192 rNTLTJENCE ON PEECIPITATION. 



or less rain fell formerly than now ; because the accumulation ol 

 water in the channel of a river depends far less upon the quantity 

 of precipitation in its valley, than upon the rapidity with which 

 it is conducted, on or under the surface of the ground, to the cen- 

 tral artery that drains the basin. But this point wiU be more 

 fully discussed in a subsequent chapter. 



In writers on the subject we are discussing, we find many posi- 

 tive 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 doubt- 

 ful recollection of unscientific observers, and I am unable to re- 

 fer to a single instance where the records of the rain-gauge, for a 

 considerable period before and after the f eUing or planting of ex- 

 tensive woods, can be appealed to in support of either side of the 

 question. The scientific reputation of many writers who have 

 maintained that precipitation has been diminished in particular 

 locaHties by the destruction of forests, or augmented by plant- 

 ing them, has led the pubhc to suppose that their assertions 

 rested on sufficient proof. We can not affirm that in none of 

 these cases did such proof exist, but I am not aware that it has 

 ever been produced.* 



* Among recent writers, Clave, Schaclit, Sir Jolin F. W. Herschel, Hohen- 

 stein, Barth, Asbjornsen, 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 pre- 

 cipitation is that attributed to Christopher Columbus in the Historie del 8. D. 

 Fernando Colombo, Venetia, 1571, cap. Iviii., 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 (Euvres, Paris, 1872, has made it at least extremely probable that 

 the Historie is a spurious work. The compiler may have found this observa- 

 tion in some of the writings of Columbus now lost ; but however that may be, 

 the fact, which Humboldt mentions in Cosmos with much interest, stUl re- 

 mains, 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. 



