“The fresh air introduced by the ventilator expelled the impure air through the other 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. They opened themselves immediately after they rose above the water. The vessel was chiefly ballasted with lead fixed to its bottom. When this was not sufficient, a quantity was placed within, more or less, according to the weight of the operator. Its ballast rendered it so solid that there was no danger of its oversetting. The vessel, with all its appendages and the operator, was of sufficient weight to settle it 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 surface of the water in case of accident. “When the operator desired to descend, he placed his foot upon the top of a brass valve, depressing it, by which he opened a large aperture in the bottom of the vessel, through which the water entered at his pleasure. When he had admitted a sufficient quantity, he descended very gradually. If he admitted too large a quantity, in order to obtain an equilibrium, he ejected as much as was necessary by the two brass forcing-pumps which were placed at each end. Whenever the vessel leaked, or he desired to ascend to the surface, he also made use of these forcing-pumps. When the skilful operator had obtained an equilibrium, he could row upward or downward, 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 oar in one direction 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, condensing the air within, and bearing the cork on its surface. By the light of the phosphorus, the ascent of the water in the gauge was rendered visible, and the depth of the vessel ascertained by a graduated scale. “An oar formed on the principle of the screw was fixed in the fore part of the vessel; its axis entered the vessel, and, being turned in one direction, rowed the vessel forward; but being turned in the other, rowed backward. It was constructed to be turned by the hand or foot.