Chap. XXV.

ON STONE BRIDGES.

1493

10 II 12 13

14 4

Fig. 2715.

Fig. 2714.

are drawn parallel to A C, intersecting the first in the points I, K, L, M, N, through whichother lines are drawn forming a polygon: on the middle of each of the sides of this polygonperpendiculars are raised, some of which intersect the semi-diameters AC and B C in thepoints d, H, and the others intersect one another at e, f g, h , which are the centres of thearcs answering to each side of the polygon; this curve approaches the nearest to theellipsis.

The arches of the bridge at Neuilly were composed of eleven portions of the arcsof circles, each of which had their respective centres, as shown in fig. 2709.; and in fig.2720. we have Perronet’s manner of tracing the curve for the formation of the centres;the small figures at the sides exhibit portions of the operation of constructing thecurve. Fig. 2721. shows how the piers were placed, and 2716, 2717, 2718, 2719, themanner in which the joints of the pendentives were set out. Fig. 2713. exhibits one ofthe arches after the centre was removed; and fig. 2731. the joints of half one of the arches.

bridge of neuilly.

Fig. 2716.

into the minute calculations made

Pig. 2717.

contained in

5 c 3