ANCIENT AND MODERN WORKS. 3 



The second, under a multiplicity of design, has for its 

 object the mechanical elevation of water from a lower to a 

 higher level, and its storage in basins or reservoirs of sufficient 

 size and elevation to answer all of the requirements. 



The third, or " Direct," scheme distributes the water by a 

 constant, applied mechanical pressure to the contemplated 

 points of delivery. In this monograph, a subdivision of the 

 second of these broad methods will be discussed, as its scope 

 is intended to cover the architectural design ; materials and 

 methods of constructing and erecting elevated storage-reser- 

 voirs, which of late years have played an important part in the 

 general economy of most water-works designs. 



Reservoir System Discussed. The detail of such con- 

 struction is subject to local condition, and ranges from designs 

 for small tanks elevated upon supporting columns to immense 

 reservoirs for the water-supply of great cities. In the general 

 scheme of a water-supply system the elevated reservoir serves 

 a dual purpose; providing for a surplus supply to be utilized 

 as required, as well as permitting a temporary suspension of 

 the mechanical operations of the plant ; its further purpose is 

 its ability to relieve internal pressures, acting in this capacity 

 as a regulator or relief-valve to the entire system of distribu- 

 tion. Considered simply as a receptacle for elevated storage, 

 its purpose and principles are obvious. 



In the natural exercise of the functions of an automatic 

 safety-valve, the results are similar to those produced by an 

 air-chamber, closely connected to the pumping machinery. 

 The force exerted in the intermittent action of an enclosed 

 column of water compressed or impelled by the forward move- 

 ment of the pistons or plungers of the pumping-engine, acts 

 as a " ram," producing rupture, according to the intensity of 

 the force exerted, to pipe-mains, connections and joints. 

 This stress may be relieved and the shock regulated by pro- 

 viding for a discharge of the water under pressure into an 



