PEDIMENTS—PLATE XVII
The Gable upon a Classical building is called a Pediment, Fig. 146. It consists of a Triangular piece of wall, called the Tympanum, which is in the same plane as the Frieze below; of a Horizontal Cornice, which divides the Tympanum from the Frieze; and of two pieces of inclined cornice that surmount the Tympanum. The inclined, or Raking, Cornice is like the cornice that crowns the wall on the sides of the building, but the Cymatium is a little wider. The Horizontal Cornice has no Cymatium, and generally terminates in a Fillet, called the Split Fillet, which divides at the angle where the two Cornices come together.
If the Cymatium is a Cavetto, the under side of the Fillet beneath it is beveled, either on the rake or along the wall; if it is an Ovolo, the same thing happens to the Fillet above it, Fig. 147. With the Cyma Reversa both occur, with the Cyma Recta, neither, the fillets having no soffit. This is one of the reasons for employing this molding in this place.
When a Cyma Recta is used in the Cymatium, it occurs in four different forms, Fig. 148; viz.: (1) the profile of the molding along the wall; (2) the profile of the raking molding; (3) the line of intersection of these two moldings this lies in a vertical plane, set at 45 degrees; (4) the, line of intersection of the two raking moldings at the top. (1), (2), and (4) have the same projection but different heights; (1) and (3) have the same height but not the same projection.
According to Vignola, the obtuse angle at the top of the Pediment is included within an arc of 90 degrees. It accordingly has a slope of 22 degrees. This is a good rule for most cases. But if a building is high and narrow, the slope needs to be steeper, and if it is low and wide, flatter. Inasmuch, however, as, for a building of a given width, the higher it is, the larger is the scale of the Order employed and of all the details of the Order, it follows that, for a given width of front, the larger the moldings are, the steeper must be the slope.
