Mr. Fulton, of the United States, the inventor of the _Torpedo_, recommends the use of a gun-harpoon for fixing this destructive engine on the side of a ship; but this plan appears liable to two objections: the resistance that would be offered by the water, should the harpoon be fired from a considerable distance; and the certainty of discovery from the report of the cannon, on a near approach to the hull of the vessel. The methods most eligible for this object appear to be, either to let the machine float with the tide, and by striking against the side of the vessel discharge a gun-lock; or else, by employing a _diving-bell_, pass beneath the surface of the water. In proof of the practicability of the latter plan, about the time of the attack made by the English at Boulogne, Buonaparte caused a small diving vessel to be made, which, at a preconcerted signal, lowered its masts, yards, &c.; and by admitting a certain quantity of water sunk it to the required depth; it was then impelled forward by means of a circular paddle or wheel turned within the vessel, and upon the air becoming foul or exhausted, the vessel was raised to the surface by means of pumps or dropping of ballast. It appears more than probable, that this is the species of vessel to which the Marquis alludes. Hook, in his _Philosophical Collections_, No. 2, describes an air-vessel possessing similar properties with the above. No. XI. How to prevent and safeguard any ship from such an attempt by day or night. NOTE. A safe and easy method of preventing the dreadful consequences attendant on the explosion of this tremendous machine, may be found in the use of a strong net, resembling that used in the salmon fishery; which must be kept at the required distance from the vessel by floating buoys placed for that purpose. It will also be necessary to fix a bell upon the upper extremity of each buoy, which will, by its ringing on a calm night, discover the approach of any hydrostatic vessel; and should the weather be stormy, the attempt must end in the destruction of the sub-marine voyagers. No. XII. A way to make a ship not possible to be sunk, though shot at an hundred times between wind and water by cannon, and should she lose a whole plank, yet, in half an hour's time, should be made as fit to sail as before. NOTE.