In the bridges at Orleans, Mantes, and Neuilly, we find the rise of the arches to be between :1 and 1- of the span; but rendered confident by success, and desirous of giving a variety to his works, Perronet. in the bridge over the Oise, at St Maxence, consisting of three arches, each 72 French, or 76.10 English feet span, make's the rise only 6 French, or 6.5 English feet, or part of the span; also, instead of making the piers each a solid, right lined on the sides, he divides each pier into two distinct parts, with an open space between them, and composes each part of two columns united by a piece of plain wall. The deviation from former works of a similar kind is here certainly sufficiently distinct ; but the propriety of this measure will be discussed under the head of Practice. This bridge was begun in 1774; the operations were suspended in 1775 ; they were re commenced in 1780 ; and the centers were struck in 1785. See Plate LX XXV.
The bridge built upon one of the arms of the Loire at Saumur, from a design of M. de Voglio. and executed chiefly under the inspection of L. A. de Cessart, may also be classed amongst the first of the French bridges. It consists of 12 elliptical arches, each 60 feet span, and 21 of rise; the piers are 12 feet thick, and the breadth of the bridge, including the parapets, is 42 French, or 44.9 English feet. It was begun in 1756, and finished in 1770.
The progress of bridge-building in England seems to have kept pace with the same art on the continent. The very singular bridge at Croyland in Lincolnshire, is said to have been built in 860. This date is likely to he correct; for Croyland Abbey was founded in 716, and the Abbey of Rumsey, in Huntingdonshire, in 974. „Bentham's _Essays.) This bridge has three distinct approaches, formed by three segments of a circle, which meeting in the middle, compose pointed arches, their bases or abutments standing upon the points of an equilateral triangle.
It is worthy of remark, that the bridge of Avignon was begun under the direction of Saint Benezet in 1176, and that of London begun to be built of stone under the direction of Peter of Colchester, a priest, in the same year (1176). The French "Brothers of the Bridge" accomplished their magnificent and useful work in 12 years, the labours of the English priest occupied 33 years; but this may be accounted for, by considering the interruptions which must be experienced in a river, where the tide rises twice every day from 13 to 18 feet. We may further 'remark, that as the constructions of the bridges of St Esprit and Lyons immediately succeeded to that of Avignon, so the bridge at Newcastle-upon Tyne was built of stone in 1281, and that over the 'Med way at Rochester, consisting of 11 arches, much about the same time.
In London bridge there are now 19 arches, and it is 45 feet in breadth. For many ages there were houses along each side of it; but these were removed, the mid dle pier was taken away, and the space, including the two adjacent arches, converted into one arch of 72 feet span, in 1758. The remaining old arches are very nar row, and the piers enormously large, being from 15 to 25 feet in thickness above the sterlings. The passage over the bridge is very commodious, but in other re spects it is very inferior to the before mentioned old French bridges. See Plate LXXXIII.
Many other old English bridges might be described, which, in conformity with the turbulence of the times, were generally fortified with gateways. It would be curious to trace their history, and delineate their fea tures; but as the limits of our present article will not admit of this, we shall pass on to those of modern times, from which our readers will derive more useful information.
In 1636, the English Palladio (Inigo Jones) gave a design for a bridge, which was erected at Llanwst in Denbighshire. It consists of 3 arches, segments of circles; the middle one is 58 feet span, and rises 17 feet, the piers are 10 feet thick, and the breadth of the soffit of the middle arch is 14 feet. The arch stones of the largest arch being only 18 inches deep, the covering over them being little, and the approaches very steep, the bridge has a very light appearance.
The bridge over the river Thames at Westminster, being not only the greatest work of the kind in Eng land, but having, in what regards laying foundations in deep water, and constructing centres for large arches upon navigable livers, formed a new school for bridge building in this island, we shall give a detailed account of it.
From reports made by Mr Labalye, (1751) it appears, that from 1734 to 1738, the time was employed in ob taining acts of parliament, and determining the precise situation and plan of this great work. In 1738, the situation was finally determined to be a little way be low New Palace Yard ; the model made by M. Labalye was approved of, ai,d he was appointed engineer. The intention at this time was to construct the piers of stone, and place a wooden superstructure upon them. This latter part was designed by Mr James King, who con tracted to complete it in 12 months after the piers were finished for 28, 00!.