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.

Length of pipes acrossManhat.valley,4105.09 ft. or 0.777 miles. DifF. of level betw'n extremes of pipes 3.86 ft. The 4th plane of Aqueduct extends 10630.89 ft. or 2.023 ...... 1.60 ft.

201117.42 ft.-- 38.090 miles . . . .43.63 ft.

Making the whole distance from the gate chamber at the Croton dam to the gate chamber at the Receiving Reservoir 201117.42 feet, or 38.09 miles, and the whole descent 43.63 feet. The descent on the first plane is about 71 inches per mile. The descent on the second and third plane is about 13} inches per mile. The descent on the fourth plane is about 9| inches per mile. In crossing Harlem River there is a fall of 2 feet more than there would have been had the Aqueduct continued across with its regular inclination : this extra fall will afford

an opportunity to adjust the number and capacity of the pipes (which descend below the level of the Aqueduct and rise again) to discharge the full quantity of water as freely as the Aqueduct, or channel-way of masonry, would have done had it continued its regular inclination across the valley.