Steam

is as a rule the motive power employed; by heat from the furnace, wafer is vaporized in the boiler, until the required pre ure is reached; the steam is then supplied to the engine, its elastic force giving motion to the piston; the reciprocal action so produced is by mechanical arrangement converted to circular motion, and imparted to the crank-shaft, causing the revolution of a screw-propeller, or paddle wheels. The types of engines are various, but several though similar in kind are differently named, owing to some peculiarity, by which they are distinguished.