Chap. VI.

FRANCE.

2 65

hy M. Uegemortc for the same purpose at the bridge -of Moulins . Tlic space betweenthe piles was then filled with elav, and, when water-tight, the pumping out was com-menced, and the whole of the vast interior rendered dry: pumps and chnpelets workedby men, and an undershot-wheel, being constantly in use for this purpose; the wholewas under the directions of M. Ilupeau, who made the designs and commenced thefoundations in 1757, and was finished by M. Perronet in 1765; it consists of three ellip-tical arches, 115 and 128 feet in span. Their springings are 3 feet 3 inches below thesurface, and the platform of the foundations 6 feet 6 inches; the height of the middlearches 37 feet 3 inches, and of those at the two sides 35 feet 8 inches. The piers are 25 feet7 inches, and the abutments 28 feet 9 inches; the width is 35 feet 5 inches.

'I ;| iilHlil

Fig. 274.

In constructing the arches of this bridge, they commenced by one of the side arches,which was almost finished, when there were only ten courses of voussoirs on the middle arch.The inequality of pressure resulting from this on the intermediate pier thrust it in ahorizontal direction. The piles took a slight inclination, and, although the voussoirs of thegreat arch were placed with the greatest possible celerity, the motion was not stopped tillthe pier had moved inches ; the arch was, however, continued, and, to prevent the effect ofpressure on the other pier, care was taken to preserve the distance from the centre by tiescomposed of pieces scarfed together. This precaution succeeded perfectly, and afterputting in the key-stones, the first pier was carried back inches towards its proper position.The details of the construction have been published by M. Perronet.

Bridge of Bord , on the OeiU built in 1764 by M. Tederc, is on the road from Moulins toAutun . It consists of a single arch 69 feet 3 inches span. All the facings are of squaredstone, and the work is very good.

Bridge of Nogent, on the Seine , built between 1766 and 1769, by M. Perronet, consists ofone elliptical arch, 96 feet in span, 29 feet 9 high from the springing to the key. Thethickness of the abutments is 19 feet, they have shoulders and terrace walls. The arch is ofvery hard sandstone, and its thickness is from 4 feet 3 inches to 5 feet 2 inches.

The bridge of Nogent has been the subject of an interesting experiment on the motionand rupture of arches. Before the centres were removed, a portion of the masonry of thehaunches had been constructed, which partly prevented the joints of the voussoirs, whichhad opened during the progress of the work, from closing as they generally do ; added tothis, the centres were struck immediately after the arch was finished, which increased thesettlement; these different circumstances rendered the points where the acting parts of thevault separate from the resisting parts very visible, and particular arrangements have beenmade with the view of ascertaining them exactly.

Bridge of Albias, on the Aveyron . This was built in 1770 by INI. Boesnier. It consistsof three elliptical arches 76 feet 9 inches and 83 feet in span. Its width is 39 feet.

Bridge of Sorges , on the Anthion , constructed hy M. llegemorte; it consists of 7 arches19 tect 3 inches in span. Gates are attached to them l>v means of which the water may be