Magazine article UNESCO Courier

The Diver's Lonely World

Magazine article UNESCO Courier

The Diver's Lonely World

Article excerpt

THE pearls described in sixth-century-BC Singhalese and indian literature and the sponges mentioned by Homer and Hippocrates must have been fished by divers. The oldest unequivocal reference to diving is in book sixteen of the iliad, in which Patroclus gives the following description of the Trojan Cebriones whom he has just hit with a stone and knocked from his chariot: "Ha! Quite an acrobat, I see, judging by that graceful dive! The man who takes so neat a header from a chariot on land could dive for oysters from a ship at sea in any weather and fetch up plenty for a feast. I did not know the Trojans had such divers." Thucydides and other historians of Antiquity also describe how divers managed to take enemy fleets by surprise.

The first skin divers certainly lived in parts of the world such as the east Mediterranean and Polynesia and on the shores of the Yellow Sea in southeast Asia where there was a combination of several favourable factors for diving, including relatively calm seas, clear water, and a temperature enabling divers to stay in the water for a reasonable time.

Until the end of the Renaissance diving was limited in time (by lung capacity) and depth (by visibility). From the time of the Roman author Vegetius in the fifth century to that of Leonardo da Vinci in the fifteenth, people thought of connecting the diver to the surface by means of an air tube, but attempts to do so came to nothing since certain principles of hydrostatics (the branch of mechanics which deals with the equilibrium of fluids) were only established by Pascal in the seventeenth century. It then became known that an underwater swimmer breathing through a tube linked to the surface needs to exert a force greater than the water pressure in order to inhale. The human respiratory muscles are weak. Two metres underwater the effort to inhale is very tiring, and impossible any deeper.

Nevertheless, experiments with diving bells were carried out during this period. These bell-shaped hulls open to the water at the bottom were modelled on saucepans or on the urns containing air which Roman divers placed on the seabed, with the mouth facing downwards, and used to supply themselves with air.

BELLS AND CAISSONS

In 1690, Edmond Halley invented a method of renewing the air inside the diving bell from barrels lowered to the seabed.

Taking up an idea formulated a hundred years before by Denis Papin, the English engineer John Smeaton (1724-1792) went one step further when he fitted a pump to the bell in order to provide it with fresh air from a ship on the surface.

But diving bells were heavy, unwieldy, and difficult to use. …

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