272 EVAPORATION. 



grow upon its borders, with the nourishment which they 

 require. From a similar course, probably results the fact 

 that it seldom or never rains in Peru. But this country is 

 so near the ocean, that the water which rises from the 

 ocean produces copious dews, which in some measure 

 supply the want of rain, and thus save the country from 

 utter sterility. Hence also a narrow strip of land, term* 

 ed Azanaga, between the desert of Sahara and the ocean, 

 is comparatively fertile. 



The northwestern part of the United States owes much 

 of its fertility to the- great lakes Superior, Huron, &c. 

 These furnish a quantity of vapor to supply the deficiency, 

 which would otherwise result from the great distance, at 

 which the States in this section of the country lie from 

 the ocean. Were these lakes to be dried up, the people 

 of those states would soon feel the effects in the dimin- 

 ished quantity of rain, which they would receive, if not 

 in seeing utter desolation spreading over their now beauti- 

 ful fields. In warm countries, even where rain is common, 

 plants often suffer for want of moisture. In some parts 

 of Spain, the fields often appear almost as if a fire had 

 passed through them ; vegetation becomes parched and 

 dried, as the heat of the summer sun and often the winds 

 blowing from Africa carry off the moisture with very 

 great rapidity. In such countries, however, vegetation, 

 when plentifully watered, and sheltered from the burning 

 heat of the sun sufficiently to prevent too rapid evapora- 

 tion, exhibits a luxuriance, which would seem surprising 

 to an inhabitant of more northern regions. There, nour- 

 ished by the combined influence of heat and moisture, 

 the palm, the magnolia, and other gigantic sons of the for- 

 est, raise their lofty heads, arrayed in perpetual verdure ; 

 while the forests, often rendered impenetrable by vines 

 and bushes of various kinds, bear witness to the powerful 

 influence of that agent, which dresses the fields of the 

 temperate zones in less luxuriant, but perhaps not less 

 beautiful verdure. In the frigid zones, where, during a 

 great part of the year, water scarcely exists in a fluid 

 state, evaporation is very scanty, and this, together with 

 the intense cold, prevents the progress of vegetation, ex- 

 cept during the few weeks of their brief summers. 



The influence of cultivation on climate and tempera- 



