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 cheaper in construction,--the labor of preparing and handling the stone, and of excavating the wider trench that stone requires, amounting to more than the cost of the tile, even with a high charge of transportation added. Incidentally it is proper to say that where tiles cannot be had, a mass of gravel or fine cinders, six inches wide and six inches deep, placed at the bottom of the drain, and _covered with well-packed soil_, is preferable even to broken stone or any other form of channel that would permit of the rapid running of water and the washing into the drains of even a slight amount of silt.