The _Argonaut_ is fitted with a White and Middleton gasoline engine of 30 h.p., which operates the screws the driving wheels, the dynamo, the air compressors, anchor hoists, and derrick-operating machinery. She is provided with two Mannesmann steel tubes, in which sufficient air may be stored, with what is contained in the boat, to last the crew for twenty-four hours without obtaining a fresh supply from the surface. In the _Argonaut_, however, and probably in all such craft used for commercial pursuits, as a usual thing, there will be a connection with the surface, through which a constant supply of air may be drawn, either by the masts, as shown in the views, one of which supplies air to the interior of the vessel, the other being utilised as an exhaust from the engine, or through suction hose extending to a buoy on the surface. While the engine is running there is about fifty cubic feet of air flowing into the boat per minute; and when the engine is closed down there may be a flow of air maintained by an auxiliary blower, so that it is possible to remain below for days, or even weeks, at a time. The course is directed by an ordinary compass when on the bottom, and it is found that the needle responds as quickly and is as accurate as when on the surface. Notwithstanding the fact that the _Argonaut_ is quite a small vessel, a crew of five men have lived aboard her during an experimental cruise extending over two months, during which she travelled over 1,000 miles under her own power, partly on the surface and partly on the bottom. The trip was made to demonstrate the practicability of vessels of her type travelling on various kinds of bottoms; also to demonstrate her seaworthiness and capabilities in searching the bottom, in working on sunken wrecks, finding and taking up submerged cables, &c. We have been in some pretty rough weather, and found that she was perfectly seaworthy. Of course, being so small and of such weight, the seas at times would wash clear over her decks. This, however, caused no inconvenience to those below, as her stability was such that she would roll or pitch very little, even though the seas were breaking over her in great volume. We have been cruising on the bottom in rivers, in Chesapeake Bay and beneath the Broad Atlantic. In the rivers we invariably found a muddy bed; in the bay we found bottoms of various kinds, in some places so soft that our divers would sink up to their knees, while in other places the ground would be hard, and at one place we ran across a bottom which was composed of a loose gravel, resembling shelled corn. Out in the ocean, however, was found the ideal submarine course, consisting of a fine gray sand, almost as hard as a macadamised road, and very level and uniform.