INFLUENCE ON PRECIPITATION. 191 



condensed and fall ; whether it will waste itself on a barren des- 

 ert, refresh upland pastures, descend iu snow on Alpine heights, 

 or contribute to swell a distant torrent which shall lay waste 

 square miles of fertile corn-land ; nor do we know whether the 

 rain which feeds our brooklets is due to the transpiration from a 

 neighboring forest, or to the evaporation from a far-off sea. If, 

 therefore, it were proved that the annual quantity of rain and 

 dew is now as great on the pkdns of Castile, for example, as it 

 was when they were covered with the native forest, it would by 

 no means foEow that those woods did not augment the amount of 

 precipitation elsewhere. 



The whole problem of the pluviometrical influence of the for- 

 est, general or local, is so exceedingly complex and difficult that 

 it can not, with our present means of knowledge, be decided upon 

 d jpriori grounds. It must now be regarded as a question of fact 

 which would probably admit of scientific explanation, if it were 

 once established what the actual fact is. Unfortunately, the evi- 

 dence is conflicting in tendency, and sometimes equivocal in in- 

 terpretation, but I believe that a majority of the foresters and 

 physicists who have studied the question are of opinion that in 

 many, if not in aU cases, the destruction of the woods has been 

 followed by a diminution in the annual quantity of rain and dew. 

 Indeed, it has long been a populai'ly settled belief that vegetation 

 and the condensation and fall of atmospheric moisture are recip- 

 rocally necessary to each other, and even the poets sing of, 



Af ric's barren sand, 

 Where nought can grow, because it raineth not. 

 And where no ram can fall to bless the land. 

 Because nought grows there.* 



Before going further with the discussion, however, it is well to 

 remark that the comparative rarity or frequency of inundations 

 in earher or later centuries is not necessarily, in most cases not 

 probably, entitled to any weight whatever, as a proof that more 



* Det golde Strog i Afrika, 



Der Intet voxe kan, da ei det regner 

 Og, omvendt, ingen Regn kan falde, da 

 Der Intet voxer. 



Palitdan-Muller, Adam Homo, ii., 408. 



