702 WINDS OF THE GLOBE. 



are as frequent in spring as northeast. This is the result of the great heat of this 

 region, when, under the influence of the nearly perpendicular rays of the sun, a 

 powerful ascending current is induced. The deficiency is supplied both from the 

 Atlantic and Pacific Oceans, and, in the latter case, probably by air from the 

 S. hemisphere. In the summer Guatemala has its regular rainy season, and the 

 heat decreases. (See Plate 7.) On the Pacific Ocean, between 5°-10° N., near 

 the coast of Central America, the movement of the air is already from the south- 

 west, except in winter, showing the equatorial belt of lowest pressure to be about 

 10° L. N. In Costa Rica, nearly in the same latitude, in a plateau between the 

 Atlantic and Pacific Oceans, the wind is still N. E. — that is, the regular trade. 

 (See Plates 5, 6, and 7.) 



The republic of Nicaragua lying in a depression between the Atlantic and 

 Pacific Oceans, but with its settled part nearer to the latter, is said to have also 

 very regular trade winds, so that its climate is thought to be one of the healthiest 

 in the tropics.^ 



The contrary seems to be the case in San Salvador, which has high mountains to 

 the N. E. It is said to have the hottest climate of Central America. Probably 

 there is a monsoon from the Pacific Ocean the whole year round, as under this low 

 latitude there is little difference between the temperature of winter and summer. 



SOUTH AMERICA. 



There are very few observations on the winds of tropical South America, and, 

 but for the regularity of the climate of these low latitudes, and the general descrip- 

 tions given by scientific travellers, we would be at a loss to say anything definite 

 about these countries. 



The same may be said relative to barometrical observations, which furnish the 

 key to the winds. They were made nearly exclusively on the coasts, and we do 

 not know how far the extensive plains of South America modify the pressure of 

 the air, if there is a depression there, at all comparable to that existing in the 

 interior of Asia, Africa, and North America. 



The want of accurate determination of heights would prevent our knowing it, 

 even were barometrical observations more numerous. When we have barometrical 

 observations from the temperate zone and see the pressure of summer fall much 

 below that of winter, we judge that there must be a depression of some magnitude, 

 even if, the accurate height of the station being unknown, we are unable to reduce 

 the barometrical observations to sea-level. Not so in a tropical country, especially 

 near the equator. The change of seasons can scarcely be said to exist, and, be the 

 pressure higher or lower in the middle of a continent than on the oceans, it will 

 -not change perceptibly during the year. 



Yet, summing up what we know of the physical geography of South America, 

 we can hardly expect a very low pressure there, especially in the equatorial Ama- 

 zonian region, as it is covered with dense forests, and the heating by the sun and 



' See Squier, Nicaragua. Waguer, Naturwissenschaftliche Reisen, etc. 



