172 DR. R. ANGUS SMITH ON 



not be used, and it is also clear that it would not be so rich as 

 that of Edinburgh, so that equal results could scarcely be 

 expected. The amount not used in this manner would flow 

 down the sewer, and would be led into the first tank or 

 reservoir, there to be precipitated. There the solid matter 

 would be kept, and the fluid, when clear, would proceed. 

 There is then a constant succession of sewers for the water 

 that has not been used on the way. Below every town and 

 district giving off much impure water, such a depositing 

 reservoir would be placed. Every person might then receive 

 from the river, water for manufacturing purposes, and the 

 making of private reservoirs, now so numerous, might be 

 almost entirely saved. There are a few cases where fine 

 colours are wanted, where this water might not be so well 

 fitted as fresh wjiter from drainage land, but these cases 

 would be few. This would be a great saving both of land 

 and labour, as well as water, to the country. 



But not to expand too much upon it, it is then to be asked 

 how is the precipitation to be effected. 



I have mentioned that the precipitation will take place in 

 the reservoirs, but if they are to be disinfected, so can the 

 sewers be disinfected ; it is not needful then that the precipitant 

 be added in the reservoirs. Besides there is a difficulty in 

 mixing the water of a reservoir, which Mr. Wrigg proposed 

 to get over by having rails across it, allowing men to go to 

 any part. This would, however, by no means get over the 

 difficulty, as a man could only mix well that part which was 

 within reach of his arm, and if the whole surface of the reser- 

 voir were covered with little whirlpools, mixing themselves in 

 every spot, the whole mass would not thereby be mixed. I 

 consider, therefore, that it would be of great advantage to 

 mix in the sewer themselves; by this means the sewers would 

 be disinfected, that great evil would be removed which we have 

 endeavoured vainly to shut in by means of traps ; some outlet, 

 however, it will decidedly make for itself, whilst being shut 



