462 QUANTITY OF WATER APPLIED. 
Lombardy are not included in these estimates of the amount of 
water applied.* 
to receive, in Germany, twenty-one centimctres of water per week, and with 
less than half that quantity it is not advisable to incur the expense of supply- 
ing it. The ground is irrigated twenty-five or thirty times, and if the full 
quantity of twenty-one centimétres is applied, it receives more than two hun- 
dred inches of water, or six times the total amount of precipitation. Puvis, 
quoted by Boussingault, after much research comes to the conclusion that a 
proper quantity is twenty centimctres [eight inches] applied twenty-five or 
thirty times, which corresponds with the estimate just stated. Puvis adds— 
and, as our author thinks, with reason—that this amount might be doubled 
without disadvantage.—Jbidem, ii., p. 248, 249. In some parts of France this 
quantity is immensely exceeded, and it is very important to observe, with 
reference to the employment of irrigation in our Northern States, that water 
is most freely supplied in the colder provinces. Thus, in the Vosges, meadows 
are literally flooded for weeks together, and while in the department of Van- 
cluse a meadow may receive, in five waterings of six and a half hours each, 
twenty-one inches of water, in the Vosges it might be deluged for twenty- 
four hundred hours in six applications, the enormous quantity of thirteen 
hundred feet of water flowing over it. See the important work of HERV& 
Mancon, Sur lemplot des eaux dans les Irrigations, chap. ix. 
Boussingault observes that rain-water is vastly more fertilizing than the 
water of irrigating canals, and therefore the supply of the latter must be 
greater. This is explained partly by the different character of the sub- 
stances held in solution or suspension by the waters of the earth and of the 
sky, partly by the higher temperature of the latter, and, possibly, partly also 
by the mode of application—the rain being finely divided in its fall or by strik- 
ing plants on the ground, river-water flowing in a continuous sheet. 
The temperature of the water is thought even more important than its com- 
position. The sources which irrigate the marcite of Lombardy—meadows so 
fertile that less than an acre furnishes grass for a cow the whole year—are 
very warm. The ground watered by them never freezes, and a first crop, for 
soiling, is cut from it in January or February. The Canal Cavour—which 
takes its supply chiefly from the Po at Chivasso, fourteen or fifteen miles be- 
low Turin—furnishes water of much higher fertilizing power than that de- 
rived from the Dora Baltea and the Sesia, both because it is warmer, and be- 
cause it transports a more abundant and aricher sediment than the latter 
streams, which are fed by Alpine ice-fields and melting snows, and which 
flow, for long distances, in channels ground smooth and bare by ancient gla- 
ciers and not now contributing much vegetable mould or fine slime to their 
waters, 
* About one-seventh of the water which flows over the marcite is absorbed 
by the soil of those meadows or evaporated from their surface, and conse- 
quently six-sevenths of the supply remain for use on ground at lower levels, 
