442 lERIGATION IN EUROPE. 



Lombardj irrigation is bestowed upon almost every crop, while 

 in our Northern States it is never employed at all in farming 

 husbandry, or indeed for any purpose except in kitchen-gardens, 

 and possibly, in rare cases, in some other small branch of agri- 

 cultural industry.* 



In general, it may be said that irrigation is employed only in 

 the seasons when the evaporating power of the sun and the 

 capacity of the air for absorbing humidity are greatest, or, in 

 other words, that the soil is nowhere artificially watered except 

 when it is so dry that little moisture would be evaporated from 

 it, and, consequently, every acre of irrigated ground is so much 

 added to the evaporable surface of the country.f When the suj)- 



fine myself to the concave vault of the heavens, and do not mean to assert 

 that terrestrial objects are generally visible at greater distances in the United 

 Stati* than in Italy. Indeed, I am rather disposed to maintain the contrary ; 

 for though I know that the lower strata of the atmosphere in Europe never 

 equal in transparency the air near the earth in New Mexico, Peru and Chili, 

 yet I think the accidents of the coast-line of the Riviera, as, for example, be- 

 tween Nice and La Spezia, and those of the incomparable Alpine panorama 

 seen from Turin, are distinguishable at gi'eater distances than they would be 

 in most parts of the United States. 



* In our comparatively rainless Western territory, irrigation is extensively 

 and very beneficially employed. In the Salt Lake valley and in California, 

 hundreds if not thousands of miles of irrigation canals have been constructed, 

 and there is little doubt that artificially watering the soil will soon be largely 

 resorted to in the older States. See valuable observations on this subject in 

 Hayden, Preliminary Report on Oeological Survey of Wyoming, 1870, pp. 194, 

 195, 258, 261. 



f The evaporative action of water in motion or at rest on the earth's surface, 

 is affected by the temperature of the ground with which it is in contact ; by 

 the temperature of the water itself ; by the hydroscopic condition of the ail 

 which rests upon it, and also by the movement of the air if not at rest. It 

 aU these conditions are favorable to evaporation, — as they generally are upon 

 irrigated soil, especially with a ploughed surface, — the evaporation will pro 

 ceed rapidly, and, of course, irrigation would have much importance as a 

 meteorological or climatic influence. Large bodies of cold water, like that ol 

 the great American lakes, evaporate slowly, and, though they produce by 

 conduction a certain amount of refrigeration, they do not sensibly affect the 

 precipitation upon or near them. Milwaukee and Mackinaw, for instance, 

 near the centre of the Great Lake system, are among the driest meteorological 

 stations in the United States. I have often observed a striking phenomenon 

 connected with this subject on Lake Champlain (43° to 45° N.L.). This lake 

 does not usually freeze until February, sometimes not at all. A few houra 

 before the ice closes over it, a great deal of fog is thrown off by it, and if the 



