506 METEOROLOGY 



forests over a large extent of country has always the effect of less 

 ening the mean annual quantity of rain. • 



It has long been said, that in equinoctial countries the rainy sea- 

 son returns each year with astonishing regularity. There can be 

 no doubt of the general accuracy of this observation, but the mete- 

 orological fact must not be announced as universal and admitting of 

 no exception ; the regular alternation of the dry and rainy season is 

 as perfect as possible in countries which present an extreme variety 

 of territory. Thus, in a country whose surface is covered with forests 

 and rivers and lakes, with mountains and plains, and table-lands, the 

 periodical seasons are quite distinct. But it is by no means so where 

 the surface is more uniform in its character. The return of the 

 rainy season will be much less regular if the soil be in general dry 

 and naked ; or if extensive agricultural operations take the place of 

 the primeval forest ; if rivers are less common, and lakes less fre- 

 quent. The rains will then be less abundant ; and such countries 

 will be exposed, from time to time, to droughts of long continuance 

 If, on the contrary, thick forests cover almost the whole of the terri- 

 tory, if its rivulets and rivers be numerous, and agriculture be limited 

 in extent, irregularity in the seasons will then take place, but in a 

 different way ; the rains will prevail, and in some seasons they will 

 become as it were incessant. 



The continent of America presents us, on the largest scale, with 

 two regions placed in the same conditions as to temperature, but in 

 which we successively encounter the circumstances which are most 

 favorable to the formation and fall of rain in one case, and to its 

 absence in the other. 



Setting out from Panama, and proceeding towards the south, we 

 encounter the Bay of Cupica, the provinces of San Bonaventura 

 Choco, and Esmeraldas ; in this country, covered with thick forests 

 and intersected with a multitude of streams, the rains are almost 

 incessant ; in the interior of Choco, scarcely a day passes without 

 rain. Beyond Tumbez, towards Payta, an order of things entirely 

 different commences : the forests have entirely disappeared, the soil 

 is sandy, agriculture scarcely exists, and here rain is almost un- 

 known. When I was at Pajrta, the inhabitants informed me that it 

 had not rained for seventeen years ! The same want of rain is 

 common in the whole of the country which surrounds the desert of 

 Sechura, and extends to Lima ; in these countries rain is as rare as 

 trees are. 



In Choco, where the soil is thickly covered with trees, it rains 

 almost continually ; and on the coasts of Peru, where the soil is 

 sandy, without trees, and devoid of verdure, it never rains ; and 

 this, as I have said, under a climate which enjoys the same tempera- 

 ture, and whose general features and distance from the mountains 

 are nearly the same. Piura is not more remote from the Andes of 

 Assuay than are the moist plains of Choco from the Western Cor- 

 dillera. 



The facts which ha>e now been laid before the reader seem to 

 authorize me to infer — 



