In land engines the injection water comes from a tank called the cold well, surrounding the condenser, and supplied by the cold water pump; in marine engines, it comes directly from the sea. In the surface condenser the steam is liquefied by being passed through tubes or other narrow passages surrounded by currents of cold water or cold air. The con denser is provided with blow-through valves, communicating with the cylinder, usually shut, but capable of being occasionally opened, and with a snifting valve opening outwards to the atmosphere; through these valves steam can be blown to expel air from the cylinder and con denser before the engine is set to work. The condenser has also a vacuum gauge, to show how much the pressure in it falls below that of the atmosphere. The water, the small por tion of steam which remains uncondensed, and the air which may be mixed with it, are sucked from the condenser by the air pump, and dis charged into the hot well, a tank from which the feed pump draws the supply of water from the boiler. The surplus water of the hot well in land engines is discharged into a tank there to cool and form a store for the cold well; in marine engines, it is ejected into the In all, except certain peculiar classes of engines, there is a parallel motion for guiding the head of the piston rod to move in a straight line, consisting either simply of straight cheeks or guides, or of a combination of levers and linkwork, invented by Watt, and more or less modified by others. The special classes of engines above referred to are — first, trunk engines, where the stuffing box is the guide; secondly, oscillating engines, in which the head of the piston rod is directly connected with the crank, and the cylinder oscillates on trun nions; thirdly, disc engines in which the func tions of a cylinder are performed by, a vessel of the figure of a spherical zone and those of a piston by a disc having a motion in that zone, and fourthly, rotary engines, in which the piston revolves round an axis. In single-acting en gines for pumping water, the pump rods are worked either by direct connection with the piston rod, or through the intervention of a beam. In double-acting engines, the power is communicated to a revolving shaft, driven by means of a crank and connecting rod, with or without the intervention of a beam. In sta tionary engines the shaft carries a fly-wheel, to distribute and equalize irregularities in the action of the power by its inertia; this func Clark, D. K., 'The Steam Engine' (London
1890) ; Corbin, T. W., 'Modern Engines> (Lon don 1918) ; Crane, W. E., 'American Stationary Engineering' (New York 1917) ; Dalby, W. E., 'Steam Power' (ib. 1915) ; Derr, L., 'Cyclo pedia of Engineering' (7 vols., Chicago 1915); Duncan, J., 'Steam and Other Engines' (Lon don 1907) ; Ewing, J. H., 'The Steam Engine' (Cambridge 1894) ; Fernald, R. H., and Orrok, G. A., 'Engineering of Power Plants' (New York 1916) ; Galloway, R. L, 'The Steam Engine and Its Inventors' (London 1881); Gebhardt, G. F., 'Steam-Power Plant Engi neering' (4th ed., New York 1913) ; Haeder, H., 'Handbook of the Steam Engifie' (London 1914) ; Heck, R. C. H., 'The Steam Engine tion is performed in marine engines by the inertia of the paddle wheels or screw, and, in locomotive engines, by the inertia of the driv ing wheels and of the engine itself. The feed pump, and other pumps which are appendages of the engine, are worked by the mechanism; so also are the induction and eduction valves, through what is called the valve gearing or valve motion— a part of the machinery which is under the control of the engineman, and so contrived as to enable him to stop and reverse the motion of the engines at will, and whose forms are very various. Most marine and loco motive engines, and many stationary engines, have, in order to equalize the action of the power, a pair of cranks at right angles to each other, driven by a pair of pistons in a pair of cylinders, with their appendages.
Bibliography.— Barton, J. K., 'Naval Recip rocating Engines' (3d ed., Annapolis 1914) ; and Turbine' (New York 1911) ; Hirshfeld, C. F., and Ulbricht, T. C., ' 'Steam Power' (ib. 1916) ; King, W. R., 'Steam Engineering' (ib. 1913) ; Peabody, C. H., 'Valve Gears for Steam Engines' (2d ed., ib. 1906) ; Perry, John, 'The Steam Engine and Gas and Oil Engines' (London 1909); Rigg, A., 'A Practi cal Treatise on the Steam Engine' (2d ed., New York 1894) ; Shealy, E. M., 'Steam Engines' (New York 1919) ; Spangler, Green and Mar shall, 'Elements of Steam Engineering' (ib. 1912) ; Stuart, 'Descriptive History of the Steam Engine' (5th ed., London about 1835) •, Swingle, C. F., 'Twentieth Century Handbook for Steam Engineers' (Chicago 1916) ; Thurs ton, Robert H., 'Manual of the Steam Engine) (6th ed., 2 vols., New York 1907) ; id., 'History of the Growth of the Steam Engine' (lb. 1890); Whitham, J. M., 'Steam Engine Design' (ib. 1914). See BOILER; ENGINE; ENGINE, TEST