[45] The now well-known principle of a steam-engine is this: there is a cylinder with its rod fixed to one end of a lever, which is worked by the combined pressure of the atmosphere and the steam upon a piston, a temporary vacuum being made below it by suddenly condensing the steam, which had been let into the cylinder where this piston works, by a jet of cold water thrown into it. A partial vacuum being thus made, the weight of the atmosphere presses down the piston and raises the other end of the straight lever, thereby drawing up water from a mine, or, by the numberless improvements made of late years, communicating a mechanical power which may set in motion every description of machinery. [46] “Woodcroft on Steam Navigation,” p. 14; “Cabinet Cyclopædia,” Mechanics, p. 258. [47] Letter to Dr. Small, with a drawing; Muirhead’s “James Watt,” London, 1854, vol. ii. pp. 4, 8, 11. [48] There seems little doubt (see Lardner, p. 186, and Muirhead’s “Life of Watt,” p. 273), that Watt was the real inventor of the crank for which Mr. Wasborough obtained the credit. Mr. Watt says distinctly, that, having noticed, in 1778 or 1779, certain defects in the “ratchet wheels” invented by Wasborough, he proceeded to remedy them, but having neglected to take out a patent for these improvements, a workman employed to make Mr. Watt’s model told “some of the people about Mr. Wasborough,” on which he took a patent for the application of the crank to steam-engines. [49] In the Patent Museum, London, may be seen now (1875), the same “Sun and Planet” engine (a great curiosity), which Watt constructed in 1788 at Soho, near Birmingham. [50] See “Specifications relating to Marine Propulsion” (Part II.), p. 109, in which the existing documents are recapitulated and described. [51] There is more in Bramah’s inventions than at first appears, and the scientific reader would do well to study that part of them referring to the “boiler.” The following remarks have reference to the screw:— “Instead of the (paddle-wheel) A, may be introduced a wheel with inclined fans or wings, similar to the fly of a smoke-jack, or the vertical sails of a windmill: this wheel or fly may be fixed on the spindle C alone, and may be wholly under water, where it would, by being turned round either way, cause the ship to be forced backwards or forwards, as the inclination of the fans or wings will act as oars with equal force both ways, and their power will be in proportion to the size and velocity of the wheel; allowing the fans to have a proper inclination, the steam-engine will also serve to clear the ship of water with singular expedition, which is a circumstance of much importance. This “apparatus for working the ship” is fixed in or beyond the stern, in or about the place where the rudder is usually placed, and its movement is occasioned by means of an horizontal spindle or axletree conveyed to the engine through the stern end of the ship.”