CHAPTER XVIII

PROTECTION OF APERTURE

§ 1. WE have hitherto considered the aperture as merely pierced in the thickness of the walls; and when its masonry is simple, and the fillings of the aperture are unimportant, it may well remain so. But when the fillings are delicate and of value, as in the case of coloured glass, finely wrought tracery, or sculpture, such as we shall often find occupying the tympanum of doorways, some protection becomes necessary against the run of the rain down the walls, and back by the bevel of the aperture to the joints or surface of the fillings.

§ 2. The first and simplest mode of obtaining this is by channelling the jambs and arch head; and this is the chief practical service of aperture mouldings, which are otherwise entirely decorative. But as this very decorative character renders them unfit to be made channels for rain water, it is well to add some external roofing to the aperture, which may protect it from the run of all the rain, except that which necessarily beats into its own area. This protection, in its most usual form, is a mere dripstone moulding carried over or round the head of the aperture. But this is, in reality, only a contracted form of a true roof, projecting from the wall over the aperture; and all protections of apertures whatsoever are to be conceived as portions of small roofs, attached to the wall behind; and supported by it, so long as their scale admits of their being so with safety, and afterwards in such manner as may be most expedient. The proper forms of these, and modes of their support, are to be the subject of our final inquiry.

§ 3. Respecting their proper form we need not stay long

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[Version 0.04: March 2008]