This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
107. Intercolumniation is the spacing of columns in the clear, especially of columns arranged in the form of a colonnade. When a figured dimension refers to the spacing it is invariably one diameter less than the distance from center to center of columns.
109. A colonnade is a row of columns spaced regularly and connected by an entablature. The space which separates these columns is called the intercolumniation. When the colonnade is composed of two or more rows of columns and the space which they enclose is covered and serves as a covered porch or entrance to a building, this porch is called a portico, and it is often crowned with a gable or pediment above the columns. Usually one side of a portico is closed by a wall, and sometimes three sides are so closed; in such a case the columns at the angles are replaced by pilasters to which the side walls are attached. Pilasters which are employed in this manner are called antae, and a portico of this kind is a portico "in antis." The term "antae" is more generally employed in Greek work and the term "pilaster" is used in Roman architecture.
110. When the portico is employed as a porch in front of an edifice, the columns are generally of an even number, and the spaces of uneven number, in order to have a space in the center opposite the door-way of the building. Even when an entrance is not placed behind the center of a colonnade it is considered inbet-ter taste to place the columns or arches so that a support does not come in the center of any such arrangement. When a pediment is placed over columns this rule is even more strictly followed. (Occasionally, usage determines that the intercolumniations of a portico shall be unecpial so that the central opening may be wider than the others, in order that the approach to the entrance to the building may be more ample.
111. The intercolumniation of the Roman Doric order is determined more or less by the fact that the columns are invariably placed directly under the triglyphs. It will be found difficult to space two columns under two adjacent triglyphs, because the bases and caps of the columns will overlap each other. Still, they may be so placed by enlarging the spaces between the triglyphs or reducing the projection of the cap and base, or both. It is not often that circumstances would justify such an alteration in the order to effect a close spacing of columns. When the columns are set under alternate triglyphs they are spaced about two and one-half diameters on centers. The intercolumniation is then one and one-half diameters, or as it is termed "monotriglyphic" or "pycnostyle," (Fig. 18). The width of the intercolumniations (spaces between columns) of a portico should seldom be less than one and one-half times the diameter of the column, and in old work it will rarely be found to exceed two and one-half diameters. In modern practice as in exceptional cases in ancient work, this spacing is, however, exceeded. When two trig-lyphs occur over the opening between the columns the intercolum-niation is about two and three-fourths diameters, and is called "ditriglyphic." Too great an intercolumniation produces a bad effect in all the orders. However, when the order is executed in wood a much wider spacing is often employed.
112. In the spacing of columns other than in Doric Order there is no such special requirement as to the location of the column under any particular part of the entablature, although where modillions or brackets are used they should be so spaced as to come over the axes of the columns. Such modillions or brackets are, however, easily varied slightly in spacing or-location, so that the system of intercolumniation in any other than the Doric Order is generally determined only by the diameter and height of the columns themselves. Columns are referred to as "coupled" when they are so placed that the bases or caps just avoid touching. This would space them about one-third to one-half their diameter apart, which is the least spacing that the outline of the column itself will allow. The various spacings of columns are generally termed coupled, pycnostyle, systyle, eustyle, diastyle, and arceostyle according as they are placed close together or are separated by 1, 1 1/2, 2, 2 1/4, 3 or 4 diameters. (Fig. 19.) The spacing of the coupled columns we have already explained. The pycnostyle intercolunmi-ation varies from one and one-quarter to one and one-half diameters. The systyle intercolmnniation has two diameters which in modern work would often seem too little. The eustyle has two and one-quarter diameters between the columns; or, as is sometimes preferred in modern practice, two and one-third diameters as in the Ionic and Corinthian orders. This corresponds more exactly to the customary spacing of dentils and modillions.
113. Closer intercolumniations are generally used on monumental work of large scale, while that of a more domestic character requires a wider spacing of columns for practical utilitarian purposes. During the Renaissance, the custom of placing columns in couples and taking each couple as a unit for working out the colonnade, was first adopted and has since, especially in France, been much employed. In modern practice the columns are placed less by rule than to satisfy the eye and the judgment of the designer. It must be remembered, however, that the axes of the columns must always be in accord with certain members of the entablature above, such as the triglyphs, dentils, or modillions, and also that, under a pediment, the columns themselves should be even in number.
114. A portico forming the front facade of an edifice, when there are not more than seven intercolumniations, may be crowned by a triangular gable or pediment which forms the roof of the porch.
115. A pediment is placed above the cornice of the entablature and is formed by two sloping cornices which are joined at the angles to the horizontal cornice. The crowning cyma-recta or cavetto follows the sloping cornice and is omitted from the horizontal cornice below the face of the pediment. The triangular face which is found between the three cornices corresponds in plane with the frieze of the entablature and is called the "tympanum" of the pediment.
The height of a pediment is determined as follows. In Fig. 20 let A be the point in which the axis of the pediment intersects the highest line of the horizontal cornice. With this point as a center and with a radius equal to one-half the width of the pediment, draw a semi-circle below the pediment as shown in the figure. This semi-circle intersects the axis of the pediment at the point B. With B as a center and with a radius equal to the distance from B to C (the extreme outside point of the horizontal cornice) draw an arc above the cornice. The point D, in which this arc intersects the axis, will be the highest point or "peak" of the pediment. Draw the lines DO and DE and the outline of the pediment will be complete.
PLATE XXII. (A reproduction at small size of Portfolio Plate XXII.)
In plate XXXIII is represented a portico of the Ionic Order with three intercolumniations which forms the front of an edifice intended for a hall or temple. The plan is a parallelogram of which the front or portico occupies one of the smaller sides.