where he fixed his residence in the city of New York. This was in the year 1839. Circumstances delayed, for some two years, the execution of their plan. With the change of the Federal Administration, Stockton was first able to obtain a favorable hearing; and having at length received the necessary authority, the Princeton was built under his superintendence, from the designs of Ericsson. She was completed and ready for sea early in 1844, when she was pronounced by Stockton "the cheapest, fastest, and most certain ship of war in the world." In this vessel, in addition to the propeller, Ericsson introduced his semicylindrical steam-engine, a beautiful invention, so compact that it occupied only one-eighth of the bulk of the British marine engine of corresponding power, and was placed more than four feet below the water-line. The boilers were also below the water-line, having a peculiar heating-apparatus attached which effected a great saving of fuel, and with their furnaces and flues so constructed as to burn anthracite as well as bituminous coal. Instead of the ordinary tall smoke-pipe,--an insuperable objection to a steamer as a ship of war,--he constructed a smoke-pipe upon the principle of the telescope, which could be elevated or depressed at pleasure; and in order to provide a draught independent of the height of the smoke-pipe, he placed centrifugal blowers in the bottom of the vessel, which were worked by separate small engines,--an arrangement originally applied by him to marine engines in the steam-packet Corsair in 1831. Thus the steam-machinery of the Princeton fulfilled the most important requisites for a war-steamer, combining lightness, compactness, simplicity, and efficiency, and being placed wholly out of reach of the enemy's fire. The armament of the ship also exhibited many peculiarities. "By the application of the various arts to the purposes of war on board of the Princeton," says Captain Stockton, in his report to the Navy Department, "it is believed that the art of gunnery for sea-service has, for the first time, been reduced to something like mathematical certainty. The distance to which the guns can throw their shot at every necessary angle of elevation has been ascertained by a series of careful experiments. The distance from the ship to any object is readily ascertained with an instrument on board, contrived for that purpose, by an observation which it requires but an instant to make, and by inspection without calculation. By self-acting locks, the guns can be fired accurately at the necessary elevation,--no matter what the motion of the ship may be." The instruments here referred to, namely, the Distance-Instrument and the Self-Acting Gun-Lock, and also the wrought-iron gun-carriage, by means of which Captain Stockton's enormous guns were readily handled and directed, all were the productions of Ericsson's fertile mechanical genius.