ve the
back-water of the stream, or pond, or marsh, into which it empties; and
high enough, too, to be protected by solid earth about it. In any case,
great care should be taken to make the outlet secure and permanent. The
process of thorough-drainage is expensive, and will only repay cost,
upon the idea that it is permanent--that once well done, it is done
forever. The tiles may be expected to operate well, for a lifetime; and
the outlet, the only exposed portion of the work, should be constructed
to endure as long as the rest.

It is true that this portion of the work may be reached and repaired
more conveniently than the tiles themselves; but it must be remembered
that the decay of the outlet obstructs the flow of the water, produces a
general stagnation throughout the drains, and so may cause their
permanent obstruction at various points, hard to be ascertained, and
difficult to be reached. Considering our liability to neglect such
things as perish by a gradual decay, as well as the many accidental
injuries to which the outlet is exposed, there is no security but in a
solid and permanent structure at the first.

To illustrate the importance attached to this point in England, as well
as to indicate the best mode of securing the outlet, the drawings below
have been taken from a pamphlet by Mr. Denton. Fig. 37 represents the
mode of constructing the common small outlets of field drainage.

[Illustration: Fig. 37.--SMALL OUTLET.]

The distinguished engineer, of whose labors we have so freely availed
ourselves, remarks as follows upon the subject:

"Too many outlets are objectionable, on account of the labor of
their maintenance: too few are objectionable, because they can only
exist where there are mains of excessive length. A limit of twenty
acres to an outlet, resulting in an average of, perhaps, fourteen
acres, will appear, by the practices of the best drainers, to be
about the proper thing. If a shilling an acre is reserved for
fixing the outlets, which should be _iron pipes, with swing
gratings_, in masonry, very substantial work may be done."

Figures 38 and 39 represent the elevation and section of larger outlets,
used in more extensive works.

[Illustration: Fig. 38.--LARGE OUTLET.]

[Illustration: Fig. 39.--LARGE OUTLET.]

It is almost essential to the efficiency of drains, that there be fall
enough beyond the outlet to allow of the quick flow of the water
disc