AQUEDUCT, or AQU1EDUCT, is usually an elevated channel for the conveyance of water. Aqueducts were most extensively used by the Romans, and in the vicinities of many of their more important cities, in Asia and Africa, as well as in Europe, remains of ex tensive constructions of the kind yet exist. Rome itself was supplied with water from sources varying from 30 to OOtnailes in dis tance, and at one period of its history no less than twenty aqueducts brought as many dif ferent streams of water across the wide plain Campagna in which the city stands. Great portions of the distance were of course in every case occupied by artificial channels winding along the sides of hills and moun tains; and long tunnels carried the streams through these natural barriers when occasion required ; but nevertheless the arcaded duct led the streams across the deep valleys, and the aqueduct was in every case required to carry it onwards from the hills over the wide plain into reservoirs in Rome. In one of these Roman aqueducts the series of arches is cal culated at nearly 7000, their height being in manyplaces more than a hundred feet. There is nothing more interesting or more really beautiful in the existing ruins of ancient Rome than the remains of these splendid works, three of which, having been restored and repaired, supply the modern city abun dantly.
Among the most celebrated modern aque ducts are that of Caserta in the kingdom of Naples, of Maintenon near Versailles in France, and that of Bemfica, called Agoas Livres, near Lisbon in Portugal.
The finest aqueduct of modern times, per haps, is the Croton Aqueduct, which supplies New York with water. It extends 42 miles across a hilly country on the east side of the Hudson river, t1.0ersified with ravines, water courses, and public roads. At a place called Sing Sing, the river Croton is dammed up for a distance of five miles, so as to attain at one point a height of forty feet above its ori ginal level. The pond of water caused by the dam covers four hundred acres of ground.
The water enters the aqueduct from this pond through a tunnel one hundred and fifty feet long ; and the gradients are so arranged that the water descends along the aqueduct at the rate of two feet per second. The channel for the conveyance of the water involves very costly engineering. There are fifteen tunnels, varying in length from 150 to 900 feet ; the tunnels through rock are left in their natural state, but those in an earthy soil are bricked. The aqueduct is carried across ravines by means of embankments, provided with cul verts for streams; and over the larger rivers and the turnpike roads it is carried by well constructed bridges. One of these bridges consists of a single elliptical arch, considered at the time of its erection to be the largest arch in America; it is 88 feet span, 33 feet versed sine, and 80 feet from the foundation to the crown of the arch. On Island there are bridges which cross eight or' ten of the public streets, over which the duct is carried. The aqueduct terminates at the part of New York called 144th Street,1 where there is a receiving reservoir which occupies 30 acres of ground. From this re servoir the water is conveyed to the distri buting reservoir on Murray Hill, covering an area of 10 acres : the channel- of conveyance from one reservoir to the other being iron pipes. The distributing reservoir is 114 feet above high-water level; and from this point the water is conducted through the city in pipes. The aqueduct crosses the Haarlem river, at a height of 120 feet, by a bridge of fifteen arches, eight of 80 feet span, and seven of 50 feet span. The expense of this great work has been about 12,000,000 dollars ; and the power of supply is stated at the enormous quantity of 50,000,000 gallons per day, so that any increase of population can be met by additional draw-pipes from the great reservoir. The reservoir being as high as the cupola of the city hall, the water can be supplied to the summits of nearly all the houses in and near New York.