Unit of Measurement of the Orders. Referring to Fig. 106, "The Parallel of the Orders," it will be possible to take up the con sideration of the main divisions of the three principal Roman Orders. The unit of measurement is again subdivided into two modules or semi-diameters. The module is further divided, in the accompanying illustrations and plates, sometimes into twelve parts, for the Tuscan and Doric Orders; into eighteen, for the Ionic, Corinthian, and Com posite; and sometimes into thirty parts, as in the Greek work. The scales shown on the plates are interchangeable, and may be used with either system, five parts of the latter exactly equaling three parts of the Ionic and Corinthian eighteen divisions, or two parts of the twelve divisions of the Doric Order. The general proportion of the heights of the columns of these five Orders is :—in the Roman Tuscan Order, seven diameters; in the Doric Order, eight diameters; in the Ionic Order, nine diameters; in the Corinthian and Composite Orders, ten diameters. The height of the entablature is always one-fourth the height of the column; thus, in the Tuscan Order, it is one and three fourths diameters; in the Doric, two diameters; in the Ionic, two and one-fourth diameters; and in the Corinthian and Composite, two and one-half diameters. TL s general statement of the proportions of the five Orders should be sufficient, at least so far as regards the first and last of the series; but the three principal Orders require more specific consideration.
At the right of the Roman Orders (Fig. 106), are shown dimen sion lines marked for proportionate divisions in height, these divisions being determined according to the unit of measurement indicated; the letter D standing for diameter and M for the module, or one-half diameter. These three columns are all of the same size and dimension at the base, so the unit of measurement throughout is of the same length.
The Pedestal. The Roman Orders are all shown with a pedestal, which is never employed with any of the Greek columns. These ped estals, in the examples shown, give the effect of being rather slender for their height. This is caused, in part, by the base being so narrow, and the die or central plain portion, as it is here drawn out, too high. Many authorities place the crown moulding of the base much higher on the die than the one here followed, and utilize a plain plinth below the base-mould to take up the extra height.
General Proportions of the Orders. The Roman Doric Order (Fig. 106), it is evident at the first glance, is radically different from its
Greek prototype. This appears in the mouldings of the cap, in the base, in the proportions of the entablature, and its triglyph arrange ment and treatment. This example, taken from Vignola, is 'supposed to have been somewhat closely adapted by him from the Doric Order used in the Theater of Marcellus at Rome; although he embodied some considerable changes from the original in this attempt at deter mining a satisfactory type form. The height of the column capital, including the necking, is one module or one-half diameter. The col umn base is the same height. The height of the entablature is two diameters; the architrave being one module, the frieze being one and one-half, and the cornice one and one-half modules in height and two modules in projection. The pedestal is two and four-sixths diameters high; with a base of five-sixths module, a cap of one-half module, and a die of four modules in height.
The Roman Ionic Order, with a column nine diameters or eigh teen modules in height, has a pedestalthree diameters high; of which five modules are reserved for the die, one-half module being for the cap and base respectively. In the column the base is one module in height; while the capital, from the necking up, is two-thirds of a module high, and from the bottom edge of the volute to the top of the abacus it is one module. The entablature is two and one-fourth diameters over all, which height is divided among the separate parts as follows:— the architrave has one and one-fourth modules; the frieze, one and three-fourths modules; and the cornice is two modules high and projects one module and thirteen parts.
The Corinthian column in Fig. 106 is ten diameters high. The pedestal is three and one-half diameters in height, with five modules and ten parts as the height of the die, two-thirds of a module for the base, and seven-ninths of a module for the cap. The base of the col umn is again one module in height. The capital is two and one-third modules high. As will be seen, the extra diameter in the height of the column is practically taken care of in the bell of the capital. The entablature is two and one-half diameters high, bearing the same relations to the column as in the two other Orders; and of this height, one and one-half modules are given to the architrave, one and one-half modules to the frieze, and two modules to the cornice, which in turn projects two modules and two parts.