AQUEDUCT 613 of a portion of one of the main bridges, 700 ft. long and 200 ft. high. Though solidly built, it is yet the rudest example of Roman work, and Aqueduct of Antioch. contrasts strangely with the bridge of the aque- duct of Nimes, or Pont du Gard, across which the waters of the river Hure were led. This bridge spanned the valley of the river Gard by a triple row of arches, the first six having a span of 60 ft. each; above these were 12 simi- lar ones ; while the upper row was composed of 36 smaller arches arranged as in the illustra- tion, the whole forming one of the finest exam- ples of Roman architecture. In 1740 the en- gineer Pitot built a roadway beside this aque- duct and level with. its lowest tier of arches. The aqueduct of Spoleto is of uncertain origin. One of the bridges is 810 ft. long, and the main arches are 240 ft. high. This work remains entire. Though the Romans con- structed their aqueducts so as to obtain a gradual descent, it is evident that they were not compelled to do so from ignorance of other methods. Prof. Leslie obtained a lead pipe supposed to have been used at the baths of Caracalla ; and Delorme states that the waters from Mount Pila crossed three valleys through inverted syphons. The water was collected in a reservoir upon one hill and conduct- ed through nine lead pipes 84- in. in diam- eter and l^z in. thick down the hillside, thence along an arcade 80 ft. high, and up the opposite slope, where it was discharged into a second reservoir. It is .estimated that the lead alone used in these three inverted syphons would now be worth $2,500,000. In modern aqueducts the system of gradual descent is only partially followed, the use of cast-iron pipes ad- mitting of frequent changes in the inclination. In the reign of Louis XIV. an aqueduct of vast expense was constructed for supplying Ver- sailles with water. The bridge of Maintenon, built for supporting this aqueduct, is about 4,400 ft. or | of a mile long, upward of 200 ft. high, and is constructed of three tiers of arches, 242 in each tier, and of a span of 50 ft. The aque- duct for supplying Marseilles is a canal 60 m. long. It passes through several chains of lime- stone mountains by 45 tunnels, the united length of which is 8 m., and across a ravine 5 m. from Aix by a structure of masonry 262 ft. high and 1,287 ft. long. The quantity of water that flows through it is 198,000 gallons per minute. The Lisbon aqueduct, completed in 1738, is about 3 leagues in length, and in some parts of its course has been excavated through hills ; but near the city it is carried over a deep valley for a length of 2,400 ft. by several bold arches, the largest of which has a height of 250 ft. and a span of 115 ft. The Oroton aqueduct of New York surpasses all modern constructions of this Croton Aqueduct, crossing Mill River. kind in extent and magnificence. It was com- pleted in 1842, having been five years in build- ing, under the superintendence of Mr. John B. Jervis, chief engineer. The whole expense.
