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44 apart, which is called the Tuscan Intercolumniation, and which makes the space between the columns about square. In modern times, also, an arrangement of coupled columns has been employed, called Areosystyle, the columns being set half a Diameter apart, and the space between the pairs of columns made three and one-half Diameters. This is greater than the Diastyle Intercolumniation and less than the Areostyle by half a Diameter. From the axis of one pair of columns to that of the next pair the distance is six Diameters. If in a Systyle Colonnade, with the columns three Diameters on centers, the alternate columns are moved along until they nearly touch the intervening ones, the result is an Areostyle Colonnade. This was first used by Perrault in the Eastern Colonnade of the Louvre, Fig. 153.

In actual practice these rules for Intercolumniation are seldom exactly followed.

DORIC INTERCOLUMNIATIONS—PLATE XVIII

In the Doric Order, since the Columns .come exactly under the Triglyphs and the Triglyphs are one and one-fourth Diameters on centers, as on edges (the width of the Triglyph being one-half of a Diameter and that of the Metopes three-fourths of a Diameter), the distance of the Columns on centers must needs be a multiple of one and one-fourth Diameters.

This makes the coupling of Doric Columns difficult, since, even if the Bases touch, the distance between axes is still one and one-third Diameters, which is more than that of the Triglyphs by one-twelfth of a Diameter. This slight discrepancy can, however, be got over by making each Base a trifle narrower, or the Triglyphs and Metopes a trifle wider, or by putting the Columns not exactly under the Triglyphs, or by employing all these devices at once.

If the Columns are set under alternate Triglyphs so that there is one Triglyph over the intervening space, their distance apart on centers is two and one-half Diameters. The Intercolumniation is then one and one-half Diameters, and is said to be Monotriglyph. This is the most common arrangement. But if the scale is small, it is usual, at least at the principal entrance of a building, to have two Triglyphs over the opening, the Columns being three and three-fourths Diameters on centers. The Intercolumniation is then two and three-fourths Diameters, and is called Ditriglypk. Still wider spacing is employed when the Architraves are of wood.

When two, four, six, eight, ten, or twelve Columns are used in a Colonnade or Portico, it is said to be Distyle, Tetrastyle, Hexastyle, Octastyle, Decastyle, or Dodecastyle, according to the Greek numerals. Examples are found at Argos, Assos, Thoricus, and Psestum of fagades with an odd number of columns, three, five, seven, and nine, a column instead of an intercolumniation coming on the axis, giving tristyle, pentastyle, heptastyle, and enneastyle porticos. But in all these cases the entrances were apparently on the sides of the buildings, where there was an even number of columns.