For small power purposes, for pressures of 50 lb. per square inch and upwards, if efficiency is defined as the ratio of the work received from the motor compared to that put into it, the following list may represent the efficiencies of various water motors when used in circumstances that suit the special types considered: - Undershot wheel, 25 to 15 per cent.; low breast, -10 to 65 per cent.; Poncelet, 60 to 70 percent.; high breast and overshot, 60 to 80 percent.; and turbines from 60 per cent, upwards. Undershot wheels and Poncelet wheels are suitable for heads of 6 ft. and under; breast wheels for heads over 6ft.; overshot wheels, from 10 ft. to 60 ft. or 70 ft.; and turbines for any heal according to the design of the wheel. A pressure of 501b. per square inch corresponds to a head of 5) x 2.31 - 115.5ft'. The Jonval (parallel or axial flow), Fourneyron (outward flow), Thomson (inward flow), and Schiele (mixed flow) turbines are suitable for pressures.