CHAPTER IV
Without the diver, treasure-hunting beneath the waves would be impossible. The salvage expert may make the most brilliant plans, collect the most up-to-date and scientific plant to assist him, but in the end it is the diver who carries the work through, and upon the courage, determination and skill of the diver the success of the expedition depends. To dive to a depth of 5 fathoms, or 30 feet, is a task that the average man could accomplish without much difficulty; most men, too, would be able to reach a depth of 10 fathoms or 60 feet, if they were in decent physical condition. But at 15 and 20 fathoms and over the body is called upon to stand exceptional strains and so exceptional men are necessary.
Quite apart from the many risks, deep diving is very arduous, and seldom are men found with the physique that will enable them to dive 100 feet and over. The deep-sea diver must be trained like an athlete, perfectly sound in wind and limb and heart, and in tip-top physical condition. A fat diver stands little chance of attaining great depths, so the finest divers are generally on the slim side, men without an ounce of superfluous fat and with muscles tough as steel.
The physical strain placed on the body and heart merely by diving to these great depths is not generally realized. To ask the human body to undergo pressures three, four and five times greater than atmospheric pressure is expecting the body to undergo strains three, four and five times greater than the body was built to stand. It is like expecting a motor-car, designed for a load of 30 cwt., to carry a load of 6 tons. We should not expect the car to do that. Yet we not only call upon the human body to perform similar feats, but the body actually does perform them without collapsing.
The crack sea-diver is almost as difficult to find as the swimmer who can conquer the English Channel. When it comes to doing actual work at depths of 100 feet and over, the strain on the diver’s body is indeed very much greater, for his exertions use up so much oxygen that his heart is called upon to pump at an increased speed in order to replace it. All the time, of course, the diver is breathing compressed air, thus the pressure of the sea on the outside of his body is practically counterbalanced by the pressure of the air inside his body. While the weight of the sea is trying to crush him inwards, the compressed air is pushing outwards, so the air pressure within equalizes the water pressure without, and the diver is enabled to work in perfect safety under a mass of water that would crush an unprotected man flat.
We might liken the water pressure to six men who are pushing hard against a door and striving to open it, while the air pressure resembles six men pushing against the other side of the door to keep it closed. With both teams equally matched in strength, the door remains quite unaffected by the contest if it be solidly built of oak. But if it is a weak door, the strain of the men pushing against it will probably break it.
Breathing compressed air not only places a strain on the lungs, but it tends to fill the body with an excess of nitrogen. This nitrogen may easily form tiny bubbles of gas, and these bubbles, if they reach the heart, might cause the death of the diver or bring on that dread paralysis known as diver’s palsy, a disease which renders the lower part of the diver’s body quite useless.
Strangely enough, it is not in going down that this danger threatens the diver, but only in coming up. If he comes up too suddenly, the excess of nitrogen in the blood bubbles like the tiny bubbles in a siphon of soda and at once his life is threatened. The bubbles are due to the pressure of the water on the outside of the body growing suddenly less than the pressure of air inside the body, consequently the nitrogen seeks to escape in bubbles just as the soda-water seeks to escape when the key of the siphon is depressed. The pressure inside the body cannot adjust itself quickly enough to the lessening pressure outside, and these bubbles are the result.
To avoid this risk, it is necessary for the diver working at great depths to come up very slowly. He may slide down the shot-rope to a depth of 120 feet in a few seconds, but, should he stay longer than half an hour at the bottom, he must not come up in less than fifty-seven minutes if he would avert danger. He may come up to 40 feet in eighty seconds, or at the rate of a foot a second. Then he must rest and exercise his legs and arms on the shot-rope for five minutes before ascending another 10 feet to the 30-foot level. Here he must rest for a further period of fifteen minutes, and do those exercises which help to rid his muscles of their excess of nitrogen. Ascending another 10 feet, which brings him to within 10 feet of the surface, he is compelled to rest for twenty-five minutes to allow the excess of nitrogen to pass from his blood, after which he may rise to the surface.
If a diver happened to remain an hour at a depth of 200 feet, he would have to spend four hours in coming to the surface to avoid any ill effects. The exceptional diver who is able to reach this depth should not, however, remain at the bottom for more than twelve minutes. This is the safe time, and he can then make the ascent to the surface in thirty-two minutes.
Remarkable diving experiments were carried out by the British Admiralty some years ago, during which naval divers attained the record depth of 210 feet, a record that was long unbeaten. As a result of these experiments, tables were drawn up showing the time that a man might remain in safety at certain depths, and indicating the rates at which he could come to the surface and the depths at which he must rest to allow the pressure inside his body to adjust itself to the pressure of the water outside. These tables are followed the wide world over, and they have made diving one of the safest of occupations, despite the grave risks the diver is continually running.
Diving was, in fact, so dangerous that exceptional precautions had to be taken, with the result that the diver who walks about the bottom of the ocean to-day may be far safer than a man walking across Piccadilly Circus. The safety of the diver is most carefully watched over, but no one can foretell when a motor vehicle is going to run down some one crossing a busy road.
Never was knight attired for the tourney more carefully than the modern diver is clad before venturing into the depths. It is cold working at the bottom of the sea, and to guard against the cold the diver dons warm woollen sweaters and socks, sometimes wearing two or three sweaters and two or three pairs of thick socks. When he is dressed in his woollies, the diving dress is fastened about him just as the armour was fastened on the knights of old. There is a certain ritual about the performance which must be obeyed. First of all the shoulder pads are carefully tied on to take the weight of the head-dress, then an assistant helps him into the rubber diving dress and opens the tight cuffs for the diver to slip his hands through. The diver sits down while the assistant ties up the inner collar of the diving-dress and adjusts the various screws that are to secure his helmet. But before that is fastened into place the feet are slipped into the boots, each with its 16 lb. sole of lead.
Ever so carefully the diver’s helmet is put on, for his life depends upon it being properly fastened. The air-pipe must be carried from the back of his helmet up under his arm to the front of his body where he can reach it easily and yet not find it in his way. The air-pumps and the valves in his helmet are most carefully tested to see that they are working properly. Then the diver gets on the ladder leading overboard and a lead weight weighing 40 lb. is adjusted across his breast and another similar weight is fastened over his back to enable him to sink to the bottom. The glass of his helmet is screwed up, the pump is set going, the diver waves his hand to indicate that all is in order, and the attendant after a final look round gives the diver a smart tap on the top of the helmet to inform him that he may go down.
Thenceforward the life of the diver is in the hands of the attendant, who never lets go of the lifeline and air-pipe until the diver comes to the surface again, feeling the diver at the end of the pipe just as an angler feels a fish at the end of a line, taking in the slack pipe to prevent it fouling rocks and wreckage, paying it out as the diver requires.
The coming of the submarine telephone has certainly lessened the risks of the diver, for he can now talk to the men in the boat and tell them what he wants and how he feels. If anything goes wrong and his lines become entangled, he can inform those at the surface, who can quickly send down another diver to assist him. In comparatively recent days it was necessary to signal by means of the lifeline and air-pipe, a certain number of pulls meaning certain things in accordance with a code in use by all divers. When a diver wished to convey a special message he had to signal for a slate to be sent down, and on the slate he would write what he wanted to convey. It was a slow and cumbersome method which has been rendered obsolete by the submarine telephone, which was invented by that famous submarine engineer, R. H. Davis, the head of Siebe, Gorman & Company.
For ages men have dived for sponges and pearls, remaining at most not more than a couple of minutes at the bottom. The ancients were fully alive to the advantages of an invention that would assist men to remain under water for considerable periods, and they were puzzling their heads about diving dresses centuries ago. These early inventions, however, were very crude, one being a sort of barrel with holes through which the arms could be passed, another a metal cylinder which covered the head down to the waist where it fitted into leather breeches. Very strange and wonderful they appear to modern eyes.
No less strange and decidedly more wonderful is the up-to-date diving dress which has grown out of the invention of Augustus Siebe in 1819. For eighteen years Siebe experimented with his first type of diving dress before he achieved, in 1837, the form of dress which is closely followed to-day. Various people have added improvements, but Siebe’s form of dress is the one in common use, and the firm of Siebe, Gorman & Company which he founded to supply his diving dresses are to-day the greatest submarine engineers in the world.
Inventors have for long been concerned with the problem of a diving dress that will allow a diver to go to any depth without danger. The greatest risk of course, is that he will be crushed to death by the pressure of the water, and to overcome this danger more than one man has invented an all-metal diving dress with flexible joints. In appearance these diving dresses seem cumbersome, and the diver looks more than ever like a knight in armour.
Another form of dress largely in use enables the diver to descend in shallow water without relying on the usual air-pipe and pump. In such dresses the diver carries certain chemicals which not only purify the air he is breathing, but also furnish him with fresh oxygen. One chemical absorbs the poisonous carbonic acid gas given off by the breath, and the other chemical gives off fresh oxygen as the moisture of the breath touches it. The smoke helmet which enables men to enter a mine after a disaster, or a building full of foul fumes, is equipped with the same chemicals and made on the same principle as the diving dress. Instead of completely covering the man, however, this dress is made like a jacket reaching to the waist, where it is securely buckled.
In this dress it was impossible to penetrate the Redding pit, near Falkirk, from which five miners were marvellously rescued after being entombed for nine days, so several naval divers in regulation dress risked their lives in an effort to penetrate the workings to see if any other men still survived and to carry stimulants to them. Divers, at best, have the appearance of creatures from another world, and the effect of a diver, with his lamp, emerging from the inky water and coming suddenly on men who had been immured for a fortnight without food and were at their last gasp had to be carefully considered. Some of the survivors might have attacked him in their delirium and deprived their comrades of all chance of succour.
To avoid so untoward an incident, the leading diver carried with him a message for those men he hoped to find: “This is a diver come to save you. Don’t touch him, as he cannot speak to you. We are driving a place for you. Don’t sit down near the water, but keep clear of the damp. If any of your mates are far through, turn their heads downhill and that will help them until you are feeling stronger. The diver cannot come up the hill out of the water to help you, because his tools are too heavy. He will come back regularly and feed you. You must not drink more than half a cupful of beef tea each. Wait and take a rest before you drink another half-cupful. On this paper write who you are. You will be got out soon.”
Alas, for human endeavour, that message never reached the poor fellows for whom it was intended! The great falls of roof choked the roads and proved an insurmountable barrier. Raging, but exhausted, the divers had to bow their heads in defeat.
So commonplace is the diving dress that it no longer excites curiosity. Yet it remains one of the wonders of modern civilization. Merely by utilizing the sap of a tree, which we know as rubber, and fresh air, men are now able to work and live at the bottom of the sea.