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oversetting is removed ; for being lighter, without the balance-weight, than an equal bulk of water, it is evident that the bell willrise, as far as the length of the rope affixed to the balance-weightwill allow it. This weight, therefore, will serve as a kind of an-chor to keep the bell at any particular depth which the divers maythink necessary ; or by pulling it quite up, the descent may becontinued to the very bottom. By another very ingenious con-trivance, Mr. Spalding rendered it possible for the divers to raisethe bell, with all the weights appended to it, even to the surface,or to stop at any particular deptn, as they think proper ; and thusthey could still be sale, even though the rope designed for pullingup the bell was broke. For this purpose the bell is divided intotwo cavities, each ol which is made as tight as possible Justabove the second bottom EF, are small slits in the sides of thebell; througti which the water, entering as the bell descends, dis-places the air originally contained in this cavity, which Hies out atthe upper orifice of the cock GH. When this is done, the diversturn tne handle G, which stops the cock; so that if any more airwas to get into the cavitv AEFB, it could not longer be discharg-ed through the orifice H as before. When this cavitv is full ofwater, the bell sinks ; but when a considerable quantity of air isadmitted, it rises. If therefore the divers have a mind to raisethemselves, they turn the small cock g, by which a communica-tion is made between the upper and under cavities of the bell.The consequence ot this is, that a quantity of air immediately en-ters the upper cavity, forces out a quantity of the water containedin it, and thus renders the bell lighter by the whole weight of thewater which is displaced. Thus, if a certain quantity of air is ad-mitted into the upper cavity, the bell will descend very slowly;if a greater quantity, it will neither ascend nor descend, but re-main stationary ; and if a larger quantity of air is still admitted, itwill arise to the top. It is to be observed, however, that the airwhich is thus let out into the upper cavity must be immediatelysupplied from the air-barrel; from which the air is to be let outvery slowly, or the bell will rise to the top with so great velocity,that the divers will be in danger of being shaken out'of their seats.But, by following these directions, every possible accident maybe prevented, and people may descend to great depths withoutthe least apprehension of danger. The bell also becomes so easilymanageable in the water, that it may be conducted from one placeto another by a small boat with the greatest ease, and with perfectsafety to those who are in it. Instead of wooden seats used byDr Ilalley, Mr. Spalding made use of ropes suspended by hooksb b b, and on these ropes the divers may sit without any inconve-nience. I and K are two windows made of thick strong glass, foradmitting light to the divers. N represents an air-cask with itstackle, and OCP tne llexible pipe through which the air is admit-ted to the hell. In the ascent and descent of this cask, the pipe iskept down by a small weight appended, as in Dr. Ilalley’s ma-chine. H is a small cock by which the hot air is discharged asoften as it becomes troublesome. Fig. 4, gives a perspective viewof the whole diving apparatus. Two air-barrels are representedin this figure; but Mr. Spalding was of opinion, that one ca-pable of containing thirty gallons is sufficient for an ordinarymachine.

Diving Bladder, a machine invented by Borelli, and byhim preferred, though without any good reason, to the diving-bell. It is a globular vessel of brass or copper, about two-feet indiameter, which contains the diver’s head. It is fixed to a goat’sskin habit exactly fitted to his person. Within the vessel arepipes; by means of which a circulation of air is contrived; andthe person carries an air-pump by his side, by which he can makehimself heavier or lighter as fishes do, by contracting or dilatingtheir air-bladder. By these means he thought all the objections towhich oth r diving machines ace liable were entirely obviated,and partic ularly that of want of air; the air which had beenbreathed, being as lie imagined, deprived of its noxious qualitiesby circulating through the pipes. I liese advantages, however, itis evident, arc ody imaginary. The diver’s limbs, being defend-ed from the pressure oi the water only by a goat’s skin, would in-fallibly be crushed if he descended to any considerable depth ;and from tne di-coveries now made by Dr. Priestley and others,it is abundantly evident, that air, which is once rendered foul bybrea'fniir, an ot in any degree be restored by circulation throughP'pvs. cjoncerning the use of copper machines in general, Mr.Spalding has remarked, that when a person lias breathed in them

a few minutes, lie feels in his mouth a very disagreeable brassytaste, which continues all the time he remains in the vessel ; sothat, on this account, copper seems by no means an eligible ma-terial.

Diving Case, a large case of strong leather, perfectly water-proof, which may hold about half a hog-head of air; invented bya gentleman of Devonshire. It is so contrived, that, when heshuts himself up in tins case, he can walk at the bottom of the sea,and go into any part of a wrecked vessel, and deliver out thegoods. This method, we are told, he lias practised for manyyears, and has thus acquired a large fortune. It would be a consi-derable improvement on this machine to condense the air in it asmuch as possible before the diver descended; as he would thusbe furnished with an atmosphere endued with elasticity sufficientto resist the weight of the water, which otherwise would squeezehis case into much less room than it originally took up. The con-1 ensed air also would serve for respiration a much longer timethan that which is in its ordinary sta'e. A curious diving-machinecalled a submarine vessel, was invented by Mr. BushneU of Con-necticut ; and of which a description is given in the Transactionsof the American Philosophical Society. The external shape ofthe submarine vessel bore some resemblance to two upper tortoise-shells, of equal size, joined together; the place of entrance into thevessel being represented by the opening made by the swell of theshells, at the head of the animal. The inside was capable of con-taining the operator, and air sufficient to support him thirty mi-nutes without receiving Iresh air. At the bottom, opposite to theentrance, was tixed a quantity of lead tor ballast. At one edge,which was directly before the operator, who sat upright, was anoar for rowing forward or backward. At the other edge was arudder for steering. An aperture, at the bottom, with its valve,was designed to admit water, lor the purpose of descending ; andtwo brass torcing-pumps served to eject the water within, whennecessary for ascending. At the top there was likewise an oar forascending or descending, or continuing at any particular depth.A water-gauge, or barometer, determined the depth of descent, acompass directed the course, and a ventilator within supplied thevessel with fresh air, when on the surface. The entrance into thevessel was elliptical, and so small as barely to admit a person.This entrance was surrounded with a broad elliptical iron band,the lower edge of which was let into the wood of which the bodyof the vessel was made, in such a manner as to give its utmost sup-port to the body of the vessel against the pressure of the water.Above the upper edge of this iron band there was a brass crown,or cover, resembling a hat w ith its crown and brim, which shutwater-tight upon the iron Land : the crown was hung to the ironband with hinges, so as to turn over sideways when opened. Tomake it perfectly secure when shut, it might be screwed downupon the band by the operator, or by a person without. Therewere in the brass crown three round doors, one directly in front,and one on each side, large enough to put the hand through.When open they admitted fresh air; their shutters were groundperfectly tight into their places with emery, hung with hinges, and-ecured in their places when shut. There were likewise severalsmall glass windows in the crown for looking through, and for ad-mitting light in the day-time, with covers to secure them. Therewere two air-pipes in the crown. A ventilator within drew freshair through one of the air-pipes, and discharged it into the lowerpart of the vessel; the fresh air introduced by the ventilator ex-pelled the impure light air through the other air-pipe. Both air-pipes were so constructed, that they shut themselves whenever thewater rose near their tops, so that no water could enter throughthem, and opened themselves immediately after they rose abovethe water. The vessel was chiefly filled with lead fixed to itsbottom ; when this was sufficient, a quantity was placed witlvn,more or less, according to the weight of the operator; its ballastmade it so stitf, that there was no danger of oversetting. Thevessel with all its apoendages, and the operator, was sufficient tosettle it very low in the water. About two hundred pounds ot thelead, at the bottom for ballast, would be let down forty or fi;tyfeet below the vessel ; this enabled the operator to rise instantlyto the surface of the water, in case of accident. When the opera-tor would descend, he placed his fool on the top cf a brass valve,depressing it, by which lie opened a large ape. tore in the bottomof the vessel, through which the water entered at his pleasure ;when he had admitted a sufficient quantity, he ascended very gra-dually *.