134 



WELLS'S NATURAL PHILOSOPHY. 



Fig. 118. 



On what prin- 

 ciple are we 

 enabled to con- 

 voy water in 

 aqueducts over 

 uneven sur- 

 faces ? 



This fact is sufficiently illustrated 

 by reference to Fig. 118. 



303. It is upon 



the application of 



the principle that 



water in pipes will 



always rise to the 

 height, or level of its source, that all ^ 

 arrangements for conveying water 

 over uneven surfaces in aqueducts, or closed pipes depend. The water 

 brought from any reservoir or source of supply, in or near a town or building, 

 may bo delivered by the efl'ect of gravity alone to every location beneath the 

 level of the reservoir; the result not being affected by the inequalities of the 

 surface over which the water pipes may pass in their connection between the 

 reservoir and the point of delivery. So long as they do not rise above the 

 level of the source of supply, so long will the water continue to flow. 



Fig. 119 represents the line of a modern aqueduct: — a a a represents the 

 water level of a pond or reservoir upon elevated ground. From this pond a 

 line of pipe is laid, passing over a bridge or viaduct at d, and under a river at 

 c. The fountains at b b, show the stream rising to the level of its source in 

 the pond a, at two points of very different elevation. 



Fig. 119. 



The ancients, in constructing aqueducts, do not seem to have ever practi- 

 cally applied this principle, that water in pipes rises to the level of its source. 

 When, in conducting water from a distant source to supply a city, it became 

 necessary to cross a ravine or valley, immense bridges, or arches of masonry 

 were built across it, with great labor and at enormous expense, in order that 

 the water-flow might be continued nearly horizontally. At the present day ' 

 the same object is effected more perfectly by means of a simple iron pipe^ 

 bending in conformity with the inequalities of surface over which it passes. 



In the construction of pipes for conveying water, it is neces- 

 sary that those parts which are much below the level of the 

 reservoir, should have a great degree of strength, since they 

 sustain the bursting pressure of a column of water whose 

 height is equal to the difference of level. A pipe with o- 

 diameter of 4 inches, 150 feet below the level of a reserv^oir, should have suf- 



In what map- 

 ner should 

 pipes for the 

 conveyance of 

 water he con- 

 structed ? 



