Page:Popular Science Monthly Volume 12.djvu/153

Rh rotary motions, and temporarily adopted that known as the "sun-and-planet wheels," subsequently using the crank.

The adaptation of the steam-engine to the production of rotary motion was soon succeeded by the introduction of the Double-Acting Engine, the Fly-ball Governor, the Counter, the Steam-Engine Indicator, and other minor but valuable improvements, which were the final steps by which the Watt steam-engine became applicable to driving mills, to use on railroads, to steam-navigation, and to the countless purposes by which it has become, as it has already been denominated, the great material agent of civilization.

40. Fig. 16 represents the Watt Double-Acting engine. It will be noticed that it differs from the Single-Acting engine in having steam-valves, B B, and exhaust-valves, E E, at each end of the cylinder, thus enabling the steam to act on each side of the piston alternately, and practically doubling the power of the engine.

The end of the beam opposite to the cylinder is usually connected with a crank-shaft.



41. At this point, the history of the steam-engine becomes the story of its applications in several different directions, the most important of which are the raising of water, which has hitherto been its only application; the propulsion of carriages, as in the locomotive the driving of mills and machinery; and steam-navigation.