Mr. Ogden, who was American Consul at Liverpool from 1829 to 1840, and at Bristol from 1840 to 1857, “is credited with having first applied the important principles of the expansive power of steam and with the employment of right-angular cranks in marine engines. In 1813 he received a patent for low-pressure engines with two cylinders, working expansively, and the cranks being adjusted at right angles, and in 1817 the first engine ever constructed on this principle was built by him in Leeds, Yorkshire. He submitted his plan to James Watt, at Soho, who declared at once that it was a beautiful engine and that the combination was certainly original.”[84] [84] Appleton’s “Cyclopædia of American Biography.” The definite adoption of the screw propeller, both for the Royal Navy and the Mercantile Marine, may be said to have taken place in 1840-41. For some years no bearings of brass or other metal could be got to stand the strain of the stern shaft, “and at one moment it seemed as if the screw must be abandoned and the paddle-wheel reverted to. Mr. Penn solved the problem by using lignum-vitæ wood bearings, which, lubricated by water, were found to act without any appreciable wear, and in this simple way the screw has already been able to reach a point of development from which we can now calmly look back upon the financial risks and terrors which beset the early days of steam navigation.”[85] [85] _The Times._ The difficulty of steering screw-propelled vessels was considerable, principally owing to the method of placing the screw in an aperture in the deadwood, while at the same time retaining the full underbody aft. The full power of the screw could not thus be exerted, and the attendant churning of the water interfered with the steering power of the rudder. A system of double rudders was brought out in an attempt to solve the difficulty, but the disadvantages it possessed were against its general adoption. These rudders were hung respectively one on each side of the forepart of a somewhat extended sternpost, against which they lay when amidships, moving out as required to steer the ship, or both could be moved outwards to help to stop her. The sternpost was really a vertical hollow box through which the screw framing passed, the screw working behind it and beyond the rudders. Later improvements in shipbuilding rendered this device unnecessary. The difficulty was solved by the simple expedient of placing the sternpost farther aft so as to give room for a greater space in the deadwood in which the propeller was to act. The superiority of the screw to paddles was now being gradually admitted, and the number of small vessels fitted with screws increased. But no one had as yet dared to launch a large screw steamer for ocean voyages.