Dictionary.net

An engine driven by steam pressure. There are many kinds of steam-engines. Of these we may notice the following :- The Condensing engine, in which the waste steam is condensed, so that the piston moves with the steam on one side and a vacuum on the other; such engines were commonly worked by steam of low pressure, and are often called Lowpressure engines. In a Non-condensing Engine, the waste steam is driven into the air ; it must be worked, therefore, by steam of high pressure, and is a High-pressure Engine Steam of high pressure is, however, often used to work condensing engines. There are also Stationary Engine, commonly working by condensation ; Locomotive Engine , which are non-condensing ; and Marine Engine, which are modified stationary engines. In the Beam Engine the piston communicates motion at one end to a large lever or beam, the other end of which works a pump, or by means of a crank gives a continuous rotation to the main shaft; in an Oscillating Engine the cylinder is capable of a small oscillating movement sufficient to enable the crank to be turned directly by the piston-rod.

n. An engine moved by steam ; a mechanical apparatus for utilizing the elasticity or expansive power of steam and its property of rapid condensation, and converting it into a motive power for driving machinery, locomotion, &c.;- steam-engines are usually classed as high pressure or non-condensing, when the action of the piston is due solely to a high pressure of the steam; and low pressure or condensing, in which the steam which propels the piston in one direction is instantly condensed and creates a vacuum, thus rendering the returning stroke more easy.