et us now return to the map of the field, and apply those
principles in planning the work to be done to make it dry.

*The Outlet* should evidently be placed at the present point of exit of
the brook which runs from the springs, collects the water of the open
ditches, and spreads over the flat in the southwest corner of the tract,
converting it into a swamp. Suppose that, by going some distance into the
next field, we can secure an outlet of 3 feet and 9 inches (3.75) below
the level of the swamp, and that we decide to allow 3 inches drop between
the bottom of the tile at that point, and the reduced level of the brook
to secure the drain against the accumulation of sand, which might result
from back water in time of heavy rain. This fixes the depth of drain at
the outlet at 3-1/2 (3.50) feet.

At that side of the swamp which lies nearest to the main depression of the
up-land, (See Fig. 21,) is the proper place at which to collect the water
from so much of the field as is now drained by the main brook, and at that
point it will be well to place a _silt basin_ or well, built up to the
surface, which may, at any time, be uncovered for an observation of the
working of the drains. The land between this point and the outlet is
absolutely level, requiring the necessary fall in the drain which connects
the two, to be gained by raising the upper end of it. As the distance is
nearly 200 feet, and as it is advisable to give a fall at least
five-tenths of a foot per hundred feet to so important an outlet as this,
the drain at the silt basin may be fixed at only 2-1/2 feet. The basin
being at the foot of a considerable rise in the ground, it will be easy,
within a short distance above, to carry the drains which come to it to a
depth of 4 feet,--were this not the case, the fall between the basin and
the outlet would have to be very much reduced.

*Main Drains.*--The valley through which the brook now runs is about 80
feet wide, with a decided rise in the land at each side. If one main drain
were laid in the center of it, all of the laterals coming to the main
would first run down a steep hillside, and then across a stretch of more
level land, requiring the grade of each lateral to be broken at the foot
of the hill, and provided with a silt basin to collect matters which might
be deposited when the fall becomes less rapid. Consequently, it is best to
provide two mains, or collecting drains, (_A_ and _C_,) one lying at the
foot of eac