28 IRRIGATION. 



As examples of the nature of these varying circum 

 stances, the following are cited : M. Herve Magnon (a 

 frequently quoted authority in works upon irrigation, and 

 already referred to here), determines the limits of supply 

 as from one to four litres per second per hectare, which 

 is equal to from one pint to two quarts per acre, per 

 second, continuously flowing. Gardens and market 

 gardens require the larger extreme. M. Pare to, another 

 French author, in his work upon the irrigation and drain 

 age of lands, (Irrigation et assainissement des terres), 

 mentions some cases in which a quantity equal to one 

 quart per second was sufficient to effectively irrigate eight 

 acres. This may be taken as the extreme minimum 

 limit of supply, very rarely occurring, and altogether ex 

 ceptional. 



The Italian canals, which irrigate 1,600,000 acres, sup 

 ply 24,000 cubic feet per second for this area. This is 

 equal to one cubic foot (30 quarts) for 66 acres, or a flow 

 of 26 cubic inches per second per acre ; or very nearly 

 one quart (which is 57 3 | 4 cubic inches) for each two acres. 

 In that country the rain-fall equals 37 to 38 inches per 

 annum, the most of which occurs in the irrigating season, 

 when there are on the average 71 rainy days in the six 

 months from March to October. There the summer tem 

 perature is from 70 to 90 degrees. It will be observed 

 that the climatic conditions of Italy closely approach 

 to those of the rainy portion of the United States. The 

 mean water-supply may therefore be taken as closely ap 

 proximating the quantity required in this country viz., 

 one pint per second, constantly flowing, or 10,800 gallons, 

 or 172 2 | 10 cubic feet every 24 hours for every acre. In India, 

 one cubic foot per second is made to serve for 200 acres of 

 grain crops. In some parts of Spain the same quantity serves 

 for 240 acres; in others the same quantity is spread over 

 1,000 acres, and the legal allowance in some recent Span 

 ish grants, varies from 70 to 260 acres per cubic foot per 



