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HISTORY OF ENGINEERING.

Rook I.

Stoneleigh Bridge , in the county of Warwick , was constructed by Mr. Rennie. It isbuilt of stone, and the centre arch is 92 feet span, with a versed sine of 13 feet. Theabutments are solid, and very ornamental; they have an opening in the middle of each12 feet.wide, with a semicircular head. The Doric entablature, which runs through the

STONELEIGH BRIDGE.

entire length of the bridge, has a good effect; it is surmounted by a balustrade, and theroadway is kept horizontal.

Wellington Bridge , over the river Aire, at Leeds , erected under the direction of Mr.Rennie. It spans the river where it is 100 feet in width, and the banks 8 feet in height.The arch is the segment of a circle, 91 feet radius, with a versed sine of 15 feet. Coffer-dams were made use of to construct the abutments, which were protected by sheet pilingand wales ; each of these abutments is in length 30 feet, and 28 feet in width at. the bot-tom, diminishing by offsets to 27 feet in length and 21 feet in width where the arch springs.These abutments are built with radiating courses within, but on the face they are horizontal,and the stones used are from 14 to 18 inches in thickness, and were accurately cut fromtemplates made to suit each course. All the lower courses of the footings were laid withoutmortar, but had their joints well grouted; the others, up to the water-line, were laid inmortar, made from magnesian limestone; the proportions used were, one of lime, one ofclean river sand, and one of forge scale, well mixed and tempered, and used quite hot. Themasonry of the arch was put together with mortar, of equal proportions of lime and sand.After the abutments were completed, the piles were driven to carry the centre, the laggingof which was laid 5 inches higher than the proposed arch, to allow for its settlement.There were six of these ribs or centres, of Memcl timber, and the whole contained 2220cube feet. The striking wedges were of oak, 6 inches in width, and 9 inches in height; themiddle one being the largest. The voussoirs in front were 7 feet on the bed at thespringing, diminishing to 4 feet at the crown; but the interior arch stones were on anaverage 3 feet in length, and 18 inches thick. After the arch was turned to the extent ofone-third on each side, the centre was loaded at the crown with 20 tons of stone, and thehaunches were not further loaded until after the key was placed, which was about three orfour weeks from its commencement. The centre was enabled to bear the weight of a thou-sand tons, yet it was found that the wedges were forced into the timber, and it was necessaryto cut them out. The arch, during the progress of the work, was squeezed down inches,and after the centre was struck another 2.^ inches. The stone used was a coarse red sand-stone, or millstone grit, from Rramley Fall, a quarry about four miles above the bridge. Itwas delivered scappled, ready for dressing, at 9a. per cube foot; the dressing and setting,exclusive of the cornice, cost 4\d. per cube foot, including the mortar 1 5d., and the corniceand parapet walls about 4d. extra. The total quantity of masonry was 80,000 cube feet,and the entire cost of the bridge was 7530/.

Waterloo Bridge, commenced on the 11th of October, 1811, after the designs of Mr.Rennie, may be considered to form a new era in the art of bridge-building. Caissoons inthis instance were abandoned, and cofferdams made use of instead, for laying in thefoundations. The width of the Thames in this part is 1326 feet at high water, which isspanned by nine equal semi-elliptical arches of 120 feet opening, with a versed sine of32 feet, and a rise of 35 feet above the surface water of spring-tides, so that the clearwater-way is 1080 feet. The diameter of the circle of curvature at the vertex of thesearches is 225 feet, the depth of the kev-stone 4 feet 6 inches. The abutments are 40 feetin thickness at their base, and gradually diminish to 30 feet at the springing of the arches,and are 140 feet in length, including the stairs. The piers are 30 feet wide at theirbase, diminishing to 20 feet at the springing of the arches, and their extreme length is