108 SOME EEMAEKS OK SEWERAGE SYSTEMS. 



any sewage to eject and compressed air to eject it. It works 

 at any speed, according to the time the sewage takes to fill 

 it and to the amount of air-compression working it. 



The advantages gained by the use of these ejectors are 

 thus stated by their promoters : — 



First. Small sewers at good inclinations, at no great 

 depth, mostly above the subsoil water-level, discharging the 

 sewage into an ejector, where it becomes effectually trapped. 



Second. The rapid transit of sewage into an ejector before 

 decomposition sets in. 



Third. Reduced cost for flushing, on account of having 

 smaller sewers. 



Fourth. Freeiom from bad smells emanating from man- 

 holes ; for the cubic capacity of the sewers being small, the 

 volume of air in contact with sewage is proportionately 

 small. 



Fifth. Less risk of spreading contagious diseases, as each 

 drainage district is independent of another. 



Sixth. Facility for extension, irrespective of levels. 



On the other hand, we have to set — 



First. The annual cost of working. This must un- 

 doubtedly be greater than for a pure gravitation system, 

 though no doubt it compares favourably with any systems 

 in which all the sewage is collected at one point, and 

 pumped from a greater depth than would be the case if it 

 were intercepted in several places, as is done with Shone's 

 ejectors. 



Second. The loss of power due to the use of compressed 

 air, such as the heat generated during compression, and 

 which passes away without doing useful work ; and the 

 leakage and friction in the engines and mains conveying 

 the power to the ejectors. 



"With regard to the first of these objections, — what is really 



