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to be attained in effecting the dispollution of the Thames;
1st, to prevent further introduction of filth, and 2nd, to
prevent the exposure of the mud at, and a little before and
after, low water. The first, as is well known, it is proposed
to effect by carrying the sewers to such a distance from the
Metropolis, that the return of the sewage by the tide would
he impossible; and the other, by narrowing and deepening
the channel of the river by means of built embankments, so
that the tide would be more rapid and efficacious in cleansing
by its down scour, and allow no surface of mud to be left
exposed. By some it is believed that the latter step alone
would be sufficient, and that it would, if done effectually,
supersede the necessity of resorting to the first enormously
expensive plan of draining.
It has also been proposed to adopt the most unequivocally
successful part of the Leicester system of drainage, rejecting
that portion of it which professes to make the sewage matter
into manure, to be sold at a profit, and retaining that which
relates only to the purifying of the sewage, abstracting from
it all its solid and some other of its constituents, and then
allowing it to flow in a harmless form into the river. Lime
is there freely used, — it is now used in our sewers, at a cost
of 150/. per diem, and although in all probability useful, it
is not used with any certainty or precision of application.
If the consumption of lime were to be continued at its
present rate, the annual expenditure would be 53,750/.;
while the interest of seven millions, which the extended
main drainage would at least cost, amounts to 350,000/.
If, in London, the sewage could be deodorized and filtered,
and then returned to the river in a purified state, a most
important problem would be solved, and the river further
purified by adapting the same plan to other cities and towns
situated on its banks.