Book III. CHxiNGING THE CONDITION OF LANDS. 329 



by obstructing perspiration and intro-susception, and thus diseasing their roots and sub- 

 merged parts. Where the surface-soil is properly constituted, and rests on a subsoil 

 moderately porous, both will hold water by capillary attraction, and what is not so 

 retained will sink into the interior strata by its gravity ; but where the subsoil is retentive, 

 it will resist, or not admit with sufficient rapidity, the percolation of water to the strata 

 below, which accumulating in the surface-soil till its proportion becomes excessive as a 

 component part, not only carries off the extractive matter, but diseases the plants. 

 Hence the origin of surface-draining, that is, laying land in ridges or beds, or intersecting 

 it with small open gutters. 



2201. Springs. Where the upper stratum is porous in some places, and retentive in 

 others, and on a retentive base, the water, in its progress along the porous bed or layer, 

 will be interrupted by the retentive places in a great variety of ways, and there accumu- 

 lating will burst through the upper surface in the form of springs, which are more 

 injurious than surface-water, as being colder, and generally permanent in their operation. 

 Hence the origin of under-draining in all its varieties of collecting, extracting, and con- 

 veying water. 



2202. The ivater of rivers may become injurious to lands on their banks, by too 

 frequently overflovdng their surface. In this case the stream may be included by 

 mounds of earth or other materials impervious to water : and thus aquatic soils rendered 

 dry and fit for useful herbage and aration. The same may be said of lands occasionally 

 overflown by the sea. Hence the origin of embanking, an art carried to a great extent 

 in Holland and Italy. (See SmeatorCs Posthumous Works; Sigismondi, Agr. Tosc ; liac- 

 colta dei Autori die trattano delV Aque ; and our article Embankment, in Supp. Enci/c. 

 Brit. 1819.) 



2203. Irrigation. Plants cannot live without water, any more than they can prosper 

 in soils where it is superabundant ; and it is therefore supplied by art on a large scale, 

 either by surface or subterraneous irrigation. In both practices the important points are 

 to imitate nature in producing motion, and in applying the water in the mornings or 

 evenings, or under a clouded sky, and also at moderate intervals. The effects of water 

 constantly employed would, in most cases, be such as attend stagnated water, aquatic soils, 

 or land-springs ; and employed in hot sunshine, or after violent heats, it may check 

 evaporation and destroy life, exactly as it happens to those who may have bathed in cold 

 spring water after long and violent exercise in a hot day. [Phytologia, xv. 3. 5.) 



2204. In surface irrigation the water is conveyed in a system of open channels, which 

 require to be most numerous in such grounds as are under drilled annual crops, and least 

 so in such as are sown in breadths, beds, or ridges, under perennial crops. This mode 

 of watering has existed from time immemorial. The children of Israel are represented 

 as sowing their seed and " watering it with their foot ;" that is, as Calmet explains it, 

 raising the water from the Nile by a machine worked by the feet, from which it was 

 conducted in such channels as we have been describing. It is general in the south of 

 France and Italy ; but less required in Britain. 



2205. The Persian wheel, or Norm, an oriental invention of great power and of the most remote 

 antiquity, was introduced into Spain by the Moors, and is yet extensively used in the southern and eastern 

 provinces of that kingdom. It consists of a series of earthen jars attached to an endless rope passing over 

 a vertical drum put into motion by a trundle and cog horizontal wheel, which last is usually turned 

 by one bullock or more. 



2206. Subterraneous irrigation may be effected by a system of drains or covered gutters 

 in the subsoil, which, proceeding from a main conduit or other supply, can be charged 

 with water at pleasure. For grounds under the culture of annual plants, this mode 

 would be more convenient, and for all others more economical, as to the use of water, 

 than surface irrigation. Where the under-stratum is gravelly, and rests on a retentive 

 stratum, this mode of watering may take place without drains, as it may also on perfectly 

 flat lands, by filling to the brim, and keeping full for several days, surrounding trenches ; 

 but the beds or fields between the trenches must not be of great extent. This practice is 

 used in Lombardy on the alluvial lands near the embouchures of the Po. In Lincoln- 

 shire the same mode is practised by shutting up the flood gates of the mouths of 

 the great drains in the dry seasons, and thus damming up the water through all the 

 ramifications of the drainage from the sea to their source. This was first suggested by 

 G. Rennie and Sir Joseph Banks, after the drainage round Boston, completed about 

 1810. A similar plan, on a smaller scale, had been practised in Scotland, where deep 

 mosses had been drained and cultivated on the surface, but where, in summer, vegetation 

 failed from deficiency of moisture. It was first adopted by J. Smith (See Essay on the 

 Improvement of Peat-moss, 1795) on a farm in Ayrshire, and has subsequently beeri 

 brought into notice by J. Johnston, the first delineator and professor of Elkington's 

 system of draining. 



2207. Flooding and warping are modes of irrigation, the former for manuring grass 

 lands, and the latter for enriching the surface of arable lands ; while both at the same 

 time gradually raise up the surface of the soil. Irrigation with a view to conveying 



