Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/382

366 IBEIGATION undulations, so that the lines of glitter curve very considerably. From the nature of the ground it may next be necessary to begin at H, and to produce HI. It will now be perceived that D and I are too far asunder, making it necessary to introduce KL, beginning at K. The higher side must be finished in like manner. " Let now fig. 2 represent a meadow, with all the lines of fig. 1 marked with the level and ploughed, but not turned out. It will be perceived that the curves of the lines form a series of loops, and that the undulations of the meadow are prettily mapped out by the curves going down round the hills and up round the valleys. It will be at once seen where the water is principally wanted, viz., just above where the curves form the greatest downward bend, as at A, fig. 2. Next draw the lines which, upon an aver age, will be at right angles to the level, but in each particular line will deviate from the right angle, more or less, according as the ground is more or less irregular. This may be done by walk- > ~" ing in advance of a plough, and leaving foot-prints to mark where the plough must folio w. Care must be taken to go as nearly through the centre of the downward loops as possible. In order to do this, first cut the lines 1, 2, 3, 4, 5, and then fill up the intervals by cutting a, b, c. The best distance for these seems to be from ten to fifteen paces apart. "The next business is to bring in the water, after just lifting the turf out of the gutters already cut. A spirit-level may be used, the gutter being allowed to drop 1J or 2 inches every 2 poles, if the nature of the ground will allow of it ; not less than J inch will do at all well. A much larger gutter is required at ^-inch drop than at 2 inches ; and, besides, it will not run itself dry so well when the water is turned off. The 2-inch drop gutters will run the water off directly ; the ^-inch will scarcely do it at all. Regard must be had to the supply of water required at the further end. In the case supposed in fig. 2, it is wanted on the rising ground, at the further end A ; therefore the gutter should drop that way, and be of a good size. If the water is wanted chiefly at the beginning of the gutter, the drop need not be so much, and the gutter should taper away so as to end nearly in a point. " The size of the stream is the next consideration. If it can water the whole piece at all times, one gutter, of sufficient size, should be made. Stops in a gutter should be avoided. Where the stream is small, make a leading gutter, and take out from it taper gutters, each of a size suited to the stream when at its smallest, so that when the stream increases (from rain or any other cause), as many taper-gutters may be used as will disperse the whole stream. The leading gutter should continually decrease in size from the place where the first taper-gutter is taken out of it, and finish in a taper ing water-gutter itself at last. In fig. 3, AB is a carriage-gutter as Fig. 3. far as c, and a watering -gutter from c to B ; a and b are watering- gutters taken out of it. When the stream is small, a stop at 1 will cause it to work in a ; a stop at 2 will work in b ; without any stop it will work in cB. If the stream is too much for cB, it will work b at the same time ; and, should there be water enough, it will also fill a without any stop at all. Care should be taken not to make AB larger than just to carry the full stream wanted ; and in every case when the gutter becomes too large by frequent clean ing out, cut it anew on one side or the other. "The hedge-trough may be made a carriage-gutter wherever it can be done conveniently, care being always taken to keep the water running in it. Covered gutters made with large tiles could also be substituted for the deep open carriage-gutter, where it is necessary to cross the middle of meadows ; this obviates the danger of the open gutter to sheep and lambs, and the tiled gutter does not re quire the annual cleaning out. "When a small stream insufficient for the whole meadow is used, the water must be confined to ground determined on by stops in the gutters which run on the two sides of it, thus : Fig. 4 is a section of the net-work of gutters ; AB is the carriage- gutter ; a is a taper watering-gutter, to the extent of which the water is supposed to be determined to be confined ; b, c, d, c, are the feeding gutters (perpendicular to the levels) ; the cross-gutters are the level ones ; b and e serve as the two side gutters of the section to be watered. The water is confined to the ground between them by stops at the crossings, arranged thus : I and c (fig. 5) are crossings on the feeders ; 1, 2, 3, 4 are stops, the purpose of which is obvious enough. The arrows show the direction the water is made to run. The . stops are pieces - of the turf taken >, out of the gutters, which, being cut j with a die, lit the gutters with exactness, and can be put in opera tion instantly, without trouble or 2 loss of time. " The gutters are not to be cut in the same places two successive years, but on one * & ^- side, as near as can be conveniently done, say about a foot and a half from the former ones ; and the turf of the new gutter is to be used to fill in the old one, the latter not being crammed too full. By this means the gutters are always new, and always the proper size. If cut on the right- hand side and above one year, the next year they should be cut the left-hand side and be low. " It will be proper now to call attention to themanner in which the water is carried, with its sus- pended matter, to the extreme end of the meadow, by the plan we are pursuing. It will be observed that the ground is covered by a sort of network of little gutters, one set being, in a sort, parallel to each other, intersected by another set at right angles to them and also parallel to each other. This would be strictly true were the surface strictly a plane surface ; but, this being very rarely the case, both sets deviate from a strictly parallel condition in order to meet the undulations of the ground, the deviations compensating each other on the aggregate. Now, instead of carrying the water down to the lower end by means of one large gutter, and then dispersing it by another large gutter (a level one), we do it by twenty or so little gutters which feed the dispensing gutter about every ten or fifteen paces ; being so small, these never fret away, and, being newly cut every year, they never increase in size. "These small gutters are sufficient when the little stops are taken out of the perpendicular gutters, and the level gutters are stopped so as to confine the water to the perpendiculars, to carry down the requisite water. The level gutter of a lower section (if a lateral section is to be watered), instead of being fed by a large stream at the end, is supplied every ten or fifteen paces by one of those little gutters, thus giving a uniform supply throughout the length of the level gutter. A larger supply than this will afford is an evil. When the water is shut out from the leading-in guttet it is not necessary to move any of the little stops ; the same per pendicular gutters that are effectual to run the water on are as effectual to run it off, leaving the surface of the meadow dry and solid. The water is evenly distributed over the surface by these minute gutters, which are made to follow all the undulations of thft land (which can never be done by the large gutters) ; and also, from the draining effect of the perpendicular gutters, the water is never suffered to accumulate in ponds. The water on the meadow is therefore never over-shoe anywhere. These gutters are no way dangerous to sheep or lambs, are never in the way of mowing, have an elegant rather than an unsightly appearance, are not perceived either in raking or carting, and suit the horse-rake or hay-making machine admirably. It may be added that the leading-in gutters can be so arranged as to tend themselves in cases of flood. " Upward or Subterranean Irrigation. In this kind of irrigation the water used rises upward through the soil, and is that which under ordinary circumstances would be carried off by the drains. The system has received considerable development in Germany, where the elaborate method invented by Petersen is recommended by many agricultural authorities. In this system the well-fitting earthenware drain-pipes are furnished at intervals with vertical shafts terminating at the surface of the ground in movable caps. Beneath each cap, and near the upper end of the shaft, are a number of vertical slits through which the drainage water which rises passes out into the conduit or trench from which the irrigating streams originate. In the vertical shaft there is first of all a grat ing which intercepts solid matters, and then, lower down, a central valve which can be opened and closed at pleasure from the top of the shaft. In the ordinary English system of upward or drainage irrigation, ditches are dug all round the field. They act the part of conductors when the land is to be flooded, and of main drains when it is to be laid dry. The water flows from the ditches as