DIVING BELL. 



keep the water wholly out of the ma- 

 chine at any depth. This bell was made 

 of wood, containing about sixty cubic feet 

 in its concavity, and was the form of a 

 truncated cone, whose diameter at the 

 top was three feet, and at the bottom 

 five. It was so loaded with lead, that it 

 woHld go down in a perpendicular direc- 

 tion and no other. In the top was a win- 

 dow to let in light, and likewise a cock 

 to let out the hot air that had been breath- 

 eel; and below, about a yard under the 

 bell, was a stage suspended by three 

 ropes, each of whidi was charged with 

 about one hundred weight, to keep it 

 steady. To supply air, the bell had a cou- 

 ple of barrels so cased with lead as to 

 sink when empty, each having a bung 

 hole in its lowest part, to let in the wa- 

 ter as the air in them condensed on their 

 descent, and to let it out again when they 

 were drawn up full from below. To a 

 hole in the uppermost part of these was 

 fixed a leathern trunk or hose, long 

 enough to fall below the bung-hole, and 

 kept down by a weight, in such a way 

 that the air in the upper part of the bar- 

 rels could not escape, unless the lower 

 ends of these hose were first lifted up. 

 These air barrels were made to rise and 

 fall like two buckets in a well ; by means 

 of these barrels fresh air was continually- 

 supplied from above, and it was done 

 with so much ease, that two men, with 

 less than half their strength, could per- 

 form all the labour required. By an ad- 

 ditional contrivance it was found practica- 

 ble for a diver to go out of the engine, 

 to some distance from it, the air being 

 conveyed to him in a continuable stream 

 by small flexible pipes. 



A great improvement in the diving 

 bell was made by the late Mr. Spalding, 

 of Edinburgh. This construction seems 

 designed to remedy some inconveniences 

 of Dr. Halley, which are very evident, 

 and of a very dangerous tendency; these 

 are, 1. by Dr. HaHey's constructions, the 

 sinking or rising of the bell depends on 

 the people who are at the surface of the 

 water : as the bell when in the water has 

 a very considerable weight, the raising it 

 not only requires a great deal of labour, 

 but there is a possibility of the rope 

 breaking, by which it is raised, and thus 

 every person in the bell would inevitably 

 perish : 2. As there are in many parts of 

 the sea, rocks which lay at a considera- 

 ble depth, the figure of which cannot pos- 

 sibly be perceived from above, there is 

 danger that some of their ragged promi- 

 nences may catch hold of one of the 

 edges of the bell in its descent, and thus 



VOL. IV. 



overset it, before any signal can be giver, 

 to those above, which would infallibly be 

 attended with the destruction of the peo- 

 ple in the bell; and as it must always be 

 unknown before trial what kind of a bot- 

 tom the sea has in any place, it is plain, 

 that, without some contrivance to obviate 

 this last danger, the descent in Dr. Hal- 

 ley's diving bell is not at all eligible. 



How these inconveniences are remedi- 

 ed by Mr. Spalding's new contrivance 

 will be easily understood from the follow- 

 ing descriptions : ABCD, fig. 3, represents 

 a section of the bell, which is made of 

 wood, ee are iron hooks, bv means of 

 which it is suspended by rope's QBF e and 

 QAE e and QS, as expressed in the figure; 

 cc are iron hooks, to which are appended 

 leaden weights, that keep the mouth of 

 the bell always parallel to the surface of 

 the water, whether the machine taken 

 altogether is lighter or heavier than an 

 equal bulk of water. By these weights 

 alone, however, the bell would not sink ; 

 another is therefore added, represented 

 at L, and which can be raised or lower- 

 ed at pleasure, by means of a rope pass- 

 ing over the pulley a, and fastened to the 

 sides of the bell M. As the bell de. 

 scends, this weight, called by Mr. Spald- 

 ing the balance weight, hangs down a 

 considerable way below the mouth of 

 the bell. In case the edges of the bell is 

 caught by any obstacle, the balance 

 weight is immediately lowered down, so 

 that it may rest upon the bottom ; by this 

 means the bell is lightened, so that all 

 danger of oversetting is removed; for, be- 

 ing lighter 'without the balance weight 

 than an equal bulk of water, it is evident 

 that the bell will rise as far as the length 

 of the rope affixed to the balance weight 

 will allow it. This weight therefore will 

 serve as a kind of anchor, to keep the bell 

 at any particular depth which the divers 

 may think necessary, or by pulling it 

 quite up, the descent may be continued 

 to" the very bottom. 



By another very ingenious contrivances 

 Mr. Spalding rendered it possible for 

 the clivers to raise the bell, with all the 

 weights appended to it, even to the sur- 

 face, or to stop at any particular depth, as 

 they think proper ; and thus they could 

 still be safe, even though the rope de- 

 signed for pulling up the bell was bro- 

 ken ; for this purpose the bell is divided 

 into two cavities, both of which are made 

 as tight as possible ; just above the se- 

 cond bottom, EF, are small slits on the 

 sides of the bell, through which the wa- 

 ter entering, as the bell descends, dis- 

 places the air originally contained in its 



D d 



