APERTURE, an opening through a body. An aperture in a wall has generally three straight sides, two of which are perpendicular to the horizon, and the third parallel to it, connecting the lower ends of the vertical ones. The stones forming the perpendicular sides are called jambs, the level side below is called the sill, and the upper part is called the head. The head of an aperture is either an arch, or a single stone, or beam.
Apertures are either made for entrance, light, or orna ment. See DOOR, RECESS, and WINDOW.
A narrow aperture may he covered with a single stone, to such horizontal dimensions as may be found convenient to raise from the quarry.
\Vhen the aperture is wide, stones in separate pieces may be joggled together, in order to form a straight arch, as it is absurdly called by workmen; or the same kind of arch may be made with radiating joints concealed within the thickness of the wall, and vertical joints on the front, secured by strings or cramps of iron, if necessary ; when an aperture is very wide, it becomes necessary to arch it over.
Too great a variety of 'apertures in the same front of a building destroys its uniformity.
The ancient Greeks and Romans made the sides of aper tures frequently incline toward each other at the top.
Apertures are sometimes made quite circular or elliptical; but these forms are not in general use. In apertures of stone-work, if the jambs be of one entire piece, every alter nate stone in the height of the aperture, next to the jambs, should be bond-stones; likewise, if the jambs consist of several stones in the height, every alternate jamb-stone should be a bond-stone. See STONE WALLS and WINDOWS, in MASONRY.
When the heads of apertures are arched, they require to he supported on centres while building ; the method of con structing which is shown under the article CENTRE. APEX, the highest point or summit of a structure.