162 THE OX AND THE DAIRY. 



suppose that the mere washing of the roots has a beneficial 

 effect, and to this in a great measure must be ascribed the 

 fertilizing effects of pure and soft running water. 



If water stagnates and is evaporated, and the noxious mat- 

 ter held in solution remains in the soil, all the advantage of 

 irrigation is lost, and the better kinds of grasses are succeeded 

 by rushes and coarse aquatic plants. The circulation of the 

 water, therefore, appears to be as necessary as its presence ; 

 and, provided there be a sufficient supply of water of a proper 

 quality, the more porous the soil, and especially the subsoil, 

 is, the more vigorous is the vegetation. It is on this prin- 

 ciple alone that we can rationally account for the great advan- 

 tage of irrigation in those climates where rain is abundant, 

 and where the soil, which is most benefited by having a 

 supply of water running through it, is of a nature to require 

 artificial draining as an indispensable preliminary to being 

 made fertile by irrigation. By keeping these principles in 

 view, great light will be thrown on the practical part of irri- 

 gation, which, having been long established by experience, 

 before these principles were thought of, depends not on their 

 correctness, but only confirm? their truth. 



The whole art of irrigation may be deduced from two simple 

 rules, which are, first, to give a sufficient supply of water 

 during all the time the plants are growing; and secondly 

 never to allow it to accumulate so long as to stagnate. 



The supply of water must come from natural lakes and 

 rivers, or from artificial wells and ponds, in which it is col- 

 lected in sufficient quantity to disperse it over a certain sur- 

 face. As the water must flow over the land, or in channels 

 through it, the supply must be above the level of the land to 

 be irrigated. This is generally the principal object to be con- 

 sidered. If no water can be conducted to a reservoir above 

 the level of the land, it cannot be irrigated. But there must 

 also be a ready exit for the water, and therefore the land must 

 not be so low as the natural level of the common receptacle of 

 the waters, whether it be a lake or the sea, to which they run. 

 The taking of the level is therefore the first step towards an 

 attempt to irrigate any lands. 



Along the banks of running streams nature points out the 

 declivity. A channel, which receives the water at a 'point 

 higher than that to which the river flows, may be dug with a 

 much smaller declivity than that of the bed of the river, and 

 made to carry the water much higher than the natural banks. 



