At the pearl fisheries, in the Bay of Condalzchy, in Ceylon, divers usually remain under water two minutes. There are some who can stay five minutes; and a diver from Anjano, engaged in this fishery in 1797, was able to remain six minutes under water. But their efforts are so great, that, when they come up, blood frequently issues from their mouths, ears, and nostrils. Notwithstanding this, they frequently dive from forty to fifty times a day, and bring up in a bag-net a hundred oysters each time.
It may be proper to observe, that the subject of sub-marine navigation was largely descanted upon by Mersennus, (Tractatus de Magnetis Proprietatibus), and by Bishop Wilkins (Mathematical Magic, 1648), who, by the way, is rather visionary. The conveniences and advantages he enumerates, are: 1. 'Privacy, as a man may thus go to any part of the world invisibly, without being discovered or prevented. 2. Safety, from the uncertainty of tides and tempests, &c. 3. It may be used to blow up, or undermine a navy: 4. Or to relieve a blockaded place, &c. But, with regard to the use of sub-marine vessels in war, Mr. David Bushnel, of Saybrook, Connecticut, appears to be entitled to the credit of the invention. His account of it may be seen in the Transactions of the American Philosophical Society. The intended object of this vessel was to destroy shipping, by the explosion of a magazine of gunpowder.
In Silliman's Journal of Science and Arts, vol. II, p. 94, is a communication by Mr. Griswold, on the subject of Bushnel's machine, with an account of the first attempt with it, in August, 1776, by Ezra Lee, a sergeant in the American army, to destroy some of the British ships then lying at New York. Mr. Griswold remarks, that, considering the invention of Mr. Bushnel as the first of its kind, it will be pronounced to be remarkably complete throughout in its construction, and that such an invention furnishes evidence of those resources and creative powers, which must rank him as a mechanical genius of the first order.
He has given a description of it; but the outline which we give is taken from Nicholson's Journal, quarto, iv, p. 229.
It is a decked boat, to go underwater: and several persons have gone under water many leagues. The difficulty is, to provide the persons in the boat with fresh air for respiration; and this is contrived, by having a reservoir of air, of suitable dimensions to the size of the boat, and the number of persons in it. By means of a condensing pump, the air, in this reservoir, is condensed about 400 times; and by a spring, the air is let out at intervals, as circumstances require, the carbonic acid produced by respiration being absorbed by quicklime. Within this boat are flaps, like those of a rundle, to move the boat, two rudders, one vertical, the other horizontal, and a pump to empty the hold, or air reservoir. The person within, can, at pleasure, come to the top of the water. The different experiments made by Mr. Bushnel may be seen in the Transactions referred to, or in Nicholson's Journal, quarto, iv, 229.
During the late war, Mr. Fulton, Mr. Mix, and some others, made various experiments with submarine machines; and during the revolution, the incendiary kegs, well known by the name of the "battle of the kegs," excited no small attention, and, had it not been for some unforeseen circumstance, they would, in all probability, have produced the effect for which they were intended.
Of Bushnel's vessel, we may observe, that, in the fore part of the brim of the crown, as it is called, was a socket, and an iron tube passing through the socket. The tube stood upright, and could slide up and down in the socket, six inches. At the top of the tube was a wood screw, fixed by means of a rod, which passed through the tube, and screwed the wood screw fast upon the top of the tube. By pushing the wood screw up against the bottom of a ship, and turning it at the same time, it would enter the planks. When the wood screw was firmly fixed, it could be cast off by unscrewing the rod, which fixed it upon the top of the tube.
Behind the submarine vessel, was a place, above the rudder, for carrying a large powder magazine. This was made of two pieces of oak timber, sufficiently large, when hollowed out, to contain 150 lbs. of powder, (130 lbs. according to Griswold,) with the apparatus used in firing it, and was secured in its place by a screw, turned by the operator. A strong piece of rope extended from the magazine to the wood screw above mentioned, and was fastened to both. When the wood screw was fixed, and to be cast off from its tube, the magazine was to be cast off likewise by unscrewing it, leaving it hanging to the wood screw; it was lighter than the water, that it might rise up against the object, and apply itself when fastened.
Mr. Griswold remarks, that the most difficult point of all to be gained, was to fasten this magazine to the bottom of a ship.