INTERPENETRATION.--A German mode of treating mouldings, as though two or more sets of them existed in the same stone and they could pass through (interpenetrate) each other. JAMB.--The side of a door or window or arch, or other opening. [Illustration: FIG. _V_.--PLAN OF A JAMB AND CENTRAL PIER OF A GOTHIC DOORWAY.] KEEP.--The tower which formed the stronghold of a mediæval castle. KING POST.--The middle post in the framing of a timber roof. LANCET ARCH.--The sharply-pointed window-head and arch, characteristic of English Gothic in the thirteenth century. LANTERN.--A conspicuous feature rising above a roof or crowning a dome, and intended usually to light a Hall, but often introduced simply as an architectural finish to the whole building. LIERNE (rib).--A rib intermediate between the main ribs in Gothic vaulting. LIGHT.--One of the divisions of a window of which the entire width is divided by one or more mullions. LINTEL.--The stone or beam covering a doorway or other opening not spanned by an arch. Sometimes applied to the architrave of an order. LOGGIA (Italian).--An open arcade with a gallery behind. LOOP.--Short for loophole. A very narrow slit in the wall of a fortress, serving as a window, or to shoot through. LUCARNE.--A spire-light. A small window like a slender dormer window. MOAT (or Fosse).--The ditch round a fortress or semi-fortified house. MOSAIC.--An ornament for pavements, walls, and the surfaces of vaults, formed by cementing together small pieces of coloured material (stone, marble, tile, &c.) so as to produce a pattern or picture. MOULDING.--A term applied to all varieties of contour or outline given to the angles, projections, or recesses of the various parts of a building. The object being either to produce an outline satisfactory to the eye; or, more frequently, to obtain a play of light and shade, and to produce the appearance of a line or a series of lines, broad or narrow, and of varying intensity of lightness or shade in the building or some of its features. The contour which a moulding would present when cut across in a direction at right angles to its length is called its profile. The profile of mouldings varied with each style of architecture and at each period (Figs. _W_ to _Z_). When ornaments are carved out of some of the moulded surfaces the latter are technically termed enriched mouldings. The enrichments in use varied with each style and each period, as the mouldings themselves did. MULLION.--The upright bars of stone frequently employed (especially in Gothic architecture) to subdivide one window into two or more lights.