This Reservoir is 420 feet square on the top, measuring on the cornice of the main wall ; it is 425 feet square at the top of the cornice of the pilasters, and 436 feet square at the base, measuring from outside to outside of the corner pilasters, covering a little over four acres. The height of the walls is 45 feet above the streets around, and about 50 feet above the foundations. The water is 36 feet deep when it reaches the level designed for its surface (which is 4 feet below the top of the walls) and the surplus, when the Reservoir is full, passes into

a well in the division wall and is conducted by a sewer in

42nd street to the Hudson River, which is one mile distant. The Reservoir is calculated to hold 20,000,000 gallons. The outside walls are constructed with openings in them so that by entering the doer on 42nd street one may walk entirely around the Reservoir within the walls. One object of this arrangement is to obtain the greatest breadth with a given quantity of material ; another is to afford an opportunity to examine the work so as to guard against leakage and another, to prevent any moisture finding its way through to the exterior so as to cause injury to the wall by the action

of frost. This kind of open work of the wall rises to within about 8 feet of top water line. Inside of these walls an