John Stevens, however, first gave the screw a practically useful form, and used it successfully, in 1804 and 1805, on the single and the twin screw boats which he built at that time. This propelling instrument was also tried by Trevithick, who planned a vessel to be propelled by a steam-engine driving a screw, at about this time, and his scheme was laid before the Navy Board in the year 1812. His plans included an iron hull. Francis Pettit Smith tried the screw also in the year 1808, and subsequently. Joseph Ressel, a Bohemian, proposed to use a screw in the propulsion of balloons, about 1812, and in the year 1826 proposed its use for marine propulsion. He is said to have built a screw-boat in the year 1829, at Trieste, which he named the Civetta. The little craft met with an accident on the trial-trip, and nothing more was done. The screw was finally brought into general use through the exertions of John Ericsson, a skillful Swedish engineer, who was residing in England in the year 1836, and of Mr. F. P. Smith, an English farmer. Ericsson patented a peculiar form of screw-propeller, and designed a steamer 40 feet in length, of 8 feet beam, and drawing 3 feet of water. The screw was double, two shafts being placed the one within the other, revolving in opposite directions, and carrying the one a right-hand and the other a left-hand screw. These screws were 5-1/4 feet in diameter. On her trial-trip this little steamer attained a speed of 10 miles an hour. Its power as a "tug" was found to be very satisfactory; it towed a schooner of 140 tons burden at the rate of 7 miles, and the large American packet-ship Toronto was towed on the Thames at a speed of 5 miles an hour. Ericsson endeavored to interest the British Admiralty in his improvements, and succeeded only so far as to induce the Lords of the Admiralty to make an excursion with him on the river. No interest was awakened in the new system, and nothing was done by the naval authorities. A note to the inventor from Captain Beaufort--one of the party--was received shortly afterward, in which it was stated that the excursionists had not found the performance of the little vessel to equal their hopes and expectations. All the interests of the then existing engine-building establishments were opposed to the innovation, and the proverbial conservatism of naval men and naval administrations aided in procuring the rejection of Ericsson's plans.