ls between them cannot be always
the same; those which are farther apart at one end than at the other
cannot be always of a depth exactly proportionate to their intervals.

In the adjustment of the lines, so as to conform as nearly to these
requirements as the shape of the ground will allow, there is room for the
exercise of much skill, and on such adjustment depend, in a great degree,
the success and economy of the work. Remembering that on the map, the line
of steepest descent is exactly perpendicular to the contour lines of the
land, it will be profitable to study carefully the system of drains first
laid out, erasing and making alterations wherever it is found possible to
simplify the arrangement.

Strictly speaking, all _angles_ are, to a certain extent, wasteful,
because, if two parallel drains will suffice to drain the land between
them, no better drainage will be effected by a third drain running across
that land. Furthermore, the angles are practically supplied with drains at
less intervals than are required,--for instance, at _C 7 a_ on the map the
triangles included within the dotted line _x_, _y_, will be doubly
drained. So, also, if any point of a 4-foot drain will drain the land
within 20 feet of it, the land included within the dotted line forming a
semi-circle about the point _C 14_, might drain into the end of the
lateral, and it no more needs the action of the main drain than does that
which lies between the laterals. Of course, angles and connecting lines
are indispensable, except where the laterals can run independently across
the entire field, and discharge beyond it. The longer the laterals can be
made, and the more angles can be avoided, the more economical will the
arrangement be; and, until the arrangement of the lines has been made as
nearly perfect as possible, the time of the drainer can be in no way so
profitably spent as in amending his plan.

The series of laterals which discharge through the mains _A_, _C_, _D_ and
_E_, on the accompanying map, have been very carefully considered, and are
submitted to the consideration of the reader, in illustration of what has
been said above.

At one point, just above the middle of the east side of the field, the
laterals are placed at a general distance of 20 feet, because, as will be
seen by reference to Fig. 4, a ledge of rock, underground, will prevent
their being made more than 3 feet deep.

The line from _H_ to _I_, (Fig. 20,) at the north sid