It is an important condition of this system that the sewage, where its quantity is small, shall be stored in tanks until a large volume has accumulated, and that it then be rapidly discharged over the soil. There is no objection to an actual saturation of the ground, provided the soil is not of such a retentive character as to be liable to become puddled, and so made impervious. The tanks being emptied, the flow ceases until they are again filled. During the interval, the liquid settles away in the soil, by which its impurities are removed. Its descent is followed by the entrance of fresh air, and the oxidizing action of this, accompanied during the growing season by the purifying effect of the growing crop, leads to an entire decomposition or destruction of all organic matters. The third system--the distribution of sewage through irrigation-pipes laid at a depth of ten or twelve inches below the surface of the ground--has its efficiency attested by numerous instances in private grounds. I have adopted this system for disposing of the sewage of the village of Lenox, Mass., where there was no other means available short of cutting an outlet, at great expense, through a considerable elevation. This method is an extremely simple one, and is available in every instance where even a small area of land lying slightly below the level of the outlet is to be commanded. The arrangement of the sub-irrigation pipes is easily made: Suppose that in land having an inclination of about one in two hundred, occupied by grass or other growth, a trench be dug twelve inches deep, that there be laid upon the bottom of this trench a narrow strip of plank to insure a uniform grade, and that upon this plank is laid a line of common agricultural land-drain tiles, say two inches in diameter. However carefully these tiles may be placed, there will be at their joints a sufficient space for the leaking out of any liquid they may contain; the tiles being laid either with collars around the joints, or with bits of paper laid over them, to prevent the rattling in of loose earth during the filling. The excavated earth is to be returned to its place, well compacted, and covered with its sod. Suppose this drain to have a cross-section equal to three square inches, and a length of one hundred feet, its capacity will equal about sixteen gallons, or a half-barrel. If this amount of liquid be rapidly discharged into the drain, the inclination being slight, it will at once be filled or nearly filled for its whole length, and the liquid will leak away in tolerably uniform proportion at every joint along the line, and will saturate the surrounding earth. The plan adopted at Lenox, and recommended for all small villages which cannot secure a better outlet, is simply a multiplication of these drains to a sufficient extent.