1884.] THE ARIDITY OF SPAIN. 121 



piecipitous ascents, in surmounting; which, losing at a higher altitude 

 the high temperature to which they had attained in passing over 

 the ocean, or before quitting Africa, they can no longer retain in 

 solution all the moisture with which they were charged ; and 

 depositing much there in the form of rain, they pass on to the land in 

 the interior of the country, comparatively dry winds; and regaining 

 a higher temperature there, tliey are better able to retain the 

 diminished moisture with which tliey are charged. And thus, trees 

 or no trees, must it have ever been. The east wind which is damp 

 and rainy on our eastern coast, is a dry wind in the west ; and the 

 west wind which here is dry, is a humid wind in the west. In both 

 cases the wind has dropt its superfluous moisture on the land over 

 which it first passed ; so is it in Spain, and thus may much of the 

 aridity of Spain be accounted for. With such facts ascertained in 

 regard to the cause of the aridity of Spain, what remedial measures 

 are applicable have next to be considered. To attempt to increase 

 the rainfall otherwise than by causing the same water to fall again 

 and again in the form of rain, would appear to be hopeless ; but 

 much may be done in retaining and utilizing what moisture has 

 been brought by the sea-breezes, and in doing this the forest 

 engineer finds an appropriate field of action. Much of what falls 

 as rain dries up, that is, it is again evaporated, and passes into the 

 atmosphere. It may be that all of this is not lost ; much of it may 

 be again attracted and absorbed by the soil, and be utilized in the 

 promotion of vegetation. The moisture passing through a vegetable 

 often, perhaps generally, far exceeds tlie quantity of the rain wliich 

 falls upon the spot in which it grows ; but it may be lost to the 

 vegetation of the district in which tlie evaporation takes place ; 

 and that as effectually as is the quantity carried off by streamlets, 

 and brooks, and rivers to the sea. The quantity of moisture lost 

 by evaporation in different localities must be ascertained. This has 

 been done, and is being done. But meanwhile something may be done 

 to prevent this loss. Most of you nmst be familiar with the fact, 

 that any portion of a road which is overshadowed by a tree, remains 

 moist after rain much longer than portions of the same road devoid 

 of any overhanging covering. A similar effect is produced by all 

 vegetation, and the mode of operation can be described ; and in view 

 of all that is known in regard to the efficacy of trees in arresting 

 vegetation, the forest officials have advocated, and, to the extent of 

 their powers, have effected the conservation, the replenishing, and the 

 extension of forests in Spain. 



I have made use of three terms — conservation, replenishing, and 

 extension of forests. 



In different countries on the Continent and elsewhere, — I may 



