1592

THEORY AND PRACTICE OF ENGINEERING.

Book II.

A line drawn through the centre of the pediment, another at half the height ofthe columns, and a third under the entablature, would divide the height into threeequal portions, proving that, in this example, the Romans made the part supported one*-third of the whole, and divided the other two between the columns and their intercolumni-ations. The shaft of each column is cut out of a single block of granite ; they are notsufficiently delicate to be exactly in the proportion of half the quantity contained in theintercolumniations; but if allowance be made for their diminution, the difference is notvery great. The whole width being 109 feet 10 inches, the third, 36 feet 7 inches and 4parts, is nearly a mean between the collected diameters of the top and bottom of the shaft,making the intercolumniations double the quantity contained in the supports, or equal tothat of the supports added to the mass they carry. The whole would then be divided intofour, as in theprevious examples of the Ionic , and two portions given to the intercolumniations.

The Pantheon Portico is a double square without the pediment, or nearly so, the lengthof the level cornice, which crowns the entablature, being double the height of the order:this, no doubt, was the outline of the proportions before the heavy pediment was placedupon it, which in all probability was heightened beyond the ordinary rise of a ninth, forthe purpose of concealing the wall behind it. The Roman proportions are frequentlymade independently of the pediment; the tetrastyle porticoes are a square, the hexastyle asquare and a half, and the octastyle, as in this instance, a double square without it.

To set out an octastyle portico, in which half the pediment should be comprised withinthe double square, after dividing the width into 24 and the height into 12, which multi-plied produce 288 squares, 72 are given to the column, the same to the entablature andhalf pediment, and double that, or 144, to the intercolumnations, or proportions similar tothose laid down for the tetrastyle and hexastyle porticoes. The columns in such a casewould be nine diameters in height, the entablature and half pediment three : supposing thelatter to rise a ninth of the span, the remainder would be distributed among architrave,frieze, and cornice.

We have endeavoured to show the proportions required in a tetrastyle, hexastyle, andoctastyle portico among the Dorians , the Ionians, and their followers the Romans: thesquare and a half, or the double square, were the outlines or boundary figures from whencethe other proportions were deduced.

The great difference of character in the Doric and Ionic designs arises from the distanceat which the columns are placed, which affects the proportions of the entablature laidupon them, as well as that of the columns themselves; where these are six diameters inheight or consist of six cubes, they are made to carry the same quantity, whatever may betheir distance apart, and where drawn out to nine diameters, they have only their ownweight to support; but the form given to this weight, or the proportions of architrave, frieze,and cornice, vary, as the intercolumniations are of one or more diameters.

It has been too generally considered that the orders derived their proportions from thelower diameter of the columns, without reference to their application : this has produced avariety of design, but at the same time occasioned a great departure from the true principles,and led to very important errors. The Tuscan, the Doric, the Ionic, the Corinthian , andComposite orders have been laid down in modules or measures of various kinds, which theyoung architect has adopted as mere isolations, regardless of the many other considerationswhich have stamped beauty on his model; hence we have imitations, but soul is wanting.

The Doric order is treated of as so many diameters in height according to its age, and theentablature is said to be heavy or light, as it was of early or late execution; the otherorders have been chronicled in a similar manner, and architecture has been fettered, and itsgreat principles lost, or at least neglected: it is true that the outline which bounds thefigure has undergone but few changes, but the subordinate parts or the filling-in are sus-ceptible of interminable variety. An object inscribed within a circle is perhaps themost easily compassed by the eye, next that within the square, and when a buildingis vast, and distance is necessary to comprise a view of the whole, the double square;beyond this the ancients seem seldom to have gone for the proportions of their fa 5 ades, orof a portico intended to be seen in front. After the masses were proportioned, their de-corations were more various than the buildings themselves; no two are perfectly alike,but the great difference is in their ornaments and enrichments, or in the number of diameterscontained in the height of the columns.

The Parthenon and Pantheon porticoes are both octastyle, each admitted to be as beau-tiful as they can be — one the perfection of sober grandeur, the other of cheerful lightness;one Greek Doric, the other Corinthian , both comprised within a double square, and havingtheir columns equal in quantity to the mass of entablature they support: where, then, is thedifference between the two examples? It results, as we have already seen, from the mate-rial in the one occupying two-thirds, and in the other only half the entire area. Inthe facade of the Parthenon the eye has one-third void only to contrast with the solidmatter, and in the Pantheon half, which proportions seem to have been established by theIonians, and usually adopted by the Romans.