Turbine, machine for directly converting the kinetic and/or thermal energy of a flowing fluid (air, hot gas, steam, or water) into useful rotational energy. The working fluid either pushes against a set of blades mounted on the drive shaft (impulse turbines) or turns the shaft by reaction when the fluid is expelled from nozzles (or nozzle-shaped vanes) around its circumference (reaction turbines). Water turbines include the vast inward-flow reaction turbines used in the generation of hydroelectricity and the smaller-scale tangential-flow “Pelton wheel” impulse types used when exploiting a very great head of water. In the 1800s, Charles Alernon Parsons (1854–1931), a British engineer, designed the first successful steam turbines, having realized that the efficient use of high-pressure steam demanded that its energy be extracted in a multitude of small stages. Steam turbines thus consist of a series of vanes mounted on a rotating drum with sat or vanes redirecting the steam in between the moving ones. They are commonly used as marine engines and in thermal and nuclear power plants. Gas turbines are not as yet widely used except in airplanes and for peak-load electricity generation.