TURBOT ward-flow and the Jonval parallel-flow tur- bines are most used in Europe. Regulation is effected by a vertically sliding gate (K, fig. 1), by a set of valves at the entrances to the wheel (figs. 4, 5, 6), or by varying the posi- tions of the guide blades themselves. The most perfect method would be by varying the velocity ratio of the wheel and the driven mechanism. The loss of efficiency in reducing the power of the wheel by regulation is often serious. Eankine states this loss as follows : Openin iT . . 1 | I | Ratio of efficiency 1 |
| Whitelaw's turbine is a simple form of wheel without guide blades. Barker's mill was a very rude apparatus consisting of a vertical spout surrounding the shaft and conducting the wa- ter to hollow horizontal arms, from the ex- tremities of which it emerged tangentially to FIG. 6. Leffel Turbine. Divided Flow. the orbit of the orifices. These wheels are usually known as reaction wheels; their effi- ciency is comparatively small. See Francis, " Lowell Hydraulic Experiments " (Boston, 1855) ; Eankine, " Steam Engine and Prime Movers " (London, 1859) ; and Mahan, " Hy- draulic Motors" (New York, 1873). TURBOT, a marine, soft-rayed fish of the flat- fish family, and genus rhombus (Cuv.), charac- terized by minute sharp teeth on the jaws and pharynx, the dorsal fin commencing on the head in front of the eyes, and like the anal ex- tending to the tail, and the eyes on the left side. The European turbot (R. maximus, Cuv.), the finest of the family, sometimes measures 6 ft. in width, and weighs over 200 Ibs. ; the left side is brown and covered with small tubercles, and the right side or lower surface smooth and white; without the tail the body is nearly round ; mouth large, opening obliquely up- ward; eyes in a vertical line, one over the other; gill openings large; pectorals small. It keeps on sandy grounds, and is a great wan- derer, usually in companies, living near the bottom, and feeding on small fish, crustaceans, and mollusks ; though voracious, it is particu- European Turbot (Rhombus maxtmus). lar in its choice of food, and will bite at none but fresh bait ; the spawning season is about August, after which it soon recovers its good condition. Its flesh is white, fat, flaky, and delicate, and has been highly esteemed from remote antiquity ; it is disputed whether this or the next species was the rhombus of the ancient Romans ; the French call it water or sea pheasant on account of its fine flavor. Though not uncommon on the coasts of Great Britain, most of the turbot sold in the English markets are caught by Dutch fishermen on the long line of sandy banks between England and Holland. The fishery begins about the end of March and closes by the middle of August, and is prosecuted both by lines and trawl nets. The brill, pearl, or smooth turbot (JR. vulga- ris, Cuv.) is a smaller and less delicate species, with smooth scales, from the same localities ; the under jaw is the longer, and the upper eye a little behind the lower ; it is reddish sandy brown, varied with darker, and sprinkled with white pearl-like specks ; under surface smooth and white ; it is found in the Mediterranean, as are several other species still less esteemed. The American or spotted turbot (R. macu- latus, Girard; pleuronectes, De Kay), called also New York plaice and watery flounder, is from 12 to 18 in. long, and 6 to 8 in. wide, sometimes attaining a weight of 20 Ibs. ; it is smooth, on the left side reddish gray with large circular or oblong darker blotches sur- rounded by a lighter margin, and with nu- merous white spots, especially on the fins ; the lower surface white and spotless ; iris silvery ; gape wide, with a single row of separate, large, sharp teeth, and a protuberance on the chin ; ends of dorsal rays free ; body elongated ; it resembles the brill more than any other Euro-
