VOL. XXIX.] PHILOSOPHICAL TRANSACTIONS. 25g 



considerable, the pressure of the water on the vessels is found by experience to 

 make the eyes blood-shot, and frequently to occasion spitting of blood. 



When therefore there has been occasion to continue long at the bottom, 

 some have contrived double flexible pipes, to circulate air down into a cavity in- 

 closing the diver as with armour, to bear off this pressure of the water, and to 

 give leave to his breast to dilate on inspiration : the fresh air being forced down 

 by one of the pipes with bellows or otherwise, and returning by the other; not 

 unlike an artery and vein. This has indeed been found sufficient for small 

 depths, not exceeding 12 or 15 feet: but when the depth surpasses 3 fathoms, 

 experience teaches us that this method is impracticable : for though the pipes, 

 and the rest of the apparatus, may be contrived to perform their office duly, yet 

 the water, its weight being now become considerable, so closely embraces and 

 clasps the limbs that are bare, or covered with a flexible covering, that it ob- 

 structs the circulation of the blood in them; and presses with so much force on 

 all the junctures, where the armour is made tight with leather or skins, or such 

 like, that if there be the least defect in any of them, the whole engine will 

 instantly fill with water, which rushes in with such violence, as to endanger the 

 life of the man below, who may be drowned before he can be drawn up. On 

 both which accounts, the danger increases with the depth. Besides, a man 

 thus shut up in a weighty case, as this must needs be, cannot but be very un- 

 wieldy and unactive, and therefore unfit to execute what he is designed to do at 

 the bottom. 



To remedy these inconveniences, the diving-bell was next thought of; in 

 which the diver is safely conveyed to any reasonable depth, and may stay more 

 or less time under water, according as the bell is of greater or less capacity. 

 This is most conveniently made in form of a truncated cone, the smaller 

 basis being closed, and the larger open ; and ought to be so poised with lead, 

 and so suspended, that the vessel may sink full of air, with its greater or open 

 basis downwards, and as near as may be in a situation parallel to the horizon, so 

 as to close with the surface of the water all at once. Under this receptacle the 

 diver setting, sinks down together with the included air to the depth desired ; 

 and if the cavity of the vessel may contain a tun of water, a single man mav 

 remain in it at least an hour, without much inconvenience, at 5 or 6 fathoms 

 deep. But this included air, as it descends lower, contracts itself according to 

 the weight of the water that compresses it; so as that about 33 feet deep the 

 bell will be half full of water, the pressure of it being then equal to that of the 

 whole atmosphere : and at all other depths, the space occupied by the com- 

 pressed air in the upper part of the bell, will be to the under part of its capacity 



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