Now, looking at the operation of drains across the slope, and supposing that each drain is draining the breadth next above it, we will suppose the drain to be running full of water. What is there to prevent the water from passing out of that drain in its progress, at every point of the tiles, and so saturating the breadth below it? Drain pipes afford the same facility for water to soak out at the lower side, as to enter on the upper, and there is the same law of gravitation to operate in each case. Mr. Denton gives instances in which he has observed, where drains were carried across the slope, in Warwickshire, lines of moisture at a regular distance below the drains. He could ascertain, he says, the depth of the drain itself, by taking the difference of hight between the line of the drain at the surface, and that of the line of moisture beneath it* He says again : I recently had an opportunity, in Scotland, of gauging the quantity of water traveling along an important drain carried obliquely across the fall, when I ascertained with certainty, that, although the land through which it passed was comparatively full of water, the drain actually lost more than it gained in a passage of several chains through it." So far as authority goes, there seems, with the exception of some advocates of the Keythorpe system, of which an account has been given, to be very little difference of opinion. Mr. Denton says: "With respect to the direction of drains, I believe very little difference of opinion exists. All the most successful drainers concur in the line of the steepest descent, as essential to effective and economical drainage. Certain exceptions are recognized in the west of England; but I believe it will be found, as practice extends in that quarter, that the exceptions have been allowed in error." In another place, he says: "The very general concurrence in the adoption of the line of greatest descent, as the proper course for the minor drains in soils free from rock, would almost lead me to declare this as an incontrovertible principle." We will suppose A, B, Fig. 42, to represent a portion of the higher field above. Then the catch water or drain across the line of greatest descent will be represented by A, H, E, H, B; and when the nature of the ground will admit, or should there be a depression toward the center of the field, the catch-water may be led from E to J, as a sub-main, being some distance below J, the main drain. The minor drains then should run parallel, or nearly so, to E, J. Where the distance from E to J is considerable, it is always advisable to run the minor drains F, F, F, etc., into sub-mains, G, G, G, G. In draining a piece of land, situated like that represented in Fig. 41, which would involve the cutting of ditches to the depth of eight cr ten feet between 1 and 2, so as to have the * French on Drainage. drains of a proper depth at 3, it will be found advisable to lead the minor drains into a sub-main from 4 to 3, and then commence a new series of drains between 2 and 1, and lead them into another sub-main at 1. Some good drainers advise, that when works stop on a slope, a drain called a header should connect the tops of the minor drains, thus preventing the water lying between the upper sub main, A, E, B, of Fig. 42, and the minor drains F, F, F, F, etc., from passing down into the ground between the minor drains, and also relieving the minor drains from the pressure of the water above them, and by which they will the more easily become clogged than when protected. However, when the sub-main is dug above the minor drains, as in the figure, the necessity of headers is very slight, except when the quantity and pressure of water is sufficient to cause it to flow over the sub-main. Capillary attrac Even the sub-main will not drain the slope above it entirely. tion, and the resistance offered to the descent of the water will prevent the submain from bringing about a complete drainage. The cuttings of our railways and high banks of rivers show that no depth of ditch can remove the moisture from a very considerable distance. This part of the subject has been more fully discussed in the Chapter on Distance of Drains. The sub-main draining the highest portion of the slope should be independent of all minor drains and branches, for being directly in contact with the head of water from above, it will necessarily carry down more mud and silt, and have a tendency, if allowed, to choke up the minor drains. It is sometimes found advantageous to construct a tank, sink, or silt basin, in both surface and covered drains. This is more especially the case where an open enters into a covered drain. From this sink the water flows off comparatively clear. This arrangement will not be found to answer its purpose, when the amount of water flowing through the drains is very great, for then the motion of the stream passing through the tank will prevent the mud from depositing. It will also be necessary to have the tank frequently cleaned from its deposit, for when filled with mud it is only an obstruction. We have now described the proper method of cutting off the supply of water from an underground spring, as well as draining the underground water from an adjoining slope, and it yet remains to say a few words upon conveying away the amount discharged by the clouds. This is a subject upon which much has been written, and is even yet an exceedingly controverted point. It is, in fact, the egg of Columbus for drainers, as it involves not only a calculation of the distance between drains, the depth of drains, fall, and size of tile, but also evaporation and filtration. All of these points have been discussed in the preceding pages. We may assume that the meteorological precipitations for Ohio, will average 43 inches per annum (see Report 1858). The precipitations then will be 10 33 inches during the spring months; 13.40 during the summer; 9 60 during autumn, and 9.66 during winter. Assuming, then, in the absence of positive experiments, that evaporation is the same pro rata, as in Continental European countries, it will amount to 15 inches per annum in Ohio, leaving 28 inches to be filtrated, and to flow off the surface. Of this, about one-half, or 14 inches, finds its way into the soil, and the remainder into brooks, creeks, etc. Now, if these assumptions are correct, then underdrained soils inaugurate a vast change in these proportions; because where observations have been correctly registered, it was found that eleven-twentieths of the summer precipitations were discharged by the drains, and often more than three fifths of the autumn and spring precipitations, while the discharges from the drains averaged more than three fourths of the winter precipitations. Hence, the assumption, that one-third of the precipitations are absorbed by filtration, is no criterion for the drainer. He must assume that at least one-half of meteorological precipitations are to be carried off by the drains. Now, the summer and autumn precipitations must not be taken as a basis, upon which to predicate either the distance between drains or the capacity of the tiles, because the soil is then in a condition to dispose of the precipitation without any obstruction. But the winter and spring precipitations will constitute a more relia. ble basis. Freezing, during the winter months, arrests the operation of the drains and when the genial weather in spring time sets in, the water of the two sea. sons have both to be drained at once. Now, if we take the amount of the pre cipitation of the three winter months, and add to it that of two spring months, this will give us the largest mass of water to be drained in the shortest period of time, so as to relive the growing crops from sustaining any injury. The period in which this water should be drained away, should never exceed fourteen days. Having given tables in the preceding pages, of fall, width between drains, and capacity of tiles, each one may make his own calculations for the piece of ground intended to be drained. CHAPTER IX. MAIN DRAINS. The main drain should be located on the lowest portion of the farm. It should be an open ditch, at least four feet deep, but when circumstances will permit, six feet. The side should have a slope of a foot and a half to each foot of depth.. If then the drain be four feet deep, and eighteen inches wide at the bottom, the width at the top will be thirteen and a half feet. The ground excavated, if thrown up on the sides, will form a capital fence. In fact the ha-ha fences of England, are built in this manner, for the reason that they occupy less space and are equally preventive as hedges are against the irruptions of unruly cattle. The main should invariably be made before the minor drains, for very obvious reasons, prominent among which is the determination of the amount of fall, and depth of the minor drains. The main drain should invariably be a foot or eighteen inches lower than the outlet of the minor drains, if they discharge immediately into the main drain; but where sub main drains are employed, the main should be at least eight inches below the outlets of the sub-malns, while the sub-mains should be at least a foot lower than the minor drains. Of course where these proportions are not practica. ble, less fall between the minor drains and sub-mains, and between the sub-mains and main, must be admissible. But where these proportions can be attained, greater security will be given to the drains, against disturbances by frogs, lizards, or other amphibious animals. Where a sub-main or minor drains empty into the main drain, the exit pipe should be secured by a system of masonry, similar to means, because these outlets are not only liable to be frozen up in winter time, but are exposed to cattle and to mischievious boys, and to become obstructed by deposits which are discharged by the drains themselves. A much better plan is to have the minor drains empty into a sub-main, as G G, emptying into J, in the lower portion of Fig. 42. The smaller the number of outlets, in any system of draining, the better. Some may object to our plan of one outlet, on the ground that, should any obstruction occur in the minor drains, it will be more difficult of inspection. This is true in a certain sense; but we think that surface indications will show when and where any serious obstruction takes place, with as much certainty as the open end of the drain. And surely the additional security of having a few openings, well protected, is a much greater advantage than a drain left open for the purpose of investigation. However, to obviate any difficulty which might arise from either of the above methods, some good drainers recommend that "peep-holes" should be placed at regular distances, by which, should any derangement occur, its locality and extent could be easily determined. The construction of these "peepholes" may be varied to suit the taste or means of the proprietor. A very easy method of making them will be to sink a stout barrel or hogshead over the drain. Incoming Outlet FIG. 44. This, however, will be but a temporary concern. Another form, more in place with the whole system, may be constructed after the annexed cut, Fig. 44, either of earthenware or cast iron. It should be well protected at the surface of the |