Down below decks is the workshop, wherein "jobs" are done on the high seas. It has quite a respectable equipment: five lathes, ranging from 15 feet to 3 1 / 2 feet in length; drilling, planing, slotting, shaping, punching machines; a carpenter's bench; fitters' benches; and a furnace for melting steel. There is also a blacksmith's shop with an hydraulic forging press and a forge blown by machinery; not to mention a large array of tools of all kinds. Special engines are installed to operate the repairs department.
The Vulcan also carries search-lights of 25,000 candle-power; bilge pumps which will deliver over 5,000 tons of water per hour; two sets of engines for supplying the hydraulic machinery; air-compressing engines to feed the Whitehead torpedoes; a distilling plant; and last, but by no means least, main engines of 12,000 h.p. drawing steam from four huge cylindrical boilers 17 feet long and 14 feet in diameter.
Altogether, the Vulcan is a very complete floating workshop, sufficiently speedy to keep up with a fleet, and even to do scouting work. Her guns and her torpedo craft would render her a very troublesome customer in a fight, though, being practically unarmoured, she would keep as clear of the conflict as possible, acting on the offensive through the proxy of her "hornets." She constitutes the first of a type of vessel which has been suggested by experts, viz. one of high speed and unarmoured, but capable of carrying a swarm of torpedo boats which could be launched in pursuit of the foe. Even if 50 per cent. of the craft were destroyed, the price would be small if a single torpedo were successfully fired at a battleship. The naval motor boat, to which reference has already been made, would just "fill the bill" for such a cruiser; and in the event of a score of them being dropped into the water at a critical moment, they might easily turn the scale in favour of their side.
[CHAPTER XIV]
THE MECHANISM OF DIVING
Diving being a profession which can be carried on in its simplest form with the simplest possible apparatus—merely a rope and a stone—its history reaches back into the dim and inexplorable past. We may well believe that the first man who explored the depths of the sea for treasure lived as long ago as the first seeker for minerals in the bosom of the earth. Even when we come to the various appliances which have been gradually developed in the course of centuries, our records are very imperfect. Alexander the Great is said to have descended in a machine which kept him dry, while he sought for fresh worlds to conquer below the waves. Aristotle mentions a device enabling men to remain some time under water. This is all the information, and a very meagre total, too, that we get from classical times.
Stepping across 1,500 years we reach the thirteenth century, about the middle of which Roger Bacon is said to have invented the diving-bell. But like some other discoveries attributed to that Middle-Age physicist, the authenticity of this rests on very slender foundations. In a book published early in the sixteenth century there appears an illustration of a diver wearing a cap or helmet, to which is attached a leather tube floated on the surface of the water by an inflated bag. This is evidently the diving dress in its crudest form; and when we read how, in 1538, two Greeks made a submarine trip under a huge inverted chamber, which kept them dry, in the presence of the great Emperor Charles V. and some 12,000 spectators, we recognise the diving-bell, now so well known.
The latter device did not reach a really practical form till 1717, when Dr. Halley, a member of the Royal Society, built a bell of wood lined with lead. The divers were supplied with air by having casks-full lowered to them as required. To quote his own words: "To supply air to this bell under water, I caused a couple of barrels of about thirty gallons each to be cased with lead, so as to sink empty, each of them having a bunghole in its lowest parts to let in the water, as the air in them condensed on their descent, and to let it out again when they were drawn up full from below. And to a hole in the uppermost parts of these barrels I fixed a leathern hose, long enough to fall below the bunghole, being kept down by a weight appended, so that the air in the upper parts of the barrels could not escape, unless the lower ends of these 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; and in their descent they were directed by lines fastened to the under edge of the bell, which passed through rings on both sides of the leathern hose in each barrel, so that, sliding down by these lines, they came readily to the hand of a man, who stood on purpose to receive them, and to take up the ends of the hose into the bell. Through these hose, as soon as their ends came above the surface of the water in the barrels, all the air that was included in the upper parts of them was blown with great force into the bell, whilst the water entered at the bungholes below and filled them, and as soon as the air of one barrel had been thus received, upon a signal given that was drawn up, and at the same time the other descended, and by an alternate succession, provided air so quick and in such plenty that I myself have been one of five who have been together at the bottom, in nine to ten fathoms water, for above an hour and a half at a time, without any sort of ill-consequence, and I might have continued there so long as I pleased for anything that appeared to the contrary." After referring to the fact that, when the sea was clear and the sun shining, he could see to read or write in the submerged bell, thanks to a glass window in it, the Doctor goes on to say: "This I take to be an invention applicable to various uses, such as fishing for pearls, diving for coral or sponges and the like, in far greater depths than has hitherto been thought possible; also for the fitting and placing of the foundations of moles, bridges, etc., in rocky bottoms, and for cleaning and scrubbing ships' bottoms when foul, in calm weather at sea. I shall only intimate that, by an additional contrivance, I have found it not impracticable for a diver to go out of an engine to a good distance from it, the air being conveyed to him with a continued stream by small flexible pipes, which pipes may serve as a clue to direct him back again when he would return to the bell."
We have italicised certain words to draw attention to the fact that Dr. Halley had invented not only the diving bell, but also the diving dress. Though he foresaw practically all the uses to which diving mechanism could be put, the absence of a means for forcing air under pressure into the bell or dress greatly limited the utility of his contrivances, since the deeper they sank below the water the further would the latter rise inside them. It was left for John Smeaton, of Eddystone Lighthouse fame, to introduce the air-pump as an auxiliary, which, by making the pressure of the air inside the bell equal to that of the water outside, kept the bell quite free of water. Smeaton replaced Halley's tub by a square, solid cast-iron box, 50 cwt. in weight, large enough to accommodate two men at a time. The modern bell is merely an enlarged edition of this type, furnished with telephones, electric lamps, and, in some cases, with a special air-lock, into which the men may pass when the bell is raised. The pressure in the air-lock is very gradually decreased after the bell has reached the surface, if work has been conducted at great depths, so that the evil effects sometimes attending a sudden change of pressure on the body may be avoided.