The fact, that the last foot of a four-foot drain costs as much labor as the first three feet, is shown in another chapter, and the deeper we go, the greater the comparative cost of the labor. With tiles at $10 per thousand, the cost of opening and filling a four-foot ditch is, in, round numbers, by the rod, equal to twice the cost of the tiles. In porous soils, therefore, where depth may be made to compensate for greater distance, it is always a matter for careful estimate, whether we shall practice true economy by laying the tiles at great depths, or at the smallest depth at which they will be safe from frost and the subsoil plow, and at shorter distances. The rule is manifest that, where labor is cheap and tiles are dear, it is true economy to dig deep and lay few tiles; and, where tiles are cheap and labor is dear, it is economy to make the number of drains, if possible, compensate for less depth. DISTANCES DEPEND UPON SYSTEM. While we would not lay down an arbitrary arrangement for any farm, except upon a particular examination, and while we would by no means advocate what has been called the gridiron system--of drains everywhere at equal depths and distances--yet some system is absolutely essential, in any operation that approaches to thorough drainage. If it be only desired to cut off some particular springs, or to assist Nature in some ravine or basin, a deep drain here and there may be expedient; but when any considerable surface is to be drained, there can be no good work without a connected plan of operations. Mains must be laid from the outfall, through the lowest parts; and into the mains the smaller drains must be conducted, upon such a system as that there may be the proper fall or inclination throughout, and that the whole field shall be embraced. Again, a perfect _plan_ of the completed work, accurately drawn on paper, should always be preserved for future reference. Now it is manifest, that it is impossible to lay out a given field, with proper mains and small drains, dividing the fall as equally as practicable between the different parts of an undulating field, preserving a system throughout, by which, with the aid of a plan, any drain may at any time be traced, without making distances conform somewhat to the system of the whole. It is easily demonstrable, too, that drains at right angles with the mains, and so parallel with each other, are the shortest possible drains in land that needs uniform drainage. They take each a more uniform share of the water, and serve a greater breadth of soil than when laid at acute angles. While, therefore, it may be supposed that in particular parts of the field, distances somewhat greater or less might be advisable, considered independently, yet in practice, it will be found best, usually, to pay becoming deference to order, "Heaven's first law," and sacrifice something of the individual good, to the leading idea of the general welfare.