1494
Book II.
THEORY AND PRACTICE OF ENGINEERING.
Neuilly ; ” it is sufficient to observe, that the engineers of that period attempted to obtainthe elegance of an elliptic arch by an assimilation of several curves, taken from as many
Fig. 2718.
Fig. 2719.
Fig. 2721.
Fig. 2722,
Fig. 2720.
circles: by a reference totheir calculations, it -will beseen how nearly they ac-complished the object theyhad in view.
The ellipsis was supposedto have no portions of itscurvature alike, but thatit varied throughout. Per-ronet, in the bridge atMantes, employed the me-thod which had been pre-viously adopted by M.Hupeau, to render portionsof a number of circles alikein form with the ellipsis.In fig. 2724. we have hismanner of tracing thearch "with three centres;in fig. 2725. it is com-posed of five arcs of acircle, with the portion ofan oval above; in fig. 2731.is represented the simplemethod of describing anarch with three centres;fig. 2732. shows one of thesmall arches of the bridgeat Mantes, with its upperand lower starlings; fig.
Fig. 2724.
2726. and 2727. the mouldings of the parapets; fig. 2731. the sort of wooden com-passes made to strike the several arcs; fig. 2729. the courses as laid in the arch, as doesfig. 2730. on a different level.