150 MR, J. P. JOULE ON THE UTILIZATION OF THE 
verting the sewage from its original course. The present 
sewers in their usual functions will have to be considered 
as taking their rise at the points where they are crossed by 
the mains. Hence their size will be larger than it ought 
to be for the diminished current, and accumulations will 
result, which latter will be carried in time of storm-over- 
flow into the Thames. A striking proof that such accu- 
mulations are, even under the present system, liable to 
take place and be carried off during storms is adduced by 
Dr. Hofmann and Mr. Witt. These chemists state that 
when after a sudden and heavy fall of rain the flow of the 
Savoy Street sewer had increased sixfold, they found that 
instead of the sewage being thereby diluted, a given volume 
actually contained more than twice the quantity of solid 
constituents which it contained under normal circum- 
stances. 
2nd. I doubt whether mains built of brick, however 
well cemented, can be depended upon to convey sewage. 
Brick is usually porous, and in that state it cannot be 
doubted that sewage-water will filtrate through it and thus 
gradually contaminate the adjacent ground. The injurious 
effects of such infiltration ought not to be overlooked in a 
system of mains extending to a total length of sixty miles. 
3rd. That portion of sewage which arrives at the out- 
falls will not be entirely prevented from returning to the 
metropolis. I arrive at this conclusion from the fact that 
the sea-water penetrates occasionally as far as London 
Bridge. The river is frequently brackish at Barking Creek 
and Woolwich. Experiments with floats may induce falla- 
cious conclusions in this respect, since it is probable that 
the scour of the flood-tide at the bottom of the estuary is 
greater than that of the ebb-tide. 
4th. The Thames will be rendered particularly nox- 
ious at the point where so vast a quantity of offensive 
matter is to be concentrated. By what justice a nuisance 
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