[77] Fitch himself thus describes the engines of his first boat in a letter which appeared in the Philadelphia newspaper of the period: “_Philadelphia, Dec. 8, 1786._ “SIR,—The reason of my so long deferring to give you a description of the steam-boat, has been in some measure owing to the complication of the works, and an apprehension that a number of drafts would be necessary in order to show the powers of the machine as clearly as you could wish. But as I have not been able to hand you herewith such drafts, I can only give you the general principles. It is in several parts similar to the late improved steam-engines in Europe, though there are some alterations. Our cylinder is to be horizontal, and the steam to work with equal force at each end. The mode by which we obtain (what I take the liberty of terming) a vacuum is, we believe, entirely new; as is also the method of letting the water into it, and throwing it off against the atmosphere without any friction. It is expected that the engine, which is a 12-inch cylinder, will move with a clear force of 11 or 12 cwt., after the frictions are deducted; this force is to act against a wheel of eighteen-inch diameter. The piston is to move about 3 feet, and each vibration of the piston gives the axis about forty evolutions. Each evolution of the axis moves twelve oars or paddles 5½ feet (which work perpendicularly, and are represented by the stroke of the paddle of a canoe). As six of the paddles are raised from the water six more are entered, and the two sets of paddles make their stroke of about 11 feet in each evolution. The cranks of the axis act upon the paddles about one-third of their length from the lower end, on which part of the oar the whole force of the axis is applied. Our engine is placed in the boat about one-third from the stern, and with the action and reaction turn the wheel in the same way. “With the most perfect respect, sir, I beg leave to subscribe myself “Your very humble servant, “JOHN FITCH.” [78] In a letter I received (May 2nd, 1875) from Commodore G. H. Preble, Commandant U.S. Navy Yard, Philadelphia, to whom I am indebted for much valuable information, he says, “John Stevens invented the twin screw-steamer in 1804, which is still preserved in the Stevens’ Institute, Hoboken, N.Y.” [79] The patent bears date 21st May, 1805, and was granted to “John Cox Stevens, of New York, but now residing in New Bond Street, Middlesex.” [80] Gill’s “Technical Repository,” 1829, vol. iv. p. 251 (for 1823), where a paper by Evans is given, but no further authority. [81] Fulton invented the drop and the double-ended steam ferry-boats now in use in all the principal cities of the U.S. [82] Stuart’s “Anecdotes of Steam-engines,” vol. ii. p. 478. [83] Letter from R. Fulton in a memoir by E. Cartwright, London, 1843, p. 142.