e water would stand highest at the points furthest distant from
the outlet. So, in the land, after a drenching rain, the water is first
removed to the full depth, near the line of the drain, and that midway
between two drains settles much more slowly, meeting more resistance from
below, and, for a long time, will remain some inches higher than the floor
of the drain. The usual condition of the soil, (except in very dry
weather,) would be somewhat as represented in the accompanying cut, (Fig.
12.)

[Illustration: Fig. 12 - LINE OF SATURATION BETWEEN DRAINS.]

Fig. 12 - LINE OF SATURATION BETWEEN DRAINS.

_YY are the draings. The curved line b is the line of saturation, which
has descended from a, and is approaching c._

To provide for this deviation of the line of saturation, in practice,
drains are placed deeper than would be necessary if the water sunk at once
to the level of the drain floor, the depth of the drains being increased
with the increasing distance between them.

Theoretically, every drop of water which falls on a field should sink
straight down to the level of the drains, and force a drop of water below
that level to rise into the drain and flow off. How exactly this is true
in nature cannot be known, and is not material. Drains made in pursuance
of this theory will be effective for any actual condition.

The _depth_ to which the water table should be withdrawn depends, not at
all on the character of the soil, but on the requirements of the crops
which are to be grown upon it, and these requirements are the same in all
soils,--consequently the depth should be the same in all.

What, then, shall that depth be? The usual practice of the most
experienced drainers seems to have fixed four feet as about the proper
depth, and the arguments against anything less than this, as well as some
reasons for supposing that to be sufficient, are so clearly stated by Mr.
Gisborne that it has been deemed best to quote his own words on the
subject:

"Take a flower-pot a foot deep, filled with dry soil. Place it in a saucer
containing three inches of water. The first effect will be, that the water
will rise through the hole in the bottom of the pot till the water which
fills the interstices between the soil is on a level with the water in the
saucer. This effect is by gravity. The upper surface of this water is our
water-table. From it water will ascend by attraction through the