PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 591 



supply from house to liuuso is restricted in amount, satisfactory operation 

 depends on the scouring- action of this supplj', and its proper concentration 

 on the solid contents received. The whole aim of the Venous system is to 

 make the water supply eflfective, and this can only be attained by the use 

 of intermediate lines, so devised in grade, caliber, tightness, and smooth- 

 ness of internal form as to accomplish with certainty the desired concen- 

 tration of flow; or, iu other words, by the u'se of circular tubes, which 

 combine the greatest power of delivery with the least frictional surface. 



This system is not only incontrovertible in theory, but the history of 

 sinvorage, ancient and modern, abounds in experimental confirmation. In 

 all those cases where trunk sewers have been erroneously built, with sizes 

 entirely disproportioned to their service, with porous and rough surfaces 

 and rough joints, they have proved as defective in action as excessive in 

 cost. They have needed constant visitation and costly excavation and 

 removal of deposits ; of 69| miles of sewers examined in the Kent and 

 Surrey districts of Lonclon, the deposit was usually two feet in depth, and 

 in some cases five feet, reeking with foul gases subject to explosion, and 

 choke damp, and in a state of noxious fermentation; such sewers are spa- 

 cious reservoirs of malignant accumulations, furnishing food and harbor 

 for vermin, and exhaling pestilential gases into the air, breathed by those 

 who work and sleep over them; bringing down storm-flow in large floods, 

 they rapidly surcharge those larger arteries with which they connect and 

 convey an erroneous impression of defective caliber, duo only to defective 

 arrangement; iu strength and durability, they are exceeded; in cost, they 

 are excessive; and in friction, seriously so, on the same wet perimeter. 

 Pipes are, therefore, to be preferred as to caliber, close and firm joints, 

 smoothness of surface, and regularity of form, strength, power of self- 

 cleansing, transportation and laying, cost, and sanitary efi'ects. 



In 1863, New York spent §59,262 in cleansing, repairing, and rebuilding 

 sewers, having n5| miles in use; the average cost of 20,315 feet con- 

 tracted for was $3."90 per foot, while the average cost of 15,874 feet laid in 

 Brooklyn was §1.41 per foot. 



As an illustration of arrangement under the theory of combined trunk 

 sewers and tubes, the following statement of the Brooklyn sewerage, built 

 or contracted for from 1858 to 1863, is given : 



Trunk Seicers. 



feet. 



72 inches diameter 2,472 



60 do 6,099 



54 do 1,425 



48 do 15,4n5 



42 do 602 



86 do 21,282 



47,345 



Tubular Syatem. 



feet. 



24 inches diameter 34, 1 23 



18 do 69,102 



15 do 112,(J49 



12 do 310,104 



51 3, ."578 



Aggregate.. ..► 562,723 



