them, causing them all to move in a direction transversely to that of the wind. Suitable means are provided for bringing the sails into a position to confront the current of the wind. The motion of the sails is transferred by gearing to any machinery required to be driven, which is most commonly mills for grinding corn. Windmills were formerly extensively employed, in Holland, to give motion to pumps for the drainage of land. The power of the wind is uncertain and variable in its intensity, and its application as a prime mover for mechanical purposes is consequently limited.

Windows were almost unknown in the religious and other monumental structures of the Egyptians, Greeks, and Romans, but they constitute an essential and distinguishing feature of the Gothic, to which style they stand in the same relation as Orders do to the temple architecture of antiquity.

Windows admit of very rich and varied decoration, and those in Beccles church, Suffolk, (represented on the opposite page,) are beautiful examples. The varied exuberance of fancy displayed in the tracery may possibly be accounted for by supposing each to have been the gift of some pious individual, who, while he perpetuated his munificence, marked also his taste and ingenuity.

The practice of window tracery every where had its origin in window-grouping, placing two or three lancet windows beside each other, and one or more foil or rosette windows above and between their heads, in order to fill out the arched cell of the vaulting, which then necessarily gave the whole group an arched outline; and this was indicated by a general dripmould or label. It then became desirable to lighten the irregular shaped masses of stone left between the perforations, and this was done

by piercing these masses, or spandrils, and reducing the solid frame of each foil or rosette to an equal thickness all round, as if several such frames or rings were packed into one great arched opening, which henceforth was regarded as one window instead of several. (For further illustration, see art. Tracery.)

Wind-sail, in navigation, a sort of ventilator, consisting of a wide tube of canvas shaped like a funnel, to convey a stream of fresh air downwards to the hold and lower deck of a ship

Wing transom, in ships, the upper

most transom of the stern-frame Winze, in mining, a sinking in a lode communicating with one level, for proving the lode or ventilating the drivings

Wipers, the cogs of a horizontal wheel Wood, in its raw state, contains a

large amount of water. This water contains more or less soluble minerals, and is called sap. By drying wood, a great part, but not all, of this water is evaporated. If wood is dried in a closed vessel, and then exposed to the atmosphere, it quickly absorbs moisture; but the moisture thus absorbed is much less than the wood originally contained.

The amount of water varies in different kinds of wood, and also varies according to the season. Wood cut in the month of April contains from 10 to 20 per cent. more water than that cut in the month of January.

The following Table shows the percentage of water in different kinds of wood dried as far as possible in the air:

38.2

39.0

45.5

47.1

48.2

51.8

Wood cut during the months of December and January is not only more solid, but it will dry faster than at any other period of the year, because the sap by that time has incorporated a great part of its soluble matter with the woody fibre; what remains is merely water. When the sap, during the months of February, March, and April, rises, it partly dissolves the woody fibre; and the drying of the wood is not only retarded, but the wood is weakened, in consequence of the solid matter thus held in solution.

The difference in chemical composition of the woody fibre, in most kinds of wood, is but slight, as the following analytical Table shows:

Hy- OxyCarbon. drogen. gen. Sugar Maple 52.65 5.25 42.10 Oak 49.43 6.07 44.50 Poplar, black 49.70 6.31 43.99 Pine 50-11 6.31 43.58

Working-big, in mining, signifies sufficiently large for a man to work in

Working drawings consist of plans, elevations, sections, and details in full, of the whole, and of all the parts of an edifice, to as large a scale as may be found convenient; generally made in outline, excepting the sectional parts, which are mostly shadowed, in order to make them more obvious to the workman, for whose use these drawings are made Worm-wheel, a wheel having teeth formed to fit into the spiral spaces of a screw, so that the wheel may be turned by the screw Wreath, in heraldry, that which is between the mantle and the crest, called also a torce; also a boar's tail, so termed among hunters Wrought iron. The chemical difference between cast iron and wrought iron consists principally in the degree in which foreign matter is present in each; which is in larger amount in the former than in the latter. This rule is applicable only to a given cast iron, and to the wrought or bar iron which is made from it. There are many cases in which wrought iron contains a larger amount of impurities than cast iron, and still continues malleable; while cast iron of the same composition may be very hard and brittle. Berzelius detected 18

per cent. of silex in a certain kind of bar iron, which was still malleable and useful. One-tenth of that amount of silex will make cast iron brittle. The foreign matters generally combined with pig iron are, carbon, silicon, silex, sulphur, phosphorus, arsenic, zinc, manganese, titanium, chrome, aluminium, magnesium, and calcium. Each of these tends to make iron brittle; therefore, in converting cast into wrought iron, it is necessary, as far as possible, to remove them.

The main difference between pig and wrought iron consists in their mechanical structure, or aggregate form. Pig iron is a homogeneous mixture of impurities and metal. Wrought or bar iron is a mixture of iron more or less pure with a mass of homogeneous impurities, or cinder, the latter filling the crevices between the crystals of the iron. Iron being fusible in proportion to the carbon it contains, if pig metal is melted, and the cinder surrounding it exposed to the atmosphere, the carbon will be volatilized in the form of carbonic acid, and iron of greater or less purity will remain. To keep this iron liquid, a higher temperature is required: unless the temperature is raised, it will crystallize. In this state of metamorphosis its infusibility will increase, and after the expulsion of the carbon, it will contract into a solid mass in opposition to the highest possible heat. By stirring and mixing the pasty iron, small crystals are formed; at first, on account of the partial fusing of the iron, in small particles; but, as the fusibility diminishes, these particles unite by the force of cohesion; and the bodies thus formed may, by exposure to a higher heat, be welded together. The mixing of cinder and iron will prevent the latter from forming large crystals: this result, of course, will be more easily prevented by diligent than by tardy manipula

tion. Where the pig iron is of such a nature as to keep liquid while the work goes on slowly, still better results will be obtained. This process is analogous to that of salt boiling, in which, by stirring the brine, the formation of large crystals is prevented. If the crystals of iron thus formed cohere, they produce, under the influence of motion, a porous, spongy mass, whose crevices are, if not filled, at least coated, with cinder. If these masses, which are the loups or balls at the puddling furnaces, are shingled or squeezed, the crystals of iron will not unite, but form coated cells with a film of cinder, of greater or less thickness, according to the fusibility of the cinder. Iron in a connected form, and cinder in separate cells, are thus blended in one homogeneous mass. The more this iron is stretched, the more it forms fibres. Fibrous bar iron resembles hickory wood, in being a combination of fibres and spaces. In bar iron, these spaces are filled with cinder. When other circumstances are equal, the strength of the iron will be proportional to the fineness of the fibres. That portion of the iron which is not melted, which crystallizes too fast, or whose premature crystallization cannot be prevented, is in the condition of cast metal, and cannot be converted into fibrous wrought iron. In the puddling furnace it is necessary to prevent crystallization by manual labour.

If the characteristic between wrought and pig iron consists only in a well-regulated mechanical mixture of cinder and iron, fibrous iron should be producible from any cast iron, whether purified or not: this is actually the case. Very fibrous bar iron, which is strong and malleable, is made from very inferior cast metal, from which no impurity has been removed. At Hyanges, in France, very inferior metal is converted by a cheap and skilful pud

dling process, into a very fibrous bar iron, of great strength and ductility. But this iron is puddled and re-heated at the lowest possible heat; it is then rolled, and is ready for the market. For hoops, rails, and nails, it is a very useful article, but is of no use to the blacksmith. Heated to any temperature above that of the puddling and re-heating furnaces, it returns to its primitive state, in which condition it becomes worse than the cast iron from which it was originally made. None but a very skilful blacksmith can weld it; for, when slightly re-heated, it falls to coarse sandy pieces, or melts like pig iron. That which thus loses its fibrous texture in heating, the smith calls burnt iron.'

The philosophy of the improvement of metal consists in the circumstance that a part of its impurities which are originally in chemical combination, are converted into mechanical admixtures. Iron containing a small amount of carbon, silicon, or phosphorus, is always more hard and strong than pure iron. Pure iron is quite soft. Impure iron has the property of crystallizing, on being suddenly cooled the size of these crystals is proportional to the amount of carbon in chemical combination with the iron, in proportion to other matter. Between the crystals minute spaces are left, which serve for the absorption of oxygen. By this means, silicon and calcium may be oxidized, but not carbon, phosphorus, and sulphur. The metal improves in quality in proportion as oxygen finds access to its impurities.

The absolute cohesion or strength of wrought iron is not dependent upon the degree of purity of the metal, but upon a given mixture of cinder and iron. Pure iron, which is always soft, may be required for various purposes, as in the manufacture of cast steel; but, in most

cases, an impure but fibrous iron is preferable. In making wrought iron, the main difficulty consists, not in producing fibres in the first stages of the operation,-for this may be accomplished by almost every experienced manufacturer,— but in retaining these fibres through every subsequent stage of the operation.

Wrought iron of good quality is silvery white and fibrous; carbon imparts to it a bluish, and often a gray colour; sulphur, a dark, dead colour, without a tinge of blue; silicon, phosphorus, and carbon, a bright colour, which is the more beautiful the more the first two elements preponderate. The lustre of iron does not depend principally upon its colour; for pure iron, although silvery white, reflects but little light. A small quantity of carbon in chemical combination, phosphorus, or silicon, increases its brilliancy. Its lustre is diminished by silex, carbon in mechanical admixture, cinder, lime, sulphur, or magnesia. Good iron should appear fresh, somewhat reflex in its fibres, and silky. A dead colour indicates a weak iron, even though it is perfectly white. Dark but very lustrous iron is always superior to that which has a bright colour and feeble lustre. Coarse fibres indicate a strong, but, if the iron is dark, an inferior article. Where the iron is of a white, bright colour, they indicate an article of superior quality for sheet iron and boiler-plate, though too soft for railroad iron. For the latter purpose, a coarse, fibrous, slightly bluish iron is required. Iron of short fibre is too pure; it is generally hot-short, and, when cold, not strong. This kind of iron is apt to result from the application of an excess of lime: its weakness is the result of the absence of all impurities. The best qualities of bar iron always contain a small amount of impurity. Steel ceases to be hard

YACHT, in navigation, a small ship for

carrying passengers

Yard, a court enclosed by walls and other buildings; also a measure of 3 feet a yard or yerd was anciently a spar or rafter in a timber roof.

Yardland, a certain quantity of land, called, in Saxon, gyrdlander; in Latin, virgata terræ: in some places it is 20 acres of land, in others 24 or 30

Yellow is the first of the primary or simple colours, nearest in relation to and partaking most of the nature of the neutral white; it is accordingly a most advancing colour, of great power in reflecting light. Compounded with the primary red, it constitutes the secondary orange and its relatives, scarlet, &c., and other warm colours.

Yellow Lake. There are several pigments of this denomination, varying in colour and appearance, ac

YEL

cording to the colouring substances used and modes of preparation. They are usually in the form of drops, and their colours are, in general, bright yellow, very transparent, and not liable to change in an impure atmosphere,-qualities which would render them very valuable pigments, were they not soon discoloured and even destroyed by the opposite influence of oxygen and light, both in water and oil, in which latter vehicle, like other lakes in general, they are bad dryers, and do not stand the action of white lead or other metallic colours. If used, therefore, it should be as simple as possible.

Yellow Ochre, called also Mineral Yellow, is a native pigment, found in most countries, and abundantly in our own. It varies considerably in constitution and colour, in which latter particular it is found from a