« EelmineJätka »
motion 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 required 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; /our, lower ;jwe, north ; six, south; seven, east; eight, 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 lite oa which it is to be placed; it is then lowered until it baa 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
Tta B.—Flu of Bell Lighter (56 feet long and 24 feet beam).
pott it from place to place, in a river navigation, is a I Figs. 4 and 6 show the disposition of the various great advantage. * I appliances in the most recent bell-lighter built by Messrs
Simons of Renfrew for the River Clyde, which was communicated 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, e the air-pumps, and d the crane for lifting stones, &c, slung by the divers.
The large cost of a diving bell limits its use to works of magnitude, especially as many submarine works can be done better by the diving dress, which is much less expensive; but there are certain operations, such as the clearing tend levelling of foundations, for which the bell is peculiarly well adapted, that still enable it to take its place as ono of the most useful appliances of the marine engineer. Mr B. B. Stoney has, in an interesting paper in the Minnie) of Proceedings of the Institution of Civil Engineers? described a diving bell, or chamber, 20 feet square, with which he successfully 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.—TJhe diving dress is peculiarly well fitted for such works as the repair or overhaul of rollers and sluices of lock-gates, cleaning or repairing ships' bottoms, descending into the hatches of wrecks to recover property, and, 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, ic, 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 trained divers.
The invention of the diving dress, like that of most useful appliances, was gradual, and the work of many minds. Some early proposals, such as that already referred to in the quotation from Dr Halley^ paper in 1/21, and others of more modern date, were made for providing the diver with a dress to enable him with safety to carry on Ids work, for an account of wlrich the reader is referred to a paper by Mr J. W. Heinke in the Minutes of Proceedings of the Institution of Civil Engineers.* But to Mr A. Siebe is due the credit of being the first to introduce a dress which was supplied with a constant stream of fresh air, and may bo 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 waterproof jacket, under which, and fitting more closely to the body, were worn trousers reaching to the arm 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 Ace 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 position. To meet this defect, Mr Siebe, in 1837, introduced the "close" dress, which is now almost universally used. Various minor improvements were introduced between 1839 and 1843 connected with the removal of the wreck ■sf the "Royal George" ship of war, conducted by the
late Sir Charles Pasley, which will be found fully describe! in the Minutes of Proceedings of the Institution of Civil Engineers? The long continued experience gained in diving while these operations were in progress suggested improvements and alterations which had a great effect in bringing the diving dresss to its present perfection as now manufactured by Siebe, Heinke, Baruett, and other makers.
The diving dress, as will be understoood from fig. 6, envelops the whole body of the.diver, the upper portion a being the " helmet," the intermediate portion 6 the " breast-plate," and the lower portion e the "dress." The hose by which the air is supplied is shown at d, and «is the "life" or "signal" line, which is attached 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 indiarubber covered 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 the joint water-tight. The breastplate 4 is made of tinned copper with an outer edgo of brass, which has screws Fla- 6--D'*ui« Drew, fitted to it projecting upwards and passing through corresponding holes in the collar of the dress. On the top of this, and 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 breastplate 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 meatis of which the diver can regulate the pressure inside his dress at will, and in this way has tho power, by simply inflating his dress more or less, of making himself of any specific gravity, so as to flo»* at any desired depth or rise to the surface without the assistauce 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 hauled up by the watchman 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 useful valve, 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
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 the 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 accidentally 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 valvo 6 to which the hose is attached is also fixed at the back of the helmet, and is so constructed as freely to admit 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 entering by the inlet valve is conducted in tubes c to the front of the helmet, so that the diver has the advantage of inhaling fresh air, and the front glasses are kept free from the condensation of Mb 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 back weights, and a brass stud to one of which the 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 S> each, and are held close to the diver's body by means of a lashing passing under his arm-pits. The boots are made of stout leather, with leaden soles, secured by two buckles and straps, each boot weighing about 20 lb.
The cost of a diving dress, with all its appliances, is about £H0.
The sponge, pearl, and coral fisheries, originally carried on only by naked divers, as already noticed, are now conducted 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 diving bell candles are employed. Mr Siebe has also constructed an electric lamp and an oil lamp which can be employed where light requires to be used by divers at great depths.
Captain Eads1 states that at the Mississippi bridge candles were at first employed, which, under a pressure of 100 feet, were 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 108 J 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, atSd it has been used in 60 feet at Dover.
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 descents to a depth of 201 feet, and at one time remained 42 minutes, supposed to be the greatest diving feat ever achieved. M. Frendenberg states that in the repair of a pump in the Scharley zinc mines in Silesia two divers went down the pump well to a depth of 85 feet, remaining from periods varying from 15 minutes to two hours.' In the knowledge of the author the greatest depth atwhich the diving dress was used in the open sea was in the Firth of Forth. A Royal Commission "on the Operation of the Acts relating to the Trawling for Herring on the Coast x>i Scotland " resolved to obtain the herring spawn from various portionsaof the exposed parts of the firth, and this doty 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.
The writer is indebted to Mr P. J. Messent, the engineer of the Tyne piers, for the following notes of his experience at that work. "On the Tyne Pier works helmet and bell divers are employed simultaneously—the former for excavating 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. He can exert but a few pounds of force in pulling downwards (unless he can fasten himself down) on account of his buoyancy, and for the same reason he cannot pull or push horizontally with much force unless he 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 projecting 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 leant of head. There ia less difficulty in making bell-divers, probably on account of their working in company, there being always two men in a bell, and the same amount of self-reliance is not needed.
1 Reports by Captain .lames B. Eadi to the President and Director! of the Illinois and St Louis Bridge Companj.
* Minutes of PromAing* of IntL of Civil Snfinter; vol xlv. p. 343.
The practice of diving oMigea the diver 10-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 ultimately becomes so great that life conld not be maintained. To descend even to tho moderate depth of 30 or 40 feet, which is about the maximum required for ordinary engineering sea works, demands soma practice and nerve on the part of tbe diver, but when greater diptbs 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 uninteresting, before concluding this article, to refer to the effect which the work has on the health of the diver, as well as on same 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 experience, 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 due 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 accommodate itself to the increase of pressure so as to avoid inconvenience. Aeronauts do 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 for 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 surface, so that the pressure, both externally and internally, is exactly balanced In passing into a denser atmosphere the increased pressure operates externally more rapidly than it does internally, more especially if the communication 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 ears and above the eyes will continue. The pain in the ears arises from the effect of tbe condensed air acting externally on the tympanic membrane of the ear, before the air within the tympanic cavity has acquired the same density to counterbalance 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 atmosphere, 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 communcation with the external air, excepting by the Eustachian tube, which leads from the cavity into the pharynx immediately behind the nose. Through this tube, therefore, tbe condensed air must pass from the pharynx to supply what is necessary within the cavity for restoring lie same equilibrium within and without. But the
Eustachian tube is a long and narrow passage; at its commencement 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 from the ear to the pharynx; but when any pressure arises in the opposite direction, it acts in some degree like a valve, shutting the passage, until the increasing pressure agaiu 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, and 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, iustsad 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 forehead 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 tho 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 upward motion is accompanied by a thick mist within the bell, which disappears when it is stationary or moving downtvardt. The explanation is that the air inside tike bell, when it is ascending, being relieved of pressure, expands, and its temperature is lowered; and as the air inside is about the point of saturation, the fall of temperature produces condensation, which becomes visible in the form of vapour or mist An analogous pheuomenon takes place in commencing to exhaust the receiver of an air-pump-.
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 athletio make. Indeed, it is well known that to some constitutions, and in some forms of disease, subjection to moderate increase of atmospheric pressure proves beneficial'. But when greater depths and high pressures have to bo 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 givea various directions, the result of his 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 or 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 descendiug 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, but 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 men 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. He had found Irishmen less able to stand the work thai) Englishmen, one of the effects being that the joints began to BwelL In other cases no evil resulted.
Captain Eads, the engineer of the St Louis bridge, built across the Mississippi in 1870, gives some interesting information, in his reports to the directors of the Illinois and St Louis Bridge Company, on the offect of working under high pressure on the men. The maximum depth to which the cylinders had to be sunk was 110J feet below summer water level, and the greatest pressure nnder 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 one 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.)
DIVISION. See Loom
DIVORCE is the dissolution of the relationship of marriage. Few social questions are surrounded with greater difficulty than this. For what causes divorce should be granted, and whether complete divorce should be granted at all in the sense of authorizing the spouses to contract new marriages, ore points on which civilized societies have arrived at very different conclusions. Modern practice and opinion are to be traced mainly to two sources of principle, viz., Boman law and the Christian religion. The effect of the spread of Christianity was to reinvest marriage with the religious character .om which in the later law of Borne it had completely escaped; and the history of divorce in modern times has been the gradual decay of the restrictions which were thought appropriate to the religious character of the institution of marriage. At the same time these restrictions have nowhere disappeared. The opinion of society visibly fluctuates between the belief that marriage is a civil contract only and the belief that it is a contract of a peculiarly sacred character, the dissolution of which must not be lightly, if at all, permitted by human legislation. - Again, divorce appears to be regarded sometimes as a penalty against the offending spouse, sometimes as a right to which the innoceut spouse is entitled. It will be granted only if a matrimonial offence is proved to have been (committed, but it will not be granted if such an offence has been committed on both sides. Hence a certain amount of inconsistency in legislation about divorce, which is in no system more remarkable than in our own, founded as it is on the doctrines of the canon law, modified by the opinions of secular judges, and altered by Actsof Parliament
In iloman law marriage was regarded as a voluntary anion which might be terminated at any time by the
consent of the parties. No legal process was required, although the abuse of the power of divorce was sometimes punished. If a wife had not passed under the manui of her husband, her father might withdraw her from the union against the wishes of both parties. A constitution of Antoninus Pius limited this power. Until the time of Justinian divorce by consent of both parties does not appear to have been subject to any restriction. Justinian, however, allowed it only in three specified cases, viz., for im potency, or when either party desired to enter on a monastic life or was for a long time in captivity. "At a later period Justinian enacted that persons dissolving a marriage by mutual consent should forfeit all their property and be confined for life to a monastery, which was to receive a third of the forfeited property, the remaining two-thirds going to the children of the marriage. This severity, so much at variance with the Boman spirit, indicates the growing power of the clergy (ut non Dei judicium eontemnatur)." (Hunter's Soman Law, p. 500.) These prohibitions were repealed in the next reign. Divorce by the husband against the wish of his wife was a power much more likely to be abused than that of dissolving marriage by mutual consent. Although the legal right was recognized, it is said not to have been acted on for a period of 500 years, and Spurius Carvilius is said to have been the first who put away his wife for barrenness. Harshness in the exercise of the power was condemned by public opinion, and sometimes puuished by the authority of censors. L. Antonius, a senator, was expelled from the senate for a harsh divorce of a young wife. The wife who had not come under the man us of the husband had the same power of repudiating the marriage at wilL Later legislation curbed this excessive licence. By the lex Julia et Papia Poppcea, a husband divorcing a wife for adultery might retain one-sixth of her dowry; for any smaller offence, only one-eighth. When a husband was guilty of adultery be had to repay the dowry at once; if the fault were less serious, in six months. Constantine allowed the wife to divorce the husband in the following cases:— 1, for murder; 2, for being a preparer of poison; 3, for violating tombs. Just causes for repudiation by the husband wore—1, adultery; 2, preparing poisons; 3, being a procuress. A wife divorcing her husband for other than the specified grounds forfeited the dowry, and might be" punished by deportation. Similarly a husband lost his interest in the dowry of his wife by an injurious divorce. Similar provisions are to be found in the legislation of Honorius anil TheodoruB (421 A.D.), of Theodosius and Valentinian (449 A.T>.) Justinian settled the grounds of divorce as follows: —The wife could divorce her husband—1, for conspiracy against the empire; 2, attempting her life; 3, attempting to induce her to commit adultery; 4, wrongfully accusing her of adultery; 5, taking a paramour to his house or frequenting any other house in the same town with a aramour. On a divorce for these reasons a wife recovered er dowry, and obtained the husband's portion as well. If she divorced for other reasons she forfeited her dowry, and could not marry for five years, as in the legislation of Theodosius and Valentiuian. So a husband might justly divorce his wife for—1, concealment of plots against the empire; 2, adultery; 3, attempting her husband's life, or concealing plots against him ; 4, going to baths or banquets with other men; 6, remaining from home against her husband's wish ; 6, going to circus, theatre, or amphitheatre against his wish. In such cases the husband retains the dowry for life, or if he has no children absolutely. In other cases penalties as fixed by previous legislation of Theodosius and Valentinian apply. The grounds for divorce specified in these various enactments axe an interesting commentary on contemporary manners.