Then, from this new amount, subtract the second number of the
fourth column, for the next number of the fifth, and so on, until,
in place of the entry in pencil, (Stake 3,) we place the exact
result of the computation.

Proceed in like manner with the next interval,--3 to 7.

10th. Subtract the numbers in the sixth column from those in the
fifth, and the remainders will be the depths to be entered in the
last.

Under the head of "Remarks," note any peculiarity of the drain
which may require attention in the field.

The main lines _A_, _D_, and _E_, and the drain _B_, should next be graded
on the plan set forth for _C_, and their laterals, all of which have
considerable fall, and being all so steep as not to require silt-basins at
any point,--can, by a very simple application of the foregoing principles,
be adjusted at the proper depths. In grading the stone and tile drain,
(_H, I_,) it is only necessary to adopt the depth of the last stakes of
the laterals, with which it is connected, as it is immaterial in which
direction the water flows. The ends of this drain,--from H to the head of
the drain _C10_, and from _I_ to the head of _C17_,--should, of course,
have a decided fall toward the drains.

The laterals which are placed at intervals of 20 feet, over the
underground rock on the east side of the field, should be continued at a
depth of about 3 feet for nearly their whole length, dropping in a
distance of 8 or 10 feet at their lower ends to the top of the tile of the
main. The intervals between the lower ends of _C7c_, _C7d_, and _C7e_,
being considerably more than 20 feet, the drains may be gradually
deepened, throughout their whole length from 3 feet at the upper ends to
the depth of the top of the main at the lower ends.

The main drains _F_ and _G_, being laid in flat land, their outlets being
fixed at a depth of 3.50, (the floor of the main outlet,) and it being
necessary to have them as deep as possible throughout their entire length,
should be graded with great care on the least admissible fall. This, in
ordinary agricultural drainage, may be fixed at .25, or 3 inches, per 100
feet. Their laterals should commence with the top of their 1/4 tile even
with the top of the 2-1/2 collar of the main,--or .15 higher than the grade
of the main,--and rise, at a uniform inclination of .25, to the upper end.

Having now computed the depth at which the tile is to lie, at each sta