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Originally appearing in Volume V17, Page 848 of the 1911 Encyclopedia Britannica.
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SECTION ON CENTRE See also:LINE See also:mss, 1 .- % See also:Stone See also:Arches.—Stone arches are very frequently used both in stone and See also:brick buildings. (For See also:general See also:definitions and terms see BRICK-See also:WORK.) They may be built in a See also:great variety of styles, either See also:flat, segmental, circular, elliptical or pointed. Each See also:block or See also:voussoir should be cut to See also:fit exactly in its appointed See also:place, the See also:joints being made as See also:fine as possible. The joints should radiate from the centre from which the See also:soffit or See also:intrados is struck, or in the See also:case of an elliptical See also:arch they should be at right angles to a tangent See also:drawn to the intrados at that point. The See also:extrados or back of the arch is usually concentric with the intrados, but is sometimes made thicker in one portion than in another; thus the arch may be deeper at the See also:crown than at the sides, or at the sides than in the centre. In some cases two or more voussoirs are of one stone, having a false See also:joint cut in the centre ; this is economical, and in some cases adds to the stability of the arch. Generally the arch is divided into an uneven number of voussoirs so as to give a See also:keystone, the voussoirs being laid from each See also:side of the keystone and fitting exactly in the centre of the arch. The keystone is not a See also:necessity, arches being frequently formed with an even number of voussoirs; some architects hold that the danger of the voussoirs cracking is thereby lessened. Where lintels are used in a stone See also:wall over openings of small span it is usual to build a relieving arch above to take the superincumbent See also:weight of See also:masonry; or the same purpose may be effected in walls of See also:ashlar by a flat relieving or " See also:save " arch, formed in the next course of three stones above the See also:lintel, the tapering keystone resting between the two side stones which are tailed well into the wall. In very many cases it is desired to See also:form square heads to openings of greater span than it is convenient to obtain lintels for in one piece, and some form of flat arch must therefore be adopted. The voussoirs are connected by joggles worked on their joints, as in fig. 17.

The weight of the superimposed wall is taken by a lintel with relieving arch above at the back of the arch. Arches built to an elliptical form when used for large spans (if of flat See also:

curve they should See also:bridge over 8 ft. or to ft.) are liable if heavily loaded to fail by the voussoirs at the centre being forced down, or else to burst up at the haunches. With arches of this description there is a large amount of outward thrust, and abutments of ample strength must be placed to receive the springers. Stone See also:Tracery.—The designs of See also:Gothic and other tracery stonework are almost See also:infinite, and there are many methods, ingenious and otherwise, of setting out such work. Nearly all diagrams of construction are planned on the principle of geometrical intersections. In the example illustrated in fig. 18 the method of setting out and See also:finishing the See also:design is very clearly shown, together with the best positions for the joints of the various parts. The jointing is a See also:matter which must be carefully considered in See also:order to avoid any See also:waste of stone and labour. It will be observed that the right-See also:hand side of the See also:elevation shows the method of setting out the tracery by the centre lines of the various intersecting branches, the other See also:half giving the completed design with the cusping drawn in and the positions of joints. All the upper construction of windows and doors and of See also:aisle arches should be protected from superincumbent pressure by strong relieving arches above the labels, as shown in the figure, which should be worked with the See also:ordinary masonry, and so set that the weight above should avoid pressure on the See also:fair work, which would be liable to flush or otherwise destroy the joints of the tracery. See also:Carving.—Stone carving is a See also:craft quite apart from the work of the ordinary stonemason, and like carving in See also:wood needs an See also:artistic feeling and See also:special training. Carving-stone should be of fine See also:grain and sufficiently soft to admit of easy working.

The See also:

Bath stones in See also:England and the See also:Caen stone of See also:France are largely used for See also:internal work, but if for the exterior they should be treated with some chemical preservative. Carving is frequently done after the stone is built into position, the See also:face being See also:left rough—" boasted "—and projecting sufficiently for the intended design. See E. See also:Viollet-le-Due, Dictionnaire raisonne de l'See also:architecture francaise; W. R. See also:Purchase, See also:Practical Masonry; J. O. See also:Baker, A See also:Treatise on Masonry Construction; C. F. See also:Mitchell, See also:Brickwork and Masonry; W. Diack, The See also:Art of Masonry in See also:Britain. (J.

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