INTKODrCTION. 33 



directed. Tliis portion of the surface of the globe ailords in 

 the smallest space the greatest possible variety of impressions 

 from the contemplation of nature. Among the colossal mount- 

 ains of Cundinamarca, of Quito, and of Peru, furrowed by 

 deep ravines, man is enabled to contemplate alike all the fam- 

 ilies of plants, and all the stars of the firmament. There, at 

 a single glance, the eye surveys majestic palms, humid forests 

 of bambusa, and the varied species of Musacese, while above 

 these forms of tropical vegetation appear oaks, medlars, the 

 sweet-brier, and umbelliferous plants, as in our European 

 homes. There, as the traveler turns his eyes to the vault of 

 heaven, a sinjjle fjlance embraces the constellation of the South- 

 em Cross, the INlagellanic clouds, and the guiding stars of the 

 constellation of the Bear, as they circle round the arctic pole. 

 There the depths of the earth and the vaults of heaven dis- 

 play all the richness of their forms and the variety of their 

 phenom.ena. There the different climates are ranged the one 

 above the other, stage by stage, like the vegetable zones, whose 

 succession they limit ; and there the observer may readily 

 trace the laws that regulate the diminution of heat, as they 

 stand indelibly inscribed on the rocky walls and abrupt decliv- 

 ities of the Cordilleras. 



Not to weary the reader with the details of the phenomena 

 which I long since endeavored graphically to represent,* I 

 will here limit myself to the consideration of a few of the gen- 

 eral results whose combination constitutes the 'phy^.ical deline- 

 ation of the torrid zone. That which, ni the vagueness of our 



point of water (see tlieil 11, s. 155, and Journal of Geog. Soc.,\o\. vi., 

 }), 215). In this valley, where the atmosphere is scarcely ever agita- 

 ted by storms, and in 34° 7' lat., snow is found, several feet in thick- 

 ness, from December to March. 



* See, generally, my Essai sur la Geographie des Plantes, et le Ta- 

 bleau physique des Regions Equinoxiales, 1807, p. 80-88. On the diur- 

 nal and nocturnal variations of temperature, see Plate 9 of my Atlat 

 Geogr. et Pkys. du Nonveau Continent; and the Tables in my work, 

 entitled De distributione Geogi'aphica Playitarum, secundum caeli tempe- 

 riem, et altitvdinem Montium, 1817, p. 90-116 ; the meteorological por- 

 tion of my Asie Centrale, t. iii., p. 212, 224; and, finally, the more 

 recent and far more exact exposition of the variations of temperature 

 experienced in correspondence with the increase of altitude on the chain 

 of the Andes, given in Boussingault's Memoir, Sur la profondenr a la' 

 queV.t or, irouve, sous les Tropiques, la couche de Temperature Invaria- 

 ble. (Ann. de thimie et de Physique, 1833, t. liii., p. 225-247.) Thi? 

 treatise contains the elevations of 128 points, included between the 

 level of the sea and the declivity of the Antisana (17,900 feet), as well 

 OS the mean temperature of the atmosphere, which varies with the 

 height between Sl° and 35° F. 



B 2 



