stones above the duct, have
been copied from one work to another for generations, and it seems never
to have occurred, even to modern writers, that the small stones might be
omitted. Any one, who knows anything of the present system of draining
with tiles, must perceive at once that, if we have the open triangular
duct or the square culvert, the water cannot be kept from finding it, by
any filling over it with such earth as is usually found in ditching.
Formerly, when tiles were used, the ditch was filled above the tiles, to
the height of a foot or more, with broken stones; but this practice has
been everywhere abandoned as expensive and useless.

An opening of any form, equal to a circle of two or three inches
diameter, will be sufficient in most cases, though the necessary size of
the duct must, of course, depend on the quantity of water which may be
expected to flow in it at the time of the greatest flood.

Whatever the form of the stone drain, care should be taken to make the
joints as close as possible, and turf, shavings, straw, tan, or some
other material, should be carefully placed over the joints, to prevent
the washing in of sand, which is the worst enemy of all drains.

It is not deemed necessary to remark particularly upon the mode of
laying large drains for water-courses, with abutments and covering
stones, forming a square duct, because it is the mode universally known
and practiced. For small drains, in thorough-draining lands, it may,
however, be remarked, that this is, perhaps, the most expensive of all
modes, because a much greater width of excavation is necessary in order
to place in position the two side stones and leave the requisite space
between them. That mode of drainage which requires the least excavation
and the least carriage of materials, and consequently the least filling
up and levelling, is usually the cheapest.

Our conclusion as to stone drains is, that, at present, they may be, in
many cases, found useful and economical; and even where tiles are to be
procured at present prices stones may well be used, where materials are
at hand, for the largest drains.

CHAPTER VI.

DRAINAGE WITH TILES.

What are Drain-Tiles?--Forms of Tiles.--Pipes.--Horse-shoe
Tiles.--Sole-Tiles--Form of Water-Passage.--Collars and their
Use.--Size of Pipes.--Velocity.--Friction.--Discharge of Water
through Pipes.--Tables of Capacity.--How Water enters Tiles.--Deep
Drains run