274

HISTORY OF ENGINEERING.

Book I.

Bridge of Nemours , on the Loing, constructed by M. Boistard from designs bv M. Per-ronet. It was completed in 1805, and 1ms three segmental arches 53 feet 3 inches in span,and 3 feet 9 inches high. The thickness of the piers is 7 feet 2 inches, their height 13feet 10 inches above the water, and 19 feet 2 inches above the platform. The footings pro-ject 3 feet 2 inches all round. 'Hie thickness of the abutments is 16 feet 10 inches, andthey are consolidated by three buttresses 17 feet long, and 6 feet 4 inches thick. Thethickness of the keystone is 3 feet 2 inches. Hie width of the bridge is 41 feet 6 inclies.

This work was constructed with the greatest care, and notwithstanding a considerableflattening of the arches, no settlement manifested itself. M. Boistard has published someexperiments which he made during its progress, and on the effect of the machines used inpumping out the water.

Bridge on the Road of the Simplon consists of two bays 42 feet 8 inches in the opening.They arc built partly on a rock and partly on a pier from 20 feet to 23 feet thick and 95feet high. This arrangement was adopted in order to afford an opportunity of breaking itdown in case of war ; otherwise the rocks might have been united by a single arch 98 feet5 inclies in span.

Bridge over the Ravines of the Cote de Maires. Hiis as well as other bridges of the samekind was built on the road from Viviers to Buy. The two arches, placed one above theother, are from 33 feet to 40 feet high. Although constructed of granite and basalt, they areconsiderably decayed; for after floods the ravines which they traverse bring down massesof rock from 10 feet to 12 feet square, which break the stone, and in some cases carry itaway. In such localities it would be infinitely preferable to raise a thick wall to block upthe valley, which is soon filled up with debris. The water then falls in cascades to thebottom of the wall, which, being founded on the rock, cannot be injured.

Bridge of Hoanne , on the Loire, was begun in 1789. It consists of seven ellipticalarches rising a third, 76 feet 9 inches in span. The thickness of the piers is 15 feet, andthe bridge is further strengthened by a general ground-work 3 feet 3 inches thick, and 3feet 3 inches below low water, composed of a bed of beton, 2 feet 1 inch thick, which wassuffered to harden for a year previous to covering it with masonry. Above and below itrows of piles were driven, and, in addition, on the lower side a jetty of rubble was con-structed, 8 feet 6 inches deep, maintained in the same manner. The width of the bridge is38 feet 4 inches, 25 feet 7 inches for the road, and 5 feet 10 inches for each footpath.

There were formerly two wooden bridges, separated by an island, which have been suc-cessively carried away : one arm being in a great measure filled up, and not allowing asufficient water-way, the bridge which crossed it was destroyed by a flood. 'The othershared the same fate a few years after, from the effects of a bar formed by poplars, which theriver brought down in great numbers.

Bridge of Bellecour , on the Sadne at Lyons, begun at nearly the same time as the prece-ding. It has 5 elliptical arches, 68 feet 2 inches in span. It is situated in a very con-tracted part of the river, where the depth was from 16 to 20 feet below low water. It wasbuilt by caissoons, and the piles are cut off 9 feet 10 inches below the surface.

Bridge of Montlion , on the Durance, commenced in 1805 by M. Delborgue-Cormont.; itis a single elliptical arch, rising one-fourth, and 101 feet 8 inches in span. On one side thefoundations are on the native rock, and on the other on piles.

Bridge of St. Diez y on the Meurthe , constructed from designs by M. Lecreulx, andconsisting of three segmental arches, 39 feet 4 inches in span, and two small semicirculararch.es 13 feet span. Hie height of the first is 3 feet 3 inches. It is raised on piers 5 feet3 inches both in height and thickness.

Bridge of Montelimait , on the Iloubion, is on the road from Lyons to Marseilles, andconsists of three elliptical arches 63 feet 11 inches in span. Its width is 28 feet 9 inches.

Bridge of Maligng , on the Serin, built by M. Werbruge. It consists of a nearly semi-circular arch, 84 feet 3 inches in span. Hie foundation is 4 feet below low water ; it isentirely rubble, from 3 to 4 inches thick, and from 10 to 11 inches long, chisel-dressed,and squared like regular masonry ; the waste was great, the stone being reduced to one-half its original bulk. To prevent the centres from starting at their summits duringthe construction of the arch, and to avoid loading them, the arches were begun in differentplaces, and were locked together by three keys ; they remained fifteen days on the centres.Hie bridge was solidly built, but the form lias become slightly altered, the two heads havingstarted from their original position, and assumed a curvature of 7 inches perpendicular.

Bridge of Rieucros, on the Douctoirc, begun 1770, finished 1790, by M. Garipuv. Itconsists of three elliptical arches, 55 feet 5 inches in span ; the piers have no starlings.

Bridge of Mireppis, on the Lers, also the work of M. Garipuy, was begun 1776, and com-pleted 1790. It has seven arches, one-sixth of a circle, 64 feet span. Hie plan of thestarlings is a mixtilincal triangle: the width is 25 feet 6 inches ; the foundations are 19feet 8 inches deep, on a solid soil.

Bridge of Frouart, on the Moselle. This fine bridge was constructed in 1788, byM. Lecreulx, to replace an old one which had been founded at the level of low water, and