TXJBBINE. 550 TTJBBOT. with the axis of rotation. In combined or mixed floio turbines, both the previously described sys- tems are combined. Another classification of tur- bines is also employed, namely, reaction turbines and impulse turbines. In a reaction tnrbine all parts are entirel.v filled or 'drowned' with mov- ing water; in the impulse turbine the construc- tion is such that the buckets are only partly occupied by the water passing through them, the atmosphere having free access to the remain- ing space. A reaction turbine is driven by the IMPCLSE TUHBINE. dynamic pressure of the flowing water, which at the same time may be under a certain static pressure, due to the fact that the inflow takes place under pressure, since the wheel is always filled with water. In the impulse turbine the inflow takes place freely against air pressure only. Most turbines are built on the reaction principle, but any turbine may be made to work eitlier as a reaction turbine or an impulse tur- bine. Structurally, a turbine consists (1) of a ring or a pair of rings, to which are attached curved vanes arranged uniformly around the circum- ference, revolving on a shaft or spindle to which the ring or pair of rings is connected by a boss and arms or other suitable means, and (2) of a casing which incloses the part just described, and which generally is provided with guide vanes be- tween which the water enters the wheel, and which cause the water to enter in the desired direction. The supply of water to the turbine is regulated by a gate or gates, which can partially or entirely close the orifice where the water en- ters or leaves. The guides and wheel with the gates and the surrounding cases are made of iron. Numerous forms of turliincs with diff'erent kinds of gates and different proportions of guides and vanes are on the market. They are made of all sizes from fi to 00 inches in diameter, and larger sizes are built for special cases. On account of their cheapness, durability, compactness, and high efficiency, turbines are now more extensively used than all other kinds of hydraulic motors. See Water Wheel and Hydbaulic-Pressure Engike. The three kinds of turbines, namely, radial, axial, and combined, may be mounted on either vertical or horizontal shafts, and the water may flow through them in both directions. Thus in a radial turbine the water may flow inward from the circumference to the centre, or outward from the centre toward the circumference: in an axial turbine it may flow from the top down- ward or from the bottom upward : and in a com- bined turbine it may flow inward and up or down or outward and up or down. Ordinarily turbines are mounted on vertical shafts and water flows through them either inward, uutward, or downward, in all cases the water should leave the turbine wdth low velocity, or, in other words, the most of the energy should have been taken up in passing through the wheel. The three ordinary forms of turbine are often called by the names of those who first invented or per- fected them ; thus the outward-flow turbine is called the Fourne.vron turbine, the inward-flow turbine is called the Francis turbine, and the downward -flow turbine is called the Jonval tur- bine. Besides these there is the combined tur- bine, in which ordinarily the flow is usually in- ward and downward. The usual efficiency of tur- bines at full gate is from 70 per cent, to 85 per cent, of the power theoretically available. The speed of rotation of a turbine is regulated by opening and closing the gate which admits the water to the wheel. Where the power used fluctuates the speed will fluctuate unless some method is adopted to adapt the power developed to the power utilized. This is usuall}- done by means of a governor, which is so devised that when little power is being used the resulting in- crease in speed will actuate it to close partly the gate, and when mvich power is being used the decrease in speed will actuate it to open the gate wider. The wheel and the shaft which it carries have to be supported from a bearing near the top, but more often they are carried on a sort of point bearing at the bottom. At Niagara Falls the weight of the wheel and shaft is supported by the upward pressure of the water against a disk in the top of the wheel case. For every turbine there is a certain velocity of rotation which gives a higher efficiency and power than any other velocity, and this may be calculated mathematically when the form and dimensions of the vanes and guides are known, or it may be determined experi- mentally. The theory of turbines is a com- plicated subject, and the reader interested in in- vestigating it should consult one of the following books: Jlerriman. Treatise on Hi/draulic Motors (New York. 1900) ; Bodmer. Hydraulic Motors, Turbines, and Pressure Engines (New York, 188(1). A description of a number of the most used turbines is given in Frizell, Water Pou-er (New York, 1901). See Water Power and Water Wheels. Steam Turbines are described under that title. TTJKBIT. A fancy breed of domestic pigeons, varying in colors and crest, with a flattened head, very small beak, ruffled breast, and other oddi- ties. See Colored Plate of Pigeons. TT7EB0T (OF. turbot, from Lat. turbo, top). The most valuable of the flatfishes {R)iombus maTimus) , and one of the most toothsome of all fishes. It abounds off the northern coast of Europe, and attains a large size, sometimes 70 to 90 poiuids in weight. Its form is shorter, broader, and deeper than that of almost any other flatfish. It is brown in color on the upper surface, which is studded with hard roundish tubercles. Like the other flatfishes, it generally keeps close to the bottom of the sea ; and is found chiefly on banks where there is a con- siderable depth of water. See Flatfish; and Plate of Flatfish and Flounders.
