ORGANIC LIFE. 339 



air In contact with the ground. The simultaneous thermic 

 and hygrometric modifications of tlie upper regions of the air 

 can only be learned (when direct observations on mountain 

 stations or aerostatic ascents are impracticable) from hypo- 

 thetical combinations, by making the barometer serve both as 

 a thermometer and an hygrometer. Important changes of 

 weather are not owing to merely local causes, situated at the 

 place of observation, but are the consequence of a disturbance 

 in the equilibrium of the aerial currents at a great distance 

 from the surface of the Earth, in the higher strata of the at- 

 mosphere, bringing cold or Avarm, dry or moist air, rendering 

 the sky cloudy or serene, and converting the accumulated 

 masses of clouds into light feathery cirri. As, therefore, the 

 inaccessibility of the phenomenon is added to the manifold 

 nature and complication of the disturbances, it has always 

 appeared to me that meteorology must first seek its founda- 

 tion and progress in the torrid zone, where the variations of 

 the atmospheric pressure, the course of hydro-meteors, and 

 the phenomena of electric explosion, are all of periodic occur- 

 rence. 



As we have now passed in review the whole sphere of In- 

 organic terrestrial lite, and have briefly considered our planet 

 with reference to its form, its internal heat, its electro-mag- 

 netic tension, its phenomena of polar light, the volcanic reac- 

 tion of its interior on its variously composed solid crust, and, 

 lastly, the phenomena of its two-fold envelopes — the aerial and 

 liquid ocean — we might, in accordance Avith the. older method 

 of treating physical geography, consider that we had com- 

 pleted our descriptive history of the globe. But the nobler 

 aim I have proposed to myself, of raising the contemplation 

 of nature to a more elevated point of view, would be defeated, 

 and this dehneation of nature would appear to lose its most 

 attractive charm, if it did not also include the sphere of or- 

 ganic life in the many stages of its tj^pical development. The 

 idea of vitality is so intimately associated with the idea of the 

 existence of the active, ever-blending natural forces which an- 

 imate the terrestrial sphere, that the creation of plants and 

 animals is ascribed in the most ancient mythical representa- 

 tions of many nations to these forces, while the condition of 

 the surface of our planet, before it was animated by vital 

 forms, is regarded as coeval with the epoch of a chaotic 

 conflict of the struggling elements. But the empirical do- 

 main of objective contemplation, and the delineation of our 

 planet in its present condition, do not include a consideration 



