HiGGiNSON. — Sanitary Sexcerage. 375 



from the lower areas is forced, that from the higher areas 

 flowing by gi-avitation, the branch mains receiving it being 

 carried up to an elevation sufficient to establish a head w^hich 

 will overcome the fiiction in the mains, thus enabling the 

 whole to flow together to the outfall. 



From the Corporation Yard, where the air-compressing 

 station would be placed, the outfall main would be carried 

 along the shore of the harbour and Evans's Bay to the same 

 point on the sand-hills as by Clark's scheme ; or, if necessary, 

 to Lyall's Bay. 



Mr. Clark, however, dealt with the sewage of a popula- 

 tion of 70,000 and a rainfall of lin. flowing off one-quarter 

 of the area occupied by the city ; while I propose to deal with 

 the sewage alone of 50,000, leaving the rainfall to flow- off by 

 existing ch-ains, and when the population exceeds 50,000 to 

 extend the system, thereby avoiding the necessity for incur- 

 ring a heavy present outlay for the benefit of future genera- 

 tions. 



The pneumatic system can be readily adapted to the in- 

 crease of population, wherein lies one of its chief merits : 

 when the necessity arises additional " ejectors " can be intro- 

 duced, and, by increasing the air-pressure, greater velocity, 

 and therefore greater discharging-power, can be given to the 

 main outfall pipe until it becomes necessary to duplicate it — 

 a work readily done without in any way interfering with the 

 works previously constructed. By Clark's scheme the inter- 

 cepting sewers and long tunnel can only discharge a certain 

 volume of sewage and rainfall ; while to increase their capacity, 

 which must eventually become necessary, means a very heavy 

 outlay. By admitting so large a proportion of the rainfall to 

 the sewers he has enormously increased the first cost and work- 

 ing-expenses of his scheme. It may have been done with the 

 object of flushing the sewers; but I maintain this can be more 

 effectually done by the adoption of automatic flush-tanks at 

 the head of the sewers. 



I will now^ describe the " pneumatic ejector " and its ac- 

 tion. 



From a central station, placed where most convenient, com- 

 pressed air is forced through small pipes to the various ejec- 

 tors, which are placed at the lowest point of each subdi\'ision 

 which it is intended to serve. Each ejector- station has its 

 own particular system of pipe-drains leading into it from such 

 subdi\ision, which, being of comparatively small extent, enables 

 these pipes, even in flat ground, to be laid to proper self-cleans- 

 ing gradients without burying them at a great depth. A drain- 

 pipe 20 chains in length laid to an inclination of 1 in 250 will 

 only have a vertical fall of 5-4:ft. This fact is one of the im- 

 portant features of this system, long lengths of sewers being 



