XXV 



vegetation, the animals, the geological facts, 

 the cultivation of the soil, the temperature 

 of the air, the limit of the perpetual snows, 

 the chemical constitution of the atmos- 

 phere, it's electrical intensity, it's barometri- 

 cal pressure, the decrement of gravitation, 

 the intensity of the azure color of the sky, 

 the diminution of the light during it's pas- 

 sage through the successive strata of the air, 

 the horizontal refractions, and the heat of 

 boiling water at different heights. Four- 

 teen scales, disposed at the side of a pro- 

 file of the Andes, indicate the modifications 

 which these phenomena undergo from the 

 influence of the elevation of the soil above 

 the level of the ocean. Each group of 

 plants is placed at the height that nature 

 has assigned, and we may follow the pro- 

 digious variety of their forms, from the 

 region of the palms and the fern-trees to 

 those of the johannesia (chuquiraga, 

 Juss.) the gramineous plants, and lichens. 

 These regions form the natural divisions of 

 the vegetable empire ; and in the same 

 manner as the perpetual snows are found 

 in every climate at a determinate height, 

 the febrifuge species of the quinquina 



