d equal fall.

ARRANGEMENT MUST HAVE REFERENCE TO THE OUTLET.

All agree that it is best to have but few general outlets. "In the whole
process of draining," says an engineer of experience, "there is nothing
so desirable as permanent and substantial work at the point of
discharge." The outlet is the place, of all others, where obstruction is
most likely to occur. Everywhere else the work is protected by the earth
above it, but here it is exposed to the action of frost, to cattle, to
mischievous boys, to reptiles, as well as to the obstructing deposits
which are discharged from the drains themselves. In regular work, under
the direction of engineers, iron pipes, with swing gratings set in
masonry, are used, to protect permanently this important part of the
system of drainage.

It may often be convenient to run parallel drains down a slope, bringing
each out into an open ditch, or at the bottom of some bank, thus making
a separate outlet for each. This practice, however, is strongly
deprecated. These numerous outlets cannot be well protected without
great cost; they will be forgotten, or, at least, neglected, and the
work will fail.

Regarding this point, of few and well-secured outlets, as of great
importance, the arrangement of all the drains must have reference to it.
When drains are brought down a slope, as just suggested, let them,
instead of discharging separately, be crossed, near the foot of the
slope, by a sub-main running a little diagonally so as to secure
sufficient fall, and so carried into a main, or discharged at a single
outlet.

It may be objected, that by thus uniting the whole system, and
discharging the water at one point, there may be difficulty in
ascertaining by inspection, whether any of the drains are obstructed, or
whether all are performing their appropriate work. There is prudence and
good sense in this suggestion, and the objection may be obviated by
placing _wells_, or "peep-holes," at proper intervals, in which the flow
of the water at various points may be observed. On the subject of wells
and peep-holes, the reader will find in another chapter a more
particular description of their construction and usefulness.

The position of the outlet must, evidently, be at a point sufficiently
low to receive all the water of the field; or, in other words, it must
be the lowest point of the work. It will be fortunate, too, if the
outlet can be at the same time high enough to be at all times abo