Tania Kovats

Cotidal Lines

The science of the sea was the lubricant of an empire with overseas expansion, trade and military victory in mind. Emerging from the Napoleonic wars as the dominant power, Britain had to understand and navigate the waters that surrounded and connected its empire. As the historian Michael S. Reidy explains in his book Tides of History: “ Efficient trade required that the British Admiralty provide correct soundings, tide tables, and sailing directions to its mariners, both military and commercial. As the Royal Navy became the protector of maritime commerce, the Admiralty increasingly turned to science to aid in overseas expansion. The result was a coordinated effort to advance the science of the sea undertaken from a powerful global perspective. By the midcentury, science moved from being practiced locally to being practiced globally, placing it squarely within European expansionism and situating scientists as dependable purveyors of knowledge for the good of the state.“

The drawing that perhaps epitomises this shift in culture is William Whewell’s chart of the cotidal lines of the world’s oceans. This is a map of the world, filled with lines that connect places across the globe that experience the moment of high tide at the same time. His chart for the first time, describes how the tide moves across the seas and arrives at different places. It is a radical image for many reasons, partly for the information it communicates for the first time – but also for the way it chooses to communicate that information. It is able to convey relations between changing variables. This drawing defined the graphic language of science. It was not a drawing of the sea or a list of numbers and data – it is a graphic representation of information – which ever since this image has become the dominant means of expression for how science exhibit results.

Whewell recognised that order and regularity are more readily and clearly recognised, when thus exhibited to the eye in a picture, than they are when presented to the mind in any other manner.‘ Philosophy of the Inductive Sciences 1840. His map makes the oceans measurable, it orders the world and services economic and political agendas. All the world’s seas and oceans have become subjected to the scientific gaze. It is as if the storm never happened.

Whewell (1794-1866) was one of the nineteenth centuary’s most important public figures. A wordsmith as well as a polymath, he invented the term scientist,  understanding his methods and approach were not covered by the term ‘natural philosopher‘. He went on to become president of the British Association for the Advancement of Science, and wrote extensively about the history and philosophy of science, as well as his development of tidology, his study of the tides. Whewell’s study of the tides could be argued to have defined the configuration of the modern scientist.

The studies of the tides began in British estuaries and flowed out into the world’s oceans. The Thames required the most urgent understanding: a uniquely complex tidal river upon which the wealth of the country and Empire depended. The study and knowledge of the tide was critical to the economic, military and politic success of the city of London.

Various forms of tidal almanacs existed but these only ever served a local context. Whewell wanted to study the tides on a global scale, funded by the state, utilising a network of observers. Data may already exist but laws and the scientific understanding of that data was still to come. Whewell was not a sailor, or connected to the sea. From his landlocked life as Master of Trinity in Cambridge he mobilised a global network of people to take recordings of tide times and had them send him their readings. This data was then gathered, interpreted, and processed with a group of mathematicians to produce his cotidal maps of the world. This sounds ordinary, like any contemporary scientific methodology, but until this tidal experiment happened in this way, science had never happened like this before.

Whewell understood that previous observations of the tides, happening at the same place, were subjected to relations of time. Comparative observations at different places were connected by relations of space. To make comparative observations between places would be almost impossible to reduce to a language of calculation; numbers could not express the progression of the tide. This needed a further translation into the graphic, into a visual and drawn form that could demonstrate what he had understood as a synoptic map.

Whewell used his contacts in the Admiralty, members of the British Association, and missionaries, to mobilise a worldwide set of observations that would have to be accurate, calibrated and coordinated, as it was imperative that the observations happened at the same time. As a precursor to the global observations he would attempt the experiment in Britain. The Coast Guard were newly formed from the surplus of men in the Royal Navy and their network encircled the coast of the United Kingdom. They would make a reliable response to Francis Beaufort’s (Whewell’s supporter) request to the Admiralty:

Mr. Whewell, wants something more: a consecutive line of observations along the coast of Great Britain made simultaneously on the same tidal wave and continued for a fortnight. Is there a possibility that you could accomplish such a grand operation for us at the whole series of your stations at one and the same time?‘


From a letter from Beaufort to Bowles

30th July 1833

This diligent and disciplined community of men registered the tides on their tide gauges and tables every fifteen minutes for two weeks in the summer of 1834 and diligently sent on their observations, with some additional proposals for better tide guages or methods to register the tide.

The tide experiment expanded and readings were being taken in all corners of the globe, Cape of Good Hope, the East Indies, Malta, America, turning Whewell’s enquiry into one of the first times scientific thinking had addressed a large scale geophysical problem.

I reflect on this when water arrives from around the world, from Antarctica, Newfoundland, India, Orkney or the Solent. The sea water collection being made by people for All the Seas has a generousity that is now at the heart of the work. My own cotidal lines are being drawn together.

I have had the tides explained to me many times, how the  gravitational pull of the moon draws out a bulge in the ocean. Once you grasp this simple explanation it dissolves into additional complexity where you have to also understand the moon’s rotation round the earth, the strength of the centrifugal force on the opposite side of the earth to where the moon is, the sun exerting its tidal forces, landmasses, continents and the topography of the sea floor, all of which have to be taken into account.

How would you ever know it was high tide in the middle of the ocean?

I can follow one of Whewell’s lines, a horizontal spatial projection flowing from one point of measurement to another, from one harbour master to another, via many places in the oceans that could never be measured. A line, an elegant arc of science, joining the dots between what we don’t know.

taken from:

Drawing Water

Drawing as Mechanism for Exploration

Tania Kovats


See further notes on this artist under Lecture section.