In some forms of overshoot wheels, an efficiency of over 90 per cent is claimed by manufacturers; and this type offers the additional advantage of utilizing small quantities of water, as well as being efficient under varying quantities of water. They utilize the falling weight of water, although by giving the water momentum at the point of delivery, by means of the proper fall, impulse too is utilized in some measure. The modern steel overshoot wheel receives water in its buckets from a spout set a few degrees back of dead center; and its buckets are so shaped that the water is retained a full half-revolution of the wheel. The old-style overshoot wheel was inefficient principally because the buckets began emptying themselves at the end of a quarter-revolution. Another advantage claimed for these wheels over the old style is that, being made of thin metal, their buckets attain the temperature of the water itself, thus reducing the danger of freezing to a minimum. They are manufactured in sizes from 6 feet in diameter to upwards of fifty feet; and with buckets of from 6 inches to 10 feet in width. In practice it is usual to deliver water to the buckets by means of a trough or pipe, through a suitable spout and gate, at a point two feet above the crown of the wheel. For this reason, the diameter of the wheel corresponds very closely to the head in feet. _The Reaction Turbine_ The reaction turbine is best adapted to low heads, with a large supply of water. It is not advisable, under ordinary circumstances, to use it under heads exceeding 100 feet, as its speed is then excessive. It may be used under falls as low as two feet. Five thousand cubic feet of water a minute would give approximately 14 actual horsepower under such a head. A sluggish creek that flows in large volume could thus be utilized for power with the reaction turbine, whereas it would be useless with an impulse wheel. Falls of from five to fifteen feet are to be found on thousands of farm streams, and the reaction turbine is admirably adapted to them.