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 wdth 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 comer 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 



