BRIDGE. 482 BRIDGE. and imitated the Roman bridges, as at Vicenza and Pisa. Among smaller bridges, the "Bridge of Sighs' at Venice (close of Sixteenth Century), connecting the Ducal Palace and the prisons, is the most famous. Such high-bridged passages were frequent in Italian cities and very pictur- esque. The work of the Brothers of the Bridge and their priestly successors carried the history of bridge-building up to about 1700, by which time such improvements had come to be regarded as the work of the (Tovernnient. During the Kighteenth Century a large num- l)er of important stone-arch bridges were built in Europe, among which may be mentioned the Blackfriars, Westminster, Winston, and Kelso bridges in England, and the Blois. Trilport, Tours, Neuilly, and Oignac bridges in France. In all respects the work of the famous department of Ponts et Chaussees in France led the world in arch-bridge construction during the Eighteenth C<>ntury. The Blackfriars Bridge across the river Thames was bcgim in 1700 and completed in 1770. It consists of nine elliptical arches, the middle one being 100 feet, and the others de- creasing gradually to 08 feet, 9.3 feet. 83 feet, and 70 feet. The Westminster Bridge was begun in 1738 and completed in 1750; it consists of fifteen Century was the so-called Pont-y-Tu-Prydd, over the river TafT in Wales, which was built by Wil- liam ICdwards, an ordinary stone-mason, in 17r)0. after two failures. The bridge, as finally completed, has a segmental arch span of 140 feet with a rise of 35 feet. A curious feature of this bridge is that its breadth increases from 14 feet 5 inches at the crown of the arch to about 16 feet at the abutments. MODERN ARCH BRIDGES. Masonry Arches. With the beginning of the Nineteenth Century, the masonry arch, which had up to this time been prominent in the field of bridge construction, encountered a rival in the metal bridge, lirst in the form of the arch and suspension bridge and later in the form where girders were employed. The close of this cen- tury saw the metal bridge paramount over the masonry arch in all respects, e.vcept when judged from the standpoint of beauty and dura- bility. These points of suiieriority, however, have maintained, and probably will continue to maintain, the masonry arch prominent among the bridge tyiies of the engineer. The number and variety of stone-arch bridges built during the Nineteenth Century preclude a mention of LUXEMBURG BTONE-AECH BIUDQE. arches, the centre one of which is 76 feet, and each succeeding one on each side four feet shorter than the preceding, except in the ease of the two end spans, which are 25 feet. The Winston Bridge over the river Tees, built in 1762. is notable for its span of 108 feet 9 inches. The Kelso Bridge over the river Tweed was com- pleted in 17!)!*, and consists of five arched spans of 72 feet each. The Blois Bridge over the river Ijoire was begun in 1720, and consists of eleven elliptical arches from 54 feet 9 inches to 86 feet 4 inches span. This was the first bridge built after the establishment of the Ponts et Chaussf-es in France. The 'J'rilport Bridge over the Maine was finished in 1760, and consisted of a middle arch of 81 feet and two side arches of 76 feel '.) inches, built on a skew, the axes of the arches making an angle of 72^ with the axis of the bridg('. The bridge of Toius on the Loire. begun in 1755, is one of the longest stone-arched bridges in France, consisting of fifteen elliptical arches of 80 feet span separated by piers 16 feet thick. The bridge of Neuilly, on the Seine, was begun in 1768 and finished in 1774, and consists of five elliptical arches of 128 feet span each. The bridge of (iignac, on the H<^rault, was fin- isheil in I79.'i; it consists of two semicircular arches of 83 feet span and an elliptical centre arch of 160 feet !) inches span. In simie respects, the most notable stone-arch bridge of the Eighteenth more than a few representative examples. In 1832 the Grosvenor Bridge over the river Dee at Chester, England, was completed with a single arch span of 200 feet. The Trezzo Bridge, con- structed over the Adda, in Italy, in 1380, and destroyed in 141(i. had a single arch span sup- posed to have lieen 251 feet, but, with this possi- ble exception, the Crosvenor Bridge was at the lime of its construction the largest stone-areh sjjan ever built. In 1857-64 the construction of the Cabin .lohn Arch near Washington. D. C, with a span of 220 feet, transferred the posses- sion of the longest stone arch in the world to .America, but as the Cabin John Arch was built to carry an aipu'duct. the Grosvenor Bridge re- mained the largest span of masonry arch bridge for transportation purposes until 1888. In 1901 there was comi)letcd at Luxemburg the largest stone arch ; it has a span of 277 feet, and is 137.76 feet above the brook which it bridges. The accompanying tiible gives the main dimen- sions of a number of the leading stone-areh bridges of the world. Struct orally, the stone- arch bridge of the Xinetcenth Century cannot be said to show much ini])rovemcnt over that of pre- ceding times, but the advance in the science of statics gave the Ninetci'iith Centurv engineer a better theoretical knowledge of such structures than was enjoyed by his predecessors. Tlw dis- tinctive development of the Nineteenth Century
