all that we
need to do, so far as subterranean work is concerned, is to furnish an
easy and sufficient channel for the removal of subsoil water.

What constitutes a sufficient drain is something very much less than
what is generally supposed. In ordinary agricultural drainage, where the
lines of tiles are forty feet apart, a well-laid tile an inch and a
quarter in diameter is sufficient for a length of one thousand
feet--that is, it is sufficient to remove the water of filtration from
an acre of land. If laid with only an inclination of six inches in one
hundred feet, its delivery will be so rapid as to amount to more than a
heavy continuous rain-fall upon this area. In road drainage, the same
rule would hold true; but, as the soil offers a certain resistance to
the rapid descent of water, it is best to give a means of outlet at
smaller intervals; and for the best work in roads thirty feet wide or
more, three drains could be used with advantage. In no case, however,
need the size of pipes be larger than above indicated, if the form of
the tiles is true, and if they are well joined together at their ends.
Tiles of less perfect form had better be an inch and a half or even two
inches in diameter; but, as a rule, they should not be of a larger size,
for the reason that the amount of water that they may be expected to
carry will not be sufficient to keep them prop erly freed from silt
unless the flow is concentrated within a narrow channel.

[Illustration: FIG. 2.]

Figure 2 shows the cross section of a country road thirty feet wide,
with three lines of tile-drain laid at a depth of about three feet below
it. Except in case of necessity, these drains should have an inclination
of not less than six inches in one hundred feet. There is no objection
to their having more than this wherever the lay of the land permits or
requires it. They may often have considerably less in case of need; but,
the smaller the rate of inclination, the greater the care needed in
securing a true grade. The water of these drains should be collected
into a single drain, and led away at intervals of from five hundred to
one thousand feet. It may be delivered into a roadside gutter, or into a
collecting under-drain, according to the requirements of the situation.

It is now possible to procure drain-tiles at reasonable cost in almost
all parts of the country; and these are not only very much better than
any form of stone drain, but they are also much