SOME REMARKS OX SEWERAGE SYSTEMS. 95 



in 16G0-79 was 800 per 1,000 ; 

 in 1746-55 „ 35"5 ,, ,, 

 in 1871 ,, 22-G „ „ 



At the present time it is 18*8 per 1 ,0(30. 



There are several methods of collecting and disposing of 

 refuse without the use of sewers ; such as, by mixture with 

 dry earth ; by collection in pails, as in Birmingham and in 

 some northern tow^ns ; or in middens or cesspools. 



The methods with which we have to do are, however, 

 those in which water or air is largely or chiefly introduced 

 as a means of transmission, and special channels or sewers 

 are constructed. We will therefore deal first with the 

 water-carriage system ; second, with the pneumatic or 

 quasi-pneumatic system. 



Water-Carriage System. 



The w^ater-carriage system is by far the most popular and 

 universal now in vogue. It is pre-eminently a gravitation 

 system, where water, naturally flowing down specially con- 

 structed courses, conveys away the refuse put into it. Its 

 chief advantages are : — 



1st. That it conveys sewage aw^ay quickly, and in the 

 manner least offensive to the eye. 



2nd. It requires little looking after. 



3rd. By its means the subsoil water may be drained. 

 This is a greater advantage than appears at first sight, as 

 it has been found that the saturation or dryness of the sub- 

 soil has an important bearing on health. It has often 

 happened that the sewers have been badly constructed and 

 are leaky, thus admitting the subsoil water ; and wdiat was 

 originally a defect has turned out to be an advantage through 

 the good effect produced by the permanent lowering of the 

 subsoil water. 



