WATER WHEEL. 358 WATER-WORKS. and the water, so to speak, flows under the wheel and pushes the paddles forward so as to cause rotation in a direction opposite to the move- ment of the hands of a watch. In the simplest industry, which is constantly calling for in- crcasad rates of speed. Keceutly a form of water wheel known as the impulse iihcel has come into extensive use. It form of undershot wheel the paddles are radi.TLl consists of a series ^of cup-shaped vanes attached and the wheel is set so that they dip just their ' " ' "" full depth into the current of a flowing stream. In the more approved form of undershot wheel the water passes under the wheel in a rectangu- lar sluice concentric with the wheel, in which the paddles revolve with as little clearance as is con- sistent with movement. The breast wheel, like BRE.ST WHEEL. the overshot wheel, has a series of buckets on its circuiiiferenoe, but they are so arranged that the wlieel revolves backward, or in a direction oppo- site to the movement of the hands of a watch. In the overshot wheel, still using the dial of a watch as an illustration, the water enters the bucket at about the point where number I on the dial is located and leaves it about the point where number V is located; in the breast wheel the water enters the bucket at about X and leaves it at about VII; in the undershot wheel the water hits the paddle at about VIII and leaves it at about VI. The numerous disadvantages of the water wheels which have been described have caused them to be almost entirely superseded by the turbine. (See Turbi.ne.) They occupy much more room than turbines of the same power, and to the periphery of a wheel and acted on by a jet of water. The water is delivered tluough a pipe having a nozzle to form a jet which im- pinges against one bucket after another, as the wheel revolves. A notable feature of this wheel is the shape of the buckets, which is such that they clear themselves of water without ob- structing in any way the propelling jet. ^ Some- times two or three nozzles are employed instead of one, the jet from each striking the wheel at a different point. Notable among the impulse wheels are those of the Pelton type, some of which have been con- IMITLM-, WHEEL. must be inclosed in buildings to prevent obstruc- tion by ice in winter. Back-water alfects them injuriously, not only by diminishing the head, but by drowning them and causing them to ex- pend their power u.selessly in 'wallowing,' a source of loss from which turbines are wholly free. The necessarily low velocity with which they move necessitates cumbrous and expensive gearing to raise the speed to the requirements of / ■tt: IMPULSE WATER WHEEL. structed as large as 18 feet 6 inches in diameter and have been employed to work air compressors in mines. A wheel of this size weighs 10.000 pounds, and runs at 110 revolutions per minute at a 7.30-foot head of water and develops over 300 horse power. The wheel is made of iron |)lates riveted together, which are held concen- tric with the shaft by radial spokes, and a truss consisting of four pairs of two-inch rods. There is a variable nozzle operated by an automatic hydraulic regulator through which the water is ap]ilicd to the wheel and causes it to run at uniform speed with varying loads. BiULiOGRAPHT. Besides the books mentioned under Water Power and Turbine, the reader will find much valuable data relating to water wheels in Woisbach, Uiidruulics nnd iJi/iJnnilir Motors (Eng. trans, by Du Bois, Xew York, 1877), and Bjorling, M'atcr or Hiidrdulic Motors (London, 1804). The best description of wheels of the impulse type will be found in variois articles in the engineering papers during the last ten years. See Water Powkr ; Turbixe. WATER-WITCH. Any of various birds quick at diving, as a groljo, bufllchcad duck, or dipper. WATER-WORKS. The various structires and (lr i(■(■^ u<cd to jirovide water for domestic and industrial uses, fire protection, and oiher public services. The term is here restricted to plants for the supply of municipalities. Works limited to the needs of a single establishment generally differ little in )u-inciple from municiiial works, liut are smaller and simpler. The main points to be discussed in this article are the quality and quantity of water to be provided;
