ILLUSTRATIONS (18). CLIMATE OF AMERICA. 97 



The mean annual temperature of the tropics, or the actual cli- 

 mate of the region of palms, is on the main land between 

 78. 2 and 85. 5 Fahr., without any sensible difference between 

 the observations made in Senegal, Pondichery, and Surinam*. 

 The great coolness, one might almost say coldness, which 

 prevails during a great portion of the year in the tropics, on 

 the coast of Peru, and which causes the mercury to fall to 

 59 Fahr., is, as I hope to show in another place, not to be 

 attributed to the effect of neighbouring mountains covered 

 with snow, but rather to the mist (garua) which obscures the 

 sun's disk, and to a current of cold sea-water commencing in 

 the antarctic regions, and which coming from the south-west, 

 strikes the coast of Chili near Valdivia and Concepcion, and is 

 thence propelled with violence, in a northerly direction, to 

 Cape Parina. On the coast of Lima, the temperature of the 

 Pacific is 60.2 Fahr., whilst it is 79.2 Fahr. under the same 

 parallel of latitude when outside the current. It is singular, 

 that so remarkable a fact should have remained unnoticed, 

 until my residence on the coast of the Pacific, in October, 1802. 

 The variations of temperature, of many parts of the earth, 

 depend principally on the character of the bottom of the 

 aerial ocean, or in other words, on the nature of the solid or 

 fluid (continental or oceanic) base on which the atmosphere 

 rests. Seas, traversed in various directions by currents of 

 warm and cold water (oceanic rivers), exert a different action 

 from articulated or inarticulated continental masses or islands, 

 which may be regarded as the shoals in the aerial ocean, and 

 which, notwithstanding their small dimensions, exercise, even 

 to great distances, a remarkable degree of influence on the 

 climate of the sea. In continental masses, we must dis- 

 tinguish between barren sandy deserts, savannahs, (grassy 

 plains,) and forest districts. In Upper Egypt and in South 

 America, Nouet and myself found, at noon, the temperature 

 of the ground,^ which was composed of granitic sand, 1^4 

 and 141 Fahr. j Numerous careful observations instituted at 

 Paris, have given, according to Arago, 122 and 126. 5 Fahr.f 

 The Savannahs, which, between the Missouri and the Missis- 

 sippi, are called Prairies, and which appear in the south at 



* Humboldt, Memoire sur les Lignes Isothermes, 1817, p. 54. Asic 

 centrale, t. iii. Mahlmann, Table IV. 

 t Asie centrale, t. iii. p. 176. 



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