The subject of submarine navigation was largely and pleasantly descanted upon by Mersennus, in his " Tractatus de Magnetis Proprietatibus," and Bishop Wilkins has given a chapter at some length on the subject, in his "Mathe matical Magick," (ed. 1648) where he affirms that Cornelius Dreble has proved, beyond all question, that the contrivance is feasible, by the experiments he made in England. The chapter of Wilkins is entertaining, for a sort of visionary faci lity with which he removes the difficul ties, and enumerates the benefits, of these submarine enterprises. For letting out and taking in such things as the nature of the voyage may require, he recom mends bags, or flexible tubes, some what resembling the scupper bags of ships. The progressive motion may, he observes, be produced by fins or oars, which will operate with ease when the vessel is truly equipoised ; and if swift ness should not be obtained, he sup poses the observations and discoveries to be made at the bottom of the sea would abundantly recompence for the defect. The greatest difficulty, in his ap prehension, would he, the necessity of renovating the air for respiration and combustion ; for remedying which, be sides the probability that custom may render men capable of living in air of in ferior purity, he has several philosophi cal views and projects. The conveni ences 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 that vex the surface ; from pirates and robbers ; and from the ices that so much endanger other voyages towards the poles. 3. It may be of use to undermine and blow up a navy of enemies. 4. Or to relieve a blockaded place. 5. And as the prospect enlarges in the mind of our author, he proceeds to contemplate the unspeakable benefit of submarine disco veries. Experiments on the ascent and descent of submerged bodies ; the ex ploration of the deep caverns and pas sages, and the waters of the ocean ; ob servatiOni on the nature and kinds of fishes, with allurements, artifices, and treacheries, which may sitccesslitlly be practised during so familiar a residence in their territories ; the food and oil they may afford ; the probability of fresh springs for a supply of water at the bot tom of the sea ; the facility of recovering submarine treasures, whether lost or na turally produced beneath the ocean ; and last °fall he adds, that " All kinds of arts and manufactures may be exercised in this vessel. The obser vations made by it may be both written, and, if need were, printed here likewise. Several colonies may thus inhabit, hav ing their children born and bred up without the knowledge of land, who could not chuse but he amazed with strange conezits upon the discovery of this upper world." The only modern instance of actual submarine navigation is that of Mr. Bush nel, recorded in the Transactions of the American Society, vol. iv. The exter nal shape of his vessel bore some resem blance to two upper tortoise shells of equal size,' joined together ; the place of entrance into the vessel being represent ed by the opening made by the well of the shells at the head of the animal. The inside was capable of containing the operator, and air sufficient to support him thirty minutes without receiving fresh air. At the bottom, opposite the entrance, was affixed a quantity of lead for ballast. At one edge, which was di rectly before the operator, who sat up right, was an oar for rowing forwards and backwards. At the other edge was a rudder for steering. An aperture at the bottom, with its valve, was designed to admit water for the purpose of descend ing ; and two brass forcing-pumps served to eject the water within when necessary for ascending. At the top there was like wise an oar for ascending or descending, or continuing at any particular depth ; a water-gauge or barometer determined the depth of descent, a compass directed the.. course, and a ventilator within sup plied the vessel with fresh air when on the surface.
The entrance into the vessel was ellip tical, and so small as barely to admit a per son. This entrance was surrounded with a broad elliptical iron band, the lower end of which was let into the wood, of which the body of the vessel was made, in such a manner as to give its utmost support to the body of the vessel against the pressure of the water. Above the upper edge of this iron band there was a brass crown or cover, resembling a hat with its crown and brim, which shut wa ter tight upon this iron The crown was hung to the iron band with hinges, so as to turn over sideways when open, To make it perfectly secure when shut, it might he screwed down upon the band by the operator, or by a person without.
There were in the brass crown three round doors, one directly in front, and one on each side, large enough to put the hand through : when open they admitted fresh air; their shutters were ground per fectly tight into their places with emery, hung with hinges, and secured in their places when shut ; there were likewise several small glass windoivs in the crown, for looking through and admitting light in' the day time, with covers to secure them. There were two air-pipes in the crown. A ventilator within drew fresh air through one of the air-pipes, and dis charged it into the lower part of the yeS sel ; the fresh air, introduced by the ven tilator, expelled the impure light air through the other air pipe. Both air, pipes were so constructed, that they shut themselves whenever the water rose near their topS, so that no. water could• enter through them, and opened themselves immediately after they rose above the water.
The vessel was chiefly ballasted with lead fixed at the bottom ; when this was not sufficient, a quantity was placed with- • in, more or less, according to the weight of the operator ; its ballast made it so stiff; that there was no danger of its over setting. The vessel, with all its appen dages, and the operator, was not of suffi cient weight to settle it very low in the water. About two hundred pounds of the lead at the bottom for ballast could be let down forty or fifty feet below the vessel ; this enabled the operator to rise instantly to the top of the water in case of accident.
When the operator would descend, he places his foot on the top of a brass valve, pressing it, by which he opened a large aperture at the bottom of the vessel; through this the water entered at his pleasure ; when he had admitted a suffi cient quantity, he descended very gra dually ; if he admitted too much, he ejected as much as was necessary to ob tain an equilibrium by the two brass forc ing pumps which were placed at each hand. Whenever the vessel leaked, or he would ascend to the surface, he also made use of these forcing pumps. When the skilful operator had obtained an equili brium, he could row upward or down ward, or continue at any particular depth, with an oar placed near the top of the vessel, formed upon the principle of the screw, the axis of the oar entering the vessel ; by turning the one way, he raised the vessel ; by turning it the other way he depressed it.
A glass tube, eighteen inches long and one inch in diameter, standing upright,. its upper end closed, and its lower end, which was open, screwed into a brass pipe, through which the external water had a passage into the glass tube, served as a water-gauge or barometer. There was a piece of cork, with phosphorus on it, put into the water-gauge. When the vessel descended, the water rose in the water-gauge, condensing the air within,, and bearing the cork with its phosphorus on its surface. By the light of the piles phorus, the ascent of the water in the guage was rendered visible, and the depth of the vessel under water ascertained by a graduated line.
An oar formed upon the principle of the screw was fixed in the fore part of the vessel ; its axis entered the vessel, and being turned one way, rowed the vessel forward, but being turned the other way, rowed it backwards ; • it was made to be turned with the hand or foot.