INTRODUCTION. 143 
The distributing reservoir is built upon ground higher than any part of the 
city south of it. The walls are built upon a foundation sunk five feet below the 
grade of the streets, and are of hydraulic stone masonry, constructed with open- 
ings, to reduce the quantity of masonry and give a more enlarged base. The 
openings are made by an exterior and an interior wall, connected at every ten 
feet by cross walls, which are carried up to within seventeen feet of the top, and 
then connected by a brick arch thrown from one to the other, and the spandrels 
between them levelled up solid, and a course of concrete put on the whole six 
inches thick, which reaches a level ten feet below the top on which the exterior 
wall is carried up single to the top. The exterior wall has a bevel of one to six, 
and is uniformly four feet thick from the bottom to the top of the connecting 
arches. The inner wall is carried up plumb with off-sets; the lower section six 
feet thick ; the middle section five feet thick. The span between the exterior and 
interior walls at 41 feet below the top is 14 feet, or 24 feet from the outside of 
exterior to the inside of interior walls, and the span between them at the spring 
of the connecting arches, in consequence of the bevel of the exterior wall, is 
reduced to 9 feet and 9 inches; and from outside of exterior to inside of 
interior walls, 17°75 feet. The cross walls are four feet thick at the bottom, and 
have an off-set of six inches on each side, at eight feet below the spring line of 
the connecting arches, and have openings at a suitable level near the bottom, to 
allow the construction of drains, and to permit persons to pass in and examine 
the work. 
On each corner of the reservoir, pilasters 40 feet in width are raised, project- 
ing four feet from the main walls, and in the centre on the streets and on the 
5th avenue, are pilasters 60 feet wide, and projecting six feet. The pilaster in 
the centre on the 5th avenue, rises seven feet above the main wall, and all the 
others four above. Doors are placed in the central pilasters on 40th and 42d 
streets, which give access to the pipe chambers. In the central pilaster an en- 
trance is made by a door to a stairway that leads to the top of the walls. On 
the outside walls is an Egyptian cornice, which accords with the general style of 
