433 



TURBARY, COMMON OF. 



TURF. 



434 



PRINCIPAL CANAL TVSNELS. Length. Cost per yard. 



Yards. t. d, 



Noirieu (Canal de St. Quentin) . . 13,128 216 



Sousey (Canal de BourgORne) . 3852 920 



Pouilly (Canal de Bourgogne) . . 3660 78 15 



Mauvages (Canal du Marne au Rhin) 5320 65 



St. Aignan (Canal des Ardennes) . 288 40 



PRINCIPAL RAILWAY TUNNELS. 

 Summit tunnel, Ashton and Manchester 



Railway 5192 



Box tunnel, Great Western . . . 3227 100 



Littleborough 2869 



Sapperton 2800 



Kilsby 2423 133 



\Vutford 1793 



Merstham 1780 



White Ball Hill 1470 



Shakespere tunnel ..... 1300 



Primrose Hill 1250 



Bletchingley 1086 80 



Saltwood 1000 140 



Rollebois (Paris and Rouen) . . . 2890 40 



Venables 291 40 



Pissy Porille (Rouen and Havre) . . 2400 4000 



Terre Noire (Lyon) 1641 30 



Camptich 1017 31 



St. Cloud 554 80 



Nerthe (Avignon to Marseille) . . 5032 



Blaisy (Lyon) 4376 



Rilly (Rheims) 3829 



Hammarting (Switzerland) . . . 3050 



Hauenstein 2731 



Railway tunnels are usually made about 24 feet wide, and from 23 

 to 25 feet high, on the narrow gauge ; those on the Great Western line 

 are made 30 feet wide by 35 feetr high ; canal tunnels are rarely 

 executed of larger dimensions than 16 feet 6 inches in breadth by 18 

 feet in height. 



There had been two or three schemes for forming a tunnel under 

 the Thames, prior to that brought forward in 1823 by Mr. (afterwards 

 Sir) Isambard Mark Brunei : one proposing to connect Gravesend with 

 Tilbury, another to commence at Rotherhithe, a little below the site 

 of the present tunnel ; and works had been actually begun at both 

 these places but soon abandoned. Brunei proposed to effect his object 

 by means of a framework or shield, which should support the face of 

 the excavation and allow the earth to be removed on many points 

 simultaneously; the frames or divisions of the shield being then 

 moved slowly forward, and closely followed by a solid mass of brick- 

 work enclosing two arched passages 16 feet 4 inches in height from 

 the invert of the arch, and 13 feet 9 inches span at the springing of 

 the arch. Great difficulties were experienced in the course of the 

 work, and some serious accidents happened from the river breaking 

 through the moist sand and clay through which the tunnel had to be 

 carried. But ultimately all obstacles were overcome, and the work 

 was in 1842 brought to a successful termination, about seventeen years 

 from the commencement of the excavations. 



TURBARY, COMMON OF, is a right to dig turf in another man's 

 land, or in the lord's waste. This description of common right may 

 be appendant or appurtenant to a house, but not to laud ; for the 

 turfs dug in virtue of the right are to be burnt in the house. The 

 right is therefore confined to such quantity as is sufficient for the con- 

 sumption of the house to which the common of turbary is appendant, 

 and never extends to a right to dig turf for sale. 



Where common of turbary is appurtenant to a house, it will pass by 

 a grant of the house with the appurtenances. (2 Hep. 37, Common.) 



TURBINE. A turbine is a water wheel fixed upon a vertical revol- 

 ving axis, receiving and discharging water in various directions round 

 its surface. This description of prime mover consists of a drum, 

 bearing a number of suitably formed vanes, curved in such a manner 

 as to allow the water leaving them, after it has glanced off' from them, 

 to escape with as little velocity or power as possible. Turbines 

 possess the advantage of occupying, comparatively with the power 

 exercised, a very small bulk ; and of being equally efficient with large 

 or small falls. 



There may be considered to be three classes of turbines: 1st. Those 

 in which the water is supplied and discharged in a direction parallel 

 to the axis ; they are technically known as the paralkl-fnw turltincn, 

 according to the classification proposed by Professor Rankine, in his 

 ' Treatise on Prime Movers." 2nd. Those in which the water is sup- 

 plied and discharged in currents radiating from the axis : or the out- 

 ward lime turbines. And 3rd. Those in which the water is supplied 

 and discharged in currents converging radially towards the axis, or 

 the inward flaw turbines. The leading principles affecting the working 

 of these various machines are the same, though the details are neces- 

 sarily dissimilar ; they may be briefly described as follows : 



Whatever description of turbine be used, it is desirable that little 

 or no change of velocity of flow should take place in the current, 

 during the passage of the water through the wheel ; and that the 

 water should enter without shock, and leave without a whirling 

 motion. The latter condition is attained when the ratio of the 



ARTS AND SCI. DIV. VOL. VIIL 



entering velocity is to the outgoing velocity in the same ratio as the 

 radius of the receiving to that of the discharging sides; or calling 



this ratio , it =1, in parallel flow turbines; -y/iJ in outward flow 

 turbines; and 4 in inward flow turbines. The angles of obliquity of 

 the blades to the line of flow, differ according to the velocity required 

 in the wheels, and to their peculiar form : thus, in the parallel flow 

 turbines, the angle may vary between 20 and 35 ; in the outward 

 flow turbines, between 144 an< l 26^ ; and in the inward flow ones, 

 between 36 and 54, the best velocity at the middle of the rings 

 of the vanes appears to be ascertained by the formula (for all kinds 

 of turbines) calling v the velocity, h the head in the supply chamber, 



and g the accelerating force of gravity : then v = 0'655 V2ffA. 



From General Moriu's experiments it would appear that the 

 efficiencies of the respective descriptious of turbines, with reference 

 to the powers exerted upon them, are comprised within the limits of 

 from 75 to 80 per cent, of the power exerted in the parallel flow 

 turbines ; in inward flow turbines the limits approach closely the 

 average of 73 per cent. ; and in outward flow ones, they are on 

 the average 68 per cent. ; on the average then, the efficiency of all 

 classes may be taken to be about 70 per cent, of the total power. 

 The reaction wheel may be considered to constitute a modification of 

 the turbine ; and it will be discussed more fully under WATER POWER. 



The best descriptions of this class of engines are to be found either 

 in Rankine's work before quoted ; in Morin's ' Lecons de Mdcanique 

 Pratique ; ' in Armengaud's ' TraitxS Pratique des Moteurs Hydrau- 

 liques ; ' and in several of the practical papers on machinery by Mr. 

 Fairbairn. M. Fourneyron has published a description of the outward 

 flow turbines he himself invented, with full instructions for ascer- 

 taining the proportions of the several details. 



TURF, the sod which covers the surface of pastures, and is composed 

 of a portion of the soil with the roots of natural grasses or other 

 plants ; which gives the whole a consistence, and allows of its being 

 raised in slices by the plough, or the paring tool made for the 

 purpose. 



The word is often also applied to the substance which is generally 

 called peat ; and when the latter is taken frnm the surface where living 

 plants are growing, the name of turf is very applicable to it It is 

 derived from the Dutch word torf, which is generally applied to perfect 

 peat as well as to turf. The origin and composition of peat have been 

 described under that head. [PEAT.] We shall here only notice the 

 uses to which turf is applied, when we mean a sod taken from the 

 surface on which some living plants are still or have lately been 

 growing. Near extensive heaths which have never beeu reclaimed, 

 and in situations where no regular peat-bogs are to be found, turf 

 becomes a very useful fuel. It is pared off the surface with the heath 

 growing on it, in dry weather, -in sods of a convenient size, generally 

 round, and about one foot in diameter. The thickness of the sod 

 depends on the depth and abundance of the roots found in it, as they 

 are the sole cause of the turf continuing to burn when the blaze caused 

 by the burning of the heath is over. As the soil of the places where 

 turf is usually cut is generally of a sandy nature, turf ashes are not so 

 valuable for manuring the land as peat ashes ; still they contain por- 

 tions of potash and other vegetable salts, and produce a very good 

 effect when spread as a top-dressing on moist meadows the soil of which 

 is chiefly composed of clay. In sufficient quantities they are excellent 

 to raise turnips ; and it is generally observed that where poor heathy 

 pastures are pared for the purpose of burning the turf on the spot and 

 spreading the ashes, the turnips sown there seldom fail. For the 

 advantages and disadvantages of this operation, see PARING and 

 BURNING. 



Where the poor can readily obtain turf for the trouble of cutting it 

 and drying it for use, a degree of comfort is diffused through their cot- 

 tages which cannot be found where fuel is scarce. In the large open 

 chimney the whole family can be seated by a pile of turf burning on 

 the hearth. 



Turf is used for many other purposes, as well as for fuel. Laid like 

 tiles on a roof, overlapping each other, they form au excellent and 

 cheap protection against rain. Cut somewhat thicker, and in the shape 

 of bricks, they serve to build the walls of cabins, which are warm and 

 durable, provided the eaves of the roof project sufficiently to cover 

 them. The soldier who has served through many campaigns knows 

 from experience that a conical hut of turf can be raised in a very short 

 time, if the material is at hand. 



When clay is burnt to improve the texture of the soil, the operation 

 is best performed in a circular hearth made of turf, with certain flues 

 to regulate the supply of air to the burning mass. The turf is a slow 

 conductor of heat, and by its means the mass is kept burning steadily 

 in the interior of the heap, without being cooled by the effect of the 

 external air. When the turf-wall itself begins to burn through, it is 

 generally the proper time to mix the whole and extinguish the fire. 



The turf which we have been considering is taken from the surface 

 of uncultivated land, and in the course of a certain number of years 

 the wild heaths and other plants natural to the soil spring up again, 

 and by their stems and roots produce a fresh turf. To assist this 

 renovation it is usual to cut the flat turfs of a circular shape with a 

 thin paring tool, as we observed before, so that there remain portions 

 of the surface which are not disturbed, and from which the heath and 



F F 



