of depth.

In tolerably porous soils, it is generally conceded that 40 or even 50
feet is sufficiently near for 4-foot drains, but, for the more retentive
clays, all distances from 18 feet to 50 feet are recommended, though those
who belong to the more narrow school are, as a rule, extending the limit,
as they see, in practice, the complete manner in which drains at wider
intervals perform their work. A careful consideration of the experience of
the past twenty years, and of the arguments of writers on drainage, leads
to the belief that there are few soils, which need draining at all, on
which it will be safe to place 4-foot drains at much wider intervals than
40 feet. In the lighter loams there are many instances of the successful
application of Professor Mapes' rule, that "3-foot drains should be placed
20 feet apart, and for each additional foot in depth the distance may be
doubled; for instance, 4-foot drains should be 40 feet apart, and 5-foot
drains 80 feet apart." But, with reference to the greater distance, (80
feet,) it is not to be recommended in stiff clays, for any depth of drain.
Where it is necessary, by reason of insufficient fall, or of underground
rock, to go only three feet deep, the drains should be as near together as
20 feet.

At first thought, it may seem akin to quackery to recommend a uniform
depth and distance, without reference to the character of the land to be
drained; and it is unquestionably true that an exact adaptation of the
work to the varying requirements of different soils would be beneficial,
though no system can be adopted which will make clay drain as freely as
sand. The fact is, that the adjustment of the distances between drains is
very far from partaking of the nature of an exact science, and there is
really very little known, by any one, of the principles on which it should
be based, or of the manner in which the bearing of those principles, in
any particular case, is affected by several circumstances which vary with
each change of soil, inclination and exposure.

In the essays on drainage which have been thus far published, there is a
vagueness in the arguments on this branch of the subject, which betrays a
want of definite conviction in the minds of the writers; and which tends
quite as much to muddle as to enlighten the ideas of the reader. In so far
as the directions are given, whether fortified by argument or not, they
are clearly empirical, and are usually very much qua