PRINCIPLES OF PROPORTION.

Chav. XXXI.

1595

different construction, and the several changes it has since undergone in form have servedto establish a variety of styles, as we shall afterwards find.

Sewers, aqueducts, bridges, theatres, amphitheatres, baths and triumphal arches, allexhibit the arch in its most useful application, and as did the halls of the baths vaultingof stupendous span; the dome of the Pantheon being 142 feet 6 inches in diameter in-ternally, covered by a hemispherical dome.

Symmetry, as understood by Vitruvius , seems to relate more to the proportions of thefacade than to those of the detail; but he doubtless intended it to be understood that

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Fig. 2990 . ARCH OF POLIPHELE.

Perfect harmony should subsist between them as well as between each particular member,however subordinate; as in the well-formed human figure, all the limbs being in due pro-portion, the whole when combined produces true symmetry : and the same author insists verystrenuously on a careful study of the rules upon which this is founded, proving that theeffect desired cannot be produced by a mere effort of fancy, or what is commonly calledtaste.