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Diving Operations

The history of men's attempts to exist under water so that they may be enabled to prosecute useful works is one of great interest. Endeavours to glean the products of the ocean bed are of the highest antiquity, but of course such endeavours were carried out without the employment of any apparatus whatever. In the present day the Ceylon pearl fisheries, and the sponge fisheries of the Mediterranean Sea, are conducted in the same primitive fashion. The people from their childhood lead a kind of amphibious life, and as they inhabit a climate where a superabundance of clothing is not a necessity, they sport in and out of the water from their earliest years. In sponge fishing the diver carries down with him a flat stone to which a cord is attached. This serves a double purpose in helping him to sink to the bottom, and serving as a kind of signpost indicating the position of the boat floating above him. After tearing off from the rocks as many sponges as he can conveniently hold, the diver signals to his companions by pulling the rope, and is once more at the surface.

Those whose experiences of diving are confined to the swimming bath have little idea of the difficulties and dangers undergone by the pearl and sponge gatherers. The pressure of the water at the great depths to which these hardy men often descend is such as to cause them serious inconvenience. They frequently come to the surface bleeding from the nose and ears, and although some of them endeavour to secure immunity from such mishaps by using pledgets of cotton wool, such remedies are seldom efficacious. It has been stated that some of these native divers can remain under water for as long as five minutes at a time, but this statement is open to grave doubt. Two minutes may be regarded as the maximum time that a man can remain submerged without a fresh supply of air.

The first idea of aiding divers by mechanical help appears in a work published in Nurnberg in 1764. Schott, the author, quotes a writer named Taisnier, who in 1548 saw in Spain two Greeks who descended into the water in a weighted kettle, in which they could burn a candle and remain a very long time. The experiment was said to be carried out in the presence of the emperor Charles V., and upon one occasion ten thousand persons witnessed the performance. Lord Bacon also refers to a method of somewhat the same character. A bell or chamber is fixed upon a heavy tripod which sinks the contrivance to the bottom of the water. The men inside then walk out on the bottom holding their breath until they are obliged to seek the bell for a fresh supply of air. The next reference to diving operations of any interest to our readers is contained in one of the books of Robert Boyle, who alludes to a kind of submarine boat invented by a Dutch physician in the reign of James I. This boat was rowed by men within it, and the air was kept pure by some special fluid. This story seems rather difficult to believe, for the only way of purifying the air would be to furnish it with fresh oxygen to take the place of that consumed by the men's lungs, and at the date named there was certainly no known liquid which would compass that end.

A vast stride in the history of diving operations was made in 1716 by the great astronomer Halley, who was the first to supply fresh air from the surface to the inmates of a diving-bell. The following description of the apparatus is in the philosopher's own words, taken from the paper which he read to the Royal Society at the time:-- "The bell I made use of was of wood with a capacity of 60 cubic feet, and was of the form of a truncated cone. This I coated with lead, so heavy that it would sink empty, and the weight so distributed that it would go down in a perpendicular direction and no other.

In the top I fixed a strong clear glass, to let in the light from above, and a tap to let out the hot air that had been breathed. "To supply air to the bell when under water, I used a couple of barrels of thirty-six gallons each, which I cased with lead so as to sink empty, each having a bunghole in its lowest part to let in the water as the air in them condensed in descending, and to let it out again when they were drawn up full from below. And to the hole in the uppermost part of these barrels I fixed a leathern hose, well rubbed with bees-wax and oil, and long enough to fall below the bunghole, being kept down by a weight appended, so that the air in the upper part of the barrels could not escape, unless the lower ends of their hose were first lifted up. "The air-barrels being thus prepared, I fitted them with tackle proper to make them rise and fall alternately, after the manner of two buckets in a well. As soon as the air of one barrel was received and emptied into the bell, a signal was given, and it was drawn up; at the same time the other descended, and this was done so speedily that I myself have been one of five who have been together at the bottom in nine or ten fathoms of water for above an hour and a half at a time, without the least inconvenience, and we might, of course, have remained as long as we thought proper. By the glass window so much light was transmitted that, when the sea was clear, and especially when the sun shone, I could see perfectly well to write or read, much more to fasten or lay hold of anything under us that was to be taken up. But when the water was thick and the light obscure, a candle would burn as brightly as in the external atmosphere."

Beyond this, Halley originated a method of supplying air to divers from the bell, by tubes connected with helmets. this is a very important step, and one which led to the adoption of the diving helmet, which is a notable feature of all modern systems. Smeaton, the well-known engineer, was the first to use an air-pump and pipe for supplying the inmates of a bell; and his system, with certain modifications and improvements, is the one which has survived to our own times.

Meanwhile, the progress of invention in the direction of diving dresses to be used independently of a bell has not been slow. The modern diving costume is made of indiarubber faced with twill, or of waterproof cloth lined with a solution of rubber. In either case, it is worn over a thick suit of flannel, to protect the wearer from the coldness of the water. The head is encased in a helmet, from which proceeds an indiarubber tube to the air-pump above. This helmet has three windows of thick plate glass, the front one being furnished with a screw frame so that it can be readily removed. By this means the diver can breathe the fresh external air when not actually below water. Now although this diving dress has done much good service, and has represented the recognised method of working below water, it is by no means free from objection. In the first place, the pressure of air within the helmet must always be kept at a point exceeding the pressure of the external water, and this constitutes a great difficulty and a certain amount of danger. We have already seen that the effect of this pressure on the native divers of Ceylon is to cause them to loose blood by the ears, nose, and eyes. It is not surprising to learn that modern divers in deep water, aided by apparatus, are subject to the same inconveniences. The following table gives the water pressure for various depths:-- Depth of Water. Pressure per Square Inch. Depth of Water. Pressure per Square Inch. 20 feet 8 1/2 pounds 90 feet 39 pounds 30 feet 12 3/4 pounds 100 feet 43 1/2 pounds 40 feet 17 1/4 pounds 110 feet 47 3/4 pounds 50 feet 21 3/4 pounds 120 feet 52 1/4 pounds 60 feet 26 1/4 pounds 130 feet 56 1/2 pounds 70 feet 30 1/2 pounds 140 feet 60 3/4 pounds 80 feet 34 3/4 pounds 150 feet 65 1/4 pounds Another inconvenience of the diving dress is represented by the air-tube, upon the safety of which the life of the wearer depends. This is, naturally, a constant source of anxiety to him, and in rapid currents, where it is carried far away, he is in constant fear lest any accident should happen to it. Its presence also is inconvenient in preventing him groping beneath wreakage, and in other ways forms a great impediment to free movement. The system is also very expensive, not only on account of the original plant, but also because of the number of necessary attendants. Thus, one diver will require the attention of two men to work the air-pump, and another to hold the signal cord, to say nothing of the assistance required if a boat is employed. A great many plans have been tried for obviating these difficulties and one, to be presently described, seems to do so in a very satisfactory manner. In 1854, a Frenchman, M. Sicard, tried a totally new kind of apparatus which dispensed with the air-pipe altogether. He took down with him a supply of compressed oxygen, and endeavoured to render the carbonic acid generated by the lungs innocuous. This plan failed in practice owing to some defective arrangements which rendered it futile. Many people have endeavoured to adapt some receptacle to the diving dress for storing compressed air, but they have failed in consequence of the huge bulk necessary to contain air sufficient to last for any reasonable time.