14 MEMOIR OF mile to the Hudson river. In each division there is a waste cock to draw the water from the bottom. The reservoir is designed for 36 feet of water, and, when full, will stand 115 feet above mean tide. The walls rise 4 feet above the water line. An iron railing is to be placed around the walls on top of the cornice. The capacity of this reservoir is 20,000,000 imperial gallons. GRADE LINE OF AQUEDUCT. The general declivity of the aqueduct in Westchester county is 0.021 foot per hundred, or a fraction over 13j inches per mile.* The top of the conduit pursuing this grade, corresponds with the top of the dam on the Croton but in order to adapt the aqueduct to draw at a lower level from the Croton ;

reservoir, the bottom grade was depressed at the head 2.93 feet, and a declivity of 0.0113 foot per 100 feet, or 0.59664 foot per mile for 4.949 miles, where it intersects the regular grade. The top of the aqueduct was depressed only 0.583 foot, and carried level 2276 feet, where it intersected the regular grade line of the top. This gave an extra height ot -

side walls, enlarging the capacity of the aqueduct, more than equivalent to the diminution of declivity, and provides for drawing -from the reservoir to a depth of 6 feet, and still leave the capacity of the conduit 35,000,000 of imperial gallons.

The grade of the aqueduct from Harlem river to Manhattan vfilley. is the same as the general declivity in Westchester county but that from Manhattan valley to the re- .;