Last year I successfully completed the first year of my Master’s degree in the Cultural History of Science and Technology, Digital Humanities and Mediation, which is offered by the Centre François Viète research laboratory at the Université de Bretagne Occidentale in Brest. A large part of the year was taken up by my research project, “An historic analysis of tide prediction machines using an adapted prosopographic approach and digital humanities tools,” which can be found here: doi.org/10.5281/zenodo.3265011. In this post I’m going to give a quick summary of what I achieved during the year in relation to this research project.
I gave a 5-minute speed lecture entitled “A New Wave of Prosopography: an Application to Tide Prediction Machines” at the International Postgraduate Port and Maritime Studies Network Conference 2019 at the University of Dundee, UK, on 25 April 2019. My presentation can be found here: doi.org/10.5281/zenodo.3003566.
Now Helen Mair Rawsthorne giving a speed lecture on her ideas on prosopographical methodology and how it can be applied to the study of objects. pic.twitter.com/N0xMlpXSVh
I won DARIAH-EU’s Digital Humanities methods and tools blog competition 2019 with my article “Tide Prediction Machines, Prosopography and Digital Humanities: what are they and how do they fit together?”, which can be found here: dhmethods.hypotheses.org/229. I was awarded a scholarship to attend the DARIAH’s Annual Event 2019 in Warsaw, Poland, and showcase my research at a poster presentation there. My poster can be found here: doi.org/10.5281/zenodo.2908250.
June 2019
I gave a 20-minute presentation entitled “The Development of Tide Prediction Machines” at the Shaped by the Sea workshop at the University of Manchester, UK, on 27 June 2019. My presentation can be found here: doi.org/10.5281/zenodo.3261817.
I gave a 20-minute presentation entitled “A New Wave of Prosopography: an Application to Tide Prediction Machines” at the Oceanext 2019 conference (within La Mer XXL exhibition) at Nantes Exhibition Centre, France, on 4 July 2019. My presentation can be found here: doi.org/10.5281/zenodo.3269511.
This post concludes the work for the first year of my Master’s degree. My life last year was completely and unexpectedly taken over by tide prediction machines, but I enjoyed the work immensely. I put a lot of time and effort into it and I am very pleased with the results. I am currently in the process of developing the subject for this year’s research project, which will be my Master’s thesis. I will shortly be starting a new blog to document this next part of my adventure – tide and time wait for no man (or woman)!
This article has been adapted from Chapters 1 and 3 of my research project entitled ‘An historic analysis of tide prediction machines using an adapted prosopographic approach and digital humanities tools’, which I wrote during the first year of my Master’s degree. A copy of the full text can be found at: http://doi.org/10.5281/zenodo.3265011.
What are tide prediction machines?
The Roberts-Légé tide prediction machine, built 1908. Photograph taken by author
at the Tide & Time exhibition, National Oceanography Centre, Liverpool, on 15 January 2019.
Tide Prediction Machines are analogue computers that were used to predict the times of high and low tides worldwide from the end of the 1800s up to the digital age. The first tide prediction machine was designed by William Thomson (1824–1907), and was built in London in 1873. It was developed as a response to increasing pressure from commercial shipping lines towards the middle of the nineteenth century who wanted a greater number of more accurate tidal predictions more quickly than could be calculated by hand. As well as helping shipping lines and navies to safely navigate the seas and the shores, tide prediction machines became crucial to the building of ports and effective flood defences. A total of 25 of the 33 tide prediction machines ever built were constructed in the UK but were then shipped to other countries who wanted to do their own calculations.
How do you calculate tidal predictions?
Tidal observation refers to the act of continuously measuring the height of a body of water at any one location, usually using a tide gauge, to produce a set of tidal observations. Such sets of tidal observations are key to calculating predictions of future (or past!) tides using the harmonic method of tidal analysis.
The harmonic method of tidal analysis uses a set of tidal observations for any given location to isolate and identify every factor, known as a constituent, that contributes to the tides there (Pouvreau 2008, p. 37). Each constituent is related to a different lunar or solar frequency with a known period T. The harmonic analysis allows for each constituent to be broken down into harmonic constants: an amplitude A and a phase φ, which are dependent on the chosen location. Inversely, harmonic tidal prediction involves summing each individual constituent that contributes to the tides at a chosen location and therefore requires the harmonic constants for that location to have already been calculated. The more constituents taken into account in the calculation, the more accurate the prediction will be. Tide prediction machines use the harmonic method of prediction to calculate the times and heights of high and low tides at any moment in time and at any location in the world, provided the corresponding harmonic constants are known.
The equation above shows the equation that tide prediction machines were designed to calculate (Bell 1962, p. 1; Woodworth 2016, p. 6). It sums over a finite number N of constituents i as a function of time t, where Ai is the amplitude of the constituent i, ωi = 2π ∕ Ti is the angular speed of the constituent i for which Ti is the period of the corresponding lunar or solar frequency, and φi is the phase of the constituent i. The equation gives as an output H(t), which is the height of the water above (H(t) > 0) or below (H(t) < 0) the mean water level at time t. The times t at which the maxima and minima of H(t) occur are the times of high and low tide respectively. The height of the water at any time is given by H(t) + H0, where H0 is the mean water level.
How do tide prediction machines work?
Tide prediction machines are made up of a system of pulleys, shown the photograph below, each representing a different constituent. The pulleys simultaneously oscillate vertically and rotate. The period of each constituent is pre-programmed into the corresponding pulley, and the amplitude and phase of each pulley is set by the machine operator according to the harmonic constituents for the chosen location. A wire wound around the pulleys allows for the movement of the pulleys to be added, giving the output of the total rise or fall of the tide above the mean water level as a function of time for the programmed place. Not all tide machines were built the same but most operated on this principle and gave the outputs in the form of graphs, on dials or in displays.
Pulley system on the Doodson-Légé tide prediction machine, built 1950. Photograph
taken by author at the Tide & Time exhibition, National Oceanography Centre, Liverpool, on
15 January 2019.
Bibliography Bell, W. H. (1962). Tide Predicting with TIDAC. en. Tech. rep. 130. Nanaimo: Pacific Oceanographic Group, Fisheries Research Board of Canada, p. 18. Pouvreau, Nicolas (2008). ‘Trois cents ans de mesures marégraphiques en France : outils, méthodes et tendances des composantes du niveau de la mer au port de Brest’. fr. Doctor of Philosophy. La Rochelle: Université de La Rochelle. Woodworth, Philip L. (2016). An inventory of tide prediction machines. en. URL: http://nora.nerc.ac.uk/id/eprint/513660 (visited on 10/10/2018).
This article has been adapted from Chapter 3 of my research project entitled ‘An historic analysis of tide prediction machines using an adapted prosopographic approach and digital humanities tools’, which I wrote during the first year of my Master’s degree. A copy of the full text can be found at: http://doi.org/10.5281/zenodo.3265011.
As with many scientific theories, the development of tidal theory and methods of predicting the tides throughout history has been motivated by practical needs. Here are just a few of the reasons why tidal predictions have been and continue to be important:
Why are tidal predictions important? From the primitive to the modern day (Rawsthorne 2019).
The most primitive reasons that motivated the search for methods of predicting times and heights of the tides include coastal dwelling, fishing and marine navigation. A need for tidal forecasts came with the development of ports, docks and harbours for their successful operation and management, and for coastal surveying. Engineers also started to make use of tidal predictions for coastal zone engineering projects, which include the construction and destruction of bridges and platforms. As for recreational activities, tidal forecasts are useful for beachgoers and for the safe practice of watersports, as well as for houseboat living. More precise predictions were called for as commercial shipping and naval operations evolved, and for the building of effective coastal and estuarine flood defences. Tidal predictions today are used for many more purposes than ever before. They are used by biologists and ecologists to better understand floating animals and plants, for habitat restoration projects and to study the effects of pollutants in bodies of tidal water (NOAA 2019). Tidal predictions and weather forecasts have a symbiotic relationship as the tides and the climate both affect each other, meaning that meteorologists make use of tidal predictions just as oceanographers make use of weather forecasts. The most recent use for tidal predictions is for harnessing tidal power, which can be converted into renewable energy.
Bibliography NOAA (2019). Tides and Water Levels: The Importance of Monitoring the Tides and Their Currents. en. URL: https://oceanservice.noaa.gov/education/tutorial_tides/tides09_monitor.html (visited on 02/05/2019). Rawsthorne, Helen Mair. (2019). ‘The Development of Tide Prediction Machines’, Shaped by the Sea workshop. University of Manchester, 27-28 June. en. DOI: 10.5281/zenodo.3261817.
This article has been adapted from Chapter 3 of my research project entitled ‘An historic analysis of tide prediction machines using an adapted prosopographic approach and digital humanities tools’, which I wrote during the first year of my Master’s degree. A copy of the full text can be found at: http://doi.org/10.5281/zenodo.3265011.
The tides
It would be difficult to talk about the history of tidal prediction without first introducing the notion of tides. Tides on Earth can be observed in bodies of water such as oceans, seas and lakes. Physically they appear as vertical movements of the surface of the water, the maximum and minimum of which are known as high water and low water, and alternating horizontal movements of the water, known as tidal currents (Gordon et al. 2015).
To understand why tides exist on Earth, it is necessary to have some knowledge of the interactions between the Earth, the Moon and the Sun. The Moon is attracted to the Earth because of gravitational attraction but is also repulsed by the Earth due to the centrifugal force that results from the Moon spinning around it. The diagram below shows the Earth (large circle on the left), the water on the surface of the Earth (oval) the Moon (small circle on the right) and the forces in play between them: the red arrows represent the direction and the intensity of the force of gravitational attraction, the blue arrows represent the direction and the intensity of the centrifugal force and the green arrows represent the direction and the intensity of the resultant tide-causing force. The intensity of the centrifugal force on the Earth is constant whilst the intensity of the gravitational attraction varies proportionally to the changing distance between the Earth and the Moon. It is the combination of these two forces that results in the tides: when the resulting force is directed towards the centre of the Earth, the water level falls, and when the force is directed away from the centre of the Earth in the plane of the Moon, the water level rises, as shown by the green arrows in the diagram. The Sun contributes to tides on Earth in exactly the same way as the Moon does, but to a lesser extent. At most locations on Earth tides are semidiurnal, which means that low tide and high tide each occur twice per day. This effect is a result of the rotation of the Earth itself and the fact that there is always high water on two opposite sides of the Earth at any one time. There is also a diurnal component to the tides, which is because of the asymmetry of the high water directed towards and away from the Moon (Ifremer 2004).
Diagram showing the forces in play between the Earth and the Moon. The red arrows represent the direction and the intensity of the force of gravitational attraction, the blue arrows represent the direction and the intensity of the centrifugal force and the green arrows represent the resultant tide-causing force. Not to scale. Diagram created by Vincent Lecoustey.
There are also certain geographical features on Earth that affect the height of the tides and their fluctuation in time. These features include the shape of the specific beach, the angle of the seabed leading up to the beach, the shape and depth of the surrounding coastline and the prevailing ocean currents (Byrd 2019). As well as these predictable astronomical and geographical tidal influences, the climate and weather have very unpredictable influences on the tides on Earth.
For all the astronomical, geographical and meteorological reasons aforementioned, the tides on Earth do not follow a repeated pattern (National Oceanography Centre 2019[b]). This means that the only way of knowing the times and heights of future tides is to forecast or predict them using an equation that takes into account the factors that cause them.
History of tidal science and prediction
Before tide prediction machines
Tidal theory is the result of centuries of observations, hypotheses, empirical research and contributions from dozens of the brightest minds from a multitude of locations across the world.
The first attempts at predicting the tides were made by those occupying lands next to tidal waters in the form of rule-of-thumb methods linked to the phase of the moon. There is evidence from centuries and millennia before the Christian era of early Indian and Arabic civilisations recognising the influence of the moon over the tides, and of their interaction with and efforts to manage the tides (Cartwright 2000, p. 1-6). The Copernican Revolution, which stemmed from an idea by Nikolaus Copernicus (1473–1543) that the Earth is not located at the centre of the universe but that it revolves around the Sun with other planets, allowed for the development of a new genre of physical theories of the tides from the sixteenth century. Distinguished polymaths and natural philosophers of the time such as Francis Bacon (1561–1626), Galileo Galilei (1564–1642), Johannes Kepler (1571–1630) and René Descartes (1596–1650) all contributed their theories of the tides, with varying levels of success (Cartwright 2000, p. 25-34). These attempts were eclipsed by a tidal theory by Isaac Newton (1643–1727), developed in the seventeenth century as part of his gravitational theory. The fundamental principles of Newton’s tidal theory remain in accordance with scientific understanding today, although some deductions drawn from them are erroneous (Cartwright 2000, p. 35). Around a century later and following many suggestions and modifications by other natural philosophers, Pierre-Simon de Laplace (1749–1827) proposed a dynamic theory of the tides, which for the first time took into account the dynamicity of the response of the ocean to tidal forces. Laplace translated his theory into a set of equations, today known as the Laplace Tidal Equations, which describe this dynamic response of the ocean (Cartwright 2000, p. 68-81).
From theories to analysis and prediction
The nineteenth century saw a shift in focus from tidal theories to the more practical analysis and prediction of tides. By expanding upon the base of data used by Laplace and making careful refinements to established theories, John William Lubbock (1803–1865) devised the so-called synthetic method of tidal analysis and prediction in the 1830s, which gave the most accurate predictions for tides at Liverpool at the time and therefore became the preferred method for calculating tide tables for British ports (Cartwright 2000, p. 91-92). The next significant advancement came in 1867 from Thomson in the form of a harmonic method of tidal analysis, based upon Laplace’s equations and works by Thomas Young (1773– 1829) and George Biddell Airy (1801–1892) (Cartwright 2000, p. 82-83, 97). This development attracted the interest of the British Association for the Advancement of Science (BAAS), who in the same year established a committee for the improvement and promotion of this newly discovered method (NOAA 2018).
The harmonic method of analysis, based upon observations of sea levels (Pouvreau 2008, p. 37), allows for the individual factors causing the tides to be isolated as unique mathematical components and provides better results for a wider range of locations than the synthetic model, but is a much more complicated calculation. Its complexity meant that doing the calculation by hand was time-consuming and prone to errors, which was part of the motivation for devising a mechanical device capable of doing this calculation.
Development of tide Prediction machines
The development of the first tide prediction machine was made possible thanks to funding from the BAAS who decided that calculations done by hand alone could no longer be relied upon to predict the tides at ports around the country. This was because of the increasing pressure from commercial shipping lines towards the middle of the nineteenth century, who wanted a greater number of more accurate predictions more quickly.
The first ever tide prediction machine, which features in the photograph below, was developed in Great Britain during a period when science and industry were growing closer together, a period of widespread mechanisation (Durand-Richard 2016, p. 127-128). However, the idea of a mechanical calculating machine was not new; Charles Babbage had already conceived the idea half a century earlier with his Difference Engine and Analytical Engine (Dasgupta 2014, p. 22). More specifically, it is known that the design for the first tide prediction machine was inspired by a mechanical device devised by Charles Wheatstone for telegraphy purposes (Cartwright 2000, p. 104).
Kelvin’s first operational tide prediction machine, built 1873. Photograph taken by H. M. Rawsthorne at the Science Museum, London, on 2 February 2019.
The construction of the first operational tide prediction machine was completed in 1873. It was designed by Thomson with the help of Edward Roberts and Alexander Légé, whose company A. Légé & Co. manufactured it in London (Woodworth 2016, p. 14). Lubbock’s synthetic method was relied upon for producing British tide tables until around 1920, by which time six further tide prediction machines had been constructed. These machines were primarily kept in Great Britain but were used to predict the tides at British colonial ports. Meanwhile, William E. Ferrel (1817–1891) and George Howard Darwin (1845–1912) were making modifications and improvements to Thomson’s harmonic method, and later Joseph Proudman (1888–1975) and Arthur Thomas Doodson (1890–1968) made significant contributions to tidal studies, and Doodson in particular to the improvement of tide prediction machines (Doodson 1921; Reidy 2008, p. 188). Eventually the transition from the synthetic method to the harmonic method in Great Britain was made, and thus the adoption of tide prediction machines for domestic ports (Cartwright 2000, p. 97-108).
Tidal prediction today
Tidal predictions today are calculated using specially-made software that run on digital computers. They use the same harmonic method as the analogue machines of the last century, but are able to take into account many more constituents. The NOC has developed a software called POLTIPS-3 that can calculate predictions for anywhere in the world using up to 240 different constituents (National Oceanography Centre 2019[a]) whilst the SHOM uses a software called MAS that uses up to 541 constituents (Pouvreau 2008, p. 39-40).
Bibliography Byrd, Deborah (2019). Tides, and the pull of the moon and sun. en. URL: https://earthsky.org/earth/tides-and-the-pull-of-the-moon-and-sun (visited on 01/05/2019). Cartwright, David Edgar (2000). Tides: A Scientific History. en. Cambridge: Cambridge University Press. ISBN: 978-0-521-79746-7. Dasgupta, Subrata (2014). It Began with Babbage: The Genesis of Computer Science. en. Oxford: Oxford University Press. ISBN: 978-0-19-930943-6. Doodson, Arthur Thomas (1921). ‘The Harmonic Development of the Tide-Generating Potential’. en. In: Proceedings of the Royal Society of London. A100.704, pp. 305–329. DOI: 10.1098/rspa.1921.0088. Durand-Richard, Marie-José (2016). ‘De la prédiction des marées : entre calcul, observations et mécanisation (1831-1876)’. fr. In: Cahiers François Viète II.8-9, pp. 105–135. Gordon, Arnold L. et al. (2015). Tide. en. URL: https://library.eb.co.uk/levels/adult/article/tide/72409 (visited on 01/05/2019). Ifremer (2004). Rôle des astres. fr. URL: http://www.ifremer.fr/lpo/cours/maree/forces.html (visited on 12/04/2019). National Oceanography Centre (2019[a]). At the Coast. en. URL: http://noc.ac.uk/business/marine-data-products/coastal (visited on 31/05/2019). — (2019[b]). Tides – Frequently Asked Questions. en. URL: https://noc.ac.uk/files/documents/business/Tides-FAQ.pdf (visited on 02/05/2019). NOAA (2018). History of Tidal Analysis and Prediction. en. URL: https://tidesandcurrents.noaa.gov/predhist.html (visited on 30/05/2019). Pouvreau, Nicolas (2008). ‘Trois cents ans de mesures marégraphiques en France : outils, méthodes et tendances des composantes du niveau de la mer au port de Brest’. fr. Doctor of Philosophy. La Rochelle: Université de La Rochelle. Reidy, Michael S. (2008). Tides of History: Ocean Science and Her Majesty’s Navy. en. Chicago, IL: University of Chicago Press. ISBN: 978-0-226-70932-1. Woodworth, Philip L. (2016). An inventory of tide prediction machines. en. URL: http://nora.nerc.ac.uk/id/eprint/513660 (visited on 10/10/2018).
Prosopography is a research approach usually used by historians to study the lives of groups of people. It involves the creation of a collective biography or the gathering of data relating to the common aspects of the lives of individuals who are part of a particular population. It can take the form of a database of all of the people within the chosen population along with information about the biographical phenomena that transcend their individual lives.
How can I apply prosopography to my project?
I am studying the life cycle of analogue tide prediction machines built in the United Kingdom: the methods used to predict tides before the construction of the first machine, the motivation for creating this machine, the manufacturers, users and uses of the machines, maintenance and repair of the machines, the decommissioning of the machines, subsequent methods of predicting tides and finally the state of the machines today in terms of conservation and scientific mediation.
The notion that objects have biographies despite not being living things is not new, but only recently has the idea of conducting prosopographical studies of collections of related objects began to be explored. This is a concept that I would like to develop and utilise in my project about the history of analogue tide prediction machines.
In my case the population of individuals becomes a group of artefacts, more specifically the 23 analogue tide prediction machines built in the UK between 1873 and 1964 (not including prototypes or portable machines). Complete biographical material for any one individual machine no longer exists, and with such a situation the beauty of prosopographical studies becomes visible. Prosopography overcomes the problem of the scarcity of historical data by collecting together all available fragments, which can then be compared, synthesised and analysed, thus compensating for any gaps in the data. Instead of looking at the exceptional and unique, prosopography focusses on the general and average. It is in this way that prosopography makes visible the particular characteristics representative of the chosen population.
The next step is to create a questionnaire to which I will subject every member of my “population” of analogue tide prediction machines. I do not expect to find an answer to each question for each machine but, as we have already discussed, that will not pose a problem in this prosopographical study; the aim is to find the common features in the lives of analogue tide prediction machines. This will give an appreciation of the importance of these machines, the extent of their use and usefulness, and an impression of the shape of their lives.
Bibliography Bray, Peter. Biography, prosopography and the density of scientific data: Some arguments from the metallurgy of Early Bronze Age Britain and Ireland, in: X. Armada, M. Murillo-Barroso & M. Charlton (ed.), Metals, Minds and Mobility: Integrating Scientific Data with Archeological Theory. Oxford: Oxbow books, 2019, p. 123-133. Kopytoff, Igor. The Cultural Biography of Things: Commoditization as Process, in: A. Appadurai (ed.), The Social Life of Things: Commodities in Cultural Perspective. Cambridge: Cambridge University Press, 1986, p. 64-91. S. Tarte, P. Willcox, H. Glaser & D. De Roure. Archetypal Narratives in Social Machines: Approaching Sociality through Prosopography. Proceedings of the SCM Web Science Conference, article no. 24. Oxford, 2015. K. Verboven, M. Carlier & J. Dumolyn. A short manual to the art of prosopography, in: K. Keats-Rohan (ed.), Prosopography Approaches and Applications. A Handbook. Oxford: Unit for Prosopographical Research (Linacre College), 2007, p. 35-69.
The 11th of February every year has become a day to recognise the crucial role played by women and girls in science and technology communities, as declared by the United Nations General Assembly in 2015.
I spent the International Day of Women and Girls in Science 2019 in the company of Valerie Doodson and Sylvia Asquith, who played a vital part in the STEM (Science, Technology, Engineering and Mathematics) industry during their working lives at Bidston Observatory on the Wirral Peninsula in north west England, from 1952 to 1962 and from 1947 to 1990 respectively. We discussed at length the evolution of their work, workplace and colleagues during the years they worked there.
Bidston Observatory had national and international responsibilities during its many years of operation from 1866 to 2004 including telling the exact time with the One O’Clock Gun, carrying out oceanographic research for Liverpool Tidal Institute, predicting the tides for the British Admiralty using analogue tide prediction machines and making meteorological observations for the UK Met Office.
Bidston Observatory, Wirral, UK. Photograph: Helen Mair Rawsthorne (08/01/2019).
Valerie and Sylvia both joined the observatory as part of a team of young women known as “computers” who were employed to operate the tide prediction machines, prepare the outputted data for publication in the British Admiralty Tide Tables, and perform meteorological observations. They explained to me the process of predicting the tides for a given port, which could be anywhere in the world. It began with setting up a tide prediction machine with the correct constituents for the port and then running the machine, reading off the numbers it displayed for each high and low tide over the desired period of time. These numbers would be plotted as a curve graph, which would be checked for “smoothness”; a non-smooth graph suggested the presence of an error. These errors were corrected and the newly-smooth predictions would be typed up ready to be published in the British Admiralty Tide Tables. They recall that the machines were very noisy during operation, although the sound was not unpleasant but rather bell-like.
A reminder of the global importance of the accuracy of the work of the female “computers” at Bidston Observatory was often given, as the lives of people at sea and the efficient running of global maritime transport depended upon it.
It was a delight to see the fondness with which Valerie and Sylvia spoke about their years at Bidston Observatory and I am very grateful to them both for their time and the patience with which they answered all my questions relating to the tide prediction machines with which they are so familiar.
Bibliography International Day of Women and Girls in Science. “From Dream to Reality.” Accessed February 15, 2019. https://womeninscienceday.org/WISID_WP/about. United Nations. “International Day of Women and Girls in Science: Background.” Accessed February 15, 2019. http://www.un.org/en/events/women-and-girls-in-science-day/background.shtml.
This video serves as an introduction to my research project about the history of tide prediction machines. Subtitles available in English and in French.
Le service hydrographique et océanographique de la Marine de France est un établissement public administratif chargé de connaître et décrire l’environnement physique marin et les zones littorales ainsi qu’en prévoir l’évolution et diffuser des informations correspondantes.
Le SHOM est un établissement d’intérêt pour moi parce que il a acheté deux machines à prévoir les marées de Liverpool Observatory and Tidal Institute à Bidston au Royaume-Uni en 1901 et en 1949. J’ai ainsi organisé un stage de deux jours avec Nicolas Pouvreau au SHOM à Brest pour faire de la recherche aux archives.
Les archives contiennent beaucoup de correspondance, surtout entre le SHOM, Liverpool Observatory and Tidal Institute et d’autres agences qui ont un rôle dans les achats étrangers, ainsi que des dossiers promotionnels, des rapports et des notices explicatives. Ces documents aident à reconstituer l’histoire des deux machines à prévoir les marées achetés par le SHOM. C’est interessant de noter que les deux machines acquis par le SHOM de Liverpool Observatory and Tidal Institute étaient d’occasion.
Ainsi que les archives précieuses, le SHOM à Brest aussi abrite la deuxième machine à prévoir les marées qu’il a acquis. Cette machine, appelé la « Bidston Kelvin Machine », était fabriqué par Kelvin Bottomley and Baird Ltd. à Glasgow au Royaume-Uni en 1924-25. Elle était d’abord utilisée à Bidston par Liverpool Observatory and Tidal Institute avant d’être transportée à Paris pour utilisation par le service hydrographique de la Marine (le SHOM de l’époque) et puis à son site actuel à Brest.
Machine à prévoir les marées “Bidston Kelvin Machine” fabriquée par Kelvin Bottomley and Baird Ltd. à Glasgow au Royaume-Uni en 1924-25 et acquis par le SHOM en 1949-50. Photographe : Helen Mair Rawsthorne (18/12/2018). Contenu : le SHOM.
Mon stage au SHOM m’a permis de découvrir beaucoup d’informations pertinents à propos des machines à prévoir les marées et leur utilisation, ce qui m’a aidé et continuera à m’aider énormément dans mon projet de recherche. J’aimerais remercier Nicolas Pouvreau pour m’avoir accueilli au SHOM, Thierry Gendrier et Xavier Romary pour m’avoir aidé aux archives, et Romain Lhullie pour ses idées concernant l’interprétation des machines.
Bibliographie Le SHOM. “Les missions.” Accessed December 28, 2018. http://www.shom.fr/le-shom/presentation-generale/les-missions. Woodworth, Philip. An inventory of tide prediction machines. Southampton: National Oceanography Centre, 2016.
Lord Kelvin (1824-1907), aussi connu sous le nom de William Thomson, est un physicien-mathématicien et ingénieur qui a été un pionnier dans des nombreux domaines, en particulier l’électromagnétisme et la thermodynamique. Cependant, son but premier était l’utilisation pratique de la science, ce qui l’a conduit à l’invention de la machine à prévoir les marées.
Credit: Wellcome Library, London. Wellcome Images images@wellcome.ac.uk http://wellcomeimages.org Portrait de Lord Kelvin (Sir William Thomson) [1824 – 1907], physicien-mathématicien et ingénieur écossais. Peinture à l’huile par : Harry Herman Salomon.
Avant la construction de cette machine, les marées étaient prévues en faisant de longs calculs à la main. Cette méthode était tellement irréalisable à long terme que la British Association for the Advancement of Science (aujourd’hui le British Science Association) a payé pour la construction d’une machine capable à faire ces calculs.
La première machine à prévoir les marées opérationnelle à été conçue par Kelvin et fabriquée entre 1872 et 1873 par l’A. Légé Company à Londres. Elle s’agit d’une calculatrice analogique qui simule la montée et la descente des marées océaniques sous forme de la somme des mouvements sinusoïdaux d’un certain nombre de composantes de marée individuelles. Ces composantes harmoniques sont liés à la position de la lune et du soleil et aussi à la location géographique des marées à prévoir. Chaque composante de la marée est représentée par le mouvement d’une roue de poulie, réglée pour se déplacer à la vitesse appropriée. Un fil enroulé sur plusieurs de ces roues additionne leur mouvement pour donner une représentation de la marée totale de l’endroit programmé. Ce mouvement est capté par un stylo et une bande de papier mobile sur laquelle le stylo trace une courbe de marée.
Après cette première machine, 35 autres machines à prévoir les marées ont été fabriquées partout dans le monde (dont 24 au Royaume-Uni), chacune avec plus de composantes et ainsi des résultats plus précises. Elles étaient utilisées jusqu’à environ 1964, quand l’invention de l’ordinateur numérique a rendu cette calculatrice analogique redondant.
Ce projet étudiera le cycle de vie des machines à prévoir les marées en provenance du Royaume-Uni : les méthodes utilisés avant la fabrication de la première machine, la motivation pour créer cette machine, les fabricants, utilisateurs et usages des machines, comment les machines ont été mises hors service, leurs successeurs éventuels et finalement le statut des machines aujourd’hui en termes de conservation et médiation scientifique.
Bibliographie Cartwright, David. Tides. Cambridge: Cambridge University Press, 2000. National Oceanography Centre. “Tide Predicting Machines.” Accessed November 29, 2018. http://www.tide-and-time.uk/tide-predicting-machines. Woodworth, Philip. An inventory of tide prediction machines. Southampton: National Oceanography Centre, 2016.
La grande idée pour le sujet de recherche concerne les machines à prévoir les marées. Seulement 36 machines à prévoir les marées ont été fabriqués dans le monde entier, entre environ 1873 et 1964, dont 25 ont été fabriqués au Royaume-Uni. Ce travail ne portera que sur les machines en provenance du Royaume-Uni.
Le projet traitera ce qui existait avant les machines à prévoir les marées et la motivation pour les créer, les fabricants, utilisateurs et usages de ces machines, et finalement ce qui est passé après la fin de leur utilisation.
Blog des étudiants en Master mention Epistémologie et Histoire des Sciences et Techniques à l'Université de Bretagne Occidentale
![Portrait de Lord Kelvin (Sir William Thomson) [1824 - 1907], physicien-mathématicien et ingénieur écossais. Peinture à l'huile par : Harry Herman Salomon.](https://m1ehst1819.hypotheses.org/files/2018/11/Lord_Kelvin_Sir_William_Thomson_1824_-_1907_Wellcome_M0000145-352x500.jpg)