Source : Webster's Revised Unabridged Dictionary (1913)

Steam engine \Steam" en"gine\
   An engine moved by steam.

   Note: In its most common forms its essential parts are a
         piston, a cylinder, and a valve gear. The piston works
         in the cylinder, to which steam is admitted by the
         action of the valve gear, and communicates motion to
         the machinery to be actuated. Steam engines are thus
         classified: 1. According to the wat the steam is used
         or applied, as condencing, noncondencing, compound,
         double-acting, single-acting, triple-expansion, etc. 2.
         According to the motion of the piston, as
         reciprocating, rotary, etc. 3. According to the motion
         imparted by the engine, as rotative and nonrotative. 4.
         According to the arrangement of the engine, as
         stationary, portable, and semiportable engines, beam
         engine, oscillating engine, direct-acting and
         back-acting engines, etc. 5. According to their uses,
         as portable, marine, locomotive, pumping, blowing,
         winding, and stationary engines. Locomotive and
         portable engines are usually high-pressure,
         noncondencing, rotative, and direct-acting. Marine
         engines are high or low pressure, rotative, and
         generally condencing, double-acting, and compound.
         Paddle engines are generally beam, side?lever,
         oscillating, or direct-acting. Screw engines are
         generally direct-acting, back-acting, or oscillating.
         Stationary engines belong to various classes, but are
         generally rotative. A horizontal or inclined stationary
         steam engine is called a left-hand or a right-hand
         engine when the crank shaft and driving pulley are on
         the left-hand side, or the right-hand side,
         respectively, or the engine, to a person looking at
         them from the cylinder, and is said to run forward or
         backward when the crank traverses the upward half, or
         lower half, respectively, of its path, while the piston
         rod makes its stroke outward from the cylinder. A
         marine engine, or the engine of a locomotive, is said
         to run forward when its motion is such as would propel
         the vessel or the locomotive forward. Steam engines are
         further classified as double-cylinder, disk,
         semicylinder, trunk engines, etc. Machines, such as
         cranes, hammers, etc., of which the steam engine forms
         a part, are called steam cranes, steam hammers, etc.
         See Illustration in Appendix.

   {Back-acting}, or {Back-action}, {steam engine}, a steam
      engine in which the motion is transmitted backward from
      the crosshead to a crank which is between the crosshead
      and the cylinder, or beyond the cylinder.

   {Portable steam engine}, a steam engine combined with, and
      attached to, a boiler which is mounted on wheels so as to
      admit of easy transportation; -- used for driving
      machinery in the field, as trashing machines, draining
      pumps, etc.

   {Semiportable steam engine}, a steam engine combined with,
      and attached to, a steam boiler, but not mounted on
      wheels.