] 64 THE OX AND THE fcAIKY 



Finally, it runs back into the river from which it was taken, at 

 a lower point of its course. 



When there is a considerable fall and a sufficient supply of 

 water, -a series of channels may be made, so situated below 

 each other, that the second collects the water which the first 

 has supplied, and in its turn becomes a feeder to irrigate the 

 lower parts of the declivity; a third channel receives the 

 water and distributes it lower down, until the last pours it 

 into the river. This is called catch-work, because the water is 

 caught from one channel to another. This method is only 

 applicable where there is a considerable fall of water, and a 

 gentle declivity towards the river. But it must be borne in 

 mind that the water is deteriorated for the purpose of irriga- 

 tion when it has passed over the land, and that it is not ad- 

 vantageous to let it flow over a great extent when a fresh 

 supply can be obtained : but where only a small portion of 

 water can be commanded, that must be made the most of; 

 and it will irrigate three or four portions of land in succession 

 without there being any very marked difference in the effect : 

 beyond this it rapidly loses its fertilizing qualities. 



In many situations the great difficulty in irrigation arises 

 from the want of a supply of water ; but even then a partial 

 irrigation may be effected, which will have its advantages. A 

 small rill which is often quite dry in summer may, by judi- 

 cious management, be made to improve a considerable portion 

 of land : its waters may be collected in a pond, or reservoir, 

 and let out occasionally, so that none be lost or run to waste. 

 If there is only a small quantity, it must be husbanded ana 

 made to flow over as great a surface as possible. If there is 

 water only at particular seasons of the year, and at a time 

 when it would not be of much use to the land, it may be kept 

 in ponds, and it will lose none of its qualities by being ex- 

 posed to the air. If animal or vegetable matter in a partial 

 state of decomposition is added to this water, it will much 

 improve its quality. 



If there is not a want of water, there may be a want of 

 declivity to enable it to flow off, which is an essential part of 

 irrigation. Art may in this case assist nature by forming a 

 passage for the water, either in its course towards the land to 

 be irrigated, or from it after it has effected its purpose. Where 

 there is no natural exit, and it might cause too great an expense 

 to make an artificial one, the water may sometimes be led into 

 shallow ponds, where a great part is evaporated ; or porous 



