The Tide; The Science and Stories Behind the Greatest Force on Earth

The Tide; The Science and Stories Behind the Greatest Force on Earth by Hugh Aldersey-Williams. W.W. Norton, 2017, paper.

Half the world’s population live on coasts subject to tides. Hugh Aldersey-Williams is one of them; he lives in Norfolk, England. A great portion of Floridians live within an hour’s drive of tidal coasts, the Gulf of Mexico and the Atlantic Ocean. It was a surprise to know that most coasts either aren’t tidal or that the tide is measured in centimeters.

Yet tides figure large in English idiomatic expressions. We are cautioned to “go with the tide.” Avoid “swimming against the tide.” Lovers of history are told that “there is a tide in the affairs of men.” A snack around 4:00 pm will hopefully “tide me over” until dinner, “Time and tide wait for no man.” Ever so many battles in history are said to be the “turning of the tide.” Fortunately for our humor, we do not know what will “betide” us.

Tides consist of an ebb and flow, the rise and fall of sea levels caused by the gravitational forces exerted by the Moon and the Sun and by the rotation of the Earth on its axis. Most often coastlines subject to tides experience them twice a day, some only once a day. Tides can vary according to the strength of wind and changes in barometric pressure. On occasion they can cause destructive surges.

Ancient Greek scientists are strangely silent about the tides. The Mediterranean Sea has little in the way of tides, with exceptions along the coast Tunisia, the upper reaches of the Adriatic (Venice), and the Pillars of Hercules (Gibraltar). Alexander the Great was dumbfounded by the tides that his army experienced in the Indus Valley. Tides are a concern of any military commander wishing to transport an armed force across the English Channel. Caesar studied about its tides carefully. As did General Eisenhower several millennia later in the other direction during the Normandy Landing in June 1944. Tides have long been a factor in battles at sea.

The Venerable Bede (673? – 735 a.d.) kept records of tides, and noticed that the tide had something to do with the stages of the moon. Tidal vocabulary is largely taken from Middle English (tiden) and before that Old English (tôdan).  Aldersey-Williams notes, however, how few records were kept of tides. That is particularly surprising in view of the Biblical tradition of the Flood in the Book of Genesis.

 The author travels around Europe and elsewhere to experience tides. From Norfolk, he could easily view the tides in the North Sea and on the major rivers that pour into the North Sea, including the Thames. A story-teller, he cannot pass up the opportunity to talk about the lore of that tidal river, including its “mud-larks” or “river finders.” They sorted through the flotsam (floating wreckage of a ship and its cargo), or jetsam (material that has been thrown overboard by ships’ crews). or lagan (goods abandoned at sea).  All were pure gold for the mud-larks, most often orphans or unemployed old people. Think of the rubbish piles of our time that are now the opportunity for the poor in Africa and Asia.

Tides generally aren’t spectacular. At least they are not from the vantage point of the throngs that gather to observe the tidal bore which races up the Bay of Fundy in Nova Scotia. This is said to be the most spectacular tidal bore in the world. During one tidal period, 115 billion tons of water flow in and out of the Bay. It can, however, be easily missed. The tides of the Bay of Fundy are semidiurnal, meaning that they happen twice a day. Should you fail to have been impressed, you can wait another six hours and thirteen minutes for the next tide.

There are animals that have learned to take advantage of the tides as a source of food or as an opportunity to breed. The horseshoe crab uses the tides on Florida’s coasts to reach the loose sands of the previous tide to plant its eggs in time for the next high tide. And there is a gathering of birds that then feed on those eggs. Aldersey-Williams describes a similar behavior involving the grunion, a fish species.

Humans have been attempting to capture the energy involved in ocean and river tides. But the infrastructure is expensive and easily damaged. Tidal mills are too dependent on the erratic running of the tides. Perhaps best to leave the tide to the tourists. 

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