14 THE TONER LECTURES. 



mine the actual, practical dry -weather flow of public sewers during 

 the hours of greatest use. The results of these gaugings fully sus- 

 tain the estimate just given. Generally, where from 50 to 100 

 houses contributed to the sewer, the discharge filled a six-inch pipe 

 from less than one to two and one-half inches deep. 



A sewer in Milwaukee draining an area of about 70 acres, and 

 serving a population of over 3,000, had the whole of its flow de- 

 livered through a six-inch pipe, which it did not entirely fill. A 

 sewer in St. Louis, draining a district having a population of over 

 11,000, had its entire flow delivered through a twelve-inch pipe 

 which it only about one-half filled. 



The belief is very general that if a given flow of sewage can 

 be discharged through a small pipe, it can surely be discharged 

 through a large one. This is not true. The whole sewage, solid 

 matters and all, will be completely removed by a small sewer, 

 while only the liquid portions and the smaller solids will be 

 removed by a large one. The solid matters, beyond the capacity 

 of the broad and flat stream to remove them, remain as a 

 deposit in the large sewer, always subject to decomposition, and 

 often liable to obstruct the water-way, to lessen the already slight 

 scouring capacity of the flow, and to invite further deposit. This 

 action proceeds without interruption, unless occasional storm-flow 

 washes away the accumulations. In aggravated cases, where the 

 sewer is very large, and where the storm-flow is slight, the whole 

 sewer becomes filled with the deposit until there is left under its 

 crown only the small channel needed for the ordinary flow. 



It is the invariable tendency of large sewers to accumulate 

 deposits in this manner, which constitutes the chief but by no 

 means the only argument in favor of their abolition, as house 

 sewers. 1 have very carefully considered the general features of 

 the existing sewers of Washington, and I believe that these can 

 never be made satisfactory imtil the larger ones are generally 

 restricted to the removal of storm-water only ; their place being 



