Diving is the art of descending under water to considerable depths, and of remaining there some time, so as to be able to collect valuable articles, such as pearls, sponges, coral, and other submarine productions, from the bottom of the sea or rivers, or property from the sunken wrecks of vessels.

This art is one of great utility, but is attended with peculiar difficulties, owing to the very limited powers which man naturally possesses within the liquid element. On the surface he may no doubt continue a long time floating or swimming; and hence arises the wonderful art of navigation. But the moment he plunges within the mass he is cut off from the vital air, and life is speedily extinguished. The necessity of a constant supply of air for the support of life is shown by simply attempting to withhold it by shutting the mouth and nostrils. No one can continue holding in the breath in this manner much longer than a minute or a minute and a half. If we begin to hold after having made an expiration, we cannot do it longer than a quarter of a minute; but if we take a large inspiration, and fill the lungs, this supply is found to last longer; so that we can readily hold breath a full minute, and, with practice and great exertion, some may even continue to do so two minutes. Now this is exactly what the diver must do to remain alive under water; and accordingly we find that in general a person cannot remain longer than half a minute without the danger of suffocation, and the most practised divers not above two minutes; such is the necessity for fresh air continually present in the lungs.

The nature and cause of this necessity for air has been illustrated by the discoveries of modern chemistry. These have proved that it arises from a certain chemical action which the atmosphere exerts on the blood as it passes through the lungs, and which is continually going on, and cannot for a moment be intermitted. The nature of this action is not yet exactly understood, but the object of it undoubtedly is to purify the blood, as it becomes vitiated by circulating through the system. For this purpose, the air inspired into the lungs, and coming there into contact with the blood, imparts to it its oxygen, a small portion of which is supposed to combine with the blood, and to give it renewed vigour; but by far the greater portion combines with the carbonaceous matter of the blood, and carries off this impurity in the shape of carbonic acid at each expiration. This is proved by a very simple experiment. Let a person, for instance, respire by means of a pipe into a bag or bladder of air of the capacity of a gallon or more; he will breathe freely enough at first, but in a very short time with great difficulty, and at last will feel the sense of suffocation the same as in holding the breath in the ordinary way. If the air in the bladder be now examined, it will be found to have entirely changed its nature; it will no longer support the flame of a candle, but extinguish it the moment it is immersed, thus showing the loss of oxygen. Hence arises that sense of closeness and oppression which is felt in crowded assemblies, where, as generally happens, the ventilation is imperfect. The same air being breathed again and again, becomes unfit for respiration, and produces those unpleasant sensations which are usually felt.

A very curious and interesting set of experiments on respiration were made by Messrs Allen and Pepys, and narrated in the Philosophical Transactions for 1808. The following bears particularly on the present subject.

"Three hundred cubic inches of common air contained in one of the mercurial gasometers were respired. In less than a minute it became necessary to take deeper and deeper inspirations, and at last the efforts were so violent that the glass was in danger of being broken. A great sense of oppression and suffocation was now felt in the chest, vision became indistinct, and after the second minute the attention of the operator seemed to be withdrawn from surrounding objects, and fixed upon the experiment. A buzzing in the ears took place, as in breathing nitrous oxide; and after the third minute there was left only sufficient recollection to close the gasometer after an expiration; after which he became insensible, having made thirty-five inspirations. The expired air contained ten per cent. of carbonic acid, four of oxygen, and eighty-six of azote."

With 300 cubic inches of air, then, in the gasometer, the quantity operator began to be insensible in the space of two minutes; and if we suppose that the lungs, which were in their natural state at the commencement of the operation, contained 100 cubic inches of atmospheric air, then it would follow that 200 inches each minute would be necessary to support life, so as to remain at the same time quite sensible." Hence, supposing the lungs to contain, with a full inspiration, 350 cubic inches, which is a pretty large allowance, it would follow that a man might hold breath, or remain under water, a minute and a quarter, which agrees very well with what occurs in ordinary cases. But a very curious fact has been mentioned to us by Professor Faraday of the Royal Institution, London, and was first noticed to him by a gentleman connected with the Asiatic Society, a fact which may often be of great importance, not only in diving, but in cases of fire, and of accidents in brewers' vats, &c. The lungs in their natural state are charged with a large quantity of impure air, being a portion of the carbonic acid gas which is formed during respiration, but after each expiration still remains lodging among the involved passages of the pulmonary vessels. In proof of this, it is only necessary to breathe by a small pipe, or roll of paper, into a common water bottle, throwing away the first portion of the expiration, and propelling the last into the lower parts of the vessel. Then insert this over a taper, and it will be instantly extinguished. Now, by breathing hard for a short time, as one does after taking any violent exercise, this impure air is expelled, and its place is filled up with atmospheric air. The consequence is, that if we then take a full inspiration, the breath can easily be held for two minutes. This experiment any one can make. On trying it in the ordinary way, we could hold breath for about three quarters of a minute, but this with great difficulty. We then made eight to ten forced respirations, and on closing the mouth and nostrils felt no inconvenience even on the first trial, till after a minute and a half, but continued, however, to the end of the second minute. The knowledge of this fact might be of essential use in diving, and, we have no doubt, might often be the means of saving life; for if in the ordinary way we can only remain a single minute under water, of what importance is it to be capable of doubling the time? A single minute in these cases must be invaluable. Whether the professed divers are aware of this circumstance or not, we do not know; but it is probable, at any rate, that in many cases the exertion induced by swimming may have the effect of clearing the lungs. Another curious fact illustrative of the same principles occurred to Mr Brunell in descending to examine the breach which the river had made in the Tunnel under the Thames. Having lower- ed the diving-bell nearly thirty feet to the mouth of the opening; this was found too narrow to admit the bell, so that no further observation could be made on the state of the Shield and other works, which were perhaps eight or ten feet deeper. Brunell, therefore, laying hold of the end of a rope, left the bell, and dived himself down the opening; his companion in the bell being alarmed at the length of his stay, now about two minutes, gave the signal for pulling up; and the diver, unprepared for the signal, had hardly time to catch hold of the rope which he had let go, and was surprised on coming up to find that so much time had elapsed. On descending again, he found that he could with ease remain fully two minutes under water. The reason evidently was, that the atmosphere in the bell being condensed by a column of water nearly thirty feet in height, contained nearly double the quantity of air in the same bulk, and thus nearly a double supply in the lungs.

Besides the difficulty of holding the breath, another arises in diving, particularly at considerable depths, from the external pressure of the fluid on the chest, and on every cavity of the body. On the chest this tends to compress it together, and to expel the air out of it, and thus increases greatly the difficulty of holding the breath. At each foot of descent this pressure will increase upwards of sixty lbs. on every square foot of the body; and if we suppose the chest to expose half a square foot, we have, at the depth of fifteen feet, a force equal to the weight of 450 lbs. loading the chest, and tending to propel the included air. A very great muscular exertion, therefore, will evidently be required to resist this enormous strain; nor is it practicable, by any breastplate or other contrivance, to defend the chest from this pressure, as this, to do any good, would require to be so large, and of such strength, as greatly to obstruct the free motions of the diver. It is this pressure of the deep water, and the violent exertion necessary to overcome it, that causes, in divers who go down frequently, the eyes to become blood-shot, and brings on a spitting of blood.

The art of diving having always in it, and particularly during the infancy of science, something of the marvellous, the most extraordinary accounts have been given, by different authors, of the feats of some of the most noted divers. The most singular of these is that given by Kircher, of the Sicilian diver Nicola Pesce, taken, as he states, from the archives of the kings of Sicily.

"In the times of Frederick king of Sicily," says Kircher, "there lived a celebrated diver, whose name was Nicholas, and who, from his amazing skill in swimming, and his perseverance under water, was surnamed the fish. This man had from his infancy been used to the sea, and earned his scanty subsistence by diving for corals and oysters, which he sold to the villagers on shore. His long acquaintance with the sea at last brought it to be almost his natural element. He was frequently known to spend five days in the midst of the waves, without any other provisions than the fish which he caught there, and ate raw. He often swam over from Sicily into Calabria, a tempestuous and dangerous passage, carrying letters from the king. He was frequently known to swim among the gulfs of the Lipari islands, noway apprehensive of danger.

"Some mariners out at sea one day observed something at some distance from them, which they regarded as a sea monster; but upon its approach it was known to be Nicholas, whom they took into their ship. When they asked him whither he was going in so stormy and rough a sea, and at such a distance from land, he showed them a packet of letters which he was carrying to one of the towns of Italy, exactly done up in a leather bag, in such a manner as that they could not be wetted by the sea. He kept them thus company for some time in their voyage, conversing and asking questions; and after eating a hearty meal with them, he took his leave, and, jumping into the sea, pursued his voyage alone.

"In order to aid these powers of enduring in the deep, nature seemed to have assisted him in a very extraordinary manner; for the spaces between his fingers and toes were webbed, as in a goose; and his chest became so very capacious that he could take in, at one inspiration, as much breath as would serve him for a whole day.

"The account of so extraordinary a person did not fail to reach the king himself, who commanded Nicholas to be brought before him. It was no easy matter to find Nicholas, who generally spent his time in the solitudes of the deep; but at last, after much searching, he was found and brought before his majesty. The curiosity of this monarch had been long excited by the accounts he had heard of the bottom of the Gulf of Charibdis; he now therefore conceived that it would be a proper opportunity to have more certain information. He therefore commanded our poor diver to examine the bottom of this dreadful whirlpool, and, as an incitement to his obedience, he ordered a golden cup to be flung into it. Nicholas was not insensible of the danger to which he was exposed, dangers best known only to himself, and therefore he presumed to remonstrate; but the hopes of the reward, the desire of pleasing the king, and the pleasure of showing his skill, at last prevailed. He instantly jumped into the gulf, and was instantly swallowed up in its bosom. He continued for three quarters of an hour below, during which time the king and his attendants remained on shore anxious for his fate; but he at last appeared, holding the cup in triumph in one hand, and making his way good among the waves with the other. It may be supposed he was received with applause when he came on shore; the cup was made the reward of his adventure; the king ordered him to be taken proper care of; and, as he was somewhat fatigued and debilitated by his labour, after a hearty meal he was put to bed, and permitted to refresh himself by sleeping."

The diver then, according to the account, gave a narrative of the wonders he had seen, which so excited the curiosity of the monarch, that he again tempted the diver to a second and fatal descent. After plunging into the whirlpool, he was never more heard of.

But to return to more authentic statements, these on Authentic the whole agree very well with the views already stated. Among the pearl divers at Ceylon and other parts of the East, instances have been known of a diver remaining six minutes under water; but these are very rare; the ordinary time seldom exceeds a minute, and sometimes it is a minute and a half, or two minutes. There are generally ten divers in each of the boats belonging to the fishery; five descend into the sea at a time, and the other five remain above to recruit their strength. In order to hasten their descent, a large stone is used, with a rope attached to it, which the diver seizes with the toes of his right foot, while he grasps a bag of net-work with those of the left. He then seizes another rope with his right hand, and keeping his nostrils shut with his left, plunges into the water, and soon reaches the bottom. Then hanging the net round his neck, he speedily collects the oysters, and resuming his former position, he makes a signal to those in the boat, and is immediately hauled up, and the stone which assisted his descent is pulled up afterwards.

The divers are all Indians, who are accustomed to this seemingly dangerous occupation from their infancy, and who fearlessly descend to considerable depths. They will frequently make from forty to fifty plunges in a day; but the exertion is so extremely violent, that in coming up they Diving.

Discharge water, and sometimes blood, from their mouths, ears, and nostrils. Some of them rub their bodies with oil, and stuff their ears to prevent the water from entering; but the greater part use no precautions whatever. They take no food while in the boats, nor till they return on shore and have bathed themselves in fresh water. The only danger to which they are exposed is from meeting, while at the bottom, with the ground-shark, which is a common inhabitant of those seas, and of which the divers are under dreadful apprehensions; some of them indeed are so expert as to avoid this enemy, even when they remain under water for a considerable time; but the uncertainty of escaping is so great, that, in order to avert the danger, they consult, before they begin, their priests or conjurers, in whom they place implicit confidence.

Dr. Halley relates, as a remarkable circumstance, that he observed a Florida Indian diver at Bermudas, who could remain two minutes under water. He states, that the divers for sponges in the Archipelago are in the practice of taking down in their mouths a piece of sponge dipped in oil, and by this are enabled to dive longer than others who have none. It is not easy to conceive how this can assist the diver's breathing; for the introduction of any foreign substance into the mouth must necessarily diminish the quantity of air he can take down. But it has been lately said that the real object of taking oil in their mouth is to calm those small waves on the surface of the sea which prevent the light being so steadily transmitted to the bottom as is necessary to enable the divers to find the small objects they search for without delay. By ejecting a little oil from their mouths, it rises to the surface, and spreading upon it, calms the waves in a most remarkable manner, and gives a brilliant light at the bottom.

Many nations, and particularly the savages in the South Sea and other islands, are remarkable for the expertness they acquire by habit in diving and moving about in the water. Being accustomed to it from their infancy, the element becomes so natural to them that they seem to have the use of all their faculties in the water the same as on the dry land. According to the accounts of voyagers, they are such expert divers, that when a nail or other piece of iron was thrown overboard, they would instantly jump into the sea after it, and never fail to recover it. On one occasion a smith's anvil is said to have fallen overboard. Not being able to bring this up, the islanders notwithstanding contrived to bring it ashore, by descending a great many times to the bottom, and rolling it over and over till it reached the land.

Such is the length to which diving has been carried by the natural powers of the body alone. But from the curious and difficult nature of the object, and the many important purposes to which the art might be employed, ingenious men were led to the invention of various contrivances for the use of the diver, which have greatly extended his powers and the usefulness of the art. A multitude of these contrivances of different descriptions have been brought forward by mechanical projectors for the last two hundred years. They all resolve themselves into three different kinds.

1st. Water-tight armour or dresses for the body, so strong as to protect it from the external pressure of the fluid; and, along with this, the means of supplying the diver with fresh air, so as to enable him to remain any time under water.

2ndly. Water-tight vessels of metal for inclosing the diver, and of such capacity as to contain a supply of air for a limited period of perhaps half an hour or an hour or more, and giving him also the use of his hands and arms externally by a sort of flexible sleeves.

3rdly. The diving-bell, which, from its simplicity, safety, and perfect efficiency, has now almost entirely superseded every other, though there is no doubt that in many cases these may still be of considerable utility in subservience to the bell.

In regard to dresses or armour, a number of different Water-plans of this kind are detailed in Leopold's Theatrum machinarum hydraulicarum. At depths of twelve or fifteen feet these may often be of essential use; but beyond this they become inapplicable, owing to the great pressure on the limbs of the diver, which must either be exposed, or covered only with a flexible material, not to impede his motions; and in that case the pressure, acting on all sides like a ligature, is liable to obstruct the circulation of the blood in the limbs, and to drive it from these into those parts of the body within the armour, causing extreme pain. In any great depth, also, the necessary strength of the armour renders it unwieldy; and it is extremely difficult, if not impracticable, to fit it tightly on every part; while the smallest opening, by admitting water, may endanger the life of the diver.

One of the best of these contrivances is perhaps that Klingert's proposed by M. Klingert, and described in a pamphlet armour, published at Breslau in 1798. The harness or armour is made of strong tin-plate, in the form of a cylinder, with a round end to inclose the head and body, and, for the convenience of putting it on, is made in two parts, the head-piece or helmet, and the body. Besides this, there is a leather jacket, with short sleeves, and a pair of drawers of the same, which are made water-tight, buttoned on the metal part where they join, and made tight with brass hoops, going round the leather and the metal upon the outside. The chief peculiarity in this machine is the mode in which fresh air is supplied, and respiration effected. This is done by two distinct flexible pipes proceeding from the inside of the helmet to the surface of the water; the one is for inhaling the air, and terminates in an ivory mouth-piece, which the diver may embrace with his lips and inhale the air; the other enters the helmet at the same place, and opens merely into the inside of the machine, so as to allow the foul air to be discharged. The diver, therefore, draws in the fresh air by the mouth, and discharges it into the helmet by the nostrils; and from the interior of the machine it is propelled by the act of inspiration, the expansion of the chest contracting the space between it and the armour, and forcing out exactly as much air as is drawn in, keeping up always a due equilibrium. This is certainly a very ingenious arrangement; for, if there were no second pipe to discharge the air, the expansion of the chest would compress the air round the body of the diver, and, unless this were of large capacity, which would be inconvenient, would create a difficulty in the operation. The construction of the apparatus will be understood from the drawing, fig. 1, Plate CCV., which is a front view of the diver, and by the following description: A is the helmet-piece, fifteen inches in height, and the diameter adapted to the size of the body of the diver; BB is the lower part of the cylinder, of the same diameter, and of such a height as to meet the other at the dotted line C; ddc is the jacket, and ffe the drawers; these are attached to the cylinder by buttons, as seen; and a, c, bb are the three brass hoops fitted over each joint to make it water-tight; the hoops are made of brass-plate, with their ends turned up, and fitted with screws, by means of which they can be drawn very tight upon the leather. The cylinder has holes for the arms, one half in the upper piece and one half in the lower; and, when the jacket is fastened on, it binds the upper and lower parts of the cylinder together. It is fastened at the arms with brass screw hoops, dd, and the Diving drawers by similar ones at \( f \); \( k \) represent the breathing pipes, the first for drawing in the air, the second for discharging it; these are united to a little metal cylinder, which screws on the helmet at the aperture \( g \); this is shown more particularly at fig. 2, where a partition will be observed in the cylinder dividing the fresh air compartment from the other, the one terminating in the ivory mouth-piece \( t \), the other just entering the machine at \( t \).

\( W \) is a small reservoir at the lower part of the pipes, for condensing any air, or receiving what may penetrate through the pipes. To resist the external pressure of the water on the limbs, the leather drawers have a framing of iron within them, represented at fig. 3; this consists of a semicircular piece \( H \), also seen at \( H \), fig. 1, extending between the legs of the diver, and fastened to the lower extremity of the cylinder at the front and back; also two irons outside the thighs, which are jointed to the cylinder, and extend down to \( f \), where they are attached to a hoop surrounding the thigh; there is another hoop for each thigh farther up at \( q \); these hoops are farther connected by irons, which at the upper end are fitted to slide upon the semicircular hoop, as at \( t \); and by this means, though the frame-work is very strong, the diver is at liberty to walk. \( q \) are weights hooked on the cylinder, to keep the diver down. \( P \) is a small pump for discharging any leakage water which may penetrate through the joints.

When the different parts of the machine have been fitted to the body of the diver, and the proper weights are attached, he enters the water till it rises as high as his eyes, while the end of the pipe is held by an assistant above the surface; and if he finds that he can breathe freely, and no water is forced into the pipe, he may venture to go deeper; and, stopping for some time, to ascertain whether respiration be not inconvenient from the want of fresh air, he may advance to still greater depths, while he makes the proper signals by means of the rope which is secured to one of his arms, or by speaking through the pipe. By this kind of exercise for some time, the diver acquires confidence and ease for conducting the necessary operations. When he is desirous of ascending he has only to unhook the weights attached to the apparatus, or to fix them to a rope let down for the purpose, that they may not be lost, and as he is then lighter than the same bulk of water, he rises to the surface.

By following these directions, any one may be able to use the apparatus, and dive to moderate depths, in a very short time. In one of the trials upon the Oder, near Breslau, the diver was a huntsman taught by the author; the water was of considerable depth, and the current strong, and there were a great number of spectators present. He sawed through the trunk of a tree which was lying at the bottom; he showed also that he could have fastened sunk bodies to a rope in order to be drawn up, and that in case any impediment should prevent the use of the saw, the trunks of trees might be hewed to pieces by an axe. On the whole, this apparatus, or one similar, might certainly be of great use in many cases, particularly in hydraulic works, where the diving-bell and the machinery connected with it might not be attainable. The water-proof cloth of Mackintosh might also be substituted with good effect for the leather.

Another mode of supplying air to the diving apparatus has been adopted in some cases. This consists in forcing the fresh air into the machine by a bellows or pump, till its elastic force is equal to the pressure of the water. The foul air may in this case be suffered to escape into the water through a valve, or may be conducted to the surface by a pipe. Of this kind is the apparatus contrived by Mr Tonkin, and employed for some time in raising parts of the wreck of the Abergavenny East India ship, which was unfortunately lost off Weymouth in 1804. It consisted of a body of copper with iron boots, put together and jointed in the manner of coats of mail; the whole is then covered with leather, and afterwards with canvas to distinguish it under water. The arms are made of strong water-proof leather; and the place for sight is about eight inches diameter, glazed over with a plate of glass an inch thick. The diver is sunk in this machine by means of weights, fastened equatorially round the waist of it; and he is suspended by a rope, by means of which his situation is changed at pleasure. A flexible air-tube communicates with an air-vessel in the boat above. Through this tube the diver gives his instructions and obtains his supply of fresh air. This machine was used with very good effect in a depth of water of near seven fathoms, and enabled the diver to direct the operations of several curious machines, such as saws for clearing away the ship's decks, and making sufficient openings to give him access to the treasure below, as well as tongs, &c., for taking up the heavy goods by tackle in the vessel above.

In regard to the second kind of diving machines, that Borelli's proposed by Borelli is only curious as showing the low state of physical knowledge in his time. He proposed to have a copper vessel, or vesica as he terms it, about two feet diameter, to contain the diver's head, and to be fixed to a habit of goat skin for the body. Within the vessel there were pipes contrived to produce a circulation of air, by which Borelli supposed that the objections to other diving machines from the want of air would be obviated; "the moisture," as he says, "by which it is clogged in respiration, and by which it is rendered unfit for the same use again, being taken from it by its circulation through the pipes, to the sides of which it would adhere, and leave the air as free as before." It also contained an air-pump, by means of which the diver could raise or lower the apparatus, by condensing or rarefying the air, on the principle of the air-bladder of fishes.

Mr Martin, in his Philosophia Britannica, mentions an apparatus contrived by an Englishman, consisting of strong diving leather, so prepared that no air could pass through. It fitted to his arms and legs, and had a glass window placed in the fore part of it. When dressed in this apparatus, which was large enough to contain half a hogshead of air, he could walk on the ground at the bottom of the sea, and enter the cabin of a sunk ship to take out the goods. The inventor is said to have himself used this machine very extensively in recovering wrecks, and with such success as to have acquired considerable property by it. We are not informed of the depths to which he descended.

Mr Klingert, the inventor of the water armour, also contrived a diving chest, of the form of a hollow cylinder, to be used along with it. This contained fifty-eight cubic feet of air, which, he estimated, would last two hours. It was suspended from a boat, but could be raised and depressed independently of this by a pump compressing or dilating the included air. Thus the ballast is so adapted to the size of the machine, as to make it sink so far that only a cubic foot of it remains above water. In this state an additional weight of a hundred pounds will depress it below the surface, or make it sink to the bottom. The effect of adding extra weights is produced by diminishing the volume of contained air, by condensing it into a smaller space. To accomplish this, a large cylinder is applied in the bottom of the vessel, and provided with a piston, which, by a rack and pinion, can be moved from one end of the cylinder to the other, when the diver turns a handle, coming through the side of the machine, and communicating motion by a worm and wheel, to the pinion of the rack before mentioned. The lower end of the cylinder is open to the water, and the upper end opens