16 



DIVING BELL. 



MftagBcD- therefore, the means of coming up nt any time ; whcre- 

 '*"".""""' as in Mr * Ml. they can only take the oppor- 



tunity of a cask of air b< I.iwn, to introduce M> 



much of it into the upper Ml as will carry them up ; 

 and even this would be very dangerous to attempt, for u 

 which the ingenious inventor seems to have 



M 



Form of 



iri- niv.- 

 bell. 



Pumps. 



overlooked. Thus si:p|M>Ni-, when at the lx>ttom in (ilj 

 feet water, the great Ml is quite full of air at a pres- 

 sure of three atmospheres. Now if the small Ml is 

 half filled with air, to give the buoyancy required to 

 raise the Ml, it will a-sceiul, but at every foot of rise 

 tl.i pressure diminishes, and the air expands itself. That 

 in the great bell escapes, by bubbling out under the 

 bottom ; but in the upper one it continues to displace 

 more and more water, giving the bell an increasing 

 power of ascent till at 33 feet depth, when it will have a 

 pressure of only two atmospheres. The small bell will 

 be quite full, thus giving to the bell a power of ascent 

 twice as great as it began with, and producing an acce- 

 lerated motion wh:.-h the divers would find it difficult 

 to controul ; for, though it might be done, by letting out 

 the air from the upper bell by degrees, it would be ha- 

 zardous, because it they once let out too much, so as 

 to destroy the power of ascent, the bell would sink, 

 and never have the means of rising again. 



On the proposed plan with air pumps, this could ne- 

 ver happen ; for, if the divers found themselves too buoy- 

 ant, they could by the pump return as much air into the 

 chamber as would restore the equilibrium. Lastly, In 

 Mr Spalding's, if they get any an- into the upper cham- 

 ber to give them a power of ascent, they depend altoge- 

 ther upon the exertions of the man who holds the ba- 

 lance weight rope to keep them down, and if this should 

 break, they rise with a dangerous velocity. 



This bell for diving to wrecks of ships, should be 

 made to contain two persons. Its most convenient 

 form will be that of the frustrum of an elliptical cone ; 

 its base to be 6 feet by 4 ; the top 3 feet fi inches by 2 

 feet 6 inches ; and 6 feet 6 inches in height. If it is to 

 have the air chamber formed by a partition in the top, 

 to receive the air condensed by the pumps. As this 

 vessel will require to be very strong, it would be \test 

 made of thiek sheet copper, and fixed in the top of the 

 bell against its crow n, being rather smaller than the bell, 

 and in the form of a hemisphere. It will leave a space 

 all round, of a similar form to tliat of the bottom of a 

 green glass bottle between it and the sides of the bell. 

 By this means the vessel will not obstruct the light which 

 t nters at the windows, made round in the side of the bell 

 at the top, or prevent it proceeding down to the divers. 

 This space round the air \ c-- 1 1 .<Ko receives the hot air 

 which has been breathed; and the cock to let it off is 

 in the very highest part. The pumps should have al- 

 most all the length of their barrels contained within the 

 copper vessel, and should have proper levers, with han- 

 dles, to work them, situated conveniently within the di- 

 ver's reach. As the bell requires to be loaded with a 

 great weight, the best plan of all, where expence is not 

 regarded, is 'to make the whole of cast iron, and then 

 its strength will be much greater, and without any dan- 

 ger of leakage. The chamber in the top may then be 

 cast in one piece with the crown. The windows should 

 be convex lenses of glass, such as are now used in ships 

 decks, being complete hemispheres on the outside, and 

 plains on the -ide which is within. They concentrate 

 the light from all directions, find throw it in the bell. 

 The bell should be painted white within to reflect the 

 light, and also on the outside, that it may be \isible to 

 those in the ship as long as possible when under water. 



To find die direction in which they would ho moved, the Diving Befl. 

 divers should have a compass hung up in tlie Ml. The S ~"V^ 1 ' 

 most convenient will IK> that kind, which capt.iini of Com l*"- 

 ships usually liave hung from the ceiling of their ca- 

 bins. The centre pin of the needle being fixed in the 

 glass of the IMIX, the card can l>e seen from beneath. It 

 will be satisfactory to the divers to know nt what depth 

 they arc from the surface ; and for this purpose a gauge, 

 represented in Fig. f>, should be fixed withinside the 

 bell. It is a glass tube a b, hermetically sealed at the 

 top, and at the bottom cemented into a metal tube b, PLATE 

 which turning at right angles, has a screw to fix it ' rxxxl - 

 into the side of the bell. To deft ml it from injury, the * **" 

 tube is bedded in a piece of board, which I. ons 



and feet marked upon it, to shew how high the water 

 ri-es in it; for it is by this that the depth or pressure 

 is shewn, because the water entering freely into the 

 lower end of the tube, condenses the air in the glass 

 tube into a space proportional to the intensity of the 

 pre-ssure. Thus at 33 feet deep, the water will rise up 

 half way to the top of the tube ; at 66 feet two-third* ; 

 at 99 three-fourths. It is, therefore, upon this principle 

 that the divisions are m.-v.lc ; or if any doubt is enter- 

 tained as to the glass being perfectly cylindrical, it may 

 be done by the experiment of letting down the bell to a 

 known depth, and tliere marking how high the water 

 The figure* 1, sJ, ;>, Sec. on the other side, op- 

 posite the several figures 33, 36, 99, &c. shew the com- 

 pression of the air at those depths to be equal to 1,2, 

 or 3 atmospheres ; or what is the same thing, that the 

 air in the tube or in the Ml is condensed into one-half, 

 one-third, &c. of the. space it occupied above. After 

 all, this instrument is rather a matter of curiosity than 

 utility, because should it be ever so accurately divided, 

 the variations of the atmosphere will render it untrue ; 

 for if the air, with which the tube is filled before the 

 descent, has a greater or less density, (as the barome- 

 ter shews it has,) it will take more or less tlian 33 feet 

 of water (the weight of which always continues the 

 same) to condense the air into half the space: hence 

 the scale will constantly vary. 



The tackle proposed for suspending and managing Suspension 

 the bell is as follows : If it is to be used at sea, it may be f r 1 > u 

 hung from the yard-arm of any ship which carries a 

 square mainsail. The bell rope may pass through a 

 block at the extremity of the yard ; then being led 

 through another block at the slings or middle of the 

 yard, so as to come down clo-e to the mast, it may be 

 conducted by a match block on the deck, for the men 

 to haul it by hand, or by the ship's windlass, though 

 the capstan will be better if she has one. If there is a 

 stream, the ship should be moved by the head with two 

 cables at an angle, so that by taking up one, and giving 

 out the other, she may be moved sidewise, to sweep the 

 bell along the ground to search for any thing ; or by 

 taking up or giving out both at once, she will be mo- 

 ved in an op]X)?ite direction, viz. ahead or astern. 

 When the place of the wreck is found, and it is only 

 requisite to move it a few feet in the latter direction, it 

 may be very conveniently done by bracing the yard, I>y a ship's 

 to carry it fore or aft by the same braces or tackles 

 which are used in the sailing of the ship ; and the bell 

 rope being conducted down from the yard close to the 

 ma.-.t, in the same manner as the topsail sheets are, it 

 will neither IK- taken up or let down at all by this mo- 

 tion of the yard-arm from which the bell is suspended. 

 It there is a steady and moderate breeze, the ship may 

 ride with one anchor, and shift her position by the sails 

 ami rudder to the required station. By their compass, 



