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and the site low in relation to other districts, the water will be kept while the soil becomes saturated to so great an extent that the processes of vegetable germination and growth are greatly impeded. The soil exists in one of three conditions; 1st, in the form of clay, being a dense mass consisting of finely comminuted particles, but all of a highly tenacious kind; in a state of slight moisture it becomes a clammy paste, and is never found so utterly devoid of moisture that its constituent particles are separable: it affords no passages for water, receiving it with difficulty, and retaining it in the same way. 2nd, in the form of sand or gravel, the particles of which are seldom or never united, and the soil is therefore full of passages or canals for water. Soil of this kind has no power either to oppose the admission or effect the retention of water poured upon it. And 3rd, existing in the form of a mixture of the aluminous, silicious, and calcarious elements, in endless variety of proportions, found as clods, and in this state affording two classes of passages for the ingress and permeation of water, viz., those remaining between the particles which are congelated in each clod, and those formed by the spaces between the clods. The former are sometimes called pores, and the latter canals. The power of admitting and retaining or discharging water exerted by these mixed soils, will exist in an endless variety of degrees, according to the mechanical formation of the constituent particles and clods. The state of soil which is most favourable for the germination and development of the plant is that of moistness, capable of being readily crumbled by the hand, and equally removed from the adhesive extreme of mud and the volatile one of dust. In this condition it will be found that the pores are filled with water but the canals are not, these latter serving as passages for

the air, which is one of the feeders of vegetable life; and we can, therefore, readily understand that, when water exists in such quantity that the soil is saturated with it, and all the pores or canals filled, its condition is unhealthy for the growth and development of plants.

16. The proper serving of water for agricultural purposes, similarly with that for domestic and manufacturing uses, requires both adequate supply and discharge. That is, if the natural supply be deficient it becomes the business of the drainer to augment it; if excessive, to reduce it; but, in either or any case, his correlative object is to provide sufficiently for the discharge of the water as rapidly as vegetation has imbibed its nutriment from it, and the supply is replenished. The recognition of this essential principle founded the era of all modern improvements in the Art of Draining. The most skilful tenders of the soil were previously satisfied to drain the surface of the land. So long as they were enabled by superficial channels to get rid of the excess of water which appeared above ground, their work seemed to them complete, and the effects of subterranean reservoirs and aluminous sponges, made visible in stunted and unhealthy vegetation, were attributed to any causes rather than the true ones. In our third section, which will show in detail the methods of determining and forming drains, these causes and the mode of treating them will be explained.

17. The facility or difficulty attending the artificial supply of water from rivers and subterranean sources, depends upon the distance of the sources from the districts to be watered, their relative levels, and the geological structure of the soil. The map of the district will exhibit the first of these circumstances, and a corresponding section will show the second; the third may

be inferred, with more or less exactness, from the superficial features of the country, but can be ascertained with certainty only by boring through the superincumbent strata until the spring or internal reservoir is arrived at.

18. The water of rivers is not generally available for the supply of the lands of districts of superior level, the expense of applying mechanical power for this purpose being too great to admit of extensive operations. For the supply of towns and buildings, however, this consideration is outweighed by the importance of the object. Pumps worked by water, steam, or other power, are applied to raise the water; and artificial channels, such as aqueducts or pipes, provided for its conveyance, with tanks. or reservoirs for containing it, and submitting it to any desired operations of cleansing or purifying. If the district to be supplied lie on a level, near to that of the feeding river, the reservoirs are usually constructed contiguous to it, and receive and cleanse the water before its conveyance through pipes or other conduits. Thus, several of the companies who now supply water to London and its suburbs have reservoirs for these purposes on the banks of the river Thames, whence their supply is derived.

19. For the irrigation and draining of adjacent lands on accessible levels, the waters of rivers are conducted by artificial courses. The system of irrigation adopted in Lombardy is complete for this purpose, and the principle of it is illustrated in figures 1 and 2; a a is the feeder to bb, the irrigating channels. The water flowing from these spreads itself as a veil over the rectangular sections of land between them, and thence passes into the draining channels cc, which are formed at a lower level than the supply channels, and is received in





the common drain dd, through which it passes, and becomes the means of irrigation and draining to other similar districts in succession. In Lombardy, the width of land between the channels b and c is usually about 22 feet, and the difference of level between the irrigating and the draining channels about 6 inches. These water-meadows, or marcite, are thus irrigated in summer during several hours about once in each week; and from the end of September to the end of March the process proceeds continuously, the water being turned off only while the grass is being cut.

20. Districts considerably above river level, or so situated that no water can be conveyed to them from that source, may be artificially supplied from wells, or by making communication with the lower and saturated strata of the soil. Thus, the ridges of land lying above the reach of the Nile were perforated with wells by the ancient Egyptians, as a substitute for the inundation by which the lower banks were fertilized. The Chinese also resort to wells for the purpose of irrigation. In many parts of the East, where the natural supply by rain is deficient, works on a very large scale have been constructed for obtaining water sufficient for irrigating. In Hindostan, Japan, China, Java, Tartary, &c., the supply is, to a great extent, drawn from wells; and in Bengal, Ceylon, the Carnatic, &c., immense tanks have been for ages constructed to contain the valuable liquid.

21. The principal rivers noted for the periodical rising of their waters, are the Nile, the Ganges, the Euphrates, and the Mississippi. Of these, the Nile, which flows from the Jibel Kumri Mountains, begins to rise in June, and by the middle of August attains an elevation of 24 to 28 feet, the inundation flooding the valley of Egypt for a width of 12 miles. The Ganges, flowing

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