In a pipe of wrought or cast iron, at least ten feet long, and having an inside diameter of two inches with a thickness of three-eighths of an inch, are made a number of longitudinal openings or perforations, about ten inches long and a quarter of an inch wide. These openings or perforations are made at intervals of ten inches, and are placed in one or two lines opposite to each other. If it is preferred, round holes of from half an inch to one inch in diameter, and about six inches distant from each other, may be substituted for the longitudinal openings. This perforated pipe is placed in an upright position in the earth, and is so situated that it receives at its top opening the waste or rain water flowing along a channel or drain constructed for that purpose. The water, after running into the top of the pipe, gradually percolates down, and passing through the perforations or openings into the earth around and underneath the pipe, moistens it to such an extent and at such a depth as to render it but little affected by the heat of the sun. The pipe is generally placed at some little distance from the building, so as to give a sufficient area of earth to be kept moistened and to prevent the walls of the building being affected by the damp. Occasionally, the pipe is made triangular or square, and with perforated branches and other metallic conductors. It is also sometimes constructed with enlargements at the top or bottom, so as to hold more water. Probably, however, the simplest plan is the best, as--if the soil be suitable--a plain round wrought-iron pipe can be driven into the earth. If a cast-iron pipe is used, a hole of a convenient size is excavated for it. In this case, great care has to be taken that the earth is thoroughly well rammed down all round the pipe. Another arrangement is to employ, instead of a cast or wrought-iron pipe, a number of round or flat-iron bars, fastened together at the top and bottom by rivetting to metal hoops in such a manner that intervals are left between each bar, through which the water can pass. Sometimes a solid pipe without the openings is used, but it is not found to be so satisfactory as the perforated pipe, because the latter allows a greater amount of water to pass through it into the soil, thereby furnishing a larger area of moist earth. The French method of carrying the conductor to the bottom of a neighbouring well is frequently adopted where it is practicable, and the water of the well is not required for drinking or cooking purposes.