SOME REMARKS ON SEWERAGE SYSTEMS. 105 



is mucli the least at night. A sump, or an enlarged outfall 

 sewer, is thus requisite, in which the sewage may be stored 

 until there is sufficient to put the pumps to work upon. 

 These storage sewers and tanks are often provided when 

 the outfall is not at all times available, such as on a sewer 

 gravitating into the sea, where the outflow may for several 

 hours be prevented by the tide. In such cases it is usual to 

 close the sewer by a penstock, and let the sewage accumu- 

 late until the tide falls sufficiently to allow of its escape. 

 We have a good example of a storage sewer in the 8-foot 

 sewer down Coronation Road, which was designed to inter- 

 cept nearly all the sewage that now flows into the Avon on 

 both sides, and store it during high-water. At best these 

 elongated cesspools are bad things, as they mean the accu- 

 mulation of decomposing sewage just where everything de- 

 mands its rapid transmission. 



Pneumatic System. 



Air has been brought in to assist in the carriage of 

 sewage by several inventors. The only two inventions 

 that have been carried into practical effect, so far as I am 

 aware, are those of (1) Capt. Liernar and (2) Isaac Shone. 

 Capt. Liemur's method comprises the laying of cast-iron 

 air-tight mains, creating a vacuum at regular intervals in 

 them by means of a large air-pump at some central station, 

 and thus drawing the sewage along. The mains are laid 

 with short steep inclines and long flatter declines, down 

 which the sewage may gravitate. Special house-fittings are 

 also used. This system does not seem to have spread be- 

 yond Holland, where the excessive flatness no doubt renders 

 it convenient to be independent of gravitation as the chief 

 agent toward motion. But there are several serious draw- 

 backs which quite account for its limited use. 



