18 Transactions of the Society. 



The smell of the river and of the mud some years ago, when 

 the amount of sewage poured into the Thames probably did not 

 amount to more than half the quantity now traversing the sewers, 

 perhaps affords some idea of what might happen if the conditions 

 favourable to the development of smell were repeated and aug- 

 mented in intensity, as will probably obtain when a very dry hot 

 summer follows a winter and spring in which the rainfall shall 

 have been considerably less than the average, unless in the mean- 

 time some more effectual and quicker means of disposal of the 

 colossal amount of the sewage should be discovered and carried into 

 practice. As London increases, therefore, every effort should be 

 made to keep up and increase the amount of water mixed with the 

 sewage at its source so that it may attain the greatest degree of 

 dilution that is practicable during its transit along the sewers. 



Any one who has seen the vast volumes of water in the upper 

 Thames during the time of flood will be convinced that there is water 

 and more than enough to flush the sewers of a city even consider- 

 ably larger than London. If only a small portion of this vast 

 quantity of wasted water could be husbanded till the time approaches 

 when the amount at our disposal for diluting the sewage could be 

 thus supplemented, the efficiency of the present system would 

 doubtless be greatly increased. Unless the plan for dealing with 

 the sewage can be completely changed, it will be necessary, as time 

 goes on, to further enlarge the present sewers, to divert into them 

 sewage which even now finds its way into some of the tribu- 

 taries of the Thames, and to carry further and further towards 

 the sea the mains which receive the sewage and drainage collected 

 from that increasing area included in Greater London. That such 

 operations would entail vast and lasting expenditure is obvious, but 

 basing our conclusion on the practical results achieved during the 

 past thirty years and more, is it not highly probable that all that 

 can be desired would be gained ? On the other hand, it may be 

 asked which of the several other suggested schemes of sewage 

 disposal has been found to succeed on a sufficiently large scale, 

 and for a sufficient length of time, to justify its adoption in place 

 of the main drainage system now in operation ? 



^ _ By mixing sewage with large quantities of water the gradual 

 disintegration and oxidation of many of its constituents and the 

 slow conversion of all its deleterious principles into substances 

 which are at any rate harmless, is insured. The changes are in 

 part mechanical and chemical, and partly due to living organisms, 

 which play no unimportant part in the ultimate reduction of 

 noxious organic matters to harmless compounds. The rapidity and 

 completeness of the purification of the contaminated water in great 

 measure depend upon the degree of dilution. If the sewage is con- 

 centrated, the decomposition which ensues is of a different kind and 



