Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 3, 1802).djvu/50

RR IRR It consists of two legs of common deal, A and B, about twelve feet in length, which are joined together at tlie top, and connected below by a cross bar, as above delineated. From the angle Ht the top, a plum- met C, is suspended bj a small cord J which, when a mark is made in the middle of the con- notating bar, and the two legs are perfectly straight, will strike such mark, so that the level may be easily ascertained. In the practical use of this in- strument. Dr. Anderson directs a wooden pin, on which one of the legs of the frame may rest, to be driven into the ground at the level of the water, where die irrigation is hitended to commence. The other leg is then to be brought round, till it touch the ground, on a level with the top of such pin, ■when another is to be driven in. After the level has in this man- ner been perfectly adjusted, the last mentioned pin is to be employed as a rest for one foot, and the other turned about, till the level is found in the same manner. Thus, the precise direction which the stream should take will at once be dis- covered, without any trouble, or Incurring any additional expence by digging through heights or fill- ing up cavities. The level being taken as di- rected, a wide ditch is to be cut as near to the dam as possible, that the water may be conveyed to the highest part of die meadow ; the sides and banks of the ditch being uniformly kept at an equal height, and elevated about three inches above the surface. Where the meadow is extensive, and the soil uneven, it will be necessary to have three works or dams in diffe- rent diredionsj each of which should be five feet in width, if tli^ meadow contain fifteen acres ; and the highest part be the most distant from the stream. A ditch, ten feet wide, and three in deptli, will, in general, be i'nlly adequate to over- tiow ten acres of land ; and if there be diree works or dams m a meadow, and flood-hntches, or flood-gates, be placed at die mouth of each, when the water is not sufficient to irrigate the whole soil at once, it may be .performed at three dillerent <?eriods ; by taking out one of the hatches or gates for the space of ten days, at the ex- piration of whici it. is to be let down, and the other two taken upi alternately for a similar period : thus each division will . receive a proper siiare of water in .its turn,- and derive from it equal benefit. Where the fall of the mcadov*- renders it practicable, the bottom of the first vork should be made as deep as the bed of die river j because the water, in proportion to its depth, carry a larger or- smaller quantity of mud with ity and consequently fertilize the soil in a more or less elfeftual manner. Small ditches, or troughs, ought likewise to be cut from the works at right angles, about 12 yards apart from each other, and their breadth should be adequate to the distance to w hich the water is tet be conveyed : thus a ti-ough two feet in widtli, and one foot deepy will irrigate a surface twelve yards-' wide, and forty feet in Itngtli. It will, however, be requisite to provide the ditches with occasional flood-gates or sluices, especially Ahen the water is rapid, in order to keep it sufliciendy high to flow through the perforaUons in the- gates, or over the sides. Btjtweea' every second trough, a drain is to ■ be