§ 1. Thus far we have been concerned with the outline only of the aperture: we were next, it will be remembered, to consider the necessary modes of filling it with valves in the case of the door, or with glass or tracery in that of the window.

(1.) Filling of doors. We concluded, in the previous chapter, that doors in buildings of any importance or size should have headings in the form of an arch. This is, however, the most inconvenient form we could choose, as respects the fitting of the valves of the doorway; for the arch-shaped head of the valves not only requires considerable nicety in fitting to the arch, but adds largely to the weight of the door,—a double disadvantage, straining the hinges and making it cumbersome in opening. And this inconvenience is so much perceived by the eye, that a door valve with a pointed head is always a disagreeable object. It becomes, therefore, a matter of true necessity so to arrange the doorway as to admit of its being fitted with rectangular valves.

§ 2. Now, in determining the form of the aperture, we supposed the jamb of the door to be of the utmost height required for entrance. The extra height of the arch is unnecessary as an opening, the arch being required for its strength only, not for its elevation.