CROTON AQUEDUCT. This beauti ful structure has been built after the plan of the Roman buildings—that is, in chan nels of masonry, rather than in metal pipes. The following account is abridged from Tower's work on the Croton Aque duct : Dr. Brown, in 1798, first called attention to the necessity of a good supply of wa ter for the city of New-York. In the next year the Manhattan Company sank wells of great depth. In 1834, an act passed the Legislature, authorizing five Water Commissioners to examine and consider all matters relative to a supply of water to the city. These Commission ers decided in favor of using the Croton River, and bringing it in a closed aque duct of masonry, at an estimate of $5,412,336 72. The work was commenced in May, 1837, and the 22d June, 1842, the aqueduct received the water from the fountain reservoir on the Croton ; on the 27th it entered the receiving reservoir in the city, and on 4th July it was admitted into the distributing reservoir. The sources of the Croton River are in Put nam county, 50 miles from New-York ; they are about twenty lakes or ponds, oc cupying about 3,800 acres. The water is so remarkably clear and pure, that the native Indians called it clear water. The dam on the Croton River is thirty-eight feet above the original level of the water flow, and sets the water back about six miles, forming the fountain reservoir, which contains an area of 400 acres. This large reservoir allows the water to settle before entering the aqueduct, and it has an available capacity of 600,000,000 gal lons ; this has been looked on as sufficient store for one-third of a million of people for ninety days, a longer period than any drought would last. The minimum flow of water in the river where the aque duct begins, is 27,000,000 gallons in twenty-four hours. The aqueduct itself is calculated to convey 60,000,000 gallons in that time. From the fountain reser voir to the receiving reservoir is thirty eight miles, the aqueduct for which is of stone, except where the Haarlem River is crossed over, and in passing a deep valley in the island, where iron pipes are used. These pipes descend and rise again, so that they are always full. The surface of the reservoir is 164 feet above the level of the tide at New-York ; that of the receiving reservoir is 119 feet, so that the fall of the river during its course through the 38 miles of aqueduct, is 47} feet. From the receiving reservoir it is carried in iron pipes (two miles) to the distributing reservoir, where the surface of the water is 115 feet above the tide level.
At suitable places on the line of aque duct six waste weirs are constructed, to discharge surplus water in such a mode, that when the water reaches a certain level, it flows off at the side.
For ventilation, hollow cylinders of stone are erected over the aqueduct, and rise 14 feet above the surface of the ground. These occur at every mile, and at every third mile there is one having a door to allow of entrance into the aque duct; these have a diameter of four feet, the former only of two ; the top is cov ered by an iron grating. Besides these there are places marked at every quarter of a mile of the course, where opening can be made readily in cases of emergency. Where streams intersect the line of aque duct, culverts are built to allow them to pass under. At each end of the aqueduct are gate chambers, with two sets of gates, the regulating and the guard gates : the former of gun metal, the latter of cast iron. The height of the interior of the aque duct is 8 feet 51 inches, and the greatest width 7 feet 5 inches. The velocity of the water is lk miles per hour when the water is two feet deep. The average depth is probably four feet.
The foundations of the channel were formed with cement, the side walls of stone, and the bottom and inside faced with brick ; the top also covered with an arch of brick. In tunnel-cutting, the na tural rock in some places served as roof. The bridge which crosses the Haarlem River is the most interesting work on the line ; its width is 21 feet, and it is 150 feet from the top of the work to the foundations in the river. The iron pipe conveying the water along this is 3 feet in diameter. In passing through the Manhattan valley two pipes are used, each 8 feet in diameter ; provision, how ever, has been made for four such.
The capacity of the receiving reservoir is 150,000,000 gallons when full. It is divided into two unequal parts, with a connecting pipe to eiiow of an equalizing of the level. The distributing reservoir is two miles lower down the island, and three miles from City Hall; the water in it is 36 feet deep, and it is calculated to hold 20,000,000 gallons. It is 40* miles distant from the fountain reservoir.
The whole of the cost of the work, ex clusive of the pipes in the city below the distributing reservoir, is about $9,000,000. It is a beautiful work of art,--a worthy rival of the finest of the Roman aque ducts. The success of this undertaking in New-York has stimulated other Atlan tic cities to supply themselves with abundance of pure water in a similar manner and the aqueduct which sup plies Boston from the Cochituate pond us highly creditable.