196 INFLUENCE OF PRECIPITATION. 
positive assertions about the diminution of rain in countries 
which have been stripped of wood within the historic period, 
but these assertions very rarely rest upon any other proof than 
the doubtful recollection of unscientific observers, and I am 
unable to refer to a single instance where the records of the 
rain-gauge, for a considerable period before and after the fell- 
ing or planting of extensive woods, can be appealed to in sup- 
port of either side of the question. The scientific reputation 
of many writers who have maintained that precipitation has 
been diminished in particular localities by the destruction of 
forests, or augmented by planting them, has led the public to 
suppose that their assertions rested on sufficient proof. We 
cannot affirm that in none of these cases did such proof exist, 
but I am not aware that it has ever been produced. * 
The effect of the forest on precipitation, then, is by no means 
free from doubt, and we cannot positively affirm that the total 
annual quantity of rain is even locally diminished or increased 
* Among recent writers, Clavé, Schacht, Sir John F. W. Herschel, Hohen- 
stein, Barth, Asbjérnsen, Boussingault, and others, maintain that forests tend 
to produce rain and clearings to diminish it, and they refer to numerous 
facts of observation in support of this doctrine; but in none of these does it 
appear that these observations are supported by actual pluviometrical measure. 
So far as I know, the earliest expression of the opinion that forests promote 
precipitation is that attributed to Christopher Columbus, in the Historie dd 
S. D. Fernando Colombo, Venetia, 1571, cap. lviii., where it is said that the 
Admiral ascribed the daily showers which fell in the West Indies about vespers 
to ‘‘ the great forests and trees of those countries,” and remarked that the same 
effect was formerly produced by the same cause in the Canary and Madeira 
islands and in the Azores, but that ‘‘ now that the many woods and trees that 
covered them have been felled, there are not produced so many clouds and 
rains as before.” 
Mr. H. Harrisse, in his very learned and able critical essay, Fernand 
Colomb, sa Vie et ses Cfuvres, Paris, 1872, has made it at least extremely 
probable that the Historie is a spurious work. The compiler may have found 
this observation in some of the writings of Columbus now lost, but however 
that may be, the fact, which Humboldt mentions in Cosmos with much in- 
terest, still remains, that the doctrine in question was held, if not by the great 
discoverer himself, at least by one of his pretended biographers, as early as 
the year 1571. 
