Evans's " Columbian" r800 or 'So', Evans began the construction of a steam-carriage to be driven by a non-condensing steam engine, but, changing his plans, he built a beam-engine having a cylinder 6 inches in diameter and 18 inches stroke, with which he successfully drove a plaster-mill. This "Columbian" engine (/5/. 8r, fig. 2), as it was called, had a beam supported at one end by a rocking column. The con necting-rod was attached to the other end and drove a crank below; the piston-rod was connected directly to the beam at a point nearer the con necting-rod, and the feed-pump piston-rod was also directly connected at a point nearer the beam-fulcrum. The beam and piston-rod constituted a sort of parallel motion. In 1804, Evans produced the steam-dredge "Oruktor Amphibolis," which had a five-horse-power engine similar to the "Columbian." (See Vol. V. p. 172.) About the same time one of his engines, which was built for a steamboat on the Lower Mississippi, was put to work in driving a saw-mill.
Cartwright's engine of 1798 took steam above the piston, the rod of which extended upward to a cross-head driving cranks above, and down ward to an air-pump piston which had the sonic stroke as that of the steam-cylinder. The bottom of the steam-cylinder was in communica tion with the condenser, the steam-piston having in it a valve which was opened automatically when the full stroke had been made. The air-pump removed the excess of air from the condenser, which was composed of two concentric cylinders within and around which the water of condensation flowed, while the exhaust steam passed into the annular space.
In tSo2, Richard Trevithick of England patented a model steam-engine carriage in which high-pressure steam was employed and the condenser was dispensed with.
During the first half of the nineteenth century progress in steam engineering was very largely in the direction of the application of the steam-engine to the propulsion of road-carriages, locomotives, and vessels; there were but few striking innovations, each inventor and builder striving to perfect construction rather than to start out in a new field of original design. Those desirous of tracing in somewhat greater detail than is here given the growth of the steam-engine during the period mentioned, will find it in the sections devoted more particularly to the locomobile, the locomotive, and the marine steam-engine. The " Oruktor Amphibolis" of Evans (ISal), Trevitliick's steam-carriage (rSo2), the steam-carriages of Griffiths, of Gurney (1827), and of Hancock (ISA show a develop ment as interesting as it was important. The locomotives of Trevithick (ISol), Medley (1812), the Stephensons, Horatio Allen, Peter Cooper (1829), Baldwin (iS31), and Jervis (1832) marked a gradual growth rather than startling flights of invention.
Corliss introduced the straight girder frame for stationary engines; he also introduced the plug-valve, and made the detent cut-off, as applied thereto and operated by the centrifugal governor, a mechanical and com mercial success. Hartnell brought out the shaft governor controlling the eccentric throw, and J. W. Thompson made it practicable and successful in connection with a balanced valve. John E. Sweet has carried the "straight-line" system of construction to a satisfactory conclusion; and to Charles T. Porter more than to any other man do we owe the success of the modern high-speed automatic cut-off stationary engine. Ball has made a good start in the line of governing by load rather than by speed, and Westinghouse has made high-speed single-acting engines, both throt tling and automatic cut-off compound and non-componnd, practicable in a high degree; while, among others, Wootten, Stevens, and Strong in the United States, Mallet in France, and Worsde11 and Webb in England, have done much to lift the locomotive out of ruts of design.
Having considered the steam-engine from an historical standpoint, with reference both to its design and construction, we shall now consider it from a more strictly technical standpoint. We shall minutely define and scientifically describe it, and shall then give those details which would be out of place in a chronological narrative of its development and growth.
Definilion.—A steam-engine is a machine by which the pressure of steam, due to its temperature, may be utilized in mechanical work. The term steam-engine is usually restricted to a motor in which a shaft is rotated directly or indirectly by the pressure of steam upon an alternat ing or a rotating piston fitting steam-tight, with as little friction as possible, in a cylindrical (or approximately cylindrical) case. A steam engine may be employed to drive a line of shafting, to run one or more machines connected to its main shaft, to actuate a pump or a blower having its piston attached to its piston-rod, to propel a boat in which it is placed, or to move a vehicle on which it is mounted.
Classifications.—Steam-engines may be classified into horizontal, verti cal, and inclined, according to the position in which the cross-head guides to the piston-rods are placed. But this classification, being merely struc tural, has theoretically little or no value. The oscillating engine has no cross-head, and consequently has no guides.