458 IRRIGATION IN EUROPE. 
on one field, to run into drains, canals, or rivers. But in most 
regions where irrigation is regularly: employed, it is necessary 
to economize the water; after passing over or through one par- 
cel of ground, it is conducted to another; no more is usually 
withdrawn from the canals at any one point than is absorbed by 
the soil it irrigates, or evaporated from it, and, consequently, it 
is not restored to liquid circulation, except by infiltration or 
precipitation. We are safe, then, in saying that the humidity 
evaporated from any artificially watered soil is increased by a 
quantity bearing a large proportion to the whole amount dis- 
tributed over it, for most even of that whichis absorbed by the 
earth is immediately given out again either by vegetables or by 
evaporation ; and the hygrometrical and thermometrical con- 
dition of the atmosphere in irrigated countries is modified pro- 
portionally to the extent of the practice, 
It isnot easy to ascertain precisely either the extent of sur- 
face thus watered, or the amount of water supplied, in any 
given country, because these quantities vary with the character 
of the season ; but there are not many districts in Southern Eu- 
rope where the management of the arrangements for irrigation 
is not one of the most important branches of agricultural labor. 
The eminent engineer Lombardini describes the system of irri- 
gation in Lombardy as, “every day in summer, diffusing over 
550,000 hectares [1,875,000 acres] of land 45,000,000 cubic 
metres [nearly 60,000,000 cubic yards] of water, which is equal 
to the entire volume of the Seine, at an ordinary flood, or a rise 
of three metres above the hydrometer at the bridge of La Tour- 
nelle at Paris.” * Niel states the quantity of land irrigated in 
the former kingdom of Sardinia, including Savoy, in 1856, at 
240,000 hectares, or not much less than 600,000 acres. This is 
about four-thirteenths of the cultivable soil of the kingdom. 
According to the same author, the irrigated lands in France did 
not exceed 100,000 hectares, or 247,000 acres, while those in 
Lombardy amounted to 450,000 hectares, more than 1,100,000 
* Memorie sui progetti per Vestensione dell’ Irrigazione, ete., tl Politecnico, for 
January, 1863, p. 6. 
