METEOROLOGICAL EFFECTS OF IRRIGATION. 463 
The meteorological effect of irrigation on a large scale, 
which would seem prima facie most probable, would be an 
rinerease of precipitation in the region watered.* Hitherto 
scientific observation has recorded no such increase, but in a 
question of so purely local a character, we must ascribe very 
great importance to a consideration which I have noticed else- 
where, but which has been frequently overlooked by meteorolo- 
gists, namely, that vapors exhaled in one district may very prob- 
ably be condensed and precipitated in another very distant 
from their source. If then it were proved that an extension 
of irrigated soil was not followed by an increase of rain-fall in 
the same territory, the probability that the precipitation was 
augmented somewhere would not be in the least diminished. 
But though we cannot show that in the irrigated portions of 
Italy the summer rain is more abundant than it was before irri- 
gation was practised—for we know nothing of the meteorolo- 
gical conditions of that country at so remote a period—the fact 
that there is a very considerable precipitation in the summer 
months in Lombardy is a strong argument in favor of such in- 
crease. In the otherwise similar climate of Rumelia and of 
much of Asia Minor, irrigation is indeed practised, but in a 
relatively small proportion. In those provinces there is little or 
no summer rain. Is it not highly probable that the difference 
between Italy and Turkey in this respect is to be ascribed, in 
part at least, to extensive irrigation in the former country, and 
the want of it in the latter? It is true that, in its accessible 
strata, the atmosphere of Lombardy is extremely dry during the 
period of irrigation, but it receives an immense quantity of 
* On the pluviometric effect of irrigation, see LOMBARDINI, Sulle Inon- 
dazioni, etc., p. 72, 74; the same author, Hssat Hydrologique sur le Nil, p. 32; 
MESSEDAGLIA, Analist dell’ opera di Champion, pp. 96, 97, note ; and BAIRD 
Situ, Italian Irrigation, i., pp. 189, 190. 
In an article in Aus der Natur, vol. 57, p. 443, it is stated that the rain on the 
Isthmus of Suez has increased since the opening of the canal, and has enlarged 
the evaporable surface of the country; but this cannot be accepted as an 
established fact without further evidence. 
