Overshot waterwheel, c 1870.
© Science Museum / Science & Society Picture Library
The engineer James Watt (1736-1819), worked on the design of the overshot wheel and this model is now part of the Motive Power Collection at the Science Museum, London. The overshot wheel is regarded as the most efficient type of water-wheel, relying on gravity rather than the force of water hitting paddles, as is the case with an undershot wheel. It is turned by the force of water falling upon the top of the wheel. In this way it harneses the gravitational force acting on the water as well as its kinetic energy. The wheel is fitted with a toothed iron ring from which the power is taken off at high speed without transmision through the axle.