268

HISTORY OF ENGINEERING.

Book I.

Of Perronct’s bridges, those at Orleans, Mantes, and Ncuillv, exhibit theknowledge of construction, and the principles of the art. The rise ofbetween a third and quarter of their span ; and the mannerin which the cofferdams were formed is also deserving ofour attention; although to an English engineer there ap-pears to be a lavish employment of material, and too muchexpended upon the temporary bridges, and tackle to supplythe stone &c. for the construction of the piers.

In the bridge at Neuilly there was a novelty introducedin the formation of the soffites of the arches, which wereshaped to suit the contracted vein of water, as formed inthe entrance and exit of pipes. This was ingeniously exe-cuted, by making the general form of the arch elliptical, butthe headers followed the segment of a circle: thus, whilstthe elliptical arch rose a quarter of the span, the segment ofthe circle had given to it a ninth rise; by this arrangementit was supposed the flood waters obtained a better passage,and also superior lightness of effect given to the bridge.

Mansard , Gabriel, Hupeau, Gautiers, and Perronet, bymeans of cofferdams, constructed the piers of bridges onvery rapid and dee]) streams; and in the published worksof the latter, the engineer will find all the detail of theiroperations very beautifully given. Water wheels wereusually employed to work bucket wheels, which threw upthe water as much as twelve feet, and thus kept the interiorof the cofferdams dry.

liridge of Neuilly , on the Seine . This celebrated work wasbuilt from the designs of M. Perronet, and was conductedunder his superintendence by M. dc Chezv; it was begun in1768, and finished in 1774, and is placed in the axis of thepalace of the Tuillcrics, and the centre walk of the ChampsElysees; the line is prolonged by the road along the risingground of Cliante Coq, where it divides, one branch to St.

Germiiin, the other to Bezons .

It consists of five elliptical arches, rising a quarter, 128feet in span. Their springings are on a level with lowwater, and there is a distance of 7 feet 5 inches betweenhigh water and the neck of the arch. The thickness of thepiers is only 13 feet 10 inches. The plan of the starlingsis a semicircle; they are slightly curved at half their height.

Behind the abutments, the thickness of which is 35 feet5 inches, are arches for warehouses 15 feet in span. Theroads to the warehouses are paved for a great distance,and the slopes arc sustained by walls extending 331 feet oneach side. The width of the bridge is 48 feet; 31 feetfor the road, and 6 feet 6 inches for each foot pavement. Thearches are brought to a iovci with the face of the bridgeby comes de vache, terminated by the prolongation of thearc which forms the summit of the ellipsis.

The foundations are on piles, and were pumped out bycofferdams 7 feet 6 inches below low water ; the breadth ofthe mass on which the piers are built is 22 feet 4 inches; itprojects 2 feet 1 inch round the whole of the foundations.

The facings are of large squared stone, and the mass ofconstruction is filled in with rubble to 26 feet above lowwater.

The river formerly divided into two branches at the pointwhere the bridge is built; one part of the island was re-moved to enlarge the arm on the side of Courbevoie , andthe other was filled up ; had not this been done, the bridgemust have been in two parts. Compared with the otherParis bridges, the water-way is too great, and we mustregret that a work so perfect in all its details should haveso great a defect in its general arrangement. The incon-veniences resulting from this are already perceptible, by anevident silting up in the islands between which it is situated.

most profoundthe arches is

mm

i II