Contrivances for the purpose of enabling persons to descend and to remain below the surface of the water for a great length of time, to perform various operations, such as examining the foundations of bridges, blasting rocks, recovering treasure from sunken vessels, etc. The apparatus most commonly employed for this purpose is the diving bell, the invention of which is generally attributed to Dr. Halley. These machines have been variously modified, but are now ordinarily made in the form of an oblong chest, open at the bottom. It is made of cast iron of considerable thickness, and has several strong convex lenses set in the upper side or roof of the bell, to admit light to the persons within. It is suspended by chains, hooked to strong staples in the upper part of the bell, and which chains are passed round a windlass supported upon the sides of two lighters or barges, so that the 1x11 can be raised or lowered, upon signals to that effect from the persons within the bell, who are supplied with fresh air by means of a flexible hose passing under the lower edge of the bell, and connected with a set of forcing pumps placed in the barges.

The air which has been respired being heated, rises to the upper part of the bell, whence it escapes by a cock An apparatus has also been devised to enable a person to quit the diving bell, and remove to a considerable distance when requisite, and still to receive the necessary supply of air. It consists of a copper helmet, fitting water-tight to the shoulders of the wearer, and furnished with a mouth piece, to which is attached a flexible hose, reaching under the bell; but recently a patent has been obtained by Mr. W. H. James for a somewhat similar apparatus, by which a diver can carry on the necessary operations independently of a diving bell. The diver is attired with a portable vessel (placed around and adapted to the figure of his body,) which is filled with condensed atmospheric air; and by means of a simple arrangement of pipes, and judiciously constructed valves, he is enabled to supply himself with fresh air for respiration during the time he is under water. In the two accompanying figures, the letters in each refer to the same parts.

Fig. 1 gives a front view of the diver fully equipped in the apparatus, and supposed to be engaged in recovering from the deep a variety of sunken property; and Fig.2 gives a section on a larger scale, for the better understanding of the several parts. A is the vessel to contain the condensed air, which is to be filled by means of a condensing air-pump; it consists of a series of strong metallic tubes, or of one continuous tube, coiled elliptically round the body, and connected together by bands, to which straps are attached to secure it in its position. At a is a valve opening inwards, through which the air is to be forced by means of a condensing pump, until it has acquired the required degree of density, which will, of course, be determined by the time it is proposed for the diver to remain under water. B is a tube made of caoutchouc (or Indian rubber), for conveying the air into the water-tight helmet C, by means of a valve so contrived as to be completely under the control of the diver.

This helmet may be made of any water-tight material, but thin copper is recommended; it is provided with a strong plate of glass in front, to enable the diver to see surrounding objects Inside the helmet is a flexible tube c, with a mouth-piece at the end, which comes near to the mouth of the diver; through this the air is discharged from his lungs, and passes out through a valve d in the top of the helmet. At the lower part of the helmet, and round the breast, back, and shoulders, a water-proof garment e is attached, fitting closely round the body of the wearer, and made fast by elastic bandages f. To secure the diver from being inconvenienced by the pressure of the air within the helmet becoming too great, a safety-valve is introduced. Notwithstanding the weight of the apparatus (amounting perhaps to 50 lbs.), the density of the water at great depths would render the body of the diver too buoyant to keep on his legs and execute his work; in these cases it will become necessary to attach weights to his person, capable of being easily removed, if desired; some are therefore shown in the figures as attached to the apparatus; these, however, it may be desirable to place lower down his person, about his legs and feet.

The same apparatus (divested of the weights) may be employed with safety and advantage in mines and other places filled with deleterious gases.

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