IRRIGATION IN EUROPE. 457 
in Piedmont and Lombardy irrigation is bestowed upon almost 
every crop, while in our Northern States it is never employed 
at all in farming husbandry, orindeed for any purpose except in 
kitchen-gardens, and possibly, im rare cases, in some other small 
branch of agricultural 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 isso 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. When the sup- 
ply of water is unlimited, it is allowed, after serving its purpose 
heavens. And yet the heat of the sun’s rays, as measured by sensation, and, 
at the same time, the evaporation, are greater than they would be with the 
thermometer atthe same point in America. I have frequently felt in Italy, 
with the mercury below 60° Fahrenheit, and with a mottled and almost opaque 
sky, a heat of solar irradiation which I can compare to nothing but the scorch- 
ing sensation experienced in America at a temperature twenty degrees higher, 
during the intervals between showers, or before a rain, when the clear blue of 
the sky seems infinite in depth and transparency. Such circumstances may 
create a necessity for irrigation where it would otherwise be superfluous, if 
not absolutely injurious. 
In speaking of the superior apparent clearness of the sky in America, I 
confine 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 States 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, 
between Nice and La Spezia, and those of the incomparable Alpine panorama 
seen from Turin, are distinguishable at greater distances than they would be 
in 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 
it 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 subjectin HAYDEN, 
Preiminary Report on Geological Survey of Wyoming, 1870, pp. 194, 195, 258- 
261, 
