face of the water ; any floating substance cannot enter it, and during the winter season when the water is frozen over no obstruction can take place to the flow into the Aqueduct, and during the summer season the water will be drawn from a level where it is cooler than at the surface. The gate chamber has two ranges, or sets of gates ; one called regulating gates, and the other guard gates : the

regulating gates are made of gun metal, and work in frames of the same material which are fitted to stone jambs and lintels : the guard gates are made of cast iron, and work in cast iron frames also attached to stone jambs and lintels. The gates are all managed by means of wrought iron rods attached to them, having a screw formed on the upper part on which a brass nut works, being set in a cast iron socket-cap. The bottom of the water way, of the Aqueduct, where it leaves the gate chamber is 11.40 feet below the surface of the Fountain Reservoir, and 154.77 feet above the level of mean tide at the city of New-York. The following table shows the length of the Aqueduct as it is divided into different planes of descent, from the gate chamber at the Croton dam to the gate chamber at the Receiving Reservoir on the Island of New- York. Commencing at the south side of the gate chamber at the Croton dam,

The 1st plane of Aqueduct extends 26099.72 ft. or 4,943 miles, and the descent 2.94 ft. The 2d plane of do. extends 148121.25ft.or28.053miles, . . . .30.69 ft. Length of pipes across Har. River, 1377.33 ft. or 0.261 miles. DifF. of level betw'n extremes of pipes 2.29 ft. The 3d plane of Aqueduct extends 10733.14 ft. or 2.033 miles, .... 2.25 ft.