What is "poncelet wheel"

The Poncelet wheel is a type of waterwheel invented by Jean-Victor Poncelet while working at the École d'Application in Metz. It roughly doubled the efficiency of existing undershot waterwheels through a series of detail improvements. The first Poncelet wheel was constructed in 1838, and the design quickly became common in France. Although the design was a great improvement on existing designs, further improvements in turbine design rendered the Poncelet wheel obsolete by the mid-century.