bell diving water pressure depth diver dress feet divers surface
DIVINATION. This term is used to mean the obtain-ing knowledge of secret or future things by revelation from oracles or omens. The derivation of the word points to divine influence communicated through the soothsayer, much as the equivalent Greek term mantike refers to the utterancos of the spiritually inspired or possessed seer, mantis. It is well seen from Cicero's treatise De Divina-gone that in classic times theology not only included in its system all revelation by oracles, which clearly belongs to it, but also claimed possession of a variety of diviner's arts, 3uch as augury and astrology, on the ground that their signs were sent by the gods, On the side of the Stoics, it is there argued that if divination is a real art, then there must be gods who gave it to mankind, which proposition is met by the counter-suggestions that signs of future events may be given by nature without any god, or that there may be gods and yet they not have bestowed on man any such art as divination. The real point of the relation of divination to religion is touched in the division of it into two kinds, - artificial divination, by- haruspication, prodigies, light-ning, augury, astrology, and lots, as contrasted with natural divination, by dreams and prophetic oracles. On a general survey of such arts among mankind, it appears that oracles, ct:e., being takan as revelations made directly by spiritual beings, fall to be considered under headings treating of religion (sce, e.g., DEMONOLOGY); bllt divining by such signs as the flight of birds or the falling of lots does not necessarily depend on the notion of intervening demons or deities. One part of its position is well stated in the argument by which Cicero makes his Stoic defend it : - If frogs by croak-ing, and oxen by snuffing the air, can give 113 signs to fore-tell the weather, why should there not be omens in the fibres of a victim's entrails, or in thunderstorms But the religious view which regards omens as divine signs seems to have been from very early ages blended with the naturalistic view, so that in a great part of the cases it is impossible to disentangle them, or even to say which is the original one. This will appear in the following brief sum-mary of the principal methods of divination. Now that the diviner's art has all but perished, we moderns are able to look back upon its history, to see how its futile proceed-ings were suggested by mistaken analogy, and how the ex-perience of ages, which ratifies true inferences and destroys false fancies, is now reducing them to curious antiquarian relics.
The various " artificial " modes of divination for the most part rest evidently on the association of ideas in analogy and symbolism (see evidence in Tylor, Early IIist. of Mankind, p. 132 ; Primitim Culture, vol. i. p. 117, &c., 78.) A tree planted at a child's birth, or any other plant mentally associated with a, person, gives a sign by its flourish-ing or withering as to that person's health or death (Ploss, Das Kind, vol. i. p. 71.) So with the sticks set up by Polynesians to see if the warriors they stand for will fall in battle, or with the cocoa-nut that is spun like a teetotum to point out a thief (Polack, New Zealanders, vol. i. p. 270 ; Mariner's Tonga Islands, ch. xx.) This kind of fanciful association appears in sortilege, or casting of lots, a proceed-ing remarkable not only for its antiquity but for the frequency with which religions have adopted it as a means of obtaining divine guidance, from the ages when classic poets sang of Homeric heroes praying to the gods when they cast lots in Agamemnon's leather cap, or of Mopsus the sooth-sayer divining with sacred lots when the Argonauts embarked ou their voyage (Homer, R., vii. 175 ; Pindar, Pyth., iv. 338), and on until modern times, when the Moravians still resorted to solemn religious lots to determine difficult questions, such as the cheice of wives. Dice or astragali (hucklebones) have been used for the pur poses of sortilege (see Suetonius, Tiberius); and cartomancy, or fortune-telling by means of playing-cards, is still com-mon. In ancient thnes omens were drawn from poets' verses, fixed on by chance, a practice well known as Sortes Virgiliance, from Virgil being often so consulted (see Smith's Dic. Gr. and Rom. Antiq., art. " Sortes ") ; and the Bible came to be afterwards so used for drawing texts, or " pricking for texts ; " this practice is still very usual in Germany (see Wuttke, Deutsche Tolksaberglaube, 2 ed., p. 227.) The haruspication, or examination of entrails, by which Roman statesmen were (or pretended to be) guided in public affairs (see Cicero, Ile Div., ii. 12 ; Plitt. IL N., xi. 73) ; and scapulimancy, or the Tatar mode of divining by the cracks and lines in a shoulder blade (Lubbock, Origin of Civilization, p. 230), formerly known in England as " reading the speal-bone " (Brand, Popular Antiquities, vol.
p. 339), depended on imaginary symbolic associations, such as that cracks in opposite directions meant good and ill fortune, that the course of particular lines indicated the course of the consulter's life, &c. This sort of false analogy may be well understood by a,ny one who will have the similar art of palmistry, or divining by the lines of the hand, applied to his own future by a fortune-teller at a fair. Omens obtained by augnry, or divining by the sight and cries of animals, especially birds (as the name indicates), are as familiar among uncivilized races as they were in ancient Rome ; their symbolism is apparent in such rules as that a hawk means victory, an owl's hoot is unlucky, and that a beast or bird on the right hand portends good, but on the left hand evil (Tylor, P. C., vol. i. p. 119). Another class of arts depend on the unconscious or half. conscious action of some person, often the diviner himself. Among these is the use of the well-known divining rod, which when held in the hands, dips to indicate a hidden spring of water, a vein of ore, or a buried treasure (Brand, vol. p. 332 ; see Chevreul, De la Baguette .Divinatoire, &c.) The use of this instrument remains' in sorne districts of England ; it is locally known as " dows-ing," whence no doubt the name of Dousterswivel in The Antiquary. Similar in principle is the ancient coscinomancy, or divining by a sieve held suspended, and giving its indications by- turning. In later times this gave place to the ordeal by the Bible arid k-ey, where the book is suspended by a key tied in with its wards between the leaves and the key supported on two persons' forefingers, and the whole turns round to prove guilty seine servant maid accused of Zleft (Brand, vol. iii. p. 351). In such cases, where the culprits' fears are apt to betray them, the pracess of divination really serves as a practical test. Dreams are not only considered visits from ghosts, but often also as supernatural signs to be interpreted symbolically, as vvhen a Kamtschatkan dreaming of dogs or lice would take it as foretelling a visit from Russians (Steller, Kanztschatka, p. 279). Of such interpretations the ancient art of oneiromcoicy consists, a,s may be seen in such rules as that if a. woman dreams of kindling a fire, she will bear a male child.; if one dreams of white clouds it means joy-, but if black clouds trouble (Brand, vol.
p. 132 ; Tylor, /.c.). It remains to mention in few words astrology, the branch of divination whose importance in the world has exceeded that of all the rest together. Researches into the ancient writings of Chaldrea have now shown how fully historians were justified in treating that country as the principal among the sources whence the star-gazers received their precepts (see Sayce, " Astronomy and Astrology of the Babylonians," in Trans. Soc. Bibl. Arch., vol. iii. ; Maury, La illagie et l'Astrologie.) The rules in such comparatively modern works as Sibly's Occult Sciences and Lilly's Astrology fairly enough represent the ancient traditions, and show their still intelligible symbolism, - how the stars rising at a child's birth are made in the horoscope to typify its destiny, and the planets and signs of the zodiac exercise " influences " often plainly drawn from their natures or names. Thus Mars has to do with soldiers, Venus with lovers, and Mercury with prattlers ; the solar man is grand and generous, the lunar man unsteadiest and inclined to change, his dwelling„ the sign Leo presides over places where wild beasts abound, but Aries over pastures. At the courts of Asiatic rulers, the state a,strologer still nominally holds a position like that of his predecessor in the ancient empires of the world, but it is evident that the last twenty years have shaken, even in the barbaric East, the power of the occult sciences over the hutnan mind. . (E. B. T.) DriTING. The art of diving to considerable depths under water to bring up pearls, corals, and sponges has been practised in the Indian seas from very early times, and if we may believe the accounts that have come down to us, the feats of early divers are truly remarkable - some of them, it is said, having been able to prolong their sub-maxine descents for periods varying from two to three minutes. It is obvious, however, that not, having the aid of any artificial appliances for supplying air, the powers of these bold adventurers, both as regards the depth to which they could descend and tho length of time they could remain submerged, vfere comparatively limited.
At an early period, therefore, the attention of philo-sophers and mechanics was turned to the discovery of a contrivance for aiding the diver in prosecuting his daring but useful calling, which was rendered all the more important from its being no longer confined to the acquisi-tion of Eastern luxuries, but to the raising of treasure from sunken vessels. It is not considered expedient to occupy space by further reference to the feats of the early divers, out rather to pass at once to the history and construction of the diving apparatus of modern times, as illustrated by the Diving Bell and the Diving Dress at present in use. And here it may be stated that in addition to the sponge and coral trade of foreign lands, which has been greatly advanced by the use of modern appliances, there are the works of the naval engineer, and more particularly of the civil engineer, in which diving apparatus is so extensively employed and so essentially necessary as to place the art of (living on a wider basis, and to give it an importance only fully developed within the present century.
Diving Bell. - The most useful of ancient contrivances is the diving bell, which, introduced at an early period and gradually improved, is now the well-known apparatus used by engineers in the present clay; and it may be interesting to trace the successive improvements that have brought it to its present state of perfection and usefulness in con-ducting submariue works.
The conception of the diving bell is very simple. The an. contained in an inverted jar sunk in a vessel of water excludes the water from the interior, and if the vessel be made of sufficient size to contain persons within it, it may be sunk without their being wetted, and they may continue to be submerged so long as the air within the bell continues pure enough to support animation. Such were the " diving-chests " of the first makers, which, though they differed in form and details, were constructed on the same principle as the modern bell, and were generally formed of wood, girded with iron hoops, like a barrel.
It will be obvious that if such a vessel were submerged. in shallow water, having a depth of say one foot of water,. a large supply of air would be inclosed in the bell, and the bottom on which it rested would, from the small depth of water upon it, be easily reached for any operation to be performed on it. But if we conceive the same bell to be lowered further below the surface, the air being compres-sible will be reduced in volume, and the water will rise iv the bell to fill its place. The result would be that at the depth of about 3'3 feet the air would be compressed into about one-half its original bulk, and the bell itself would be half filled with water ; and the bottom of the sea on which it rested would no longer be so conveniently reached as when the water was only a, few inches above the lips of the bell. :Moreover, the air by repeated inspiration becomes unfit to support life, and the ancient bells had to be raised to the surface at very short intervals of time that fresh air ntight be supplied to the men employed. Although, therefore, the original diving hell was a step towards the perfect appliatices afterwards introduced, it will readily be seen that its use in diving operations was very limited indeed.
Dr Halley, the secretary of the Royal Society, who seems 1 to have taken an interest in diving and divers, and com-passionated their want of fresh air, communicated a paper to the Royal Society in which, to use his own words, he proposes a plan " for carrying the patulynt vitce down te the divers, who must without being supplied therew ith return very- soon to the surface or: perish." The following is the description of his arrangements for this purpose. After describing the bell itself, which was of wood of the form of a truncated cone, with a capacity of GO cubic feet, and was suspended by a sprit from the mast of a ship, Le says - " To simply air to this bell when under water, I caused a couple of barrels, of about 36 gallons each, to be cased with lead, so as to sink empty, each of them having a bung-hole 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 front below. And to a hole in the nppermost part of these banels I fixed a leathern hose, long enough to fall below the bung-hole, 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 these hose \vere first lifted up.
"The air-barrels being thus prepared, I fitted them with tackht proper to make them rise and fall alternately, after the manner of two bnckets in a well ; and in their descent they were directed by lines fastened to the under edge of the bell, which pas.sed 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 pnrpose 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 tipper parts of them Ni-itS blOWII With great force into the bell, whilst the water entered at the bung-holes below and filled them, and as soon as thc 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, famished air so quick, and in so great 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 scat of ill consequence, and I might have continued there so long as 1 pleased, for anything that appeared to the contrary. 1 only observed that it was necessary to be let down gradually at first, nt about feet at a, time ; and then to stop and drive out the air that entered, by receiving 3 or 4 barrels of fresh air before I descended further. lint being arrived at the depth designed, I then let out as numb of the hot air that had been breathed as each barrel would replenish with cool, by means of the cock at the top of the bell, through whose aperture, though very small, the air would insh wails° much violence as to make the smface of the sea boil, and to cover it with a white foam, notwithstanding the weight of the water over us.
"Thus I found that I could do anything that required to be done just under us, and that I could, for a space as wide as the circuit of the bell, lay the bottom of the sea so far dry, as not to be over shoes thereon. And, 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 fa,ten or lay hold on anything under us that was to be taken up ; and, by the return of the air bhrrels, I often sent up orders, written with an iron pen on small plates of lead, directing how to move up from place to place as occasion required. At other times when the air was troubled and thick, it would be as dark as night below ; but in such cases I have been able to keep a candle burning in the bell as long as pleased, notwithstanding the great expense of air m,cessary to maintain flame. This I take to be an invention appli-cable 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 found-ations of molea, bridges, kc., in rocky bottoms, and for cleaning and scrubbing of ships' bottoms when foul, in calm weather at sea. I shall only intimate that, by an additional contrivance, nave 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 lie would return to the bell."
Such is an account of Dr 1-Talley's apparatus, which un-doubtedly etTected an important improvement ; but it small depth of water, to work in, he contrived a bell to the small depth of water, did not require to be wholly subwater by means of a hose screwed into an air-hole in the top of the bell. The following is Smea.ton's description of his, last improvement : - It will thus be seen that Smeaton's Ilamsgate bell con-tained all the elements of the present appliances, which, as improved in details, and constructed by 'Messrs Rennie, has been so extensively employed in harbour works.
ting light ; and in the screwed for admitting and in tile centre is a lifting chain to which stones are naotion at right angles across the work. so that the position of the bell can be altered with the greatest ease so as to bring it over any spot within the area of the staging.
In proceeding to work, the men take their seats in the bell from a boat, and the bell is then lowered to the reqnired depth. If the work be that of building a, wall a stone is lowered at the same time. The changes in the position of the bell are all made according to signs given by the divers by strokes of a hammer on the bell, which experience has shown can be heard at any depth at which the diving bell has been employed. The signals are - one stroke, more air ; two, hold on ; three, raise ; four, lower ;live, north ; six, south ; seven, Bast ; ei ght, west. These signals are narrowly observed by a watchman stationed in a boat, and reported to the men working the bell carriage. The rule for the supply of air both to the bell and diving dress is to give it so freely that there shall be a constant escape of air rising to the surface in air-bubbles all the time the men are under water. After being lowered, the bell is first moved over the stone to be laid ; the divers then unhook the lowering chain from the lewis in the stone, and at the same time make fast the stone to the tackle within the bell, which is at once signalled to be raised, and. carries the stone with it. The bell is then moved over the site on which it is to be placed ; it is then lowered until it has nearly reached its bed, on which it is finally deposited. The lewis is then removed and the bell raised for another stone ; and with trained workmen it is surprising how expeditiously the bell is moved from place to place, and stone after stone is built in the walls. The staff of men required to work the bell is two divers, one watchman, four men working the air-pump, and four working the bell carriage, besides the men required to bring forward and send down the stones. The men engaged generally work in shifts of from 3 to 6 hours according to the depth, and the diving work may be continued as long as in ordinary day-work, as in clear water the light is good to the greatest depth at which the bell is used in harbour building.
When engaged in blasting, the bore is made in the ordinary way, and charged with a shot inclosed in a water-tight canvas case, to which is attached a length of 6 or 8 feet of patent fuse. The bell is then moved from above the bore, and the fuse ignited, and when the shot is fired the smoke rises to the surface clear of the bell.
When employed for removing rock or boulder stones - for example, in a river navigation, - it is of advantage that the bell be capable of being easily transported, and in that case it is swung from a barge or lighter, which contains the machinery for working the bell and air-pumps, and a crane for raising tne boulders as the divers sling them. It is of course attended with greater trouble and risk to the divers to work the bell from a lighter than from a stage ; but, on tbe other hand, the convenience in being enabled to trans port it from place to place, in a river navigation, is a great advantage.
Simons of Renfrew for the River Clyde, which was com-municated by Mr Deas, the engineer, to the Clyde Trustees. Fig. 4 is a longitudinal section, and fig. 5 a plan in which a is the bell, b the bell crab, c the air-pumps, and d the crane for lifting stones, Sic., slung by the divers.
The large cost of a, diving bell limits its use to works of magnitude, especially as many submaxine works can be done better by the diving dress, which is much less expensive; but there are certain operations, such /LS the clearing and levelling of foundations, for which the bell is peculiarly well adapted, that still enable it to take its place as one of the most useful appli-ances of the marine engineer. Mr B. B. Stone,y ha.s, in an interesting paper in the Minutes qt. Proceedings of the Institution of Civil Engineers,1 described a diving bell, or chamber, 20 feet square, with which he success-fully built the foundation of the quays of Dublin. Mr Stoney's apparatus does not come under the article diving, but belongs more properly to the subject of the compressed air cylinders used in bridge building, which are described under the article BRIDGE.
Diving Dress. - The diving dress is peculiarly well fitted for such works.as the repair or overhaul of rollers and sluices lock-g,ates, cleaning or repairing ships' bottoms, descend-ing into the hatches of wrecks to recover property, aud, in short, everything that cannot be done from the interior of a bell. The inexpensiveness also of the diving dress, dispensing with all costly staging, and its ease of transport and appliance, are much in favour of its use. It is, indeed, so convenient in the repair of propellers, examining ships' bottoms, recovering anchors, &c., that all ships in Her Majesty's navy of sufficient size to be commanded by captains are now supplied with a diving dress or apparatus, and bear a certain number of divers in their complements ; and all sea-going flagships and iron clads on foreign stations carry two sets of diving apparatus, and are allowed a suitable number of traine,d divers.
The invention of the diving dress, like that of most use-ful appliances, was gradual, and the work of many minds. Some early proposals, such as that already referred to in the quotation from Dr Halley's paper in 1721, and others of more modern date, were made for providing the diver with a dress to enable him with safety to carry on his work, for an account of which the reader is referred "co a paper by Mr J. W. Heinke in the Minutes of Proceedings y the Institution of Civil Engineers.2 But to Mr A. Siebc is due the credit of being the first to introduce a dress which was supplied with a constant stream of fresh air, and may be said to have been the precursor of the dress now in use. We allude to what was called the " open dress " invented in 1829, which consisted of a helmet and water-proof jacket, under which, and fitting more closely to the body, were worn trousers reaching to the arna-pits, and between the jacket and trousers the air pumped in at the helmet was allowed to force its way and escape to the surface as in the diving bell, and hence it was called "open." Although some divers of the old school are said still to give a preference to the open dress, its danger became manifest ; for if a diver stumbled and fell on his face or side, the water entered his dress, and unless quickly brought to the surface he was in danger of being drowned - a, necessary requirement of the open dress being that he should remain in an upright or gently stooping posi-tion. To meet this defect, Mr Siebe, in 1837, introduced the "close " dress, which is new almost universally used. Various minor improvements were introduced between 1839 and 1843 connected with the removal of the wreck of the " Royal George" ship of war, conducted by the late Sir Charles Pasley, which will be found fully described in the Minutes of Proceedings of the Institution of Civil Engineers.3 The long continued experience gained in diving while these operations were in progress sugYested improvements and alterations which had a great eeect bringing the divinc, dresss to its present perfection as now manufactured lay Siebe, Heinke, Barnett, and other makers.
The diving dress, as will be underst000d from fig. G, envelops the whole body of the diver, the upper por-tion a being the " helmet," the intermediate portion b the " breast-plate," and the lower portion c the "dress." The hose by which the air is supplied is shown at (l, and e is the " life" or " sig-nal" line, which is attache,d to the diver's waist, and by which he makes signals and is hauled to the surface. The water-proof material of which the dress is made is very generally sheet india-rubber zovered on both sides with tanned twill to protect the india rubber from injury. The cuffs fit tightly round the wrists, leaving the hands free, and india-rubber bands slipped. over them render flu) joint water-tight. The breast-plate b is made of tinned copper with an outer edge of brass, which has screws fitted to it projecting upwards and passing through cor-respondina holes in the collar of the dress. On the top of this, an% with holes in it corresponding to the screws, four pieces of a metal band are firmly- screwed down by wing nuts, nipping the soft material of the collar between the metal of the breast-plate and band, and thus ensuring a water-tight joint. On the front of the breast-plat€: two studs are fastened for securing the back and front weights g. Some makers put a, valve h on the front of the breast-plate, by means of which the diver can regulate the pressure inside his dress at will, aud in this way has the power, by simply inflating his dress more or less, of makinbc, himself of any spe,cific gravity, so as to float at any desired depth or rise to the surface without the assistance of the attendant. This arrangement in the hands of a skilled diver is undoubtedly a great convenience. But it is still a matter of difference of opinion whether it is not safer to trust to being hanled up by the watchrna,n on the surface, whose duty it is to hold the life or signal line in one hand, and the air hose in the other, while the diver is at work, and to attend to whatever signal he may give by pulling the life line. The inconvenience of the air bubbling up in front of the bulls' eyes, and the danger of inexperienced divers becoming giddy and turning the valve the wrong way, have induced some makers to do away with this use-ful va,lve, and to substitute at the back of the helmet a, valve which the diver can regulate by the pressure of his hand, but which rights itself the moment his hand is removed. The neck of the breast-plate is fitted with a " segmental screw bayonet joint " (introduced by Messrs Siebe), and to this the helmet, the neck of which is fitted with a corresponding screw, can be attached or removed by one eighth of a turn. The helmet, a side view of which is given in fig. 7, is made of tinned copper, and fitted in front with three strong plate-glass win-dows, or bulls' eyes, in brass frames protected with guards. Messrs Heinke introduced slid-ing covers to draw over these win-dows in case of their getting bro-ken. The front eye piece is made so that it can be unscrewed, and in this way the diver on ascend-ing can rest him-self for a short time orgive orders without removing the rest of his dress. Messrs Barnett have introduced instead of this a hinged glazed frame, which fits tightly into a conical vulcanized india-rubber seat like tho ordinary port hole of a ship, so that it can be- opened by the diver himself the moment his head is above water, and being attached to the helmet it cannot be dropped acciden-tally into the sea or otherwise mislaid. An outlet valve a is fixed at the back of the helmet, which, opening outwards, permits the escape of the foul air but prevents the entrance of water. The inlet valve b to which the hose is attached is also fixed at the back of the helmet, and is so constructed as freely to adtnit the air from the, force pump ; but should anything occur to the hose or pumps the valve at once shuts, inclosing a sufficient supply of air in the dress to support the diver till he can be hauled. to the surface. The air after enterino. by the inlet valve is conducted in tubes c to the front of the helmet, su that the diver has the advantage of inhaling fresh air, and the front glasses are kept free from the condensation of his breath which would otherwise take place. On each side of the helmet is a hook over which the cords pass which carry the front and black weights, and a brass stud to one of which tho life line, and to the other the air tube, are attached ; d d is the joint by which the helmet is screwed upon the breast-plate. The back and front weights weigh about 40 lb each, and are held close to the diver's body by means of a lashing passing under his arm-pits. The boots aro made of stout leather, with leaden soles, secured by two buckles and straps, each boot weighin, about 20 lb.
The cost of a diving Clress, with all its appliances, is about £140.
The sponge, pearl, and coral fisheries, orieinally carried on only by naked divers, as already noticed'', are now con-ducted to a great extent by the help of artificial aids ; and, according to 'Mr Siebe, upwards of 300 sets of diving dresses are employed in the. Mediterranean sponge fisheries alone, and they are being introduced in the Bahamas, Bermudas, Ceylon, the West Indian Islands, and on the coast of Australia.
As already stated, at moderate depths not exceeding 30 to 40 feet, and with clear water, sufficient light is transmitted to enable the diver to perform any ordinary work, and in working in turbid water with the divine. bell candles are employed. Mr Siebe has also constructe'd an electric lamp and an oil lamp which can be employed where light requires to be used by divers at great depths.
Captain Eadsl states that at the Mississippi bridge candles were at first employed, which, under a pressure of 100 feet, wero found to be burnt down in about three-fifths of the time required in the open air; under a pressure of 80 feet it was found that a candle if blown out by the breath would immediately reignite ; and at the depth of 1081 feet a candle was blown out thirteen consecutive times in the course of half a minute, and each time excepting the last was reignited.
The depth at which diving can be safely conducted is a question of importance. The ordinary depth at which the diving bell has been employed in harbour works is from 30 to 35 feet, and it has been used in 60 feet at Doren With the diving dress much greater depths have been attained. Mr Siebe relates that in removing the cargo of the ship " Cape Horn," wrecked off the coast of South America, a diver named Hooper made 7 de.seents to a, depth of 201 feet, and at one time remained 42 minutes, sup-posed to be the greatest diving feat ever achieved. 1M. Frendenberg states that in the repair of a pump in the Seharley zinc mines in Silesia, two divers went clown tile pump well to a depth of 85 feet, remaining from periods varying from 15 minutes to two hours.3 In the knowledge of the author the greatest depth at which the diving dress was used in the open sea, was in the Firth of Porth. A Royal Commission " on the Operation of the Acts relating to the Trawling for Herring on the Coast of Scotland " resolved to obtain the herring spawn from various portions of the exposed parts of the firth, and this duty was successfully accomplished in depths of from 14 to 16 fathoms, from the deck of the " Princess Royal " cutter, under the command of Mr 'Macdonald.
'_L'he writer is indebted to Mr P. J. Messent, the engineer of the Tyne piers, for the following notes of his experience work at that work. " On the Tyne Pier works helmet and bell the T divers are employed simultaneously - the, former for excavat-ing for and fixing the feet of the piles of which the staging is formed, the bell divers for levelling the foundations and fixing the blocks of which the pier is composed. The helmet diver has greatest power in lifting. Ile can exert but a few pounds of force in pulling downwards (unless he ca,n fasten himself down) on account of his buoyancy, and for the same reason be cannot pull or push horizontally with much force unles3 be has a fulcrum or stop for his feet or body. Thus, in boring an augur hole in a pile he would have to lash himself to it, unless there was a pro-jecting rock or stone that he could get his foot against. In the use of a hammer and other tools for striking he is restricted by the water," but Mr Messent has known good men do fair work with a hammer and chisel. It is difficult for them to walk against even a moderate tide, and men who by accident get on the (lee) tide side of their work, generally have to be hauled up to their boat and lowered down again in order to get on the (windward) tideward side of it ; again experience enables many of these difficulties to be met or modified, but it is advantageous to bear them in mind in arranging work for divers. Most of the divers at the Tyne have been made or instructed on the works, and of the men who have tried helmet diving not more than one out of three or four succeed .or become divers, the failure being sometimes from physical causes, but more often from want of head. There is less difficulty in making bell-divers, probably on accouut of their work-ing in company, there being always two men in a bell, and the same amount of self-relianco is not needed.
The practice of diving obliges the diver to conduct his work under a pressure greater than that of the atmosphere at the surface of the earth. All diving work is done under an abnormal atmospheric pressure, which increases with the depth at which the diver is submerged in water. This pressure, when he is submerged to the depth of 33 feet, is twice that of the normal superficial atmospheric pressure. At greater depths the pressure is proportionately increased, and ultitnately becomes so great that life could. not be maintained. To descend even to the moderate depth of 30 or 40 feet, which is about the maximum required for ordinary engineering sea works, demands some practice and nerve on the part of the diver, but when greater depths have to be explored, in raising sunk vessels, for example, the energy and power of endurance of the diver are much more severely taxed, and it seems not uninterest-ing, before concluding this article, to refer to the effect which the work has on the health of the diver, as well as on some physiological facts of interest in general science.
The sensations experienced in a diving bell are common, it is believed, to all divers. According to the writer's ex-perience, very soon after the lips of the bell have touched the surface of the water pain is felt in the ears and above the eyes, which continues with greater or less intensity according to the rate of descent until the bell has attained the bottom. So long as the bell continues there no pain is felt, the only feeling being that of depression duo to the depth to which the diver is submerged. As soon as the upward movement commences the pain in the ears and above the eyes returns, and continues till the surface is reached. The motion of the bell is very gradual, sometimes not exceeding 3 feet per minute, but even at that slow rate the head does not accotnmodate itself to the increase of pressure so as to avoid inconvenience. Aeronauts clo not suffer to the same extent in their ascents in balloons, because the alteration of pressure is much more gradual in passing through the atmosphere than through a medium having the density of water.
Several suggestions have been offered as accounting fur the sensations which are experienced in diving, and the following explanation, which the author has submitted to Professor Turner of Edinburgh, is believed to afford the true solution.
Under the ordinary atmospheric conditions, the air presses not only on the surface of the body, but into every cavity within the body which communicates with the sur-face, so that the pressure, both externally and internally, is exactly balanced. In passing into a denser atmosphere the increased pressure opera,tes externally more rapidly than it does internally, more especially if the, communica. tion of the internal cavities with the surface is by tortuous passages ; and so long as this inequality in the pressure exists the disagreeable sensations in the cars and above the eyes will continue. The pain in the ears arises from the effect of the condensed air acting externally on the tympanic membrane of the ear, before the air within the tympanic cavity has acquired the same density to counter-balance it, The tympanic membrane stretches across the bottom of the passage or meatus, which leads from the outer ear into the side of the head (see ANATOMY, fig. 80.) This passage is in direct communication with the atmo-sphere, the pressure of which, therefore, acts instantaneously on the tympanic membrane. But on its inside the tympanic membrane bounds the tympanic cavity, which has no communeation with the external air, excepting by-the Enst•achian tube, which leads from the cavity into the pharynx immediately behind the nose. Through this tube, therefore, the condensed air must pass from the pharynx to supply what is necessary within the cavity for restoring tile same equilibriuru within and without. But the Eustachian tube is a long and narrow passage ; at its com-mencement in the ear it has a bony structure, but towards its termination in the pharynx behind the nostrils, it becomes soft, so that its walls can be forced together. It admits an easy passage front the ear to the pharynx ; but when any pressure arises in the opposite direc-tion, it acts in some degree like a, valve, shutting the passage, until the increasing pressure again forces it open. Some time then elapses before all this can be accomplished ; and during this time the external air, pressing with full force on the tympanic membrane, produces the pain which is felt. When the Eustachian tube opens, it is generally all of a, sudden, aud with a slight explosion or pop, which • is followed by instant relief from the pain. This relief may often be produced by filling the mouth, or gulping the air and passing it into the tube.
That the above is what really takes place may be shown experimentally by shutting the mouth and nostrils, and exhausting the air from them by the action of the lungs, The air in the tympanic cavity immediately rushing through the Eustachian tube into the mouth, the external air acts on the tympanic membrane and produces a slight sensation of deafness, such as is felt in the bell. But if, instead of exhausting the air, we attempt to compress it, and force it through the tube into the tympanic cavity, at first no effect is produced ; but after exerting a, considerable pressure a slight pop is felt, and a little pain in the ear, which is just the sudden opening of the tube.
The pain above the eyes is doubtless due to the inequality between the pressure of the air on the surface of the fore-head and that of the air in the frontal sinuses, or air spaces in the frontal and other bones which form the boundaries of the orbits, The return of the disagreeable sensations during the upward ascent of the bell is due to the pressure on the outer surface of the tympanic membrane and of the forehead being diminished, before the air within the tympanic cavity and the air spaces in the bones of the orbits has accommodated itself to the diminished external pressure.
It may further be interesting to notice that any vpward motion is accompanied by a thick mist within the bell, which disappears when it is stationa,ry or moving down-wards. The explanation is that the air inside the bell, when it is ascending, being relieved of pressure, expands, and its temperature is lowered ; and as the air inside ia about the point of saturation, the fall of temperature pro-duces condensation, which becom-es visible in the form of vapour or mist. An analogous phenomenon takes place in commencing to exhaust the receiver of an air-pumv.
The question of the effect produced on the health of the men employed in diving is of interest and importance. So far as the author's experience goes, he is not aware that divers suffer from prosecuting their submarine work under the pressure of one or two atmospheres to which they are subjected in ordinary harbour works, the men selected for such duty being generally healthy young men of athletic make. Indeed, it is well known that to some constitutions, and in some forms of disease, subjection to moderato increase of atmospheric pressure proves beneficial. But when greater depths and high pressures have to be sustained the case may be very different.
Mr Siebe, who states the greatest depth to which a diver has descended to be 201 feet, with a pressure of 87 lb on the square inch (but who states 150 feet as the limit for safe work), has given various directions, the result of 1113 experience, as to the selection of men for deep diving, and advises that men should not be employed who are of full habit of body, who suffer from headache or deafness, who have at any time had spitting, of blood or palpitation of the heart, who are pale and whose circulation is languid, er who are of intemperate habits. He also says that the rate of descent and ascent must depend very much on the constitution and experience of the diver, about 2 feet a second for a strong man for depths not exceeding 80 feet, and for descending to greater depths additional care must be used. The greatest pressures to which men are subjected in engineering works are experienced in the compressed air cylinders used in bridge building (see article BRIDGE). At Saltash bridge it was found that the men could not work long shifts at the depth of 86 feet without serious inconvenience - some of them, after working seven hours, being slightly paralyzed, butt in two or three days they quite recovered. With three hours' shifts the men could work for several months consecutively.
At Londonderry bridge, where the MCD wrought under a pressure of 75 feet, or about two atmospheres, Sir John Hawkshaw found that there was considerable difference in the relative ability of men to stand the pressure. Tie had found Irishraen less able to stand the work than English-men, one of the effects being that the joints began to swell. In other cases no evil resulted.
Captain Eads, the engineer of the St Louis bridge, built across the Mississippi in 1870, gives some interesting in-formation, in his reports to the directors of the Illinois and St Louis Bridge Company, on the effect of working under high pressure on the men. The maximum depth to which the cylinders had to be sunk was 110i feet below summer water level, and the greatest pressure tinder which the men worked was 50 or 51 lb on the square inch. When the depth of 60 feet had been reached some of the men were affected by paralysis of the lower limbs, which usually passed off in a, day or two. At greater depths the symptoms were more severe. The duration of working in the air chamber was gradually shortened from four hours to ono hour. The total number of men employed in working under pressure was 352, of whom 30 were seriously affected and 12 cases proved fatal. (D. s.)