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weight of the water which compresses it; so being thus prepared, I'fitted them with tackle that at thirty-three feet deep the bell becomes proper to make them rise and fall alternately, half full of water, the pressure of the incumbent after the manner of two buckets in a well, which water being then equal to that of the atmosphere; was done with so much ease, that two men, with and at all other depths the space occupied by the less than half their strength, could perform all compressed air in the upper part of the bell will the labor required : and in their descent they be to the under part of its capacity filled with were directed by lines fastened to the under water as thirty-three feet to the surface of the edge of the bell, which passed through rings water in the bell below the common surface of on both sides the leathern hose in each barrel; it. One inconvenience that attends this con so that, sliding down by these lines, they came densed air is found in the ears, within which readily to the hand of a man who stood on the there are cavities which open only outwards, and stage on purpose to receive them, and to take up that by pores so small as not to give admission the ends of the hose into the bell. Through these even to the air itself, unless they be dilated and hose, as soon as their ends came above the surdistended by a considerable force. Hence, on face of the water in the barrels, all the air that the first descent of the bell, a pressure begins to was included in the upper parts of them was be felt on the ear; which, by degrees, grows blown with great force into the bell; whilst the painful, till, the force overcoming the obstacle, water entered at the bung-holes below, and filled what constringes these pores yields to the pres- them: and as soon as the air of one barrel had sure, and, letting condensed air slip in, ease pre- been thus received, upon a signal given, that sently ensues. The bell descending lower, the was drawn up, and at the same time the other pain is renewed, and again eased in the same descended; and, by an alternate succession, fur
But the greatest inconvenience of this nished air so quick, and in so great plenty, that engine is, that the water entering it, contracts the I myself have been one of five who have been bulk of air into so small a compass, that it soon together at the bottom in nine or ten fathom heats and becomes unfit for respiration, so that water, for above an hour and a half at a time, there is a necessity for its being drawn up to re- without any ill consequence: and I might have cruit it; besides the uncomfortable situation of continued there as long as I pleased, for any the diver almost covered with water.
thing that appeared to the contrary. Besides, To obviate the difficulties of the foregoing the whole cavity of the bell was kept entirely kind of diving bell, Dr. Halley contrived further free from water, so that I sat on a bench which apparatus, whereby not only to recruit and re was diametrically placed near the bottom, wholly fresh the air from time to time, but also to keep dressed, with all my clothes on. I only observed the water wholly out of it at any depth. The that it was necessary to be let down gradually manner in which this was effected, he relates in at first, as about twelve feet at a time, and then the following words :-—' The bell I made use of to stop and drive out the water that entered, by was of wood, containing about sixty cubic feet receiving three or four barrels of fresh air before in its concavity, and was of the form of a trun- I descended further. But being arrived at the cated cone, whose diameter at the top was three depth designed, I then let out as much of the feet and at the bottom five. This I coated with hot air that had been breathed, as each barrel lead so heavy that it would sink empty; and I would replenish with cool, by means of the cock distributed the weight so about its bottom, that at the top of the bell; through whose aperture, it would go down in a perpendicular direction, though very small, the air would rush with so and no other. In the top i fixed a strong but much violence, as to make the surface of the sea clear glass, as a window, to let in the light from boil, and to cover it with a white foam, notwithabove, and likewise a cock to iet out the hot air standing the weight of the water over us. Thus that had been breathed ; and below, about a yard I found that I could do any thing that required under the bell, I plared a stage which hung by to be done just under us; and that, by taking three ropes, each of which was charged with off the stage, I could, for a space as wide as the about 100 weight to keep it steady. This ma circuit of the bell, lay the bottom of the sea so chine I suspended from the mast of a ship by far dry as not to be overshoes thereon. And, by a sprit, which was sufficiently secured by stays the glass window, so much light was transmitto the mast head, and was directed by braces to ted, that when the sea was clear, and especially capry it overboard clear of the ship's side, and to when the sun shone, I could see perfectly well bring it again within board as occasion required. to write or read; much more to fasten or lay To supply air when under water, I caused a hold on any thing under us that was to be taken couple of barrels, of about thirty-six gallons each, up. And, by the return of the air barrels, I to be cased with lead, so as to sink empty, each often sent up orders, written with an iron pen of them having a bung-hole in its lowest part to on small plates of lead, directing how to move let in the water, as the air in them condensed on us from place to place, as occasion required. their descent; and to let it out again when they At other times, when the water was troubled and were drawn up full from below. And to a hole thick, it would be as dark as night below; but in the uppermost part of these barrels I fixed a in such cases I have been able to keep a candle leathern trunk or nuse, well liquored with bees' burning in the bell as long as I pleased, notwithwax and oil, and long enough to fall below the standing the great expense of air necessary to bung-hole, being kept down by a weight ap- maintain flame. By an additional contrivance, pended : so that the air in the upper part of the I have found it not impracticable for a diver to barrels could not escape unless the lower ends of go out of an engine to a good distance from it, these hose were first lifted up. The air-barrels the air being conveyed to him with a continued
out very slowly, or the bell will rise to the top was affixed to the canister, long enough to reach with so great velocity, that the divers will be in above the surface of the water. When all was danger of being shaken out of their seats. But, prepared, the bell was drawn up out of the way, by following these directions, every possible acci- and a nail or other small piece of iron heated red dent may be prevented, and people may descend hot, was dropped into the tin pipe, thereby to to great depths without the least apprehension of descend to the powder. danger. The bell also becomes so easily manage As the diving bell is, however, in any stage of able in the water, that it may be conducted from improvement, necessarily very large and unone place to another by a small boat with the wieldy, several attempts have been made to engreatest ease, and with perfect safety to those case a man sufficiently to enable him to breathe who are in it. Instead of wooden seats used by and bear the pressure of the water. Among Dr. Halley, Mr. Spalding made use of ropes these the most successful is that of Klingert of suspended by hooks b, b,b; and, on these ropes, Breslau, which is made of strong tin plate, in the the divers may sit without any inconvenience. form of a cylinder, which goes over the diver's KK are two windows made of thick strong glass, head, and which consists of two parts, that he for admitting light to the divers. N represents may conveniently thrust his arms through it and an air-cask with its tackle, and OC P the flexible put it on; also a jacket with short sleeves, and pipe through which the air is admitted to the drawers of strong leather. All these being waterbell. In the ascent and descent of this cask, the tight, and closely jointed round the body of the pipe is kept down by a small weight appended, diver, secure every part of him, but his arms and as in Dr. Halley's machine. R is a small cock legs, from the pressure of the water, which, at by which the hot air is discharged as often as it the depth of twenty feet, will occasion po inconbecomes troublesome.
venience to these parts. Plate, Diving BELLS, A considerable modern improvement is that &c., fig. 4, represents the diver covered with the of supplying air to a diving-bell, by means of a harness and drawers. Figs. 5 and 6 are represyringe or pump, which forces the air down in sentations of the cylinder, the diameter of which a continual stream into the bell, whence it es- is equal to the breadth of a man at the top of the capes from beneath the lower edges of the bell, hipbone. It is fifteen inches in height, has a or from a waste pipe, as fast as it is supplied. In globular top, and is made of the strongest tin this way the air is kept very pure, and the plate. In the inside of the cylinder, at a, is a people in the bell have no kind of trouble to strong broad iron hoop, to enable it to withstand obtain a supply. Mr. Smeaton was the first becter the pressure' of the water; and in the inwho put in practice the method to which we side of the top there are two pieces of a strong allude, though it had been frequently proposed hoop of the same kind, placed over each other in by other inventors. His first attempt was in the form of a cross at b; a strong ring of brass 1786, in shallow water, the bell being only in- wire is soldered upon the outside at c, that the tended to enable workmen to examine and re- jacket may be fastened to it with an elastic bao. pair the foundations of a bridge at Hexham, in dage, to prevent it from slipping downwards; at Northumberland.
dd are the upper halves of the apertures for the Mr. Smeaton, a few years afterwards, con arms; and e, e, are holes to afford light, and into structed another bell upon the same principle, for which the eye-glasses are screwed: f is the openthe works at Ramsgate harbour. It was used to ing into which the mouth-piece of the breathingraise up large stones, which had formerly been pipe is screwed, and g is an aperture for looking thrown into the sea around the base of the pier. through, as well as for the purpose of breathing
The bell was made of cast iron, of sufficient when out of the water, and which, by means of weight to sink without any extra ballast. In the cover h suspended from it, can be screwed the top were lenses for the admission of light, and up before the diver enters the water. a strong shackle for the chain by which the bell The lower part of the cylinder, which is also was suspended. A strong leathern pipe was con- fifteen inches in height, is strengthened at i and nected with the top of the bell, to convey air into k by iron hoops on the inside, in the same manit from an air-pump placed either in a boat or on ner as the former. To the lower hoop k are the shore.
soldered four small rings, to which are fastened This kind of diving-bell has since been ap- strong leather straps, three inches in breadth, that plied to the purposes of building foundations of can be buckled across over the shoulder, and masonry in deep water, under the direction of support the whole machine; l, l, are the under the late Mr. Rennie, who constructed machinery halves of the apertures for the arms; m is also a to move the bell under water in any direction, ring of brass wire soldered to the cylinder, which and which acts with such facility, that the masons serves to keep fast the jacket when buckled on, in the bell make great despatch in laying the and to support the upper cylinder ddb, which stones. It was used in Plymouth Sound to slips over the under one; and on that account the sweep the bottom for old anchors, &c. At Houth, under one is a little smaller, so as to fit into the in Dublin county, Ireland, the foundations for upper one: there is also another such ring at n, in the pier were wholly laid by this machine. In order to prevent the drawers from falling down. many parts the rocky bottoni was too uneven to At o is a strong semicircular piece of iron, the work upon, and it was then necessary to blast it use of which is to prevent the drawers, when with powder. The divers bored the hole in the pressed by the water, from touching the under rock, and placed the powder in a tin cartridge, part of the body, otherwise the pressure, even at which was well secured in the hole, by running the depth of six feet, would be insupportable. in small fragments of stone. A small tin pipe As it is not possible to sew the leather so closely