal science in Liverpool and its development as a port.
There is a lot of renewed interest in tide prediction machines and, after many years hidden away in storerooms, some of the machines made in the UK are on permanent display once again. Kelvin’s original 10-component machine is now part of the new Winton Gallery for Mathematics at the Science Museum in London alongside Ishiguro’s storm surge simulator. Two of the machines that were used at Bidston can now be seen at the National Oceanography Centre building in Brownlow Street in Liverpool.
As you may know from articles mentioned in the Resources section of this web site, the tide prediction machines were a way of simulating the tide in terms of its many harmonic components. Each component would be represented by an amplitude and phase lag, called the ‘harmonic constants’, and the machine, which can be considered as a sort of analogue computer, would be programmed to run by providing it with these constants. Of course, the constants would differ from port to port.
That raises the obvious question of where people like Arthur Doodson, and the other operators of the machines, got their constants from in the first place. This short article reviews the main characteristics of one of the machines (the so-called Doodson-Légé machine now on display at NOC) and then attempts to answer the question of how Doodson obtained the constants.
Research on Earth tides and ocean tide loading has an even longer history at Bidston Observatory than the work on ocean tides. This article gives a brief overview of the developments in these research areas following the measurements at Bidston in 1909 by John Milne, with particular emphasis on the contributions of the research groups at Bidston to the advances in these topics.
Bidston Observatory was built in 1866, when the expansion of Waterloo Dock forced Liverpool Observatory to re-locate to Bidston Hill. It was built alongside Bidston Lighthouse and Signals Station, on land owned by the Mersey Docks and Harbour Board. George Fosbery Lyster was the architect.
Most people know that the tide rises and falls periodically at the coast but not everyone is as aware of the periodic flood and ebb of tidal currents. These are of particular importance for mariners and need to be taken into account for navigation. Where currents become particularly strong, they can become known as a ‘tidal race’, which can be unnavigable at certain states of the tide.
Around the coast of the British Isles are many locations where a tidal race forms, usually in a constricted channel between two islands or an island and the mainland. In Scotland, between the islands of Jura and Scarba is the famous ‘Whirlpool of Corryvreckan’ – possibly the third largest whirlpool in the world (after Saltstraumen and Moskstraumen, off the coast of Norway). The Gulf of Corryvreckan, also called the Strait of Corryvreckan, is a narrow strait between the islands of Jura and Scarba, in Argyll and Bute, off the west coast of mainland Scotland.
One of the main objectives of the research at Bidston Observatory was to understand more about the dynamics of the ocean tides, that is to say, the physical reasons for why the tide propagates through the ocean as it is observed to do. Before the advent of digital computers, the only way to approach these questions was from basic mathematical perspectives, in which eminent scientists such as Pierre-Simon Laplace in France excelled in the 19th century, and in which Joseph Proudman at Bidston was an acknowledged expert in the 20th century.
Similarly, there has always been considerable interest in the reasons for large non-tidal changes in sea level, including in particular those which occur due to the ‘storm surges’ generated by strong winds and low air pressures in winter. For example, following the Thames floods of January 1928, Arthur Doodson at Bidston chaired a committee for London County Council that undertook a detailed study of the reasons for the storm surge that caused the flooding, and made recommendations for protecting the city in the future.
Everyone knows that the level of the sea goes up and down. Most of these changes in level are due to the ocean tide (at Liverpool the level changes due to the tide by more than 8 metres at ‘spring tides’), but changes of several metres can also occur due to ‘storm surges’ that occur during bad weather, while slow changes in level can take place due to climate change and because of the geology of the adjacent land.
Changes in sea level are measured by devices called ‘tide gauges’: the more suitable name of ‘sea level recorders’ has never been widely adopted in the UK although Americans often call them ‘water level recorders’. There are as many types of tide gauge such as:
This article originally appeared in the newsletter of the Friends of Bidston Hill in February 2016. It is reproduced here with the permission of the author, Philip Woodworth.
The role of Bidston Observatory has changed several times through the years. In its early decades, following the decision in the 1860s by the Mersey Docks and Harbour Board to move the Liverpool Observatory from Waterloo Dock to Bidston Hill, the focus was on astronomical measurements. These were required in order, amongst other things, to determine accurately the latitude and longitude of the site. Famous names involved included John Hartnup and his son (also John) and W.E. Plummer. Other areas of science undertaken by the Observatory included meteorology and seismology. In addition, it provided several local services, such as the calibration of accurate chronometers for port users and precise timing via the “One O’Clock Gun”.