Chap. XXV.
ON STONE BRIDGES.
1515
by a vault; these piers are very massive, and the bridge referred to is the only one in whichit has been attempted to carry arches on so feeble and isolated pointsof support: but this construction has no particular utility, since itdiminishes the expense but little: the crowning of the starlings is
PIER OF BRIDGE OF 3T. MAXENCE.
Fig. 2767.
formed by a conical surface of moderate height, and the pier beingthin is constructed of a single stone.
Figs. 2768. and 2769. represent one of the piers of the bridgeof Louis XVI., at Paris ; the starling is formed by a column set inthe square body of the pier, about ^ of its diameter, and surmountedby a capital, above which is placed a short architrave, over which
runs a cornice with which the whole of the bridge is crowned,and which carries a square socle.
Figs. 2770. and 2771. represent a pier of the bridge ofNeuilly ; the plan of both ends of the starlings is a half oval,which commences under the vault itself, at the inferior originof the come de vaches; the crowning is terminated by aconical surface of little height. Sometimes the starlings ofpiers have been raised to the level of the upper parts of thebridge, making them carry columns, obelisks, figures, or evensmall shops, as in the Pont Neuf, at Paris : sometimes alsothe starlings form a space surrounded by a parapet, whichtowers above the bridge, serving as a shelter for passengers,and is serviceable when bridges are used as a promenade,
Fig.2770.
Fig 2771. PIER 0F NEUILLY bridge.
That portion of the pier that carries the arch always preserves its oblong form, with itssides right lined and parallel; and under low water, this is increased in breadth downwardsto the foundation, at the rate of from 1 to 9 inches for every foot in height, and the platformextending from 2 to 6 inches beyond the masonry; the rate of this increase of breadthmust be governed by the nature of the bed of the river. At Neuilly , the thickness of thepiers being at the springing of the arches only one-mnth of the span, it was necessary tospread the base very considerably.