284

HISTORY OF ENGINEERING.

Book I.

France; and no one has done more to explain the principles defined in our examples thanM. Dupin: there is yet wanting, however, such daring efforts as the Southwark Bridge;and there has been no attempt at the construction of an arch equal in span to those of

- - _ l _ ELEVATION*

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Fig. 295.

PONT DU JARDIN DU ROI.

stone, and the state of the iron trade in France does not promise that much will be donewith that material for the purposes of building.

After the bridge had been finished three years, its defective construction was apparentand it became necessary to introduce a considerable addition of iron work to render itsecure, and to prevent the effects that change of temperature had produced upon theseveral voussoirs.

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Pont on the CroxL, near St. Denis, was built in 1808; its span is 39 feet 3 inches, and itsversed sine 30 inches. It is composed of three principal ribs, a little more than 5 feetapart. About nine tons of iron were used in it, and the cost was 15,879 francs.