“A pair of cylindrical flexible vessels, rendered impervious both to air and water by means of elastic resin, and a four-barrelled pump for inflating them. As the contents of cylinders increase in proportion to the squares of their diameters, such may be enlarged or diminished to equal the power in request; consequently both the pumps and air-vessels may be readily apportioned to the duty they have to perform. From the diameter of the cylinders of the pump, to judge of their discharge, we must consider the length of the stroke within the reach of middle-sized men, and the number of discharges which may be made in a given time. With the aid of simple mechanism, I have accomplished a perpendicular stroke of two feet, capable of being repeated from sixty to seventy times with ease, and from eighty to an hundred, if requested, in a minute.
“Air is a fluid of so volatile a nature, that the slightest pressure impels it forward; four men, therefore, can pump in more air than four hundred men can pump out water.
“That vessels of canvas may be made, at the same time, both flexible and air-tight, hath been demonstratively proved already. Such vessels, in their flaccid state, occupy little more space than a folded sail, and consequently are stowable in a narrow compass, till wanted. When immersed and inflated, they remove a quantity of water adequate to the air which they contain, and, if fixed to a ponderous body, give it a degree of buoyancy proportionate to the water they displace. If this be equal to the difference in weight between that body and an equal bulk of the fluid which surrounds it, the whole will rest suspended even with or near the surface of the fluid. Enlarge their contents, and turn the balance in favour of the sinking body, it will rise and float. Fix sufficient buoyant powers, therefore, to the sides of a ship, in such manner that they cannot break loose; though a plank should start in her bottom, she still would float.
“One method, then, of preventing a ship from sinking may be by a brace of air-vessels occasionally lashed to her sides. Another is, that of inflating a brace within her. To bring the former to effect requires a more perfect knowledge of the strength of cordage than the most experienced rope-maker can boast. Our best calculators egregiously err in this particular; for, instead of its increasing in proportion to the square[[14]] of the diameter of the cordage, it comes far nearer to the proportion of the simple diameter only, as numerous experiments with the best new town-made ropes of various sizes have convinced me. In the first mode, therefore, several difficulties remain to be overcome. The other is easy, consisting only in the simple operation of inflating air-vessels within her. Let such be placed in confinement either in the hold, between the decks, or under lashings in small open sloops (to which your attention, Sir, seems chiefly paid), and they will operate with the most certain and powerful effect. For, though water, through its density, will expel air when at liberty, it can never incroach upon it when properly confined. Secure, then, but a due portion of the lighter fluid in eligible situations, and the ingress of the grosser will be prevented. Consequently, though the sea run mountains high, and break over the sloop with the most tremendous surge, if the crew can secure themselves by lashing to the mast or rigging, and can at times have opportunity to supply the loss of air (which, through the inaccuracy of valves, air-cocks, &c. will sometimes happen), by a few additional strokes at the pumps, she will continue buoyant, in spight of elements, and be safe from the danger of sinking. Small vessels, under such circumstances, are liable, however, to be driven on shore; but, as they draw little water, their crews would probably be preserved.
[14]. See Falconer’s Marine Dictionary, article Cable.
“As yours, Sir, is the cause of humanity, I have troubled you with these particulars; and hope, that, as a possibility of relief appears, some Philanthropic Society or other will be induced to exert their endeavours for the preservation of the glorious tars of Britain.”
As the preceding scheme is supported, by its ingenious author, on true philosophical principles, and seems well calculated to keep a packet boat, or vessel of small size, buoyant, as some successful trials on the model seem to evince; yet, as the apparatus rests on the instable basis of air and water, might not some difficulty arise, during a sea storm, particularly in securing the air-cylinders, when destined to act externally on a large scale? It ought, therefore, to be subjected to the test of further experiment, both internally and externally, on vessels of different rates, as the invention certainly merits the attention of those who preside over maritime affairs. For, what keeps afloat a first-rate ship of war, with its immense freight of guns, stores, ammunition, and men, but the difference of specific gravity between air and water? What causes the ship to founder, but the accidental ingress of water, with a proportionate egress of air? Impervious air-vessels, therefore, properly placed, and inflated within the ship, would prevent the spaces thus occupied from being filled with water, and consequently bid fair to keep her buoyant, even though her upper deck became level with the surface of the sea. It was thus that the ship Guardian was prevented from foundering, whose packages and stores containing lighter fluids, such as spirits and air, which the water being unable to expel, alone kept the vessel afloat. Hence appears the utility even of empty casks if rendered impervious and immoveably fixed between the decks of a ship in distress.
The importance of the Art of Swimming and Diving.
According to the observations of a late able writer, we are assured that, on board the King’s ships, not half, scarcely a third part, of the crew can swim; and that, for want of this, several, in the course of a voyage, have been drowned[[15]].
[15]. See Mr. Jeremy Bentham’s Inquiry on Pauper Management, in Young’s Annals, for 1798, No 174.