Chap. XXXI.

PRINCIPLES OF PROPORTION.

1597

bounded the propor-tions, as shown in fig.

2995. The severalRoman examples se-lected differ in ar-rangement, but notin principle, from thedescription given byPoliphele: takeawaythe pedestals on whichthe columns areplaced, and then foursquares in height in-clude half the tym-panum, and eighteensquares the entirefigure, 6 of whichmay be considered asdevoted to the arch,and the other 12 tosupports: or, if wecomprise the wholefacade in 20 squares,and abstract the 8which belong to theopening between thepedestals, we have 4for each pier or sup-port, and 4 for the en-tablature, the support* d being only | the quantity contained in the two supports: resistanceto the arch, or its thrust, requires a different arrangement from that of a portico, but wenevertheless find definite proportions made use of, and a double quantity given to masseswhich have to bear weight as well as resist thrust.

The Arch of Augustus at Rimini has the height of its order determined by the lengthof the frieze.

The Arch of Augustus at Aosta resembles that of Titus in arrangement j it is a perfectsquare comprising the attic.

ARCH OF AUGUSTUS AT RIMINI.

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ARCH OF AUGUSTUS AT AOSTA.