atment of
this liquid so as to purify its effluent water, and retain in a solid
form, and in combination with certain valuable added ingredients, all of
its undissolved impurities. None of these processes can as yet claim
consideration in regulating public works.

The cheapest way to get rid of sewage is to discharge it into a running
stream or into tide-water. So far as the community itself is concerned,
this is often the best way; but there will very often arise the
objection that the community has no moral or legal right to foul a
stream of which others make use in its further course. Where the amount
of water constantly flowing is very large, and where the discharge is
rapid,--any given part of the sewage reaching the open air within a few
hours from the time of its entering the pipes,--and where it flows in
moving water for a considerable distance before reaching others who may
have occasion to use the stream, no practical danger is to be
apprehended. But where the sewage is more foul, more sluggish, or
exposed in the open current for a shorter time, the danger may be
serious. The pouring of sewage into tide-water is always admissible
where floats show that there is no danger of a return and deposit of
solid filth; but the delivery at all stages of the tide, in the
immediate neighborhood of salt marshes and mud flats, and in land-locked
harbors, is to be avoided.

Where an unobjectionable natural outflow cannot be provided, the
irrigation of agricultural lands affords the best relief. The action of
vegetation, the oxidation which takes in the upper and well-aerated
layers of soil, and the well-known but not yet fully explained
disinfecting qualities of common earth, are effective in removing the
dangerous and offensive impurities, and in converting them into a more
or less important source of fertility. Precisely how far this system
may be available during winter, it is not easy to say. While the earth
is locked with frost, there must be very little, if any, infiltration;
but, as an offset, the action of a low temperature upon the sewage
matters will clearly be antiseptic; and it is only necessary to provide
against an undue washing away of the surface of the ground during thaws,
and against the flowing of the sewage beyond the proper limits.

Generally in the neighborhood of villages it will be easy to find lands
over which the delivery may be carried on throughout the year without
objection. The sewer, or some