IRRIGATION 



be placed, face downwards, between it 

 and the land it is to overflow; being 

 made firm and level, by beating with 

 the flat of a spade. As the penstocks are 

 situated just below the lines of the branch- 

 drains above described, they keep up the 

 water, so as to fill, and to cause their 

 overflowing into the next inferior talus 

 or slope, as shown m fig. 1 and 2, where 

 A is the mam dram, taken from the water- 

 head or river, B ; the drain C, C, C, C, 

 shows the secondary dram, which, being 

 on a declivity,, would carry off all the 

 water, were it not kept up at the places 

 where the catch-drains or branches, D, 

 D, D, D, proceed laterally from it, by the 

 sluices E, E, E E By this means, any 



others; the water being kept on by the 

 sluice above, and can-fed away by the 

 sluice appertaining to each level re- 

 spectivelv. Or, if other meads at some 

 distance are to be watered, the secondary 

 channel, having all its sluices open, will 

 convey it to them without interruption, 

 when all its sluices are opened. 



It is evident, that in this manner the 

 whole of the water is carried down to 

 the lowest level: hence it becomes a 

 matter of no small importance to ascer- 

 tain, that the whole shall either be ab- 

 sorbed or be carried off ; so as not to in- 

 jure the last level, which might otherwise 

 be subjected to very considerable injury, 

 were the inundation to be too lono- sup- 

 ported. The judicious computer will be 

 cautious not to allow so much to remain 

 as may rot his grass ; in lieu of causing it 

 to vegetate vigorously. This, in some 

 situations, presents a'veiy serious diffi- 

 culty ; for if the water is debarred free 

 access to the lowest levels, they will be 

 less fruitful than the others, which, ex- 

 elusive of the great fecundity derived 

 from first receiving the fluid, receive ab- 

 solutely a larger portion of moisture. The 

 greatest care is therefore requisite, to in- 

 sure that the tail, or spent-water, shall be 

 carried off. Where the declivity is con- 

 siderable, and that the stream, or any 

 other water-course, offers itself to receive 

 such tail-water, at a due level beneath, 

 there is no difficulty ; but where the 

 stream takes another course, and the 

 descent is trifling, some artificial means 

 must be resorted to. Perhaps no more 

 simple or efficacious plan can be hit upon, 

 than that of forming a fish-pond, of a suit- 

 able extent and depth, to receive the 

 tail-water ; whereby the apprehended 

 damage may be avoided, and a useful 

 store be created. 



We shall show what we may term a 

 truly ingenious device, whereby water 

 may be laid upon lands that are above the 

 level of the stream : it consists merely of 

 an air-vessel, A, fig. 3, into which the 

 water descends forcibly from the stream, 

 B, and by compressing the air in the up- 

 per part, C, is itself forced to ascend 

 through the conducting pipe, D, with such 

 force as to rise to a level, E, far above 

 that at which it formerly stood. This is 

 the principle of the common fire-engine, 

 w hj c h we are all sensible, can, when exert- 

 e d, throw water to a great height. By 

 such mea ns, the tail-water may also be 

 forced up to such a level as may cause it 

 to return into the stream. 

 , Where the stream runs through the 

 lan ds tbat al ? watered, and that its de- 

 chvity is moderate, it will sometimes be 

 found difficult to restore the tail-water to 

 lts level> To ***** this with as little ex- 

 pence as possible, wooden pipes should 

 be ****** pelowe* level of the land 

 lon S the bank of the stream, but earned 

 horizontally on a bank, to such extent as 

 "W s ^ ce * convey the tail-water to 

 the ce of the surface. This, how- 

 ever, is not applicable to all situations ; 

 for . where tbe , stream is very slow, its de- 

 chvit y would be . ver y trifling. Where 

 that happens, the air vessel will be found 

 a S ood P lan Prided the height to which 

 the water 1S to be returned, be not con- 

 siderable. In many situations, a water- 

 wheel mi S ht answer wel1 ' observing, that 

 m dee P slow waters, that are broad, and 

 under the speculator's own management, 

 ' A will be best to throw a weir across, and 

 then to let the whole body of the stream 

 rusb through a narrow slip, so as to turn 

 * wheel placed immediately in the line of 

 the water's run. By this device, the cur- 

 rent may be made to pass that particular 

 spot with sufficient velocity to turn a 

 wheel; whereby water might either be 

 raised out of the river, to supply a main 

 dra i" or the tail-water might be restor- 

 ed to the stream : in either case, one or 

 more pumps would be necessary. (See 

 fig- 4.) 



The second mode of laying water over 

 the land is by means of ridges, whose 

 centres are occupied by small horizontal 

 drains, out of which the water, furnished 

 by the main drain, is allowed to flow to 

 the depth of about an inch down each 

 side of the pitch. These ridges should 

 be from four to six feet measurement for 

 each face ; the drain being about a 

 foot broad, and four inches deep ; thus 

 the whole breadth of a pitch, declining 



