152 IRRIGATION. 



arrived at perfection : and the conclusion we 

 would draw from this is, that water owes its fer- 

 tilizing power as much to the foreign sub- 

 stances it contains, as to its moisture. 



This being the case, we have only to reflect 

 on the large quantity of soluble matter every 

 river and every stream brings with it; almost 

 all of which is deposited in its transit over the 

 surface of an absorbent meadow, to be satisfied 

 that this is one of the principal sources of the 

 fertilizino^ effects of irrio^ation. 



Much, however, depends upon the character 

 of the water, the sources from which it springs, 

 and the character of the soil through which it 

 passes, its local position in or near to large 

 towns, from which an incalculable supply of 

 matter is always obtained. 



In speaking of the kind of water most ser- 

 viceable as a fertilizer, hard water is perhaps 

 to be preferred, because it owes this character 

 to the quantity of sulphate of lime (gypsum) it 

 contains in solution, and which being depo- 

 sited on the lands over which it passes, acts in 

 the same way as gypsum applied as a top 

 dressing. 



Sir Humphrey Davy was of opinion, that the 

 temperature of water exerted a considerable 

 influence on the growth and development of 

 vegetation — and there is no doubt but that this 

 has its effect — but it is n'ow supposed to be sub- 

 ordinate in its effects to those produced by the 

 causes already stated, and by the oxidizement 

 of various matters contained in the soil; and 

 which being thus effected by the continual 



