reading

Introduction

Halfway along the causeway that crosses the sandflats and marshes to the holy Northumbrian island of Lindisfarne, with its ancient priory and castle, is a little refuge, a hut built on stilts with wooden steps up to the door. Notices fixed to the door state the purpose of this odd structure. It is there for the use of unwary travellers who find themselves caught out on the three-mile crossing by the rising tide. Among the notices is a sun-bleached cartoon from a local newspaper. It shows a family huddled together on the roof of their car as the rising seawater begins to lap at its windows. The caption has one parent complaining to the other: ‘I didn’t think that tides applied to tourists.’

On the islands of Britain, we live surrounded by water that rises and falls according to rules that are a mystery to almost all of us. We are adrift on a sea whose movements we do not understand. Many are the summers on the stretch of coast where I live in Norfolk that a child is swept out to sea on the tide, to be washed up dead days or months later many miles along the coast. Half of the world’s population lives in coastal regions lapped by tidal waters, and yet, unless we depend directly upon the ocean for our living, we remain inattentive to its strange rhythms and ignorant of their complicated causes.

We do not understand, therefore, why the pleasure boat trip cannot depart on the Sunday morning that would fall in best with our weekend plans. We do not understand why the sandy beach we remember from a visit long ago is today a strip of uninviting shingle. We do not understand that the reason why we live the way we do, why we speak the language that we do, may be traceable to a particular seaborne invasion or a particular naval battle whose outcome hinged on the turning of a single tide. We do not understand why the sessile oyster, which depends on each new tide to replenish its food supply, was once a staple food of the destitute. We do not understand our dependence on the astonishing diversity of life that inhabits the intertidal zone, or appreciate that the evolution of life itself may have been reliant upon the ebb and flow of great oceans to create the conditions under which the correct chemical ingredients could mingle to produce the first primitive organisms.

The tide? What’s that got to do with the price of fish? Well, a very great deal as it happens. The American variant of this expression is: What’s that got to do with the price of tea in China? Well, the tide may not much affect the price of tea in China, but it has been important in determining the price of Chinese tea, for in the days when tea clippers raced round the Cape of Good Hope to be first to bring the new-picked leaves to London or Boston, the state of the tide as they closed upon their port of destination could decide the winner, who was then able to sell his cargo at a premium. The tide has always influenced where important marine resources are concentrated; and over the centuries, the tide has often been a hidden factor in determining the location of great ports and in governing their subsequent success in commerce.

My own formative encounter with the tide happened in waters just off the coast of the Isle of Wight, a locale of such comical tameness, lapping an ice-cream island of garden gnomes and miniature railways, that it still amazes me years later that we could have been in mortal danger.

We were sailing from Weymouth to Yarmouth in the wooden boat that my father had hand-built over a period of twelve years. Over the ground, the distance was thirty miles or so, which would be a full day’s sailing in our small craft. The journey would take us eastward along the Dorset coast past the Isle of Purbeck and Bournemouth and then up the Needles channel into the Solent. The Needles channel was a tricky stretch of water, bounded by a gravel bank known as the Shingles on one side and by the jagged promontories of the Isle of Wight on the other. The tide runs fast, especially at Hurst Point where a spit juts out from the mainland, forcing the waters through a gap less than a mile wide.

It is also one of the world’s busiest shipping lanes, and for this reason has been generously strewn with navigation buoys – red ones to denote the port side of the channel, green ones for starboard – and others known as cardinal marks that indicate the location of isolated underwater obstructions. None of these markers in the least resemble the squashy plastic buoys you see used for moorings in sheltered waters. They are placed by Trinity House, the national authority responsible for safe ‘signposting’ at sea, and are substantial objects to find floating in the water. The cardinal marks in particular are imposing steel structures, tall gantries rising to the height of a double-decker bus above the waves, with just as much ironwork hidden below the waterline in buoyancy compartments and ballast. Some three metres in diameter and weighing six tonnes, they are not the kind of thing you argue with in a vessel of any size, and certainly not in a small wooden yacht.

Any passage under sail must be planned bearing in mind the likely weather conditions, in particular the strength and direction of the wind, and also the tidal movements likely to be encountered during the expected period at sea. A journey of a few hours under favourable conditions might not be possible at all if attempted at the wrong state of the tide. In the English Channel, as in most coastal bodies of water around the world, the tide runs for approximately six hours in one direction before reversing and running in the opposite direction for the next six hours. Our thirty-mile route was long enough that we would not be able to complete the whole journey with the tide helping us all the way.

The navigational challenge, then, was to decide upon a time of departure that would ensure we had the tide running with us for as much of the journey as possible, and especially when crossing those stretches of water where the tidal stream ran fastest, where we might otherwise be brought to a halt or even find ourselves going backwards in relation to the land. In particular, we had to time our trip to avoid the ‘tidal gate’ being against us at Hurst Point where the current can run at four knots or more – faster than we could sail under most conditions and faster than we could make way under engine in even the calmest sea.

We had all the information we needed. We had the right charts – Bill of Portland to The Needles and Solent: Western Approaches – which I remember my mother kept religiously up to date using a special violet ink sold for the express purpose of making the official chart corrections issued in weekly Admiralty Notices to Mariners. We also had a tidal atlas, a booklet with pages showing the same body of water at each hour before and after high water for a full tidal cycle of twelve hours. By means of arrows of varying thickness, each map denoted the expected speed and direction of the tide at the given hour across the entire charted area of sea.

My father made his calculation, and we cast off from the quay at Weymouth that September morning at ten past eight on the falling tide. The aim was to sail against the tide where it was weak in Weymouth Bay, and then on through slack water before using the rising tide to carry us into the Solent. By the time we reached the gate, all being well, we would have a gently favourable tide running with us and would be home in Yarmouth before dark.

The wind was slow to get up that morning, and we were obliged to motor for several hours before a gentle breeze filled in from the west, allowing us to set the spinnaker. We made soporific progress eastward until mid-afternoon when the outline of the Isle of Wight finally picked itself out of the haze.

Some hours later, in now fading light, we passed the Needles. The tide, which had been running gently against us, had by now turned in our favour. We peered ahead for the next marks: Shingle Elbow, which was due to appear ahead of us to port, and its opposite number marking the starboard side of the channel, a buoy named Bridge. This latter was a cardinal mark placed at the western extremity of an underwater ridge of rocks extending out from the Needles (and extending, in geological terms, as a band under the sea to the chalk of Purbeck that we had left behind earlier in the day). If we could have seen them, the cones on top of the mark would have been pointing towards each other, telling us that we should steer to the west of it. Instead, it being now nearly dark, we identified the buoy by its light, marked on the chart as VQ (9)10s, meaning that it emits nine very quick flashes every ten seconds. It was hard to gauge its distance, but it seemed to be some way off on our starboard bow.

We sailed slowly on through the syrupy water, the light of the buoy getting closer with each strobe-like sequence of flashes. These flashes, though, did not begin to slip past us on our starboard side as we expected with a tide bearing us straight up the channel, but remained on a constant bearing to our heading. With each ten-second burst, the lights grew brighter and larger, but stayed stubbornly forward of us at the same angle off our bow. Slowly, we began to understand what was happening. Our boat was sliding sideways as well as sailing forwards. The tide, which we had assumed to be running along the channel, was in fact setting strongly across it, sweeping us eastwards, closer to the submerged ridge. Our deliberate motion through the water combined with our drifting on the tide was holding us on a collision course with the buoy. In fact, our speed through the water was modest. It seemed it was the buoy that was making the greater headway, as we now became horribly aware, hearing the sloshing of the ‘bow wave’ it was making as it apparently forged through the tidal current towards us.

From the land, I had often observed the Solent tides ripping past the buoys set close to the island shore, the buoys leaning with the strain on the cables anchoring them to the seabed, shouldering the force of the current, and streaming out a foamy wake as if they were ferries running to a schedule. I had occasionally drifted off to sleep at home on a stormy night hearing the distant wave-made sound of the clanging bell of one of these buoys, even though it was fully a mile away. Inexorably, every six hours or so, the tide would turn and each buoy would shuttle back on its endless tethered commute. In between times, near high or low water when the tide was slack, the metal buoy would lie massive and silent, as if nothing on earth could ever be so powerful as to give it this impression of urgent business. Doubtless, in an hour or two, the Bridge buoy would come to such a rest. But this was no help to us now.

To counter the effect of the tide, we swiftly altered course, my father pushing the tiller away as the rest of us trimmed the sails in the hope that we could point closer to the wind and overhaul the buoy. The manoeuvre made no difference. The combined angle of our sailing direction and the flow of the tide still held our fragile wooden boat on course to strike six tonnes of Trinity House steel. The next burst of ‘very quick’ flashes took on an edge of urgency. Suddenly, I saw that we were not going to be able to get past the buoy on the correct side – the boat would simply stall if we headed further up into the wind and we would be powerless to do anything. Impulsively, I seized the tiller and pulled it sharply to windward, so that the boat bore away from the wind, and we shot past the buoy on the down-tide side – the ‘wrong’ side – seemingly just inches away.

Out of the pompous belief that it was the proper thing to do aboard any ship, we had always kept a logbook. In it, one of us would note the details of even the shortest sailing excursion at the end of the day – the weather conditions, the times and places of departure and arrival, and so on. Occasionally, there were instructive remarks about the speed achieved in a given wind with this sail as opposed to that, or the particular arrangements for mooring in an unfamiliar harbour. Quite a few measurements we recorded were concerned with maximizing the speed we could reach under engine, noting variations in the pitch of the propeller and the revolutions of the engine that would nudge it ever closer to a speed of four knots, which seemed to be a theoretical maximum limit. These experiments reflected our acute consciousness that the tide in these waters could at times run at least this fast, leaving us potentially at its mercy.

Yet the log reveals little of the drama of that September night. The day’s recorded run was 52.77 nautical miles, almost twice the actual distance over the seabed, showing that much of our journey had been a slow battle against the tide, and that our progress overall had been hindered rather more than it had been helped. ‘Now completely dark,’ reads the entry for 20.00 hours. ‘Very nearly hit Bridge Buoy due to set of tide while steering by Hurst leading lights.’ The subtext is clear enough. We did not nearly hit the buoy because of our own inexperience or poor seamanship, thank you. We were doing the right thing, steering by the lights. No. We nearly hit the buoy ‘due to set of tide’. The tide was to blame. The tide, that capricious, malevolent, world-dominating force.

This is not a book about the sea. It does not feature long days before the mast, scurvy, whaleboats, pirates, ship’s biscuits and tots of rum. It does not brave hurricanes or typhoons. It does not centre on a man condemned for ever to sail the oceans, nor does it have mermaids to lure him astray. It is not about the vasty deep, and man’s battle with it, and his often curious reasons for going into that battle in the first place.

This is a book about the sea. It is about the sea that we all know – the beach, the coast, land’s edge, land’s end. The sea we regard as our holiday playground, yet understand hardly at all. The sea that we move cautiously upon, and that moves us in mysterious ways, both physically and emotionally.

The tides are complicated and some people find they obtain their most elegant explanation in the form of mathematics. Yet even if you are able to interpret the symbols and equations, you immediately lose the visceral sense of the oceans’ rising and falling, the sense of the tide’s upper hand over humankind’s maritime adventuring. The tide has simple physical power over small craft at sea, but it also has power over the senses and the mind. To stand and gaze out from aboard a boat held at anchor upon a tidal body of water within sight of land is to subject oneself to a hallucination of bewildering intensity. For during those regular periods when the tide is running strongly in one direction or another, it will seem that the boat is cleaving purposefully through the sea even though reason tells you it is going nowhere. It is a powerful and disturbing illusion, enhanced in its hypnotic effect perhaps by sunbeams bouncing off the streaming water or the rhythmic undulation of the boat, or by your own hunger or thirst. You blink hard to dismiss it, but when you open your eyes it is still there – the boat is definitely moving forwards, anchor chain and all, this last determinedly probing the waters ahead like a narwhal’s tusk.

After a while, your brain reframes the illusion. Mesmerized by the scintillating wavelets, it now conceives that it is the water that is static while you and the boat are racing together with the distant land towards some shared destination. The surface of the water may be glassy and smooth, wrinkled only slightly by the deep turbulence of the tidal flow itself, or it may be choppy, as it is when the wind blows against the tide and friction between the air and the water kicks up short, steep waves. It doesn’t matter. Your impression nevertheless is that all this water must be essentially stationary. For what great power could convey such a mass of ocean back and forth so swiftly without apparent effort or cause?

We learn at school, of course, that the main answer to this question is the moon and its gravitational pull on the earth, and by adulthood we have assimilated this information without demur. We stupidly take the force of gravity as read, and reserve our wonder for more modern oddities such as quantum theory or dark matter. Yet how very odd the colossal, invisible force of gravity still is if we stop to think about it at all. With the rushing tide, we have a visible, soaking, undeniable expression of that weirdness.

Before we understood them in a scientific sense, the tides were already comprehended in their way by myth-makers and storytellers. The actual power of the tide to drag sailors to their death is surely enough to explain the lure of the siren and the sucking tentacles of the kraken. The sea has no need of assistance from malevolent creatures, which are the mere invention of ignorant seafarers, made up because they offer a more believable story than the horrid idea that something as routine and automatic as the unaided tide has the power to take a person’s life. The fabulous sea monsters that adorn the peripheries of old explorers’ maps may similarly be unfamiliar deep-sea species whirled up into the light by tidal upwellings, while the tidal bores of various rivers earn themselves the names of gods and monsters.

Scientific knowledge offers an alternative explanation for some of these stories, but the stories live on. Science has begun to investigate the mysteries of the oceans – only just begun, really: oceanography is one of the youngest of the sciences, and the subject is all too obviously a large one. The investigation of the oceans has begun, but we can hardly be said to have tamed them. We can now predict the tide theoretically to a high degree of accuracy – far more accurately, in fact, than it ever occurs in our real experience, where other factors interfere with it. Why the drive to know in such obsessive detail? In part, it is because the tides provide a perfect example of the complex problem that should be exactly soluble. All the variables are known, it is only a matter of doing the sums. The tide offers an irresistible mathematical tease, which is undoubtedly why historically it has attracted some of the world’s finest physicists and astronomers. But there are also practical reasons why it is important to have precise answers beyond the needs of navigators and fishermen, and these turn out to have relevance for the future of us all.

There is a good reason why, despite all this, there has been no accessible book about the science of the tides. It is because the topic swiftly becomes more complex than lends itself to explanation in words. The author of a field guide to the salt marshes of New England gave his drily brief synopsis of the subject this heading: ‘Tides in Perhaps More Detail Than I Should Include in This Book’. I know how he feels. Harmonic equations give the scientist a far more versatile tool for understanding what goes on. But I know that I cannot follow this route – for your sake, and for mine.

Instead, I have tried a different approach. I have given an episodic history of the science of tides from the earliest times up until the present day. This course allows me to voyage from the earliest science of Aristotle, who is said to have drowned himself when he failed to figure out the Greek tides, to the better informed investigations of Galileo and Newton, and then on to a scientific understanding so complete that we are now able to predict the tides with that high degree of accuracy (far greater than any sailor needs), which is yielding important new evidence of our own impact on this watery planet. Along the way, we drop anchor in less familiar harbours, too, pausing to acknowledge the unexpected contribution to the understanding of the tides by figures such as Bede and St Thomas Aquinas, men not primarily thought of as scientists, but whose great minds could not ignore this cosmic puzzle.

I have interwoven the scientific strand of my narrative with two others: one in which stories of events – be they historical, artistic or entirely fabulous – where the tide plays a crucial role get their due; and another in which I go in search of special places made by the tide. I include these episodes to show that the tide is not only a scientific challenge, but also a force of a quite different kind – a physical and a psychological influence on our culture whose presence cannot be denied. The tides have determined the course of battles and have inspired poets and artists. And they continue to do so today.

In weaving these strands together, strict chronology is occasionally sacrificed for the sake of a thematic connection. The science is, I hope, made simple but not simplistic. This is not a textbook about the tides. It is a book of stories and journeys. I hope you find yourself able to go with the flow. It is always unwise to fight the tide.

Which came first, time or tide? It is impossible to arrive at a clear answer. Both words have Anglo-Saxon roots. Phonetically, our tide is linked to the German Zeit, which still means time, while the newer German word Gezeiten now denotes the tides of the sea. In early English, tide was not especially a quality of the sea, but more a way of describing a significant time, a usage we retain in the archaic suffixes of events in the Church calendar such as Shrovetide and Whitsuntide. The old English heahtid, or ‘high tide’, had the simple terrestrial meaning of a festival or high day. However, for those whose livelihoods depended on the sea, the most important tide was always the day’s high or low water.

Some sources indicate that tide only came to refer chiefly to the rise and fall of the sea in the fourteenth century, when this medieval neologism took its place alongside ebb and flood, or ebba and flod, which stem from Old Norse and proto-Germanic, and which have still older and more distant roots in Indo-European language. The flood is simply the incoming tide, and it is clear there is no intrinsic conflict between this meaning, exclusively to do with the sea, and the more general meaning of the word as a threateningly raised level of water from any source. The ebb is the receding tide. The figurative senses both of flood, as in a flood of tears, and of ebb, as a kind of last chance, still in widespread rhetorical usage today, were also established by the fifteenth century.

In his tidal adventure Passage to Juneau, Jonathan Raban suggests that it was the invention of the compass that gave man the temerity to think he might sail in straight lines across the sea. The evidence of this boldness is etched in medieval portolan charts showing sailing directions, criss-crossed with dozens of dead-straight rhumb lines. By contrast, a more natural navigator in tune with the elements would simply feel the currents under his hull and use the tides to advantage without worrying what his course might look like on some hypothetical map. In like fashion, it was perhaps only the invention of the clock that finally enabled the more abstract concept of time to supplant the earthly tide as many people’s measure of days.

We are left with only a few linguistic relics of the age before technology forced time and tide apart. If, for instance, in colloquial usage, somebody offers to ‘tide me over’, it means they will support me for a time, usually with money. But the original meaning of the phrase is nautical. To tide a boat over a sandbar, for example, is to use the period of high water to get past shallows that would be impassable at other states of the tide.

With their easy assonance and their entwined historical usage, it is no great surprise to find time and tide forced together in memorable sayings. The aphorism ‘time and tide wait for no man’ is the best known of these. It sounds like Shakespeare, or perhaps Chaucer. But it is even older, attributed by some to a shadowy St Marher from the early thirteenth century. It contains both a truth and a deception. For, of course, it is true that both time and tide are governed by celestial laws, and so lie beyond the control of man. But whereas time passes for ever, the tide always returns. Time is a continuum, the backdrop against which all things happen; the tide is always an event in time.

The senses in which time and tide do not wait are thus subtly different. If we miss an appointment because time does not wait, the moment has passed and may never come again. If we miss a tide, there is the same sense of an opportunity not taken, but there is also implicit in this expression a fairly certain knowledge that the opportunity, or something very much like it, will re-present itself in due course.

And there are other important differences. Time’s arrow is weightless, but the tide has massive force behind it. Its flux and reflux are sensible. As we stand in the waves, the flood smacks our chest, the ebb drags on our shins. Struck by these sensations, we momentarily forget that the tide is a cyclical phenomenon, in which each motion is endlessly repeated with infinite small variations, and feel just the singular event. This visceral power is reflected in our adaption of the tide’s special vocabulary – the word tide itself, as well as ebb and flow – to broader linguistic purposes.

Thus the high tide may bring unique opportunity, as Shakespeare reminds us in the famous speech of Brutus on the eve of the Battle of Philippi:

There is a tide in the affairs of men,

Which, taken at the flood, leads on to fortune;

Omitted, all the voyage of their life

Is bound in shallows and in miseries.

On such a full sea are we now afloat;

And we must take the current when it serves,

Or lose our ventures.

When the waters rise high enough, they enable the voyage of (self) discovery to begin.

There is, meanwhile, a desolation about the ebb, a physical emptiness that is echoed by a psychological emptiness, the loss of seawater equated in our primitive memory with loss of the water of life. The water rushes out to join the ocean – it runs away to sea, in fact. The action has about it some of the naivety and desperation implicit in that expression. It is bound on its destiny, and leaves behind it a bereft expanse of sand or mud.

With the ebb goes life and life’s chances, or so it might seem to us. But nature doesn’t regard it like this. Nature’s richest seams are often where two habitats chafe together – birds often prefer hedgerows, not open fields or the heart of the forest; amphibians need the water’s edge, not deep water or parched earth. Margins provide choice – food to one side, perhaps, refuge to the other. And where that margin is always shifting about, as it is on the tide’s edge, within that glistening ribbon of land that lies between the high-water mark and the low, the stock is constantly replenished with new riches. This intertidal zone, which stretches and shimmies its way for perhaps a million kilometres (it depends how you measure it) in continuous lines round all the continents, contains some of the world’s most biodiverse regions. Or, to put it another way, it crawls with ‘the damndest collection o’ creeps you ever seen’, in the lyrics of Rodgers and Hammerstein’s Pipe Dream, perhaps the only musical ever to feature a marine biologist in the central role, adapted from John Steinbeck’s stories of Cannery Row.

It is the regular rise and fall of the sea that restocks the shelves of the world’s continents twice a day more efficiently than any supermarket. Nature is organized on the principle of conserving energy. The objective of all organisms is to survive and propagate while making the minimum effort to do so. If a migration can be accomplished by hitching a ride, if food can be delivered to your doorstep for free, then so much the better. This is the essential service that the tide provides – a vast source of physical energy ready to be tapped by any animal or plant that can adapt to its demanding schedule.

This is a book about the discovery and science of the cosmic rhythm that governs our planet. But it is also a book about places. Along that nearly infinite shoreline of the earth’s continents lie points where the irresistible force of the tide and the immovable matter of the earth converge in such a way as to create special sites – natural harbours, river mouths, firths and fjords, isthmuses and promontories – that take the particular shape they do because of the sculpting action of the tide.

For the seagoing few, the tide concocts other, more terrifying places – whirlpools, tidal races and overfalls of destructive waves, as well as locations of huge tidal range and others, far out in the ocean, where, even though tides swirl all around, the sea level never varies. These places may not appear in landlubbers’ atlases, but they are indicated on nautical charts, a few of them at least. They are places, but they are also theatrical events. They occur only in these special places at scheduled times, and then only if the actors feel like turning up. A spectacular tidal whirlpool or river bore may arise on one tide, but not on another one equally high, simply because local and temporary factors conspire to prevent it.

These places of excess and anomaly arise wherever the rise and fall of the ocean is suitably constrained by the local shape of the seabed and coastline. They may be equatorial or polar, stormy or placid, populous or remote. I chose to travel to Nova Scotia in Canada where the tides are the greatest in the world, although I might have visited the coasts of Argentina or north-west Australia, where they are nearly as great. I saw surging currents and vast whirlpools in Arctic Norway, although I might have seen them in Japan or the Magellan Strait or Vancouver Bay. It matters not. These features are replicated in some degree on every coast of every ocean.

Furthermore, I can accomplish much of my task closer to home. For it happens that the coast of the British Isles is one of the most tidally lubricated coasts anywhere in the world. Surely no coastal nation has, when the velocities and vertical ranges are measured along its entire length, more tide than Britain. What does this mean? More washes up, more washes away, there is more damage, more erosion, more sediment, more life, more death. We kid ourselves that we are a maritime nation, yet our ignorance of all this activity going on ceaselessly around our shores is quite astonishing.

The tide’s evanescent places don’t leave scars, create tracks or memorialize themselves, as famous roads or mountain peaks do on land. They live through seeing and telling only. This is why my history of the science of the tide is interwoven with tales of the fantastic and with my own travels.

Finally, if a state of the tide has the power to make a place, then a whole tidal cycle must trace a path. Simply by remaining static in one coastal spot and watching the tide, I should find myself transported into new terrain and then back to where I began with such magical completeness that I would be left to wonder whether what I had seen was truth or illusion.

I decided this was how I would begin. I have seen coastal places at high water and at low. I have used the sea at both extremes of the tide: around high water for sailing in the shallows, and at low water for rock-pooling. But now I realize I have never taken due note of the whole natural cycle. I have never seen exactly what happens when the tide moves. Perhaps I could understand the tide intuitively by communing with it, as well as in a theoretical way by grappling with its science. At the least, I thought, the experience would reveal the questions I should ask.

Let us take our seats. Nature’s greatest marine drama is about to begin. The performance will last approximately twelve hours and thirty minutes.

Hugh Aldersey-Williams

TIDE

The science and lore of the greatest force on earth

VIKING

Contents

THE BEGINNING

By the same author

List of illustrations

Author’s note

Introduction