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.

In crossing Manhattan Valley there is an extra fall of 3 feet for the same reasons as before stated for that at Harlem

River. In both cases, by using the pipes, there is a loss of the head of water for the City Reservoirs, equal to the amount of this extra fall ; but this small loss of head was not considered of such importance as to induce the building of structures across these valleys up to the plane of Aqueduct grade. The bottom of the water-way of the Aqueduct at the gate chamber where it enters the Receiving Reservoir, is 7.86 feet below the level of top water line in the Reservoir, thus when the Reservoir is full the water will rise to within 7} inches of the top of the interior of the Aqueduct at that

place, and the height from top water to the top of the interior will increase, going northward according to the inclination of the plane of Aqueduct grade, until it reach the surface level of the flow of water in the Aqueduct. The height of the interior of the Aqueduct is 8 feet 5Jr inches, and the greatest width is 7 feet 5 inches. The sectional area of the interior is 53.34 square feet. On the first plane, the Aqueduct is larger ; being 2.05 feet higher at the gate chamber, 2.31 feet higher at 2244. feet from the chamber, and then diminishing, to the head of the second plane, where it assumes the size above mentioned and continues of that size throughout the remainder except in tunnels, where