WATER WITHDRAWN FOR IRRIGATION. 
379 
The quantity of water artificially withdrawn from running 
streams for the purpose of irrigation is such as very sensibly 
to affect their volume, and it is, therefore, an important ele¬ 
ment in the geography of rivers. Brooks of no trifling current 
stances disappear almost immediately from the solution; the soil with¬ 
draws them from the water. Only such substances are completely with¬ 
drawn by the soil as are indispensable articles of food for plants; all others 
remain wholly or in part in solution.” 
The first of the paragraphs just quoted is not in accordance with the 
alleged experience of agriculturists in those parts of Italy where irrigation 
is most successfully applied. They believe that the constituents of vege¬ 
table growth are washed out of the soil by excessive and long-continued 
watering., They consider it also established as a fact of observation, that 
water which has flowed through or over rich ground is far more valuable 
for irrigation than water from the same source, which has not been im¬ 
pregnated with fertilizing substances by passing through soils containing 
them; and, on the other hand, that water, rich in the elements of vege¬ 
tation, parts with them in serving to irrigate a poor soil, and is therefore 
less valuable as a fertilizer of lower grounds to which it may afterward be 
conducted. 
The practice of irrigation—except in mountainous countries where 
springs and rivulets are numerous—is attended with very serious econo¬ 
mical, social, and political evils. The construction of canals and their 
immensely ramified branches, and the grading and scarping of the ground 
to be watered, are always expensive operations, and they very often require 
an amount of capital which can be commanded only by the state, by 
moneyed corporations, or by very wealthy proprietors; the capacity of 
the canals must be calculated with reference to the area intended to be 
irrigated, and when they and their branches are once constructed, it is 
very difficult to extend them, or to accommodate any of their original ar¬ 
rangements to changes in the condition of the soil, or in the modes or 
objects of cultivation; the flow of the water being limited by the abun¬ 
dance of the source or the capacity of the canals, the individual proprietor 
cannot be allowed to withdraw water at will, according to his own private 
interest or convenience, but both the time and the quantity of supply must 
be regulated by a general system applicable, as far as may be, to the whole 
area irrigated by the same canal, and every cultivator must conform his 
industry to a plan which may be quite at variance with his special objects 
or with his views of good husbandry. The clashing interests and the 
jealousies of proprietors depending on the same means of supply are a 
source of incessant contention and litigation, and the caprices or partial¬ 
ities of the officers who control, or of contractors who farm the canala, 
